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Ch 26 Lecture

Terms in this set (60)

What percentage of your body mass is water?
Depends on age. Infants=73%+, Adult Male~60%, Adult Female~50%, Old age declines to 45%
Fluid Compartments: Where in the body is water found?
1. Intracellular fluid (ICF) compartment - Fluid within the cells
2. Extracellular fluid (ECF) compartment - outside cell membrane: Plasma, Interstitial fluid, other (lymph, CSF, humors of the eye, synovial fluid, and gastrointestinal secretions
Composition of body fluids
electrolyte or nonelectrolyte
Nonelectrolyte
most are organic, do not dissociate in water: glucose, lipids, creatinine, urea
Electrolytes
-Dissociate into ions in water: inorganic salts, all acids and bases, and some proteins.
-Most abundant solute in body fluid
-Greater osmotic power than nonelectrolytes, may contribute to fluid shifts
-Determine the chemical and physical reactions of fluids
Expressing Electrolyte Concentration
Milliequivalents per liter (mEq/L): measure of the number of electrical charges per liter of solution.
mEq/L=
[ion concentration (mg/L)/atomic weight of ion (mg/mmol)] * # of electrical charges on one ion
Need to know
1. Ion concentration in the plasma (pg.997)
2. Atomic weight of the ion (Appendix E)
3. Ionic charge (Appendix E)
Compare Extracellular and Intracellular Fluids
-Each has distinctive pattern of electrolytes
-Extracellular Fluid: similar, except higher protein content in plasma (major cation: Na+, major anion: Cl-)
-Intracellular Fluid: Low Na+ & Cl- (major cation: K+, major anion: HPO4^2-
Extra/Intra cellular Fluids
Bulk of dissolved solutes: Proteins and nonelectrolytes (phospoholipids, cholesterol, neutral fats)
-90% in plasma
-60% in Interstitial fluid
-97% in Intracellular fluid
Fluid Movement Among Compartments
-Regulated by osmotic and hydrostatic pressures
-Water moves freely by osmosis; osmolalities of all body fluids are almost always equal
-Ion movements require active transport or channel carriers
-Change in solute concentration of any compartment leads to change in net water flow
Water Balance and ECF Osmolality
-For body to remain hydrated hydrated, water intake must = water output (2500mL/day)
-Water intake: beverages, food and metabolic water (water produced by cellular metabolism; aka water of oxidation)
-Water output: urine, insensible water loss (skin and lungs), perspiration and feces
-We can maintain tonicity of body fluids in very narrow limits
Rise/Decline in plasma osmolality
-Rise in plasma osmolality: 1) you become thirsty, drink water; 2) ADH is released, causes kidneys to conserve water and concentrate urine
-Decline in plasma osmolality: 1) Inhibition of thirst; 2) Inhibition of ADH and kidneys allow water to be released via urine
Regulation of Water Intake
-Thirst mechanism is the driving force for water intake
-Hypothalamus thirst center osmoreceptors are stimulated by: decline in plasma osmolality of 2-3%, Angiotensin II or baroreceptor input, Dry mouth, Substantial decrease in blood volume or pressure
-Drinking water creates inhibition of thirst center
-Inhibitory feedback signals include: Relief of dry mouth & activation of stomach and intestinal stretch receptors
Regulation of Water Output
-Obligatory water losses: Insensible (from lungs or skin), Feces, Minimum daily sensible loss of 500 mL in urine to excrete wastes
-Body water and Na+ content are regulated in tandem by mechanisms that maintain cardiovascular function and blood pressure
Regulation of Water Output: Influence of ADH
-Water reabsorption in collecting ducts is proportional to ADH release
-decrease in ADH -> dilute urine and dec. volume of body fluids
-increase in ADH -> concentrated urine
-Hypothalamic osmoreceptors trigger or inhibit ADH release
-Other factors that may trigger ADH release: fever, sweating, vomitting, diarrhea, blood loss, traumatic burn
Disorder: Dehydration
-ECF water loss due to: hemorrhage, severe burns, prolonged comiting or diarrhea, profuse sweating, water deprivation, diuretic abuse
-signs/symptoms: thirst, dry flushed skin, oliguria
-May lead to weight loss, fever, mental confusion, hypovolemic shock, loss of electrolytes
Oliguria
Urinating a lot
Can you die from drinking too much water?
Yes!
28 y/o Jennifer Strange died from excessive consumption of water in 2007, Wii contest
Disorder: Hypotonic Hydration
-Cellular overhydration, or water intoxication
-Occurs with renal insufficiency or rapid excess water ingestion
-ECF is diluted -> hyponatremia -> net osmosis into tissue cells -> swelling of cells -> severe metabolic disturbances (nausea, vomiting, muscular cramping, cerebral edema typically leading to headaches) -> possible death
Disorder: Edema
-Atypical accumulation of IF Fluid -> tissue swelling
-Due to anything that increases flow of fluid out of the blood or hinders its return: Inc blood pressure, inc capillary permeability, incompetent venous valves/localized blood vessel blockage, Congestive heart failure/hypertension/inc. blood volume.
Edema
-Hindered fluid return occurs with an imbalance in colloid osmotic pressures (e.g. hypoproteinemia = dec plasma proteins) 1.Fluids fail to return at the cenous ends of capillary beds, 2.Results from protein malnutrition, liver disease, or glomerulonephritis
-Blocked (or surgically removed) lymph vessels 1.Cause leaked proteins to accumulate in IF, 2.Inc Colloid osmotic pressure of IF draws fluid from the blood, 3. Results in low BP and severely impaired circulation
Electrolyte Balance
-Electrolytes are salts, acids and bases
-Electrolyte balance usually refers only to salt balance
-Salts enter the body by ingestion and are lost via perspiration, feces, and urine
What is the importance of salts?
1. Controlling fluid movements
2. Excitability
3. Secretory activity
4. Membrane permeability
Central Role of Sodium in Fluid and Electrolyte Balance
-Most abundant cation in the ECF
-Sodium salts in ECF contribute to 280 mOsm of the total 300 mOsm ECF solute concentration (# of millimoles of a solute per 1 kg of solvent)
-Na+ leaks into cells and is pumped out against its electrochemical gradient
-Na+ content may change, but ECF Na+ concentration remains stable due to osmosis
-Changes in plasma sodium levels affect: 1. plasma volume, BP, 2. ICF and IF volumes
-Renal acid-base control mechanisms are coupled to sodium ion transport
-No receptors are known that monitor Na+ levels
-Na+-water balance is linked to BP and blood volume control mechanisms
Regulation of Sodium Balance: Aldosterone
-Na+ reabsorption: 65% is reabsorbed in the proximal tubules, 25% is reclaimed in the loops of Henle
-Aldosterone ->active reabsorption of remaining Na+
-Water follows Na+ if ADH is present
-Renin-angiotensin mechanism is the main trigger for aldosterone release. JG cells of JGA secrete renin in response to: 1. Sympathetic nervous system stimulation, 2. Dec. Filtrate osmolality, 3. Dec Stretch (due to dec. BP)
-Renin catalyzes the production of angiotensin II -> prompts Aldosterone release from adrenal cortex
-Aldosterone release is also triggeres by elevated K+ levels in ECF
- Aldosterone brings about effects slowly (hrs-days)
Regulation of Sodium Balance: by ANP
-ANP = Atrial Natriuretic Peptide
-Released by atrial cells in response to stretch (^ BP)
-Effects
-v BP and blood volume: 1. v ADH, renin and aldosterone production, 2. ^ excretion of Na+ and water, 3. Promotes vasodilation directly and also by decreasing production of angiotensin II
Sodium Balance: Influence of other Hormones
1. Estrogens: ^ NaCl reabsorption similar to aldosterone H2O retention during menstrual cycles and pregnancy because NaCl is being retained, Helps give ladies that wonderful bloated feeling->where ever NaCl goes, water follows
2. Progesterone: v Na+ reabsorption by blocking aldosterone activity in renal rubules, *promotes Na+ and H2O loss
3. Glucocorticoids: enhance Na+ reabsorption and ^ glomerular filtration rate (GFR), *high levels of glucocorticoids promote aldosterone like effects -> ^NaCl reabsorption causing edema
Cardiovascular Baroreceptors
-Baroreceptors alert the brain of ^ in blood volume and BP
-If baroreceptors detect a rise in BP the following happens: 1.Sympathetic nervous system impulses the kidneys to decline, 2. Afferent arterioles dilate, 3. GFR increases, 4.Na+ and water output ^, 5.v in BP
Potassium Importance (review)
1. Huge affects on resting membrane potential of excitable cells (neurons and cardiac muscle)
-^ of extracellular (EC) K+ -> depolarization of resting membrane potential -> reduced excitability
-v of EC K+ -> hyperpolarization of resting membrane potential ->nonresponsiveness
-severe alterations in K+ levels in the heart can cause sudden cardiac death (chemical execution)
2. K+ also plays role in maintaining pH balance
-Acidosis: K+ leaves cell, hydrogen enters cell, ECF levels of K+ rise
-Alkalosis: K+ enters ell, hydrogen leaves cell, EC levels of K+ decline
-Changes in ECF levels of K+ alters activity of excitable cells
Regulation of K+ Balance
-Controlled by the cortical collecting ducts by changing the amount of K+ secreted into the filtrate
Na+ is never secreted into the filtrate 60-80% of filtered K+ is reabsorbed in proximal tubule, 10-20% is reabsorbed in the thick ascending loop of Henle, 10% in collecting ducts
-High K+ contect in extracellular fluid, principal cell secretion of K+; *more K+ ends up in urine is what this means
-Low K+ levels in extracellular fluid, type A intercalated cells reabsorb K+ left in the filtrate; *what is a type A intercalated cell? Cell in the collecting duct the reabsorbs K+, excretes hydrogen to help maintain pH balance
-Keep in mind: main job of the kidneys is to excrete K+
Regulation of K+ balance by Aldosterone
-Stimulates K+ secretion (and Na+ reabsorption) by Principal Cells
-^ K+ in the adrenal cortex causes release of aldosterone K+ secretion
Regulation of Calcium
Importance of Calcium in the body: 1)Neuromuscular excitability, 2) Blood clotting, 3) Cell membrane permeability, 4)Secretory activities.
-Imbalances: Hypocalcemia: increases excitability and muscle tetany, Hypercalcemia: Inhibits neurons and muscle cells, may cause heart arrhythmias.
Regulation of Calcium by PTH
-Calcium balance is controlled by Parathyroid Hormone (PTH) and calcitonin, *bones are the largest reservoir for Ca^2+ and phosphates.
-PTH promotes increase in calcium levels by targeting bones, kidneys, and small intestine (indirectly thru VitD)
-Most calcium in passively reabsorbed in the proximal convoluted tubule and actively transported in the distal portion of the nephron, *98% is reabsorbed
-If extracellular fluid levels of calcium in high, *PTH is inhibited; calcium is excreted into the urine and feces
Regulation of Anions
-Chloride is the major anion in extracellular fluid, helps maintain the osmotic pressure of the bood, 99% of Cl- is reabsorbed under normal pH conditions
-When acidosis occurs, fewer chloride ions are reabsorbed, while bicarbonate ions are reabsorbed, *this helps re-establish a normal pH
pH of Body Fluids
-pH affects all functional proteins and biochemical reactions
-Normal pH of body fluids: Arterial blood=7.4, venous blood and interstitial fluid=7.35, *Intracellular fluid=7.0
-Alkalosis or alkalemia: arterial blood pH >7.45
-Acidosis or acidemia: arterial pH<7.35
Acid and Base properties in Water
-Strong acids dissociate completely in water; can dramatically affect pH
-Weak acids dissociate partially in water; are efficient at preventing pH changes
-Strong bases dissociate easily in water; quickly tie up H+
-Weak bases accept H+ more slowly
Acid-Base Balance
-Most H+ (acid) is produced by metabolism, phosphoric acid from breakdown of phosphorus-containing proteins in extracellular fluid, Lactic acid from anaerobic respiration of glucose, Fatty acids and ketone bodies from fat metabolism, H+ liberated when CO2 is converted to HCO3- in blood
-Regulation of pH, 1)chemical buffer systems: rapid; happens first, 2)Brain stem respiratory centers; act within 1-3 minutes, 3)Renal mechanisms: most potent, but require hours to days to effect pH changes
Chemical Buffer Systems
-What is a chemical buffer? *System of 1+ compounds that act to reset pH changes when strong acid or base is added
-What system does the body have? 1)Bicarbonate buffer system, 2) Phosphate buffer system, 3)protein buffer system
Bicarbonate Buffer system
-Is the single most important buffer system in the extracellular fluid, *It does work as a buffer in the intracellular fluid too
-What is it? *Mixture of carbonis acid (H2CO3; weak acid) and sodium bicarbonate (NaHCO3; weak base)
Bicarbonate Buffer System working the presence of strong acid
Example: Hydrochloric Acid
-HCO3- ties up H+ and forms H2CO3
HCl + NaHCO3 -> H2CO3 + NaCl
st acid wk base wk acid salt
-pH will decrease slightly, *unless all acailable HCO3- (alkaline reserve) is used up
-HCO3- concentration is closely regulated by the kidneys
Bicarbonate Buffer System Working in the presence of a strong Base
Example: Sodium Hydroxide
-causes H2CO3 to dissociate and donate H+
-H+ ties up the base (OH-)
NaOH + H2CO3 -> NaHCO3 + H2O
st base wk acid wk base water
-pH rises only slightly
-H2CO3 supply is almost limitless (from CO2 released by respiration)
-Regulated by respiratory controls
Phosphate buffer system
-Action is nearly identical to the bicarbonate buffer
-components are sodium slats of: Dihydrogen phosphate (H2PO4-), a weak acid, Monohydrogen phosphate (HPO4^2-), a weak base
-Effective buffer in urine and intracellular fluid, where phosphate concentrations are high
Protein buffer system
-intracellular proteins are plentiful and powerful buffers; plasma proteins are also important
-Protein molecules are amphoteric, amphoteric-capsule of functioning as both a weak acid and a weak base depending of whether it needs to be an acid or base, when pH rises, organic acid or carboxyl (COOH) groups release H+, *when pH falls, NH2, groups bind H+
-Example: hemoglobin
Physiological Buffer Systems
-chemical buffers cannot eliminate excess acids or bases from the body; physiological buffers do this
-But what is it? *An organ system that works to control pH levels in the body, slow acting but have a greater buffering capacity than chemical buffer systems, 1)Respiratory system, 2) Renal System
-Terms associated with physiological buffers
*Volatile Acid: an acid that can be eliminated by the lungs (carbonic acid)
*Fixed (metabolic) acid: an acid generated by cellular respiration and has to be eliminated by the kidneys
Respiratory Regulation of Acidic pH levels
-A reversible equilibrium exists in the blood:
*CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
*respiratory system eliminates CO2
-During CO2 unloading the reaction shifts to the left (and H+ is incorporated into H2O)
-During CO2 loading the reaction shifts to the right (and H+ is buffered by proteins)
-Notice part of this equation is identical to the bicarbonate buffer system, *Bicarbonate is how CO2 is transported in erythrocytes
Respiratory Regulation of Acidic pH Levels
-Hypercapnia: Very high levels of CO2 in blook
*CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
~Will push the balance of the equation to the left, causing increased acidity (lower pH)
~The high CO2 levels will be detected by medullary chemoreceptors
~The low pH level will be detected by peripheral chemoreceptors
~Both trigger an increase in respiration to get lower pH and CO2
Know/Understand this equation
CO2 + H2O <-> H2CO3 <-> H+ +HCO3-
Acid-Base Balance
-What would happen if blood pH levels become alkaline? *Respiratory centers become depressed, decreasing respiration
-What happens next? *Slow down breathing and push equation opposite direction
-Respiratory system impairment causes acid-base imbalances Hypoventilation -> respiratory acidosis Hyperventilation -> respiratory alkalosis
Renal Mechanisms of Acid-Base Balance
-Renal Mechanisms: 1)Conserving (reabsorbing) or generating new HCO3- generating/reabsording HCO3- is the same as losing one H+, 2)Excreting HCO3-, Excreting HCO3- is the same as gaining one H+
-Renal regulation of acid-base balance depends on secretion of H+
-H+ secretion occurs in the proximal convoluted tubule and in collecting duct type A intercalated cells, *The H+ comes from H2CO3 produced in reactions catalyzed by carbonic anhydrase inside the cells
Reabsorption of Bicarbonate
-PCT cell luminal membranes are impermeable to HCO3-, 1)CO2 combines with water in PCT cells, forming H2CO3, 2)H2CO3 dissociates, 3)H+ is secreted, and HCO3- is reabsorbed into capillary blood, 4)Secreted H+ unites with HCO3- to form H2CO3 in filtrate, which generates CO2 and H2O
-HCO3- disappears from filtrate at the same rate that it enters the peritubular capillary blood
Generating New Bicarboate ions
-Two mechanisms generate new HCO3- to be added to the alkaline reserve, *occurs in PCT and collecting duct type A intercalated cells
-Both involve renal excretion of acid via secretion and excretion of H+ or NH4+
Excretion of Buffered H+
-Dietary H+ must be balanced by generating new HCO3-
-Most filtered HCO3- is used up before filtrate reaches the collecting duct
-Intercalated cells actively secrete H+ into urine, which is buffered by phosphates and excreted
-Generated 'new' HCO3- moves into the interstitial space via a cotransport system and then moves passively into peritubular capillary blood
*Cl-coming in, is driving HCO3- out
Ammonium Ion Excretion
-Involves metabolism of glutamine in PCT cells
-Each glutamine produces 2 NH4+ and 2 'new' HCO3-
-HCO3- moves to the blood and NH4+ is excreted in urine
Bicarbonate Ion Secretion
-During alkalosis, type B intercalated cells start working to help restore pH, 1)Secrete HCO3-, 2)Reclaim H+ and acidify the blood
-Mechanism is the opposite of the bicarbonate ion reabsorption process by type A intercalated cells
-Even during alkalosis, the nephrons and collecting ducts excrete fewer HCO3- than they conserve
Respiratory Acidosis and Alkalosis
-the most important indicator of adequacy of respiratory function in Pco2 level (normally 35-45 mmHg),
~Pco2 above 45 mmHG -> respiratory acidosis, Most common cause of acid-base imbalances, due to decrease in ventilation or gas exchange, *characterized by falling blood pH and rising Pco2
~Pco2 below 35 mmHg -> respiratory alkalosis, *A common result of hyperventilation due to stress or pain
Metabolic acidosis and Alkalosis
-Cause of metabolic acidosis, 1)ingestion of too much alcohol (->acetic acid), 2)Excessive loss of HCO3- (eg, persistent diarrhea), 3)Accumulation of lactic acid, shock, ketosis in diabetic crisis, starvation, and kidney failure
-Metabolic alkalosis is much less common that metabolic acidosis, 1)indicated by rising blood pH and HCO3-, 2)Caused by vomiting of the acid contents of the stomach or by intake of excess base (antacids)
Effects of Acidosis and Alkalosis
-Blood pH below 7 -> depression of CNS -> coma-> death
-Blood pH above 7.8 -> excitation of nervous system->muscle tetany, extreme nervousness, convulsions, respiratory arrest
-If acid-base imbalance is due to malfunction of a physiological buffer system, the other one compensates, respiratory system attempts to correct metabolic acid-base imbalances, kidneys attempt to correct respiratory acid-base imbalances
Respiratory Compensation
-In metabolic acidosis, High H+ levels stimulate the respiratory centers, Rate and depth of breathing are elevated, Blood pH is below 7.35 and HCO3- level is low, As CO2 is eliminated by the respiratory system, Pco2 falls below normal
-In metabolic alkalosis, slow, shallow breathing, allowing CO2 accumulation in the blood, high pH (over 7.45) and elevated HCO3- levels
Renal Compensation
-Hypoventilation (respiratory acidosis) causes elevated Pco2, *renal compensation is indicated by high HCO3- levels
-Respiratory alkalosis exhibits low Pco2 and high pH, *Renal compensation is indicated by decreasing HCO3- levels
Developmental Aspects
-Infants have proportionately more extracellular fluid than adults until about 2 y/o
-Problems with fluid, electrolyte and acid-base balance are most common in infancy, reflecting, 1)low residual lung volume, 2)high rate of fluid intake and output, 3) high metabolic rate, yielding more metabolic wastes, 4)high rate of insensible water loss, 5)Inefficiency of kidneys, especially during the first month
-At puberty, sexual differences in body water contect arise as makes develop greater muscle mass
-In old age, total body water often decreases
-Homeostatic mechanisms slow down with age
-Elders may be unresponsive to thirst clues and are at risk of dehydration
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