Glomerular Filtration

Question 1

Explain how a large amount of filtrate allows for greater control of the composition of the final urine output.

Question 2

describe the structure of the renal corpuscle.

Answer 2

contains 2 layers, the visceral and parietal which are around the glomerulus and mesangial cells

Question 3

what factors affect glomerular filtration

Answer 3

1. fenestrate endothelium -glycocalyx
2. GBM - proteoglycans
3. Podocyte filtration slits: slit diaphragms - glycocalyx

Question 4

what determines the filtration rate?

Answer 4

GFR = Pnet x Kf

Pnet (net filtration presssure)
Kf (filtration coefficient based on surface area and membrane permeability)

Question 5

filtration in the capillary beds of the nephron is ___ higher than others, how does this affect Kf?

Answer 5

400x higher, it increases Kf

Question 6

in the glomerulus, substances are filtered based off of what 2 factors?

Answer 6

1. size: larger molecules are not filtered out of the blood stream (most influential)
2. charge: positively charged substances more readily filtered out of the blood (does not apply to small ions like Cl)

Question 7

Net Filtration Pressure

Answer 7

the difference between net hydrostatic pressure and net osmotic pressure in the kidney

Pnet = pressure pushing OUT of the blood stream (hydrostatic pressure in the glomerulus + oncotic pressure in the capsular space (should be zero)) - pressure pushing IN (hydrostatic pressure in the capillary space + oncotic pressure in the glomerulus)

Question 8

what is the primary driving force of filtration in the glomerulus?

Answer 8

glomerular capillary hydrostatic pressure

Question 9

how does increased arteriole resistance affect GFR?

Answer 9

increased resistance = increased renal blood flow = decreased GFR

Question 10

what are the two mechanisms of renal autoregulation?

Answer 10

1. myogenic mechanism
2. juxtaglomerular apparatus

Question 11

myogenic mechanism

Answer 11

contraction of smooth muscle when stretched and relaxation/dilation of smooth muscle when pressure is low to maintain constant blood flow

Question 12

Juxtaglomerular apparatus components and their functions?

Answer 12

1. Granular cells:
   - contract when stimulated by stretch
   - make, store and release renin
2. Macula densa:
   - detects changes in NaCl concentrations
   - signals to JG cells to release renin via paracrine signaling
3. Extraglomerular mesangial cells
   - function not well understood, but they exist

Question 13

what are the limitations to renal auto-regulation

Answer 13

kidneys are only able to maintain GFR on their own between systolic blood pressure of 80-180mmHg

Question 14

How does the sympathetic nervous system affect GFR?

Answer 14

• causes renin production
• causes vasoconstrictions to redirect blood flow from the kidney to the heart, brain, and muscles, leading to reduced GFR and urine output

Question 15

how does RAAS affect GFR?

Answer 15

production of angiotensin II by RAAS activation leads to :
- systemic vasoconstriction/increased blood pressure
- increases thirst, causing increased water intake
- stimulates aldosterone production (causing water retention and increased BP)

Question 16

How does atrial natriuretic peptide affect GFR?

Answer 16

ANP is releases from the cardiac atria in response to stretch due to increased venous return and causes
- relaxation of afferent arterioles
- inhibition of renin release
- relaxation of mesangial cells to increase surface area for filtration

*all lead to increased GFR in order to reduce blood volume to decrease venous return to the heart

Question 17

increased afferent arteriolar resistance leads to?

Answer 17

decreases in renal blood flow and net ultrafiltration pressure

Question 18

decreased afferent arteriolar resistance leads to?

Answer 18

increases in renal blood flow and net ultrafiltration pressure

Question 19

increased efferent pressure resistance leads to?

Answer 19

decreased renal blood flow, increased net ultrafiltration pressure

Question 20

decreased efferent arteriolar pressure leads to?

Answer 20

increased renal blood flow, decreased net ultrafiltration pressure