Urinary System Physiology

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Name 3 processes used to form urine and adjust blood composition.

1. glomerular filtration
2. tubular reabsorption
3. tubular secretion

Glomerular filtration takes place in the renal _______ and produces a cell- and protein-free filtrate.

corpuscle

Tubular reabsorption is the process of selectively moving substances from the ______ back into the blood.

filtrate

____ ________ takes place in the renal tubules and collecting ducts.

Tubular reabsorption

Tubular reabsorption reclaims almost everything filtered. Anything that is not reabsorbed becomes ______.

urine

____ ________ is the process of selectively moving substances from the blood into the filtrate. It occurs along the length of the tubule and collecting duct.

Tubular secretion

_____ml of blood pass thru the glomeruli each minute. Some 650ml is plasma, and about 1/5 of this is forced into the glomerular capsules as ______.

1200ml
filtrate.

The kidneys use up ______% of all O2 used by the body at rest.

20-25%

What does filtrate contain?

Filtrate contains everything found in blood plasma except for proteins.

Urine contains the ________ substances such as excess salts and metabolic waste.

unneeded

The kidneys process about ____L of blood-derived fluids daily. Less than 1% leaves the body as urine. the rest returns to the circulation.

180

____ _______ is a passive process in which hydrostatic pressure forces fluids and solutes thru a membrane.

Glomerular Filtration

The glomeruli can be viewed as simple ________ filters because filtrate formation does not directly consume metabolic energy.

mechanical

The filtration ______ lies between the blood and the interior of the glomerular capsule.

membrane

The membrane is porous and allows free passage of ______- and solutes smaller than plasma proteins.

water

The fenestrations of the glomerular capillaries allow all blood components except ____ _____ to pas thru.

blood cells

The basement membrane lies between the other two layers and is composed of their fused ____ _______. It forms a a physical barrier that blocks all but the smallest proteins white still permitting most other solutes to pass.

basal laminae

The glycoproteins of the gel-like basement membrane give it a ______ charge. As a result, the basement membrane electrically repels many negatively charged macromolecular anions such as ______ _______, reinforcing the blockage based on molecular size.

negative
plasma proteins

Foot processes of podocytes of the glomerular capsule: the _____ layer of the glomerular capsule is made of podocytes that have filtration slits between their foot processes.

visceral

If any macromolecules manage to make it thru the basement brane, ______ ______, thin membranes that extend across the filtration slits, prevent almost all of them from traveling further.

slit diaphragms

Macromolecules that get hung up in the filtration membrane are engulfed by specialized pericytes called ______ _______ ________.

glomerular mesangial cells

Molecules smaller than 3 nm in diameter suchs as water, glucose, ____ ____, and _______ waste, pass freely from the blood into the glomerular capsule.

amino acids
nitrogenous

Larger molecules pass with greater difficulty and those larger than ____nm are generally barred from entering the tubule.

5

Keeping the plasma proteins in the capillaries maintains the colloid ______ pressure of the glomerular blood, preventing the loss of all of its water to the capsular space.

osmotic

The presence of proteins or blood cells in the urine usually indicates a problem with the ____ ________.

filtration membrane.

The principles that govern _________ from the glomerulus are the same as those that govern any capillary bed.

filtration

Outward/Inward pressures promote filtrate formation.

Outward

The hydrostatic pressure in glomerular capillaries (HP) is essentially glomerular blood _____. It is the chief force pushing water and solute out of the blood and across the filtration membrane.

pressure

The b/p in the glomerulus is very high----approx ____mm Hg compared to an avg of 26mm Hg in the other capillary bed. It remains high across the entire capillary bed.

55

Why is the pressure so high?

The high pressure is because the glomerular capillaries are drained by a high-resistance efferent arteriole who diameter is smaller than the afferent arteriole that feeds them.

________ occurs along the entire length of each glomerular capillary and reabsorption does not occur as it would in other capillary beds.

Filtration

Name the 2 inward pressures that inhibit filtrate formation.

1. hydrostatic pressure in the capsular space (HP)
2. colloid osmotic pressure in glomerular capillaries (OP)

Hydrostatic pressure in the capsular space is the pressure exerted by filtrate in the glomerular capsule. It is much higher than hydrostatic pressure surrounding most capillaries. Why?

because filtrate is confined in a small space with a narrow outlet

The colloid osmotic pressure in glomerular capillaries is the pressure exerted by the _____ in the blood.

proteins

These pressures determine th______ ________ pressure (NFP). NFP largely determines the glomerular filtration rate or GFR.

net filtration

The GFR is the ________ of filtrate formed each minute by the combine activity of all 2 million glomeruli of the kidneys.

volume

____ ______ ________ is the main controllable factor. This pressure can be controlled by changing the diameter of the afferent and sometime the efferent arterioles.

Net filtration pressure

Total surface area: Glomerular _________ cells surrounding these capillaries can fine tune GFR by contracting to adjust the total surface area available for filtration.

mesangial

Glomerular capillaries are thousands of times more permeable than other capillaries because of their ______.

fenestrations.

What is a normal GFR?

120-125 ml/min

Increased GFR increases urine output, which reduces blood ______ and blood ________.

volume
pressure.

________ controls (renal autoregulation) act locally within the kidney to maintain GFR.

Intrinsic

________ controls by the nervous and endocrine system maintain bp.

Extrinsic

If the glomerular _____ ______ rises, NFP rises and so does GFR.

hydrostatic pressure

Defined as adjusting to its own resistance to blood flow. This process is called ____ __________.

renal autoregulation

Name the 2 mechanisms the autoregulation system has.

myogenic mechanism
tubuloglomerular feedback mechanism.

The myogenic mechanism reflects a property of vascular smooth muscle. It ________ when stretched and relaxes when not stretched.

contracts

Rising systemic pressure stretches vascular smooth muscle in the arteriolar walls, causing the afferent arterioles to _______. This _______ blood flow into the glomerular and prevents glomerular b/p from rising to damaging levels.

constrict
restricts

Declining systemic bp causes ________ of afferent arterioles and raises GHP.

dilation

Tubuloglomerular feedback mechanism is direct by the ____ _______ cells of the juxtaglomerular complex.

macula densa

These cells are located in the walls of the ________ limb of the nephron loop. They respond to filtrate ____ concentration.

ascending
NaCl

When GFR increases, there is not enough time for reabsorption and the concentration of NaCl in the filtrate remains high. The macula densa cells respond by releasing _________ chemicals that cause intense constriction of the afferent arteriole, increasing/reducing blood flow into the glomerulus.

vasoconstrictor
reducing

This drop in blood flow decreases the NFP and GFR, slowing the flow of _____ and allowing more time for filtrate processing (NaCl resorption).

filtrate

On the other hand, the low NaCl concentration of slowing flowing filtrate inhibits ____ release from macula densa cells, causing vasodilation of the afferent arterioles. This allow more/less blood to flow into the glomerulus, thus increasing NFP and GFR.

ATP

If the mean arterial pressure drops below ___ mm Hg, autoregulation ceases and extrinsic controls take over.

80

What is the purpose of the extrinsic controls?

to maintain systemic bp

When the volume of the extracellular fluid is normal and the SNS is at rest, the renal blood vessels are _____ and renal autoregulation mechanisms prevail.

dilated

However, when the extracellular fluid volume is extremely low, it is necessary to shunt blood to vital organ and neural controls override. This could reduce renal blood flow to the point of damaging the ______.

kidneys.

When bp falls, norepinephrine released by sympathetic nerve fibers (and epinephrine rel'd by the adrenal medulla) causes vascular smooth muscle to constrict, increasing peripheral _________ and bringing bp back up towards normal.

resistance

As part of this reflex, the afferent arterioles also ______, which decreases GFR and so helps restore blood volume and bp to wnl.

constricts

Low bp causes the granular cells of the juxtaglomerular complex to release ___ by one or more of 3 pathways.

renine

Direct stimulation of granular cells: renal sympathetic nerves activate ________ receptors that cause the granule cells to rel renin.

b1-adrenergic

Stimulation of the granular cells by input from activated macula densa cells: Low bp of the afferent arterioles by the sympathetic nervous system reduces GFR, slowing down the flow of filtrate thru the renal tubules. When macula densa cells sense the low _____ concentration, they signal the granule cells for release of renin.

NaCl

The macula densa cells may signal by releasing ____ (also thought to be the tubuloglomerular feedback messenger), by releasing more of the ________ PGE2, or both.

ATP
prostaglandin

Reduced stretch of granular cells: Granular cells acts as ______. a drop in mean arterial bp reduces the tension in the cell's plasma membranes and stimulate s them to rel more renin.

mechanoreceptors

Abnormally low urinary output is called ______. It may indicate that glomerular bp is too low to cause filtration. Can be caused by acute nephritis, transfusion reactions and crush injuries.

anuria

Renal cells produce a lot of chemicals, many of which act as _____ (local signaling molecules) affecting renal arterioles. These include adenosine and prostaglandin E2.

paracrines

Calculate net filtration pressure given the following values: gHP=50mm Hg, blood colloid OP = 25, capsular hydrostatic pressure = 20hg.

NFP is 5. 50 - (25+20mm) = 5

Which of the pressure that determine NFP is regulated by both intrinsic and extrinsic controls of GFR?

Hydrostatic pressure in the glomerular capillaries (HPgc)

Tubular reabsorption is a selective transepithelial process that beings when?

as soon as the filtrate enters the proximal tubules

Name the two routes of Tubular reabsorption

transcellular
paracellular

In the transcellular rte, transported substances move thru the ______membrane, the cytosol, and the basolateral membrane of the tubule cell and then the _______ of the peritubular capillaries.

apical
endothelium

Movement of substances in the paracellular rte (between the tubule cells) is liited by the tight ______ connecting these cells.

junctions

In the proximal nephron, these tight junctions are leaky and allow water and some important ions to pass thru. Name 4 ions allowed to pass.

Ca2+, Mg2+, K+, and some Na+

Virtually all organic nutrients such as glucose and amino acids are completely reabsorbed to maintain or restore normal _______ concentration.

plasma

The reabsorption process may be active or passive. Active requires ___ either directly or indirectly..

ATP

Passive encompasses _______processes in which substances move down their electrochemical gradients.

diffusion

______ ions are the single most abundant cation in the filtrate and about ___% of the energy used for active transport is devoted to reabsorbing them.

Na
80

Na transport across the basolateral membrane: Na+ is actively transported out of the tubule cell by primary ______ transport which is a Na+-K+ ATPase pump in the basolateral membrane.

active

From there, the bulk flow of water sweeps Na+ into adjacent peritubular capillaries. This bulk flow of water and solutes is slow/rapid because the blood there has low HP and high OP.

rapid

Na transport across the apical membrane: active pumping of Na+ from the tubule cells results in a strong electrochemical gradient that favors its entry at the apical face via ______ ____ ____ carriers.

secondary active transport

Or via facilitated diffusion thru channels. This occurs because the pump maintains the intracellular Na concentration at low levels and the K+ pumped into the tubule cells almost immediately _______ out into the blood stream.

diffuses

The reabsorption of Na+ by primary active transport provides the ____ and the means for reabsorbing almost every substance, including water.

energy

Substance reabsorbed by ________ active transport (the push comes from the gradient created by Na-K pump at the basolateral membrane) include glucose, amino acids, some ions, and ______.

secondary
vitamins

In nearly all these cases,an a____ _____ moves Na down its concentration gradient as it co-transports another solute.

pical carrier

Co-transported solutes move across the basolateral membrane by ______ diffusion via other transport proteins before moving into the peritubular capillaries.

facilitated

The movement of Na and other solutes establishes a strong ______ gradient and water moves by osmosis into the peritubular capillaries. This is passive tubular reabsorption of water.

osmotic

Transmembrane proteins called _____ aid this process by acting as water channels across cell membranes.

aquaporins

The ____ tubule cells are most active in reabsorption.

proximal

Most of the nutrients, ___% of the water, and sodium ions, and the bulk of actively transported ions are reabsorbed in the proximal convoluted tubules.

65%

Reabsorption of additional sodium ions and water occurs in the ____ tubules and collecting ____ and is hormonally controlled.

distal
ducts

________increases the reabsorption of sodium.

aldosterone

_______ ________ enhances water reabsorption by collecting ducts.

ADH antidiuretic hormone

Tubular _______ adds substances to the filtrate from the blood or tubule cells.

secretion

Tubular secretion is an ______ process that is important in eliminating drugs, certain wastes, and excess ions and in maintaining the acid-base balance of the blood.

active

How are primary and secondary active transport process different?

In pri active transport, the energy for the process is provided directly by the cleavage of ATP. In secondary, the energy for the process is provided by the Na gradient.

LIst several substances that are secreted into the kidney tubules.

glucose
amino acids
Cl
water

The graduated hyperosmolality of the ________ fluids (largely due to the cycling of NaCl and urea) ensures that filtrate reaching the distal convoluted tubule is dilue (hyp-osmolar). This allows urine with osmolalities ranging from 50-1200 mOsm to be formed.

medullary

The descending limb of the nephron loop is permeable to water, which leaves the filtrate and enters the medullary interstitial space. The filtrate and medullary fluid at the bend of the nephron loop are hypo-osmolar/hyperosmolar.

hyperosmolar

The ascending limb is impermeable to water. Na and Cl move out of the filtrate into the interstitial space, passively in the thin portion and actively in the thick portion. The filtrate becomes more ____.

dilute

As filtrate flows thru the collecting ducts in the inner medulla, ______ diffuses into the interstitial space.

urea

From here, urea reenters the ______ thin limb and is recycled.

ascending

The blood flow in the ____ ______ is sluggish and the contained blood equilibrates with the medullary interstitial fluid.

vasa recta

Hence, blood exiting the medulla in the vasa recta is nearly isotonic to blood plasma and the high ______ concentration of the medulla is maintained.

solute

In the absence of _____, dilute urine is formed because the dilated filtrate reaching the collecting duct is simply allowed to pass from the kidneys.

ADH

When extracellular fluid osmolality rises, blood levels of ADH rise, and the collecting ducts become more ___ to water.

permeable

Water moves out of the filtrate as it flows thru the hyperosmotic medullary areas. Consequently, more concentrated urine is produced, and in smaller/larger amts.

smaller

Renal _____ is the volume of plasma that is completely cleared of a particular substance per minute.

clearance

Studies of renal clearance provide info about renal function or the course of renal ________.

disease

Renal failure has serious consequences: The kidneys are unable to concentrate _____, acid-base band electrolyte imbalances occur,and _______ wastes accumulate in the blood.

urine
nitrogenous

Urine is typically clear, yellow aromatic, and slightly _____.

acidic

Its specific gravity ranges _____ to_______.

1.001 to 1.035

Urine is ___% water, solutes include nitrogenous wastes (urea, uric acid, and creatinine), and various ions (always sodium, potassium , and ________.

95
phosphate

Substances not normally found in urine include: bile pigments, hgb, leukocytes, erythrocytes, _____, and ______.

glucose
protein

The ureters are slender tubes running retrospectively from each kidney to the the ______.

bladder.

The ureters conduct urine by ____ from the renal pelvis to the bladder.

peristalsis

Describe the special characteristics of the descending and ascending limbs of the nephron loop that cause the formation of the medullary osmotic gradient.

The descending limb of the nephron loop is permeable to water and impermeable to NaCl. The ascending limb is the opposite.

Under what conditions is ADH rel'd from the posterior pituitary?

ADH is rel'd in response to hyperosmotic extracellular fluid as sensed by the hypothalamic osmoreceptors

What effects does ADH have on the collecting ducts?

ADH causes insertion of aquaporins into the apical membrane of the principal cells of the collecting ducts.

What is the equation used to calculate the renal clearance?

C=UV/P U+ concentration of the substance in urine. V=flow rate of urine formation. P+concentration of the substance in plasma

Chronic renal disease is defined as a GFR of less than ___ ml for at least 3 months. Often develops silently over many yrs. Filtrate formation decreases gradually. Nitrogenous wastes accumulate in the blood. Blood pH drifts toward the acidic range.

60

What is the leading cause of CRF?

diabetes

GFR < 15ml indicates renal ______.

failure

The clinical syndrome associated with renal failure is called _____. Includes fatigue, nausea, mental changes, anorexia, and muscle cramps.

uremia

______ uses an artificial kidney apparatus, passing the pts blood thru a membrane tubing that is permeable only to selected substances.

hemodialysis

Pigment that results when the body destroys hemoglobin is called ______ and gives the urine its color.

urochrome

Normal urine pH is ____.

6

______ is a metabolite of creatine phosphate, which is found in lg amts in skeletal muscle tissue where it stores energy to regenerate ATP.

Creatinine

What is the end product of nuclei acid metabolism called?

uric acid

what would you expect the normal clearance value for amino acids to be?

normal clearance for amino acids is zero

What are the 3 major nitrogenous wastes excreted in urine?

urea, creatinine, uric acid

Kidney stones are called ___ ______. They are a result of calc, magnesium or uric acid salts in urine that crystallize and precipitate in the renal pelvis.

renal calculi

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