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A&P II - Exam 3

A dust particle is inhaled and gets into an alveolus without being trapped along the way. Describe the path it takes, naming all air passages from external naris to alveolus. What would happen to it after arrival in the alveolus?
>external naris > vestibule > nasal cavity > nasopharynx > oropharynx > laryngopharynx > larynx > trachea > main bronchi > lobar bronchi > segmental bronchi > bronchioles > respiratory brochioles > alveolar ducts > atrium > alveoli

>> it would be phagocytized by alveolar macrophages (dust cells)
Describe the histology of the epithelium and lamina propria of the nasal cavity and the functions of the cell types present.
- olfactory - cilia bind odor particles

-respiratory epithelium - ciliated (mobile), pseudostratified columnar epithelium > goblet cells secrete mucus & its ciliated cells propel the mucus toward pharynx

- lamina propria - blood vessels & lymphocytes for defense & moisturizing air
Describe the roles of the intrinsic muscles, conciliate cartilages, and arytenoids cartilages in speech.
- intrinsic muscles - control vocal cords by pulling on the conciliate & arytenoid cartilages, causing them to pivot > forcing air between them so they vibrate

- arytenoids - adduct/abduct vocal cords, depending on direction of rotation
Contrast the epithelium of the brochioles with that of the alveoli and explain how the structural difference is related to their functional difference.
- BRONCHOLES - ciliated cuboidal epithelium to move mucus & a well developed layer of smooth muscle

- ALVEOLI - thin, broad cells (squamous alveolar cells) - thinness allows for rapid gas diffusion between air & blood
> Type 2 cuboidal cells (great alveolar cells) - repair alveolar epithelium, secrete pulmonary surfactant
Explain why contraction of the diaphragm causes inspiration but contraction of the transverse abdominal muscle causes expiration.
-CONTRACTION OF DIAPHRAGM - tenses and flattens > enlarges dimensions of throacic cavity > decreases its internal pressure and produces an inflow of air

-ABDOMINAL MUSCLE - increase pressure in abdominal cavity and pushes up some viscera up against diaphragm
Which brainstem respiratory nucleus is indispensable to respiration?
Ventral Respiratory Group (VRG) - elongated nucleus in medulla > generates rhythm of breathing
Explain why Boyle's law is relevant to the action of the respiratory muscles.
>> at a constant temperature, the pressure of a given quantity of gas in INVERSELY proportional to its volume

>respiratory muscles contract > increase space > decrease pressure > forcing air in
Explain why eupnoea requires little or no action by the muscles of expiration.
due to elastic recoil of lungs
Identify a benefit and a disadvantage of normal (non-pathological) bronchoconstriction.
protection from damage due to heat loss in cold BUT can be bad if brought about the asthma or anaphylactic shock
Why is the composition of alveolar air different from that of the atmosphere?
1) it is humidified by contact w/mucous membranes

2) it mixes with residual air left from previous respiratory cycle (O2 is diluted and enriched with CO2)

3) it exchanges O2 and CO2 with the blood
What 4 factors affect the efficiency of alveolar gas exchange?
1) pressure gradients of the gasses

2) solubility of gasses

3) membrane thickness

4) membrane area
Explain how perfusion of a pulmonary lobule changes if it is poorly ventilated.
it stimulates local vasoconstrictors > redirecting blood to better ventilated areas of lung
How is most oxygen transported in the blood? Why does carbon monoxide interfere with this?
- hemoglobin > binds 95% of O2

- CO competes with O2 for the same binding site > binds 210x as tightly, tying up hemoglobin for a long time, preventing uptake
What are 3 ways in which blood transports CO2?
1) attached to hemoglobin

2) carbonic acid > bicarbonate buffer system

3) dissolved gas
Give 2 reasons why highly active tissues can extract more oxygen from the blood than less active tissues.
1) active tissues release more CO2 that reacts to produce bicarbonate & H > the H causes hemoglobin to release more O2

2) they are warmer
Define hypocapnia and hypercapnia. Name the pH imbalances that result from these conditions and explain the relationship between Pco2 and pH.
-HYPOCAPNIA - Pco2 less than 37mm Hg (most common cause of alkalosis: blood pH>7.45)

- HYPERCAPNIA - Pco2 greater than 43mm Hg (most common cause of acidosis: blood pH<7.35)
What is the most potent chemical stimulus to respiration, and where are the most effective chemoreceptors for it located?
- pH - central chemoreceptors in brain
Explain how changes in pulmonary ventilation can correct pH imbalances.
if blood is too acidic, like seen in diabetics, respiration rate increases, blowing off extra CO2 & increasing pH
Describe the 4 classes of hypoxia
1) HYPOXEMIC - inadequate pulmonary gas exchange - low arterial Po2
>high altitude, drowning, respiratory arrest, degenerative lung disease, CO poisoning

2) ISCHEMIC - inadequate circulation
>congestive heart failure

3) ANEMIC - inability of blood to carry adequate O2

4) HISTOTOXIC - metabolic poison prevents tissues from using O2 delivered to them
>cyanide poisoning
Name and compare 2 COPDs and describe some pathological effects that they have in common.
1) CHRONIC BRONCHITIS - produce excess mucus - cilia are immobilized and reduces in number while goblet cells enlarge
>increase infection, swelling

2) EMPHYSEMA - alveolar walls break down and the lungs exhibit larger but fewer alveoli > there is much less respiratory membrane available for gas exchange
>less elasticity of lungs
In what lung tissue does lung cancer originate? How does it kill?
- mucous membranes of the large bronchi

> as a tumor invades the bronchial wall and grows around it, it compresses the airway and may cause collapse of more distal parts of lung
3 meanings of respiration
1) ventilation of the lungs (breathing)

2) the exchange of gases between the air and blood, and between blood and the tissue fluid

3) the use of oxygen in cellular metabolism
functions of the respiratory system
- O2 and CO2 exchange between blood and air
- speech
- smell
- affect pH of body fluids by eliminating CO2 (makes blood acidic)
- affects blood pressure (synthesis of vasoconstrictor, angiotensin II)
- breathing creates pressure gradients between thorax and abdomen that promote the flow of lymph and venous blood)
- breath-holding helps expel abdominal contents (valsalva maneuver)
principal organs of respiratory system
nose, pharynx, larynx, trachea, bronchi, lungs
respiratory division of the respiratory system
alveloi and other gas exchange regions
upper respiratory tract
- in head and neck

-nose through larynx
lower respiratory tract
- organs of the thorax

-trachea through lungs
the nose (functions)
- warms, cleanses, and humidifies inhaled air

-detects odors in the airstream

- serves as a resonating chamber that amplifies the voice
nasal fossae
right and left halves of the nasal cavity

> nasal septum - divides nasal cavity > composed of bone and hyaline cartilage

> paranasal sinuses and nasolacrimal duct drain into nasal cavity
- beginning of nasal cavity (small dilated chamber just inside nostrils)

- vibrissae - stiff guard hairs that block insects and debris from entering nose
olfactory epithelium
- detect odors

-ciliated pseudostratified columnar epithelium w/goblet cells >>immobile cilia to bind odorant molecules
respiratory epithelium
- lines rest of nasal cavity except vestibule

- pseudostratified ciliated columnar epithelium w/goblet cells >>motile cilia > goblet cells secrete mucus & cilia propel the mucous posteriorly toward pharynx > swallowed into digestive tract
- THROAT - a muscular funnel extending about 13cm from the choanae to the larynx
3 regions of pharynx
1) nasopharynx - receives auditory tubes and contains pharyngeal tonsil
> passes ONLY air and is lined by pseudostrat. columnar epi.
> 90' downward turn traps large particles

2) oropharynx - contains palatine tonsils

3) laryngopharynx - epiglottis to cricoid cartilage > esophagus begins at that point

>>oro. and laryngo. pass air, food, and drink and are lined by strat. squamous
- VOICE BOX - cartilaginous chamber

- primary function - to keep food and drink out of the airway
> phonation - production of sound

- epiglottis - closes airway and directs food to the esophagus behind it
> vestibular folds of larynx play greater role in keeping food and drink out of the airway

>> framework made up of 9 cartilages
walls of larynx
- deep intrinsic muscles - operate vocal cords

- superior extrinsic muscles - connect larynx to hyoid bone > elevate larynx during swallowing

- superior vestibular folds - play no role in speech > close larynx during swallowing

-inferior vocal cords - produce sound when air passes between them
> contain vocal ligaments
> covered with strat. squamous - best suited to endure vibration and contact between the cords
the vocal cords and the opening between them
action of vocal cords
- controlled by intrinsic muscles
- air forced between adducted vocal cords vibrates them
> taut - high pitch
> more slack - lower pitch

-adult male cords are: usually longer and thicker, vibrate more slowly, produce lower pitched sound

>LOUDNESS is determined by the force of air passing between the vocal cords

> vocal cords produce CRUDE SOUNDS that are formed into words by actions of pharynx, oral cavity, tongue, and lips
-WINDPIPE - anterior to esophagus
-supported by C-shaped rings of hyaline cartilage > reinforces trachea and keeps it from collapsing when you inhale

> trachealis muscle spans opening in rings
- to make a temporary opening in the trachea inferior to the larynx and insert a tube to allow airflow

> prevents asphyxiation due to upper airway obstruction
-right - shorter than L because the liver rises higher on the right >> 3 lobes

- left - taller and narrower because the heart tilts toward the L and occupies more space on this side of mediastinum >> 2 lobes
> has indentation - cardiac impression
path of air flow
nasal cavity > pharynx > larynx > trachea > main bronchus > lobar bronchus > segmental bronchus > bronchiole > terminal bronchiole > respiratory division > respiratory bronchiole > alveolar duct > atrium > alveolus
-150mil in each lung

-squamous (type I) cells - thin, broad > allow for rapid gas diffusion between alveolus and bloodstream
>95% of alveolus surface area

- great (type II) cells - round to cuboidal > repair alveolar epithelium when squamous cells are damaged
** secrete PULMONARY SURFACTANT - mixture of phospholipids and proteins that coats the alveoli and prevents them from collapsing when we exhale

- alveolar macrophages (dust cells) - most numerous of all cells in the lung; wander the lumen and connective tissue between alveoli > phagocytize dust particles
> 100mil dust cells perish each day as they ride up the mucocilary escalator to be swallowed and digested with their load of debris
respiratory membrane
- the barrier between the alveolar air and blood

- each alveolus surrounded by a basket of blood capillaries supplied by the pulmonary artery

> important to prevent fluid from accumulating in alveoli: alveoli are kept dry by absorption of excess liquid by blood capillaries
the pleurae and pleural fluid
- visceral pleura - serous membrane that covers lungs

- parietal pleura - adheres to mediastinum, inner surface of the rib cage, and superior surface of the diaphragm

- pleural fluid - film between membranes

> functions of pleurae and pleural fluid:
1) reduce friction
2) create pressure gradient - lower pressure than atmospheric pressure and assists lung inflation
3) compartmentalization - prevents spread of infection from one organ in the mediastinum to others
pulmonary ventilation
- everytime you take a breath > breathing consists of a repetitive cycle one cycle of inspiration and expiration
respiratory cycle
- one complete inspiration and expiration
quiet respiration
- while at rest, effortless, and automatic
forced expiration
- deep rapid breathing, such as during exercise
pressure difference
flow of air in and out of lung depends on a pressure difference between air pressure within lungs and outside the body

- contraction flattens diaphragm, enlarging thoracic cavity and pulling air into lungs

- relaxation allows diaphragm to bulge upward again, compressing the lungs and expelling air

> accounts for 2/3 of air flow
internal and external intercostal muscles
- between ribs - synergist to diaphragm

- stiffen the thoracic cage during respiration > prevents it from caving inward when diaphragm descends

- contribute to enlargement and contraction of throacic cage

- adds about 1/3 of the air that ventilates the lungs
- synergist to diaphragm

- QUIET RESPIRATION - holds ribs 1 and 2 stationary
accessory muscles
of respiration act mainly in FORCED respiration
forced inspiration
greatly increase thoracic volume
normal quiet expiration
- an energy-saving PASSIVE process achieved by the elasticity (elastic RECOIL) of the lungs and thoracic cage

- as muscles relax, structures recoil to original shape and original size of thoracic cavity > results in air flow out of the lungs
forced expiration
- greatly increased abdominal pressure pushes viscera up against diaphragm increasing thoracic pressure, forcing air OUT
valsalva maneuver
consists of taking a deep breath, holding it by closing the glottis, and then contracting the abdominal muscles to raise abdominal pressure and pushing organ contents out

>> childbirth, urination, defecation, vomiting
anxiety triggered state in which breathing is so rapid that it expels CO2 from the body faster than it is produced > as blood CO2 levels drop, the pH rises, causing the cerebral arteries to constrict reducing cerebral perfusion which may cause dizziness or fainting

> can be brought under control by having the person rebreathe the expired CO2 from a paper bag
central chemoreceptors
brainstem neurons that respond to changes in pH of cerebrospinal fluid

> pH of cerebrospinal fluid reflects the CO2 level in the blood >> by regulating respiration to maintain stable pH, respiratory center also ensures stable CO2 level in the blood
peripheral chemoreceptors
located in carotid and aortic bodies of the large arteries above the heart >> respond to the O2 and CO2 content and the pH of blood
pressure and airflow
- respiratory airflow is governed by the same principles of flow, pressure and resistance as blood flow

> the flow of a fluid is directly proportional to the pressure difference between two points

> the flow of a fluid is inversely proportional to the resistance

- ATMOSPHERIC PRESSURE drives respiration > the weight of the air above us
Boyle's law
- at a CONSTANT temperature, the pressure of a given quantity of gas in INVERSELY proportional to its volume

> if the lung volume increases, the internal pressure (intrapulmonary pressure) falls & vice versa
- the 2 pleural layers, their cohesive attraction to each other, and their connections to the lungs and their lining of the rib cage bring about inspiration

> the entire lung expands along the thoracic cage > as it increases in volume, its internal pressure drops and air flows in
Charles' Law
the given quantity of gas is DIRECTLY proportional to its absolute TEMPERATURE

- thermal expansion will contribute to the inflation of the lungs
expiration - relaxed breathing
- passive process achieved mainly by the elastic recoil of the thoracic cage

> volume of thoracic cavity decreases
- raises intrapulmonary pressure
- air flows down the pressure gradient and out of the lungs
expiration - forced breathing
- accessory muscles raise intrapulmonary pressure as

- massive amounts of air moves out of the lungs
determinants of airflow
1) pressure

2) resistance > the greater the resistance, the slower the flow
3 factors influencing airway resistance
1) diameter of bronchioles - bronchodilation or bronchoconstriction

2) pulmonary compliance - the ease with which the lungs can expand

3) surface tension of the alveoli and distal bronchioles
>> surfactant - reduces surface tension of water
alveolar surface tension
- thin film of water needed for gas exchange

-pulmonary surfactant produced by the great alveolar cells > decreases surface tension by disrupting the hydrogen bonding in water
alveolar ventilation
- only air that enters the alveoli is available for gas exchange, not all inhaled air gets there
alveolar ventilation rate - AVR
= air the ventilates alveoli (350mL) x respiratory rate (12bpm) = 4200 mL/min

>> of all the measurements, this one is most directly relevant to the body's ability to get oxygen to the tissues and dispose of carbon dioxide
residual volume
= 1300 mL that CANNOT be exhaled with max. effort
respiratory volume - TIDAL VOLUME
- volume of air inhaled and exhaled in one cycle during QUIET breathing (500mL)

>> normal, relaxed breathing
- air in excess of tidal volume that can be inhaled with maximum effort (3000mL)
respiratory volume - EXPIRATORY RESERVE VOLUME
- air in EXCESS of TV that can be exhaled with maximum effort (1200mL)
respiratory volume - RESIDUAL VOLUME
- air remaining in lungs after maximum expiration (1300mL)
- the measurement of pulmonary function

> aid in diagnosis and assessment of restrictive and obstructive lung disorders
restrictive disorders
- those that reduce pulmonary compliance

> limit the amount to which the lungs can be inflated
- any disease that produces pulmonary fibrosis (elastic tissue replaced with scar tissue)

-black-lung, tuberculosis
obstructive disorders
- those that interfere with airflow by narrowing or blocking the airway
relaxed, quiet breathing
temporary cessation of breathing
labored, gasping breathing; shortness of breath
increased rate and depth of breathing in response to exercise, pain, or other conditions
increased pulmonary ventilation in excess of metabolic demand
reduced pulmonary ventilation
Kussmaul respiration
deep, rapid breathing often induced by acidosis
dyspnea that occurs when a person is lying down
composition of air
-78.6% nitrogen
- 20.9% Oxygen
- 0.04% CO2
- 0-4% water vapor (depending on temp and humidity) and minor gases (argon, neon, helium, methane and ozone)
Dalton's law
the total atmospheric pressure is the sum of the contributions of the individual gases
differences in composition of inspired and alveolar air
1) air is humidified by contact with mucous membranes

2) freshly inspired air mixes with residual air left from the previous respiratory cycle

3) alveolar air exchanges O2 and CO2 with the blood
alveolar gas exchange
- the back and forth traffic of O2 and CO2 across alveolar epithelium

- air in the alveolus is in contact with a film of water covering the alveolar epithelium
for oxygen to get into the blood
it must dissove in the film of water & pass through the respiratory membrane separating the air from the bloodstream

> gases diffuse down their own concentration gradient until the partial pressure of each gas in the air is equal to its partial pressure in water
for carbon dioxide to leave the blood
it must pass the other way > diffuse out of the water film into the alveolar air
factors affecting gas exchange
1) pressure gradient of the gases

2) solubility of the gases
> CO2 is 20X as soluble as O2
> O2 is 2X as soluble as N2

3) membrane thickness

4) membrane surface area
ventilation-perfusion coupling
the ability to match ventilation and perfusion to each other
> gas exchange requires both good ventilation of alveolus and good perfusion of the capillaries
oxygen transport
- 95% bound to hemoglobin in RBC

- 1.5% dissolved in plasma
carbon dioxide transport
- 70% as bicarbonate ion

- 23% bound to hemoglobin

- 7% dissolved in plasma
carbon monoxide poisoning
- CO competes for the O2 binding sites on the hemoglobin molecule

- binds 210x as tightly as o'xygen > ties up hemoglobin for a long time
systemic gas exchange
- the unloading of O2 and loading of CO2 at the systemic capillaries
CO2 loading > chloride shift
- Cl has to moved around in order for RBC to pick up unload CO2
adjustment to the metabolic needs of individual tissues
hemoglobin unloads O2 to match metabolic needs of different states of activity of the tissues
4 factors that adjust the rate of oxygen unloading
1) ambient PO2 - active tissue has decreased PO2; O2 is released from Hb

2) temperature - active tissue has increased temperature > promotes unloading

3) Bohr effect - active tissure has increased CO2 > lowers pH of blood > promoting O2 unloading

4) bisphosphoglycerate (BPC) - RBCs produce BPG which binds to Hb > O2 is unloaded
rate and depth of breathing adjust to maintain levels of
in this order:

1) pH - 7.35-7.45 (75% of the change in respiration induced by pH shift)

2) PCO2 - 40mm Hg

3) PO2 - 25mm Hg
respiration acidosis/ respiratory alkalosis
pH imbalances resulting from a mismatch between the rate of pulmonary ventilation and the rate of CO2 production
- a corrective homeostatic response to acidosis
> "blowing offf" CO2 faster than the body produces it
deficiency of oxygen in a tissue or the inability to use oxygen

> a consequence of respiratory disseases
State 4 functions of the kidneys other than forming urine.
1) filter blood plasma and excrete metabolic toxic wastes

2) regulate blood volume, pressure, and osmolarity by regulating H2O output

3) secrete erythropoietin

4) regulate electrolyte and acid-base balance of body fluids

5) calcium homeostasis
List 4 nitrogenous wastes and their metabolic sources.
1) UREA > byproduct of protein catabolism
2) AMMONIA > proteins
3) URIC ACID > nucleic acids
4) CREATININE > creatine phosphate
Name some wastes eliminated by 3 systems other than the urinary system.
1) respiratory > CO2, water, other gases

2) integumentary > water, inorganic salts, lactic acid, urea in sweat

3) digestive > water, salts, CO2, lipids, bile pigments, cholesterol, food residue
Arrange the following in order from the MOST numerous to the LEAST numerous structures in a kidney: glomeration, major calyces, minor calyces, interlobular arteries, interlobar arteries.
glomeruli > interlobular A > interlobar > minor calyces > major calyces
Trace the path taken by one RBC from the renal artery to the renal vein.
renal A > segmental A > interlobar A > arcuate A > interlobular A > afferent arterioles > glomerulus > efferent arterioles > peritubular capillaries > interlobular V > arcuate V > interlobar V > renal vein
Consider one molecule of urea in the urine. Trace the route that it took from the point when it left the bloodstream to the point where it left the body.
glomerular capsule > proximal convoluted tubule > nephron loop > distal convoluted tubule > collecting duct > papillary duct > minor calyx > major calyx > renal pelvis > ureter > urinary bladder > urethra
Name the 4 major processes in urine production.
1) glomerular filtration - creates plasma-like filtrate of blood

2) tubular reabsorption - removes useful solutes from filtrate, returns them to the blood

3) tubular secreation - removes additional wastes from blood, adds them to the filtrate

4) water conservation - removes water from the urine and returns it to blood; concentrates wastes
Trace the movement of a urea molecule from the blood to the capsular space and name the barriers it passes through.
fenestrated capillary endothelium > negatively charged basement membrane > podocyte filtration slits
Calculate the net filtration pressure in a patient whose blood COP is only 10mm Hg because of hypoproteinemia. Assume other relevant variable to be normal.
> outward pressure - hydrostatic pressure - colloid osmotic pressure
> 60out - 18in - 10in = 32mm Hg out
Assume a person is moderately dehydrated and has low blood pressure. Describe the homeostatic mechanisms that would help the kidneys maintain a normal GPR.
- low BP > the afferent arteriole relaxes, allowing more blood in (to a point); they (J cells) also secrete renin to increase BP

- dehydration > the renin/angiotensin system triggers thirst and sodium/water retention/reabsorption so waste is removed but H2O is kept
The reabsorption of water, CL, and glucose by the PCT is linked to the reabsorption of Na, but in three very different ways. Contrast these 3 mechanisms.
1) WATER - follows solutes by osmosis through both PARACELLULAR and transcellular routes (aquaporins)

2) CHLORIDE - negatively charged are attracted to Na+ and follow into cell through ANTIPORTS

3) GLUCOSE - cotransported win Na+ by SYMPORTS (SGLTs)
Explain why a substance appears in the urine if its rate of glomerular filtration exceeds the Tm of the renal tubule.
If the amount of a substance is so high that its levels exceed the ability to transport it out, some will be left in the urine >> saturation of transport proteins
Contrast the effects of aldosterone and ANP on the renal tubule.
- ALDOSTERONE - causes tubules to absorb more Na+ and secrete more K+ >> H2O follows Cl- > follows Na+

- ANP (natriuretic peptides) - dilates afferent arterioles, inhibits NaCl reabsorption
Predict how ADH hypersecretion would affect the sodium concentration of the urine and explain why.
- increase in ADH causes H2O absorption by INCREASING aquaporins, leaving sodium behind in tubular fluid
Concisely contrast the role of the countercurrent multiplier with that of the countercurrent exchange.
- countercurrent MULTIPLIER (of nephron loop) - recaptures salt and returns it to the deep medullary tissue > increasing salinity & osmolarity

- countercurrent EXCHANGE (blood vessel) - preserves salinity by blood vessel that takes up NaCl > also excretes NaCl, balancing out levels and not decreasing osmolarity
How would the function of the collecting duct change if the nephron loop did not exist?
would have to absorb MORE H2O and secrete LESS urea
Define oliguria and polyuria. Which of these is a characteristic of diabetes?
- OLIGURIA - urine output < 500mL/day

- POLYURIA - urine output > 2L/day
*characteristic of diabetes*
Identify a cause of glycosuria other than diabetes mellitus.
gestational diabetes (due to decrease in insulin sensitivity)
How is the diuresis produced by furosemide like the diuresis produced by diabetes mellitus? How are they different?
- BOTH cause H2O not to be reabsorbed

- in diabetes the H2O follows glucose in uring and with lasics salt stays in urine so H2O follows that
Explain why GFR cannot be determined by measuring the amount of NaCl in the urine.
because NaCl is BOTH excreted and reabsorbed
Describe the location and function of the detrusor muscle.
muscle layer of bladder that contracts > urine
Compare and contrast the function of the internal and external urethral sphincters.
- INTERNAL - (smooth muscle) involuntary control - compresses urethra and retains urine in bladder

- EXTERNAL - (skeletal muscle) voluntary control - voiding of urine
In males, the sympathetic nervous system triggers ejaculation and, at the same time, stimulates constriction of the internal urethral sphincter. What purpose is served by the latter action?
prevents urine from mixing with sperm
"to live... to metabolize"

> metabolism creates a variety of toxic waste products
urinary system
- principal means of waste removal
urinary system & reproductive system
- the two are closely associated >> "urogenital system"

> share embryonic development
> share adult anatomical relationship
> male urethra serves as a common passage for urine and sperm
organs of the urinary system
2 kidneys, 2 ureters, urinary bladder and urethra
functions of the kidney
1) filters blood plasma, separates waste from useful chemicals, returns useful substances to blood, ELIMINATES WASTES
> 20% of cardiac output filters through kidneys

2) regulate BLOOD VOLUME and PRESSURE by eliminating or conserving water

3) regulate OSMOLARITY of the body fluids by controlling the relative amounts of water and solutes eliminated

4) secretes enzyme, RENIN > activates hormonal mechanisms that control blood pressure and electrolyte balance

5) secretes the hormone, ERYTHROPOIETIN > stimulates production of RBCs

6) collaborate with lungs to regulate the PCO2 and ACID-BASE BALANCE of body fluids

7) final step in synthesizing CALCITRIOL > contributes to calcium homeostasis

8) GLUCOGENESIS - from amino acids in extreme starvation
- any substance that is useless to the body or present in excess of the body's needs
metabolic waste
- waste substance produced by the body
urea formation
proteins > amino acids > NH2 removed > forms ammonia (toxic to the body) > liver converts to urea
- separation of wastes from body fluids and eliminating them
renal parenchyma
- glandular tissue that forms urine

- 2 zones: outer renal cortex & inner renal medulla

> encircles the renal sinus
renal sinus
- contains blood and lymphatic vessels, nerves, and urine-collecting structures
> adipose fills the remaining cavity and holds structures into place
renal circulation
> the kidneys account for only 0.4% of body weight but the receive about 21% of the cardiac output (renal fraction)
functional unit of the kidney
Interchange between blood and urine.

> composed of 2 parts:
1) renal corpuscle - filters the blood plasma
2) renal tubule - long coiled tube that converts the filtrate into urine
>> divided into 4 regions:
1-3) PCT, nephron loop, DCT
4) collecting duct - received fluid from many nephrons
renal innervation - renal plexus
- nerves and ganglia wrapped around each renal artery
> carries SYMPATHETIC innervation from the abdominal aortic plexus
>> stimulation reduces glomerular blood flow and rate of urine production
>> respond to falling blood pressure by stimulating the kidneys to secrete RENIN (an enzyme that activates hormonal mechanisms to restore blood pressure)

> carries PARASYMPATHETIC innervation from the vagus nerve >> increases rate of urine production
overview of urine formation
- kidneys convert blood plasma to urine in 3 stages:

1) glomerular filtration
2) tubular reabsorption and secretion
3) water conservation
glomerular filtration
- a special case of the capillary fluid exchange process in which water and some solutes in the blood plasma pass from the capillaries of the glomerulus into the capsular space of the nephron
filtration membrane
3 barriers through which fluid passes:

1) fenestrated endothelium of glomerular capillaries - 70-90nm filtration pores exclude blood cells; highly permeable

2) basement membrane - negative charge; excludes molecules greater than 8nm; albumin repelled by negative charge (blood plasma is 7% protein, filtrate is only 0.03%)

3) filtration slits -
> podocyte cell extension wrap around the capillaries to form a barrier layer with 30nm filtration slits
> negatively charged which is an additional obstacle for large anions
molecules that CAN pass through filtration membrane
- almost any molecule smaller than 3nm can pass freely through the filtration membrane
>> water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, vitamins

- some substances of low molecular weight are bound to the plasma proteins and cannot get through the membrane
>> most calcium, iron, and thyroid hormone > unbound fraction passes freely into the filtrate
kidney infections and trauma
- can damage the filtration membrane and allow albumin or blood cells to filter

> proteinuria - presence of protein in the urine
> hematuria - blood in urine
filtration pressure
- BLOOD HYDROSTATIC PRESSURE - much higher in glomerular capillaries b/c Afferent arteriole is larger than Efferent arteriole > larger inlet and smaller outlet

- HYDROSTATIC PRESSURE in capsular space - 18mm Hg due to high filtration rate and continual accumulation of fluid in the capsule

- COLLOID OSMOTIC PRESSURE OF BLOOD - about the same here as elsewhere - glomerular filtrate is almost protein free and has no significant COP
net filtration pressure
- higher OUTward pressure of 60mm Hg, opposed by two inward pressures of 18mm Hg and 32mm Hg

>>60out - 18in - 32in = 10mm Hg
high BP in glomerulus
- makes kidneys vulnerable to hypertension

> can lead to rupture of glomerular capilaries
> produce scarring of the kidneys (nephrosclerosis) and atherosclerosis of renal blood vessels > ultimately leading to renal failure
glomerular filtration rate (GFR)
= the amount of filtrate formed per minute by the 2 kidneys combined

- males = 125mL/min OR 180L/day
- females = 105mL/min OR 150L/day

> total amount of filtrate produced equals 50-60X the amount of blood in the body
>> 99% of filtrate is reabsorbed since only 1-2L urine excreted/day
GFR too high
- fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes

- urine output rises

- chance of dehydration and electrolyte depletion
GFR too low
- wastes reabsorbed

-azotemia may occur
GFR control
- it is controlled by adjusting GLOMERULAR BLOOD PRESSURE from moment to moment

- achieved by 3 homeostatic mechanisms
1) renal autoregulation
2) sympathetic control
3) hormonal control
renal autoregulation
- the ability of the nephrons to adjust their own bloodflow and GFR without external (nervous or hormonal) control

- enables them to maintain a relatively stable GFR in spite of changes in systemic arterial BP

-two methods
1) myogenic mechanism - based on the tendency of smooth muscle to contract when stretched

2) tubuloglomerular feedback - mechanism by which glomerulus receives feedback on the status of the downstream tubular fluid and adjust filtration to regulate the composition of the fluid, stabilize its own performance, and compensate for fluctuation in systemic BP
> juxtaglomerular apparatus
juxtaglomerular apparatus
- complex structure found at the very end of the nephron loop where it has just reentered the renal cortex

- loop comes into contact with the afferent and efferent arterioles at the vascular pole of the renal corpuscle

- 3 special kind of cells:
1) macula densa - at end of nephron loop on the side of the tubules facing the arterioles > senses variation in flow or fluid composition and secretes a paracrine that stimulates JG cells

2) juxtaglomerular (JG) cells - smooth muscle cells in the afferent arteriole directly across from macula densa > dilate or constrict the arterioles when stimulated by the macula; also contain granules of renin, which they secrete in response to drop in BP

3) mesangial cells - in cleft between the afferent and efferent arterioles and among the capillaries of the glomerulus > connected to macula densa dn JG cells by gap junctions and communicate by paracrines > build supportive matrix for glomerulus, constrict or relax capillaries to regulate flow
juxtaglomerular apparatus and GFR
>the flow of tubular fluid increases and more NaCl is reabsorbed
> macula densa stimulated JG cells with a paracrine
> JG cells contract which constricts afferent arteriole, reducing GFR to normal OR
> mesangial cells may contract, constricting the capillaries and reducing filtration

> macula relaxes afferent arterioles and mesangial cells
> blood flow increases and GFR rises back to normal
effectiveness of autoregulation
- maintains a dynamic equilibrium - GFR fluctuates within narrow limits only
> blood pressure changes do affect GFR and urine output somewhat

>> renal autoregulation can not compensate for EXTREME blood pressure variation
sympathetic control of GFR
- sympathetic nervous system and adrenal epinephrine CONSTRICT the afferent arterioles in strenuous exercise or acute conditions like circulatory shock

> reduces GFR and urine output
> redirects blood from the kidneys to the heart, brain, and skeletal muscles
> GFR may be as low as a few milliliters per minute
hormonal control
> renin-angiotensin-aldosterone mechanism

- RENIN secreted by justaglomerular cells if BP DROPS dramatically > renin converts angiotensinogen (a blood protein) into ANGIOTENSIN I > in the lungs and kidneys, ANGIOTENSIN-CONVERTING ENZYME (ACE) converts angiotensin I to ANGIOTENSIN II, the active hormone >> works in several ways to restore fluid volume and BP
urine formation - tubular reabsorption and secretion
- conversion of glomerular filtrate to urine involves the removal and addition of chemicals by tubular reabsorption and secretion
> occurs through PCT to DCT
> tubular fluid is modified

- steps involved:
1) tubular reabsorption
2) tubular secretion
3) water conservation
tubular reabsorption
- process of reclaiming water and solutes from the tubular fluid and returning them to the blood

-2 routes:
1) transcellular - through cells
2) paracellular - between cells
> solvent drag - water carries with it a variety of dissolved solutes

- taken up by paratubular capillaries
sodium chloride - sodium reabsorption
* the KEY to everything else *

- creates osmotic and electrical gradient that drives the reabsorption of water and other solutes

- most abundant cation in filtrate

- 2 types of transport proteins:
1) symports - simultaneously bind Na+ and other solutes (glucose, amino acids, lactate)
2) antiport - Na-H - pulls Na into the cell while pumping out H into tubular fluid

- sodium is prevented from accumulating in the epithelial cells by Na-K pumps

- negative CHLORIDE IONS follow the positive sodium ions by electrical attraction
reabsorption in the PCT - other electrolytes
- potassium, magnesium, and phosphate ions diffuse through the paracellular route with water

- phosphate is also cotransported into the epithelial cells with Na

- some calcium is reabsorbed through the paracellular route in the PCT, but most occurs later in the NEPHRON

-glucose is cotransported with Na by SGLT proteins

- urea diffuses through the tubule epithelium with water - reabsorbs 40-60% in tubular fluid
water reabsorption
- kidneys reduce 180L of glomerular filtrate to 1 or 2 L of urine EACH DAY

- 2/3 of water in filtrate is reabsorbed by the PCT

- reabsorption of all the salt and organic solutes makes the tubule cells and tissue fluid hypertonic
> aquaporins
> obligatory water reabsorption - in PCT, water is reabsorbed at a constant rate
uptake by the peritubular capillaries
- 3 factors promote osmosis into the capillaries:
1) accumulation of reabsorbed fluid > high interstitial fluid pressure drives water into the capillaries
2) narrowness of efferent arterioles - lowers blood hydrostatic pressure in peritubular capillaries so there is less resistance to absorption
3) proteins remain in blood after filtration > elevates colloid osmotic pressure >> RBCs help pull fluid in
transport maximum of glucose
- limited number of transport proteins in plasma membrane

- each solute has its own transport maximum
> any blood glucose level above 220mg/dL results in glycosuria
tubular secretion
- process in which the renal tubule extracts chemicals from the capillary blood and secretes them into tubular fluid

- 2 purposes in proximal convoluted tubule and nephron loop
1) waste removal
> explains need to take prescriptions 3-4 times/day to keep pace with the rate of clearance

2) acid-base balance - secretion of hydrogen and bicarbonate ions help regulate the pH of the body fluids >> pumps out extra H+
primary function of nephron loop
- to generate salinity gradient that enables collecting duct to concentrate the urine and conserve water

- electrolyte reabsorption from filtrate
> thick segment reabsorbs 25% of Na, K, and Cl
>> ions leave cells by active transport and diffusion > NaCl remains in the tissue fluid of renal medulla > water cannot follow since thick segment is IMPERMEABLE

- tissue fluid very dilute as it enters distal convoluted tubule
DCT and Collecting Duct
- fluid arriving in the DCT still contains about 20% of the water and 7% of the salts from glomerular filtrate

- both reabsorb variable amounts of water and salt and are regulated by several hormones > aldosterone, ANP, ADH, and parathyroid hormone

- 2 kinds of cells:
1) principal cells - most numerous; have receptors for hormones; involved in salt and water balance
2) intercalated cells - involved in acid/base balance by secreting H+ ions into tubule lumen and reabsorbing K+

- steroid secreted by adrenal cortex:
> when blood Na falls or
> when K rises or
> drop in BP > renin release > angiotensin II formation > stimulates adrenal cortex to secrete aldosterone
functions of aldosterone
- acts on thick segment of nephron loop, DCT, and cortical portion of collecting duct

> stimulates the reabsorption of MORE Na and secretion of K >> H2O and Cl follow Na
>> net effect is that the body retains NaCl and water (helps maintain blood volume and pressure)
>> urine volume is reduced > conserving more H2O
atrial natriuretic peptide (ANP)
- secreted by atrial myocardium of the heart > in response to HIGH BP

- 4 actions that result in the excretion of more salt and water in the urine, thus reducing blood volume and pressure
1) dilates AFFERENT arteriole (coming in), constricts EFFERENT (going out) > increase GFR (increase pressure, increase amount of fluid leaving)

2) inhibits renin and aldosterone secretion

3) inhibits secretion of ADH

4) inhibits NaCl reabsorption by collecting duct
antidiuretic hormone (ADH)
- secreted by posterior lobe of pituitary in response to dehydration and rising blood osmolarity

- makes collecting duct more permeable to water > can remove H2O without removing salt
>> water in tubular fluid reenters the tissue fluid and bloodstream rather than being lost in urine
parathyroid hormone (PTH)
- secreted in response to calcium deficiency (hypocalcemia)

- increases phosphate content and lowers calcium content in urine

- because phosphate is not retained, the calcium ions stay in circulation rather than precipitating into the bone tissue as calcium phosphate
summary of tubular reabsorption and secretion
- PCT reabsorbs 65% of glomerular filtrate and returns it to peritubular capillaries
> much reabsorption by osmosis & cotransport mechanisms linked to active transport of sodium
> nephron loop absorbs another 25% of filtrate

- DCT reabsorbs Na, Cl, and water under hormonal control, expecially aldosterone and ANP

- the tubules also extract drugs, wastes, and some solutes from the blood and SECRETE them into the tubular fluid

- DCT completes the process of determining the chemical composition of urine

- CD conserves water
urine formation - water conservation
- the kidney eliminates metabolic wastes from the body, but also prevents excessive water loss as well

- as the kidney returns water to the tissue fluid and bloodstream, the fluid remaining in the renal tubules passes as urine, and becomes more concentrated
collecting duct concentrates urine
- CD begins in the cortex where it receives tubular fluid from several nephrons

- as CD passes through the medulla, it reabsorbs water and concentrates urine up to 4X

- medullary portion of CD is more permeable to water than to NaCl ( pulls more H2O out than salt)

- as urine passes through the increasingly salty medulla, water leaves by osmosis concentrating urine
control of water loss
- how concentrated the urine becomes depends on body's state of hydration

- WATER DIURESIS - drinking large volumes of water will produce a large volume of HYPOTONIC urine

- producing HYPERTONIC urine - dehydration causes the urine to become scanty and more concentrated > more H2O is reabsorbed by CD so urine is more concentrated

if BP is low in a dehydrated person, GFR will be low
> filtrate moves more slowly and more time for reabsorption
> more salt removed, more water reabsorbed and less urine produced
countercurrent multiplier
- the ability of kidney to concentrate urine depends on salinity gradient in renal medulla >> 4X as salty in the renal medulla than the cortex

- nephron loop acts as countercurrent multiplier
> MULTIPLIER - continually recaptures salt and returns it to extracellular fluid of medulla which multiplies the salinity in adrenal medulla
> COUNTERCURRENT - because of fluid flowing in opposite directions in adjacent tubules of nephron loop

- descending limb - permeable to H2O but not to NaCl; water passes from tubule into the ECF leaving salt behind

-ascending limb - impermeable to water
recycling of urea
- lower end of CD permeable to urea

- urea contributes to the osmolarity of deep medullary tissue

- continually cycled from collecting duct to the nephron loop and back
vasa recta
- capillary branching off efferent arteriole in medulla

> provides blood supply to medulla and does not remove NaCl and urea from medullary ECF
countercurrent system
- formed by BLOOD flowing in opposite directions in adjacent parallel capillaries

- descending capillaries > exchanges H2O for salt; H2O diffuses out of capillaries and salt diffuses in
>> as blood flows back up to the cortex the opposite occurs

- ascending capillaries > exchanges salt for H2O; water diffuses into and NaCl diffuses out of blood
>> absorb MORE H2O on the way out than the way in, and thus carry away water reabsorbed from the urine by collecting duct and nephron loop
- any metabolic disorder resulting in chronic POLYURIA (urine output in excess of 2L/day)

> diabetes mellitus type1, type 2, and gestational >> high concentration of glucose in renal tubule

> diabetes insipidus >> ADH hyposecretion causing not enough water to be reabsorbed in the CD (more H2O passes in urine)
- any chemical that INCREASES urine volume

- some increase GFR > caffeine dilates the afferent arteriole

- reduce tubular reabsorption of water > alcohol inhibits ADH secretion

- act on nephron loop (loop diuretic) > inhibit Na-K-Cl symport >> impairs coutercurrent multiplier; CD unable to reabsorb as much water as usual

>> commonly used to treat hypertension and congestive heart failure by reducing the body's fluid volume and BP
renal clearance
- the volume of blood plasma from which a particular waste is completely removed in 1 minute

- glomerular filtration of the waste
+ amount added by tubular secretion
- amount removed by tubular reabsorption
- kidney disease often results in lowering of GFR > need to measure patient's GFR >> fewer nephrons = less output
> cannot use clearance rate of urea >> some urea filtered by glomerulus is reabsorbed in the tubule & some is secreted into the tubule

> inulin - a plant polysaccharide to determine GFR
urine storage and elimination
- urine is produced continually

- does not drain continually from the body

- urination is episodic > occurring when we allow it

- made possible by storage apparatus & neural controls of this timely release
voiding urine
- between acts of urination, the bladder is filling
> detrusor muscle relaxes
> urethral sphincters are tightly closed
the act of urinating
micturition reflex
spinal reflex that partly controls urination
renal insufficiency
- a state in which the kidneys cannot maintain homeostasis due to extensive destruction of their nephrons

> can survive with 1/3 of kidney
> when 75% of nephrons are lost and urine output of 30mL/hr (normal 50-60mL/hr) is insufficient to maintain homeostasis
List 5 routes of water loss. Which one accounts for the greatest loss?
1) urine > greatest loss
2) feces
3) expired breath
4) sweat > most controllable
5) cutaneous transpiration - (not sweat) - H2O that diffuses through epidermis and evaporates
Explain why even a severly dehydrated person inevitable experiences further fluid loss.
- obligatory water loss > unavoidable output (can't be controlled)

>> expired air, cutanoeus transpiration, sweat, fecal moisture, min. urine output
Suppose there were no mechanisms to stop the sense of thirst until the blood became sufficiently hydrated. Explain why we would routinely suffer hypotonic hydration.
- excessive water intake > because changes require 30 MINUTES to take effect and decrease the osmolarity of blood
Summarize the effect of ADH on total body water and blood osmolarity.
- ADH makes a person thirsty and increases reabsorption from DCT and CD > independent of Na
Name and define the 4 types of fluid imbalance and give an example of a situation that could produce each type.
1) volume depletion (hypovolemia) - fluid depletion with normal osmolarity; proportionate amounts of H2O and Na are lost WITHOUT replacement
>> hemorrhage

2) dehydration (negative H2O balance) - body eliminates significantly more H2O than sodium
>> not drinking enough water

3) volume excess - both Na & H2O are retained and the ECF remains isotonic
>> renal failure

4) hypotonic hydration - more water than sodium is retained (water intoxication, positive water balance)
>> lose a large amount of H2O & salt through urine and sweat and replace it by drinking PLAIN water
Which do you think would have the most serious effect and why: a -5mEq/L INCREASE in the plasma concentration of sodium, potassium, chloride, or calcium?
Ca+ > causes muscle weakness and cardiac arrhythmia
Which do you think would have the most serious effect and why: a -5mEq/L DECREASE in the plasma concentration of sodium, potassium, chloride, or calcium?
Ca+ > there is only 3mEq/L in plasma and a drop of 5 would be 0 >> causing muscular systems to be overly excitable
Explain why ADH is more likely than aldosterone to change the osmolarity of the blood plasma.
- ADH saves H2O without salt

- aldosterone causes salt and retention thus H2O retention
Explain why aldosterone hyposecretion could cause hypochloremia.
- because aldosterone causes sodium to be absorbed

- if not enough Na+ is absorbed then not enough Cl- will follow, giving the body a low level of Cl-
Why are more phosphate ions required in the ICF than in the ECF? How does this affect the distribution of calcium ions between these fluid compartments?
- they are a component of ATP and nucleic acids

> calcium ions are kept to a minimum inside the cell because calcium phosphate crystals would precipitate
Why are phosphate buffers more effective in the cytoplasm than in the blood plasma?
- phosphates are more concentrated in cytoplasm than plasma
Renal tubules cannot absorb HCO3-; yet HCO3- concentration in the tubular fluid falls while in the blood plasma it rises. Explain this apparent contradiction.
- the PCT have carbonic anhydrase on brush borders to break down H2CO3 to CO2+H2O

>> CO2 is absorbed and promptly converted back to bicarbonate to be excreted into blood
In acidosis, the renal tubules secrete more ammonia. Why?
- because the ammonia is used to buffer the extra H+ ions that are excreted
3 types of homeostatic balance
1) water - average daily water intake and loss are equal

2) electrolyte - the amount of electrolytes absorbed by the small intestine balance with the amount lost from the body, usually in urine

3) acid-base - the body rids itself of acid (H+) at a rate that balances metabolic production
fluid compartments
- 65% ICF

- 35% ECF:
> 25% tissue fluid (interstitial)
> 8% blood plasma
> 2% transcellular ("catch all" category)
water movement between fluid compartments
• fluid continually exchanged between compartments
• water moves by osmosis
• because water moves so easily through plasma membranes, osmotic gradients never last for very long
osmosis from one fluid compartment to another...
- is determined by the relative concentrations of solutes in each compartment

> electrolytes - the most abundant solute particles
> sodium salts in ECF
> potassium salts in ICF
- play principal role in governing the body's water distribution and total water content
water gain
- 2 sources:

1) preformed water (2300mL/day) > food and drink
2) metabolic water (200mL/day) > by-product of aerobic metabolism and dehydration synthesis
water loss
- SENSIBLE water loss > observable
>> urine, feces, sweat in resting adult

- INSENSIBLE water loss > unnoticed
>> expired breath, cutaneous transpiration; varies greatly with environment and activity

- OBLIGATORY - unavoidable
>> expired air, cutaneous transpiration, sweat, fecal moisture, urine output
- reduced blood volume and blood pressure
- increases blood osmolarity

>> so you are thirsty
- in hypothalamus
> respond to angiotensin II produced when BP drops and to rise in osmolarity of ECF with drop in BV

> hypothalamus produces ADH > promotes water conservation

> cerebral cortex produces conscious SENSE OF THIRST

> salivation is inhibited with thirst
long term inhibition of thirst
- absorption of water from small intestine reduces osmolarity of blood
>> changes require 30min or longer to take effect
short term inhibition of thirst
- cooling and moistening of mouth quenches thirst

- distension of stomach and small intestine

>> 30-45min of satisfaction > must be followed by water being absorbed into the bloodstream or thirst returns

- short term response designed to prevent overdrinking
regulation of H2O output
- only way to control output significantly, is through variation in urine volume

- mechanisms:
> changes in urine volume linked to adjustments in Na+ reabsorption (H2O follows Na)
> concentrate the urine through action of ADH
> ADH secretion stimulated by hypothalamic osmoreceptors in response to dehydration
> AQUAPORINS synthesized in response to ADH - membrane proteins in renal CD - channel H2O back into to renal medulla, Na is still excreted
ADH release inhibited...
- when blood volume and pressure is too high OR

- blood osmolarity is too low

> effective way to compensate for hypertension
fluid imbalance
- the body is in a state of fluid imbalance if there is an abnormality of total volume, concentration, or distribution of fluid among the compartments

- fluid deficiency - fluid output exceeds intake over long period of time

- fluid excess - less common than fluid deficiency because the kidneys are highly effective in compensating for excessive intake by excreting more urine

>> kidneys compensate very well for excessive fluid intake, but not for inadequate fluid intake
serious effects of water balance disorder
- circulatory shock due to loss of blood volume
- neurological dysfunction due to dehydration of brain cells
- infant mortality from diarrhea
fluid balance in cold weather
- the body conserves heat by constricting blood vessels of the skin forcing blood to deeper circulation

> raises BP which inhibits secretion of ADH
> increases secretion of ANP
> urine output is increased and BV is reduced

- cold air is drier and increases respiratory and urinary loses cause a state of reduced blood volume
dehydration from excessive sweating
- water loss from sweating
- sweat produced by capillary filtration
- blood volume and pressure drop, osmolarity rises
- blood absorbs tissue fluid to replace loss
- tissue fluid pulled from ICF
- all three compartments lose water
- 300mL from tissue fluid and 700mL from ICF
fluid sequestration
- a condition in which excess fluid accumulates in a particular location

- total body H2O may be normal, but volume of circulating blood may drop to a point causing swelling of the tissues
physiological functions of electrolytes
- chemically reactive and participate in metabolism

- determine electrical potential across cell membranes

- strongly affect osmolarity of body fluids

- affect body's water content and distribution
major cations
> Na+, K+, Ca2+, and H+
major anions
> Cl-, HCO3- (bicarbonate), and PO43-
functions of sodium
- principal ions responsible for the resting membrane potentials
> inflow of sodium through membrane gates is an essential event in the depolarization that underlies nerve and muscle function

- principal cation in ECF
> accounts for 90-95% osmolarity of ECF
> most significant solute in determining total body water and distribution of water among the fluid compartments
> Na+ gradient a source of potential energy for cotransport of other solutes such as glucose, potassium, and calcium

- Na+-K+ pump
> exchanges IC Na+ for EC K+
>** generates body heat

- NaHCO3 has a major role in buffering pH in ECF
sodium homeostasis
- adult needs about 0.5g of sodium/day
> typical American diet contains 3-7g/day

- primary concern > excretion of excess dietary sodium
sodium concentration coordinated by...
- ALDOSTERONE - "salt retaining hormone"
> primary role in adjusting sodium excretion
> it is a steroid that binds to nuclear receptors (protein) > activates transcription of a gene for the Na-K pumps
> primary effects: the urine contains less NaCl and more potassium and a lower pH
> elevated BP inhibits the renin-angiotensin-aldosterone mechanism
>> kidneys reabsorb almost no sodium
>> urine contains up to 30g of sodium/ day instead of normal 5g

- ADH - modifies water excretion independently of sodium excretion
> kidneys reabsorb MORE water (collecting ducts)
> slows down further increase in blood sodium concentration
> more water is excreted, raising the sodium level in the blood

- ANP & BNP -
> inhibit sodium and water reabsorption, and the secretion of renin and ADH (in response to high BP)

- others:
> ESTROGEN - mimics aldosterone and women retain water during pregnancy
> PROGESTERONE - reduces sodium reabsorption and has a diuretic effect
sodium imbalances
- hypernatremia > plasma sodium concentration greater than 145mEq/L
> from admin. of IV saline
> water pretension, hypertension and edema

- hyponatremia > plasma sodium concentration less than 130mEq/l
> person loses large volumes of sweat or urine, replacing it with drinking plain water
> result of excess body water quickly corrected by excretion of excess water
potassium - functions
- most abundant cation of ICF

- greatest determinant of intracellular olsmolarity and cell volume

- produces (with sodium) the resting membrane potential and action potentials of nerve and muscle cells
potassium - homeostasis
- closely linked to that of sodium
- 90% of K+ in glomerular filtrate is reabsorbed by the PCT
- aldosterone stimulates renal secretion of K+
potassium - imbalances
** most dangerous imbalances of electrolytes

- hyperkalemia - effects depend on whether the potassium concentration rises quickly or slowly
> quickly - (crush injury) - the sudden increase in EC K+ makes nerve and muscle cells abnormally excitable

> slow onset - inactivates voltage-regulated Na+ channels, nerve and muscle cells become less excitable >> can produce cardiac arrest

- hypokalemia - from sweating, chronic vomiting or diarrhea
> nerve and muscle cells less excitable >> muscle weakness, loss of muscle tone, decreased reflexes, and arrhythmias from irregular electrical activity in the heart
chloride - functions
- most abundant ANION in ECF
- required for the formation of stomach acid >> hydrochloric acid (HCl)

- chloride shift - that accompanies CO2 loading and unloading in RBCs

- major role in regulating body pH
chloride - homeostasis
- strong attraction to Na, K, and Ca2+, which chloride passively follows

- primary homeostasis achieved as an effect of Na+ homeostasis
> as sodium is retained, chloride ions passively follow
chloride imbalances
- hyperchloremia > result of dietary excess or administration of IV saline

- hypochloremia > side effect of hyponatremia

>> primary effects > disturbances in acid-base balance
calcium - functions
- lends strength to the skeleton
- activates sliding filament mechanism of muscle contraction
- serves as a second messenger for some hormones and neurotransmitters
- activates exocytosis of neurotransmitters and other cellular secretions
- essential factor in blood clotting
calcium- homeostasis
- chiefly regulated by PTH, calcitriol (vit D), and calcitonin (in children)
> affect bone deposition and resorption
> intestinal absorption and urinary excretion

- cells maintain very low intracellular Ca2+ levels
> to prevent calcium phosphate crystal precipitation > phosphate levels are high in the ICF
> cells must pump Ca out
> keeps intracellular concentration low
> or sequester Ca2+ in smooth ER and release it when needed

- calsequestrin > protein that binds Ca and keeps it unreactive in Ca storage cells
calcium - imbalances
- hypercalcemia
> alkalosis, hyperparathyroidism, hypothyroidism
> reduces membrane Na permeability, inhibits depolarization of nerve and muscle cells
> can cause muscle weakness, depressed reflexes, cardiac arrhythmia

- hypocalcemia
> vit D deficiency, diarrhea, pregnancy, acidosis, lactation, hypoparathyroidism, hyperthyroidism
> increases membrane Na permeability, causing nervous and muscular systems to be abnormally excitable
> very low levels result in tetanus, laryngospasm, death
phosphates - functions
- relatively concentrated in ICF due to hydrolysis of ATP and other phosphate compounds

- components of nucleic acids, phospholipids, ATP, GTP, cAMP, and creatine phosphate

- activates many metabolic pathways by phosphorylating enzymes and substrates such as glucose

> buffers that help stabilize the pH of body fluids
phosphates - homeostasis
> normally phosphate is continually lost by glomerular filtration
> if plasma concentration drops, renal tubules reabsorb all filtered phosphate

> increases excretion of phosphate which increases concentration of free calcium in the ECF
> lowering the ECF concentration minimizes the formation of calcium phosphate and helps support plasma Ca+ concentrations

>> imbalances not as critical
acid-base balance
- one of the most important aspects of homeostasis
> metabolism depends on enzymes, and enzymes are sensitive to pH
> slight deviation from the normal pH can shut down entire metabolic pathways & alter the structure and function of macromolecues
normal pH range of blood and tissue fluid
challenges to acid-base balance
- metabolism constantly produces acid
> lactic acids from anaerobic fermentation
> phosphoric acid from nucleic acid catabolism
> fatty acids and ketones from fat catabolism
> carbonic acid from CO2
pH of a solution
is determined SOLELY by its hydrogen ions (H+)
- any chemical that RELEASES H+ in a solution
> strong acids: HCl (gives up most of its H+) >> markedly lower pH of a solution
> weak acids: carbonic acid (H2CO3) >>keeps most H+ chemically bound, does not affect pH
- any chemical that ACCEPTS H+
> strong: OH- >> strong tendency to bind to H+, markedly raising pH
> weak: bicarbonate ion (HCO3) >> bind less available H+; has less effect on pH
- any mechanism that resists change in pH
> converts strong acids or bases to weak ones
physiological buffer
- system that controls output of acids, bases, or CO2

> urinary system - buffers greatest quantity of acid or base
>> takes several hours to days to exert its effect

> respiratory system - buffers within minutes
>> cannot alter the pH as much as the urinary system
chemical buffer
- a substance that binds H+ and removes it from solution as its concentration falls
>> temporary until urinary system takes over

- restore normal pH in fractions of a second

- 3 major chemical buffers: bicarbonate, phosphate, and protein systems
bicarbonate buffer system
- solution of carbonic acid and bicarbonate ions

> functions best in LUNGS and KIDNEYS to constantly remove CO2
>> to lower pH - kidneys excrete HCO3
>> to raise pH - kidney's excrete H+ and lungs excrete CO2

- all bicarbonate ions in tubular fluid are consumed, neutralizing H+
> the more acid the kidneys secrete, less sodium is in the urine
phosphate buffer system
- more important buffering the ICF and RENAL TUBULES
> where phosphates are more concentrated and function closer to their optimum pH of 6.8

- dibasic sodium phosphate is contained in glomerular filtrate > reacts with some of the H+, replacing a Na+ in the buffer which passes into the urine
protein buffer system
- proteins are more concentrated than bicarbonate or phosphate systems, especially in the ICF

- accounts for about 3/4 of all chemical buffering in the body fluids

- its ability is due to certain side groups of their amino acid residues
respiratory control of pH
- adjusting CO2 level in blood
> addition of CO2 to body fluids > raises H+ and lowers pH
> removal of CO2 has opposite effect

- neutralizes 2-3X as much acid as chemical buffers

- CO2 is constantly produced by aerobic metabolism

- increased CO2 and decreased pH stimulate pulmonary ventilation, while an increased pH inhibits pulmonary ventilation
renal control of pH
- kidneys can neutralize more acid or base than either respiratory system or chemical buffers

- tubules secrete H+ into the tubular fluid
> most binds to bicarbonate, ammonia, and phosphate buffers
> bound and free H+ are excreted in the urine actually expelling H+ from the body

>> other systems only reduce its concentration by binding it to other chemicals
- from amino acid catabolism > acts as a base to neutralize acid
disorders of acid-base balance
- depends on bicarbonate buffer system
- pH below 7.35

- H+ diffuses into cells and drives out K+, elevating K+ concentration in ECF

- H+ buffered by protein in ICF, causes membrane hyperpolarization, nerve and muscle cells are hard to stimulate;
> CNS depression may lead to confusion, disorientation, coma, and possibly death

>> not able to stimulate diaphragm
- pH above 7.45

- H+ diffuses out of cells and K+ diffuses in
- membranes depolarized, nerves overstimulated, muscles causing spasms, tetany, convulsions, respiratory paralysis

>> a person cannot live for more than a few hours if the blood pH is below 7.0 or above 7.7
respiratory acidosis
- occurs when rate of alveolar ventilation fails to keep pace with the body's rate of CO2 production

- CO2 accumulates in the ECF and lowers its pH

- occurs in emphysema where there is a severe reduction of functional alveoli
respiratory alkalosis
- results from hyperventilation

- CO2 eliminated faster than it is produced
metabolic acidosis
- increased production of organic acids such as lactic acid in anaerobic fermentation, and ketone bodies seen in alcoholism, and diabetes mellitus

- ingestion of acidic drugs (asprin)

- loss of base due to chronic diarrhea, laxative overuse
metabolic alkalosis
- RARE but can result from:
> overuse of bicarbonates (antacids and IV bicarbonate solutions)

> loss of stomach acid (chronic vomiting)
compensation for acid-base imbalances
- COMPENSATED: either kidneys compensate for pH imbalances of respiratory origin or the respiratory system compensates for pH imbalances of metabolic origin

- UNCOMPENSATED: a pH imbalance that the body cannot correct without clinical intervention
compensation for acid-base imbalances: respiratory compensation
- changes in pulmonary ventilation to correct changes in pH of body fluids by expelling or retaining CO2

> HYPERCAPNIA (excess CO2) - stimulates pulmonary ventilation, eliminating CO2 and allowing pH to rise

> HYPOCAPNIA (deficiency of CO2) - reduces ventilation and allows CO2 to accumulate, lowering pH
compensation for acid-base imbalances: renal compensation
- an adjustment of pH by changing the rate of H+ secretion by the renal tubules
> slow, but better at restoring a fully normal pH

- kidneys cannot act quickly enough to compensate for short-term imbalances

- effective at compensating for pH imbalances that lasts for a few days or longer
What is the term for the serious membrane that suspends the intestines from the abdominal wall?
- mesenteries
Which physiological process of the digestive system truly moves a nutrient from the outside to the inside of the body?
- absorption
> because the digestive tract is considered OPEN/external to the body until absorbed by the epithelial cells of the alimentary canal
What one type of reaction is the basis of all chemical digestion?
- hydrolysis reactions
> breaks macromolecules into their monomers (residues) >> carried out by digestive enzymes
Name some nutrients that are absorbed without being digested.
vitamins, free amino acids, minerals, cholesterol, water
List as many functions of the tongue as you can.
manipulates food, sensitive to texture, taste
Imagine a line from the mandibular bone to the root canal of a tooth. Name the tissues, in order, through which this line would pass.
mandibular bone > periodontal ligament > cementum > dentine > root canal
What is the difference in function and location between intrinsic and extrinsic salivary glands? Name the extrinsic salivary glands and describe their locations.
- INTRINSIC - located inside oral tissue
> secretes saliva at a fairly constant rate
> lingual lipase keeps mouth moist and inhibits bacterial growth

- EXTRINSIC - outside oral mucosa
> require ducts
> secrete saliva mainly in response to food in the mouth
> secretes mucous, amylase, electrolytes
1) parotid glands > anterior to ear
2) submandibular glands >
3) sublingual > floor of mouth
Describe the muscularis externa of the esophagus and its action in peristalsis.
- upper 1/3 - skeletal muscle
- mid 1/3 - mixture of skeletal and smooth muscle
- lower 1/3 - smooth muscle

> contraction of smooth muscle propels contents >> peristalsis
Describe the mechanisms that prevent food from entering the nasal cavity and larynx during swallowing.
1) the root of the tongue blocks the oral cavity
2) the soft palate rises and blocks the nasopharynx
3) the infrahyoid muscles pull the larynx up to meet the epiglottis
Name four types of epithelial cells of the gastric and pyloric glands and state what each one secretes.
1) mucous cells > mucus

2) parietal cells > hydrochloric acid

3) chief cells > enzymes, gastric lipase, and pepsinogen

4) enteroendocrine > hormones & paracrines that regulate digestion
Explain how the gastric glands produce hydrochloric acid and why this produces an alkaline tide.
When carbonic acid is formed in the cell it is broken down into bicarbonate and H+ so the H can be pumped into the stomach to make it acidic > the bicarb goes into the blood > blood leaving the stomach has a higher pH when digestion is occurring than when the stomach is empty >> high pH blood = alkaline tide
What positive feedback cycle can you identify in the formation and action of pepsin?
pepsin has an autocatalytic effect > as some pepsin is formed, it converts pepsinogen into more pepsin
How does food in the duodenum inhibit motility and secretion in the stomach?
enterogastric reflex > w/hormones secretion & CCK
What does the liver contribute to the digestion?
secretion of bile
Trace the pathway taken by bile acids from the liver and back. What is the pathway called?
- ENTEROHEPATIC CIRCULATION - bile salts are made in the liver > gallbladder > SI where they aid in fat digestion/absorption) > liver
What stimulated cholecystokinin (CCK) secretion, and how does CCK affect other parts of the digestive system?
- secreted in response to fats in small intestine

> causes gallbladder contractions > bile release
What 3 structures increase the absorptive surface area of the small intestine?
1) circular folds
2) villi
3) microvilli
Distinguish between segmentation and the migrating motor complex of the small intestine. How do these differ in function?
- SEGMENTATION - mixes and cuts contents > churns
> most common type of intestinal contraction

- MIGRATING MOTOR COMPLEX - successive, overlapping waves of contraction (peristalsis) to move contents along
What 3 classes of nutrients are most abundant? What are the end products of enzymatic digestion of each?
1) carbohydrates > glucose
2) proteins > amino acids
3) fats > monoglycerides
What 2 digestive enzymes occur in the saliva? Why is one of these more active in the stomach than in the mouth?
- amylase

- lingual lipase > intrinsic salivary glands of tongue > becomes more active at the acidic pH of stomach

>> lipase only works in low pH in stomach
Explain the distinctions between an emulsification droplet, a micelle, and a chylomicron.
- EMULSIFICATION DROPLET - fat droplet and bile acid

- MICELLE - droplets in bile that aid in absorption of 2 FFAs and a monoglyceride

- CHYLOMICRON - packaged into secretory vesicles that migrate to basal surface
What happens to digestive enzymes after they have done their job? What happens to dead epithelial cells that slough off the gastrointestinal mucosa? Explain.
neutralized and becomes part of feces
How does the mucosa of the large intestine differ from that of the small intestine? How does the muscularis externa differ?
- mucosa has simple comumnar epi, no circular folds or villi

- muscularis externa - longitudinal muscle forms 3 ribbon like stripes > pouches called haustra
Name and briefly describe 2 types of contractions that occur in the colon and nowhere else in the alimentary canal.
1) HAUSTRAL CONTRACTIONS - (every 30min) - most common > curns & mixes the residue, promotes water and salt absorption and passes the residue distally to another haustrum

2) MASS MOVEMENTS - (1-3X/day, last 15 min) > move several cm at a time
Describe the reflexes that cause defecation in an infant. Describe the neural controls that function following toilet-training.
- INTRINSIC DEFECATION REFLEX - stretch signals in muscles activates peristaltic waves that drives feces downward

- PARASYMPATHETIC DEFECATION REFLEX - stretch signal > spinal cord > trigger peristalsis and relax sphincters

>> voluntary control of the external anal sphincter
the digestive system is..
- the organ system that processes food, extracts nutrients from it, and eliminates the residue

- essentially a "disassembly line:

> to break down nutrients into a form that can be used by the body

> to absorb them so they can be distributed to the tissues
5 stages of digestion
1) ingestion - selective intake of food

2) digestion - mechanical and chemical breakdown of food into a form usable by the body

3) absorption - uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph

4) compaction - absorbing water and consolidating the indigestible residue into feces

5) defecation - elimination of feces
mechanical digestion
- the physical breakdown of food into smaller particles

> cutting and grinding action of the teeth

> churning action of stomach and small intestines

> exposes more food surface to the action of digestive enzymes
chemical digestion
- a series of hydrolysis reactions that breaks dietary macromolecules into their monomers (residues)
digestive tract
- alimentary canal (start to finish)

- mouth > pharynx > esophagus > stomach > small intestine > large intestine
gastrointestinal tract (GI)
the stomach and intestines
accessory organs
teeth, tongue, salivary glands, liver, gallbladder, and pancreas
enteric nervous system
- a nervous network in the esophagus, stomach, and intestines that regulate digestive tract motility, secretion, and blood flow

> functions completely independently of the CNS

- 2 networks of neurons: submucosal plexus & myenteric plexus

> enteric nervous system contains sensory neurons that monitor tension in gut wall and conditions in lumen
- connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall

> allows stomach and intestines to undergo strenuous contractions

> allow freedom of movement in the abdominal cavity

> prevents the intestines from becoming twisted and tangled by changes in body position and by its own contractions

> provides passage of blood vessels and nerves that supply digestive tract

> contain many lymph nodes and lymphatic vessels
regulation of digestive tract
- motility and secretion of the digestive tract are controlled by:

1) neural control - short (myenteric) reflexes - stretch or chemical stimulation acts through myenteric plexus
> stimulates parastaltic contractions of swallowing

2) hormones - gastrin and secretin

3) paracrine secretions - chemical messengers that diffuse through the tissue fluids to stimulate nearby target cells
- breaks food into smaller pieces to be swallowed and exposes more surface to the action of digestive enzymes

> first step in mechanical digestion

> food stimulates oral receptors that trigger *involuntary chewing reflex
- moisten mouth
- begin starch and fat digestion
- cleanse teeth
- inhibit bacterial growth
- dissolves molecules so they can stimulate the taste buds
- moistens food and bind it together into bolus to aid in swallowing

>> pH of 6.8-7
saliva - hypotonic solution of...
- 97%-99.5% water and the following solutes
salivary amylase
- enzyme that begins starch digestion in the mouth
lingual lipase
enzyme that is activated by stomach acid and digests fat after the food is swallowed
binds and lubricates the mass of food and aids in swallowing
enzyme that kills bacteria
immunoglobulin A (IgA)
an antibody that is inhibits bacterial growth > has secretory unit that keeps it from being broken down by stomach acid
Na, K, Cl, phosphate and bicarbonate
mass swallowed as a result of saliva binding food particles into a soft, slippery, easily swallowed mass
- a muscular funnel that connects oral cavity to esophagus and allows entrance of air from nasal cavity to larynx
> common passageway: digestive and respiratory tracts intersect
- straight, muscular tube 25-30cm long

- extends from pharynx to cardiac orifice of stomach passing through esophageal hiatus in diaphragm
lower esophageal sphincter
- food pauses at this point because of this constriction
> prevents stomach contents from regurgitating into the esophagus
> protects esophageal mucosa from erosive effect of the stomach acid

- *heartburn - burning sensation produced by acid reflux into the esophagus

- covered with adventitia
swallowing (deglutition)
- a complex action involving over 22 muscles in the mouth, pharynx, and esophagus
swallowing center
- pair of nuclei in medulla oblongata that coordinates swallowing
2 phases of swallowing
1) buccal phase - voluntary control

2) pharyngoesophageal phase - involuntary
> bolus enters esophagus, stretches it, and stimulates peristalsis
- primarily functions as a food storage organ

- internal volume - about 50mL when empty
- 1-1.5L after typical meal

> mechanically breaks up food particles, liquefies the food, and begins chemical digestion of protein and fat
>> *chyme - soupy of pasty mixture of semi-digested food in the stomach
( most digestion occurs AFTER the chyme passes on to the small intestine)
4 regions of stomach
1) cardiac region (cardia)

2) fundic region (fundia)

3) body (corpus)

4) pyloric region
> pyloris - narrow passage to duodenum
pyloric sphincter
regulates the passage of chyme into the duodenum
cells of gastric glands: mucous cells
- secrete mucus
> predominate in cardiac and pyloric glands
cells of gastric glands: regenerative cells
- stem cells > divide rapidly and produce a continual supply of new cells to replace cells that die
cells of gastric glands: parietal cells
- secrete HCl, intrinsic factor, and a hunger hormone (ghrelin)
cells of gastric glands: chief cells
- most numerous

- secrete gastric lipase and pepsinogen
cells of gastric glands: enterendocrine cells
- secrete hormones and paracrine messengers that regulate digestion
gastric juice
2-3L per day produced by the gastric glands

> mainly a mixture of H2O, HCl, and pepsin
hydrochloric acid
- gastric juice has a high concentration of it > pH as low as 0.8

- parietal cells produce HCl and contain carbonic anhydrase (CAH)
functions of HCl
- activates pepsin and lingual lipase
- breaks up connective tissues and plant cell walls > helps liquify food to form chyme
- converts ingested ferric(Fe3) ions to ferrous (Fe2) ions > absorbed and used for hemoglobin synthesis
- contributes to nonspecific disease resistance by destroying most ingested pathogens
- ZYMOGENS - digestive enzymes secreted as *inactive proteins
> converted to active enzymes by removing some of their amino acids

- PEPSINOGENS - zymogen secreted by the chief cells
> HCl removes some of its amino acids and forms pepsin tha digests proteins
> autocayalytic effect

>> digests dietary proteins into shorter peptide chains
> protein digestion is completed in the small intestine
gastric lipase
- produced by chief cells
- play minor role in digesting dietary fats
intrinsic factor
- glycoprotein secreted by parietal cells
- essential to absorption of vitamin B12 by the small intestine
> binds vitamin B12 and intestinal cells absorb this complex by receptor-mediated endocytosis
> B12 needed to synthesize hemoglobin >> prevents pernicious anemia

*** secretion of intrinsic factor is the ONLY INDISPENSABLE function of the stomach
> digestion can continue if stomach is removed but B12 supplements will be needed
chemical messengers
- gastric an pyloric glands have various kinds of enterendocrine cells that produce as many as 20 chemical messengers
> some are hormones
> paracrine
> several are peptides: produced in both the digestive tract and the CNS >> gut-brain peptides
gastric motility
- swallowing center of medulla oblongata signals stomach to relax
> food stretches stomach activating a receptive-relaxation response (resists stretching briefly, but relaxes to hold more food)
> soon stomach shows a rhythm of peristaltic contractions controlled by pacemaker cells in longitudinal layer of muscularis externa

- only 3mL of chyme enter the duodenum at a time > enables the duodenum to neutralize the stomach acid & digest nutrients little by little
digestion and absorption
- salivary and gastric enzymes partially digest protein and lesser amounts of starch and fat in the stomach

> most digestion and nearly all absorption occur after the chyme has passed into the small intestine

- stomach does not absorb any significant amount of nutrients >> aspirin & some lipid-soluble drugs

- alcohol is absorbed mainly by small intestine
> intoxicating effects depends partly on how rapidly the stomach is emptied
protection of the stomach
- protected in 3 ways from the harsh acidic and enzymatic environment it creates:

1) mucous coat - thick, highly alkaline mucus

2) tight junctions - between epithelial cells prevent gastric juice from seeping between them and digesting the connective tissue of the lamina propria and beyond

3) epithelial cell replacement - stomach epi. cells live only 3-6 days

> breakdown of these protective measures can result in inflammation and peptic ulcer
- inflammation of the stomach can lead to a peptic ulcer as pepsin and HCl erode the stomach wall
gastric activity is divided into 3 phases
1) cephalic phase

2) gastric phase

3) intestinal phase

>> phases can overlap and occur simultaneously
cephalic phase
- stomach being controlled by brain

- stomach responds to sight, smell, taste, or thought of food
> sensory and mental inputs converge on the hypothalamus >> relays signals to medulla oblongata

- enteric nervous system of stomach, in turn, stimulates gastric secretion
gastric phase
- stomach controlling itself

- period in which swallowed food and semi-digested protein activates gastric activity
>> 2/3 of gastric secretion occurs in this phase

- ingested food stimulates gastric activity in 2 ways:
1) by stretching the stomach
2) by increasing the pH of its contents

- gastric secretion is stimulated by 3 chemicals:
1) ACh
2) histamine
3) gastrin
intestinal phase
- stomach being controlled by small intestine

- the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes

- duodenum initially enhances gastric secretion, but soon inhibits it
> enterogastric reflex - duodenum sends inhibitory signals to the stomach by way of the enteric nervous system and signals to the medulla

> chyme stimulates duodenal enterendocrine cells to release secretin and CCK >> stimulate pancreas and gall bladder & suppress gastric secretion

> pyloric sphincter contracts tightly to limit chyme intering duodenum >> gives duodenum time to work on chyme
- body's largest gland
- secretes bile which contributes to digestion (especially of fatty foods)
hepatic lobules
- tiny innumerable cylinders that fill the interior of the liver

- consist of:
> central vein - passing down the core
> hepatocytes
functions of hepatocytes
- after a meal > absorb from the blood >> glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage

- removes and degrades > hormones, toxins, bile pigments, drugs

- secretes into the blood > albumin, lipoproteins, clotting factors, angiotensinogen

- between meals > breaks down stored glycogen and releases glucose into the blood
gall bladder
- serves to store and concentrate bile >> by a factor of 20 by absorbing water and electrolytes
- yellow-green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids
- principal pigment derived from the decomposition of hemoglobin
bile acids
- bile salts > steroids synthesized from cholesterol

- 80% are reabsorbed in the ileum and returned to the liver
- 20% are excreted in the feces >> the body's ONLY way of eliminating excess cholesterol
- endocrine portion - pancreatic islets that secrete insulin and glucagon

- exocrine portion - 99% of pancreas that secretes 1200-1500mL of pancreatic juice per day
pancreatic duct
- hepatopancreatic sphincter > controls release of both bile and pancreatic juice into the duodenum
pancreatic juice
- alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes
> need to neutralize chyme
small intestine
- nearly all chemical digestion and nutrient absorption occurs here

- 3 regions
1) duodenum (first 25cm)- stomach acid is neutralized here; fats are physically broken up (emulsified) by the bile acids

2) jejunum - (first 40% of SI beyond duodenum) - especially rich BLOOD SUPPLY >> most nutrient absorption occurs here

3) ileum - last part - no blood supply; Peyer patches > keeps an eye on bacteria
ileocecal valve
regulates passage of food residue into the large intestine
intestinal motility
- contractions of small intestine serve 3 functions:

1) to mix chyme with intestinal juice, bile, and pancreatic juice >> neutralize acid, digest nutrients more effectively

2) to churn chyme and bring it in contact with the mucosa for contact digestion and nutrient absorption

3) to move residue toward large intestine

- SEGMENTATION - mvmt in which stationary ringlike constrictions appear in several places along the intestine

- PERISTALSIS - gradual movement of contents towards colon; begins in the duodenum

- MIGRATING MOTOR COMPLEX - successive, overlapping waves of contraction milk chyme toward colon over a period of 2 hours