Renal Physiology Part I

Question 1

List some ways kidneys participate in homeostasis

Answer 1

homeostasis: regulate H20 volume and [solute], acid/base balance, excrete toxins/wastes/ drugs, produce EPO/Renin, activate vitamin D, gluconeogenesis

Question 2

Describe the structure of the filtration membrane as it relates to its function in glomerular filtration.

Answer 2

fenestrated endothelium of glomerular capillaries on one side, filtration slits between foot processes of glomerular capsule on the other, basement membrane between them

Question 3

Describe the pressure that promotes glomerular filtration.

Answer 3

hydrostatic pressure of blood in glomerulus promotes filtration of water and solutes (HPgc = 55 mmHg),

Question 4

Define glomerular filtration rate.

Answer 4

vol of filtrate formed by kidneys per min = 120-125 ml/min,
directly proportional to net filtration pressure, total surface area available for filtration, filtration membrane permeability

Question 5

Explain how the body can make adjustments to the glomerular blood pressure with the myogenic mechanism

Answer 5

when MAP increases, stretch of afferent arteriole increases, increasing permeability to Ca2+, increasing intracellular Ca2+, stimulating smooth muscle contraction in afferent arteriole, causing decreased diameter and increased resistance, decreasing blood flow into glomerulus, decreasing glomerular filtration rate & protecting glomerulus from high BP and instead keeping it constant around 55 mmHg

Question 6

Explain how the body can make adjustments to the glomerular blood pressure with the tubuloglomerular feedback mechanism

Answer 6

negative feedback loop, higher GFR = higher [NaCl] in filtrate > afferent arteriole constriction; higher GFR means less time for renal tubule cells to grab salt out of filtrate as it passes, so higher [NaCl] remains in solute (rather than being reabsorbed into bloodstream, ascending loop of henle has macula densa cells that detect [NaCl] (chemoreceptors) > macula densa cells release ATP which travels to afferent arteriole’s smooth muscle cells, they constrict, decreasing blood flow into glomerulus, lowering net filtration pressure and filtration rate, more time for NaCl to be reabsorbed into blood, [NaCl] decreases in filtrate, macula densa cells stop releasing ATP

Question 7

Explain how the body can make adjustments to the glomerular blood pressure with the sympathetic nervous system

Answer 7

MAP <80 mmHg > baroreceptors in corotids and aortic arch detect drop and CNS releases NE from sympathetic fibers, E and NE from adrenal medulla > vasoconstriction including afferent arterioles, decreases GFR and urine output, maintain blood volume and blood pressure

Question 8

Explain how the body can make adjustments to the glomerular blood pressure with the renin-angiotensin-aldosterone system (RAAS)

Answer 8

main mechanism for increasing BP, renin released in response to drop in BP, goes into bloodstream, finds angiotensinogen and converts it to angiotensin I, converted to II by ACE, angiotensin II binds to receptors and increases BP

Question 9

Compare the intrinsic and extrinsic controls of glomerular filtration with respect to
under what conditions each occurs

Answer 9

intrinsic: when MAP increases, afferent arteriole diameter decreases > resistance increases > constant RBF, NFR, GFR constant; works best when MAP is 80-180 mmHg; extrinsic controls override if outside that range; increased GFR > increased urine output > lower blood pressure and vice versa

Question 10

Compare the intrinsic and extrinsic controls of glomerular filtration with respect to the ultimate goals of each

Answer 10

goal of intrinsic is maintain constant GFR of ~55 mmHg, goal of extrinsic is maintain systemic blood pressure

Question 11

List the 3 major renal processes.

Answer 11

glomerular filtration, tubular reabsorption, tubular secretion

Question 12

What is filtrate?

Answer 12

Pulled from blood, almost same as blood plasma, except missing big pieces like proteins <1% becomes urine

Question 13

Define glomerular filatration

Answer 13

pulling fluid out of bloodstream from glomerular capillaries and into Bowman’s space in nephron, produces cell- and protein-free filtrate

Question 14

Define tubular reabsorption

Answer 14

99% of filtrate is ultimately reabsorbed and put back into bloodstream at one point in nephron or another

Question 15

Define tubular secretion

Answer 15

certain substances removed from bloodstream and put into filtrate

Question 16

What can fit through filtration membrane? What can’t?

Answer 16

things less than 3nm can fit, so water, glucose, AAs, nitrogenous wastes; blood cells and proteins (albumins) can’t fit

Question 17

glomerular mesangial cells

Answer 17

engulf any macromolecules that get trapped in filtration membrane, contract to adjust surface area and change filtration rate (contraction reduces available surface area and decreases filtration rate)

Question 18

Describe the pressures that counteract glomerular filtration

Answer 18

hydrostatic pressure in capsular space ~15 mmHg AND colloid osmotic pressure / “pull” of proteins in blood counteracts filtration to prevent all water from leaving blood OPgc ~30 mmHg for total of about ~45 mmHg pressure counteracting filtration / inward pressure

Question 19

3 ways to get more renin released

Answer 19

1 sympathetic nervous system directly stimulates granular cells, 2 low [NaCl] activates macula densa cells which communicate to granular cells via extraglomerular mesangial messenger cells, 3 reduced stretch of granular cells
all three depend on drop in BP

Question 20

anuria

Answer 20

non-passage of urine, can indicate that blood pressure in glomerular capillaries is low, filtrate not pulled out as quickly as necessary, caused by crush injury, enlarged prostate > obstruction or kidney failure/nephritis, infections or heart failure, transfusion reactions

Question 21

which hormone is a vasoconstrictor that also stimulates the secretion of aldosterone

Answer 21

angiotensin II

Question 22

Why is the bulk flow of water and solutes into the peritubular capillaries rapid?

Answer 22

because the blood there has low hydrostatic pressure and high osmotic pressure (remember, most proteins remain in the blood instead of filtering out into the tubule).

Question 23

relate a property of smooth muscle to protection of the glomerulus

Answer 23

The myogenic mechanism reflects a property of vascular smooth muscle—it contracts when stretched and relaxes when not stretched. Rising systemic blood pressure stretches vascular smooth muscle in the arteriolar walls, causing the afferent arterioles to constrict. This constriction restricts blood flow into the glomerulus and prevents glomerular blood pressure from rising to damaging levels.

Question 24

What could cause anuria?

Answer 24

Abnormally low urinary output (less than 50 ml/day), called anuria, may indicate that glomerular blood pressure is too low to cause filtration. Renal failure and anuria can also result from situations in which the nephrons stop functioning, including acute nephritis, transfusion reactions, and crush injuries.

Question 25

Which glomerular regulator responds to filtrate NaCl concentrations?

Answer 25

tubuloglomerular feedback mechanism
Autoregulation by the flow-dependent tubuloglomerular feedback mechanism is “directed” by the macula densa cells of the juxtaglomerular complex. These cells, located in the walls of the ascending limb of the nephron loop, respond to filtrate NaCl concentration (which varies directly with filtrate flow rate). 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 to high levels of NaCl in filtrate by releasing vasoconstrictor chemicals (ATP and others) that cause intense constriction of the afferent arteriole, reducing blood flow into the glomerulus.

Question 26

Which hormone promotes reabsorption of sodium at the distal convoluted tubule?

Answer 26

aldosterone

Question 27

Which part of the nephron is influenced by hormones to absorb sodium and water?

Answer 27

distal convoluted tubule

Question 28

macula densa cells

Answer 28

The macula densa (mak′u-lah den′sah; “dense spot”) is a group of tall, closely packed cells in the ascending limb of the nephron loop that lies adjacent to the granular cells. The macula densa cells are chemoreceptors that monitor the NaCl content of the filtrate entering the distal convoluted tubule.