Lecture 2: Renal Blood Flow and GFR

Question 1

at rest, what % of cardiac output reaches the kidneys

Answer 1

20%

Question 2

What are the functions of blood flow through the kidneys

Answer 2

• deliver O2, nutrients and hormones to the cells of the nephron while returning CO2 and reabsorbed fluids + solutes to general circulation
• determines the GFR
• modifies the rate of reabsorption by the proximal tubule
• concentration and dilution of urine
• delivery of substrates for excretion in urinef

Question 3

what determines the GFR

Answer 3

blood flow through the kidneys

Question 4

what renal functions are compromised during renal failure

Answer 4

• excretion of metabolic waste
• regulation of water, electrolytes, extracellular fluid volume and BP

Question 5

the volume of plasma filtered into Bowman’s space per unit time

Answer 5

GFR

Question 6

what things determine GFR

Answer 6

• permeability (glomerular filtration barrier)
• surface area
• net filtration pressure = the difference b/w the differentials of hydrostatic and oncotic pressure

Question 7

what is the equation for GFR?

Answer 7

Question 8

what factor(s) increase the filtration coefficient, K?

Answer 8

an increase in glomerular SA caused by the relaxation of mesangial cells

GFR increases

Question 9

what factor(s) increase PGC

Answer 9

an increase in renal arterial pressure and dilation of afferent arteriole

GFR increases

Question 10

what factor(s) increase PBS, what is this effect on GFR

Answer 10

an increase in intratubular pressure (ex: obstruction)

GFR decreases

Question 11

What factor(s) increase πGC

Answer 11

An increase in systemic plasma oncotic pressure

GFR decreases

Question 12

what is nephrolithiasis

Answer 12

renal stones in kidney

Question 13

what is Urolithiasis

Answer 13

occurs when renal kidney stones exit the renal pelvis and move into the remainder of the urinary collecting system (ureters, bladder, urethra)

Question 14

what disease causes a drop in plasma oncotic pressure

Answer 14

liver disease —> hypolbuminemia (low levels of blood albumin)

Question 15

what can cause a decreased arterial oncotic pressure (which tends to increase GFR)

Answer 15

a decrease in arterial plasma protein concentration

Question 16

what is the average capillary oncotic pressure?

Answer 16

28 mmHg

Question 17

what happens to protein concentration as blood moves from the afferent to the efferent end of the glomerular capillary?

Answer 17

protein concentration increases

Question 18

factors that affect afferent/efferent arteriolar resistance also effect what?

Answer 18

PGC

Question 19

what happens if GFR gets too low?

Answer 19

the excretion of waste products becomes insufficient

Question 20

what happens in GFR gets too high?

Answer 20

tubules might be overwhelmed with salt and water reabsorption. Furthermore, high vascular pressure could cause hypertensive damage.

Question 21

Hydrostatic pressure is ______ in glomerular capillaries and falls to _____in the peritubular capillaries

Answer 21

60mmHg in glomerular capillaries and 20mmHg in peritubular capillaries

Question 22

where does hydrostatic pressure remain relatively constant?

Answer 22

within the glomerulus

Question 23

Dilation of the afferent arterioles raises hydrostatic pressure in ??

Answer 23

glomerular capillaries and GFR

Question 24

what causes a decrease in hydrostatic
pressure in glomerular capillaries and GFR?

Answer 24

Constriction of the afferent arterioles

Question 25

what causes a decreased hydrostatic pressure in glomerular capillaries and GFR

Answer 25

Dilation of the efferent arterioles

Question 26

what happens if afferent and efferent arteriolar resistance change in the same direction

Answer 26

they exert opposite effects on hydrostatic pressure in glomerular capillaries and GFR

Question 27

what are the autoregulatory mechanisms the kidneys have to keep RBF, PGC and GFR within a limited range?

Answer 27

myogenic response
tubulo-glomerular feedback

Question 28

what is the purpose of keeping GFR within a limited range during changes in arterial pressure?

Answer 28

preventing changes in GFR prevents hypertensive damage

Question 29

what is the myogenic response ?

Answer 29

Contraction and relaxation of arteriolar smooth muscle in response to changes in vascular pressure

Question 30

what is the juxtaglomerular apparatus ?

Answer 30

s a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole

Question 31

what increases the flow of tubular fluid

Answer 31

increased glomerular blood flow

Question 32

what is the effect of increased glomerular blood flow on salt reabsorption in the LoH and salt delivery to the macula densa

Answer 32

it increases salt reabsorption as well as increasing the delivery of salt to the macula densa

Question 33

what component of the macula densa senses changes in salt concentration

Answer 33

Na+ ‐K+‐2Cl− cotransporter (NKCC) in its luminal membrane.

Question 34

what vasoactive substance is released during tubuloglomerular feedback and what is its effect

Answer 34

Adenosine
- increases afferent tone
- renin production / secretion decreases

Question 35

what prostaglandins are vasodilators that work primarily on afferent arterioles

Answer 35

PGE2, PGI2

Question 36

what stimulates the release of vasodilator prostaglandins

Answer 36

• increased renal sympathetic nerve activity
• increased levels of angiotensin II

Question 37

NSAIDs block ….

Answer 37

prostaglandins, compromising vasodilation

Question 38

NE effect on afferent arteriole

Answer 38

causes vasoconstriction = increased afferent renal sympathetic nerve activity, decreases RBF and GFR

Question 39

NE effect on collecting duct

Answer 39

increases Na and K exchange –> increases Na reabsorption and water retention

Question 40

NE effect on Juxtaglomerular apparatus

Answer 40

stimulates renin release –> activate RAAS