Renal Filtration

Question 1

What is the formula for Glomerular Filtration Rate (GFR)?

Answer 1

                Plasma conc. 

GFR = K(f) (NFP)
i.e. = K(f) [P(GC) - ( pie(PC) + P(BC) ]

** K(f) –> Filtration coefficient determined by permeability of membrane

Question 2

What is Glomerular Filtration Rate (GFR) a measure of?

Answer 2

TOTAL KIDNEY FUNCTION

Question 3

What substance is used as a guide of GFR?

Answer 3

CREATININE

a by-product of muscle metabolism

Question 4

What type of substance can be used as a guide for GFR?

Answer 4

A substance that is:
 freely filtered
 not reabsorbed
 not secreted
 has a steady state plasma conc.

Question 5

Give the formula for Net (Glomerular) Filtration P (NFP).

Answer 5

P(GC) - ( pie(PC) + P(BC) )

P(GC) = glomerular capillary hydrostatic P   (out capill.)
pie(PC) = plasma colloid osmotic P               (into capill.)
P(BC) = Bowmans capsule hydrostatic P      (into capill.)

Question 6

What controls GFR?

Answer 6

1. Myogenic mechanism

2. Tubularglomerular feedback

Question 7

What is the Myogenic mechanism

Answer 7

Automatic contraction in response to stretch from high blood flow.

Question 8

What is Tubularglomerular feedback

Answer 8

MACULA DENSA detects:

• changes in filtrate flow
• delivery of Na+ and Cl- through distal tubule

–> If flow rate HIGH;
greater delivery of salt to Mac. Densa
THUS, vasoactive mediators cause VASOCONSTRICTION of afferent arteriole to DECREASE GFR!

–> If flow rate LOW;
VICE-VERSA!

Question 9

What are Podocytes?

Answer 9

Cells that cover the basement mem.
(whilst leaving slits/gaps for filtration)

Separated by (-) charged diaphragm 
  (to stop escape of proteins & cells)

Question 10

What happens when podocytes contract?

Answer 10

Seal off the diaphragms;
THUS, 
-decrease SA for filtration
THUS,
-decrease GFR

Question 11

Give 3 examples of disruption to the Basement Membrane.

Answer 11

• destruction of podocytes
• ” “ diaphragm integrity
• ” “ charge barrier

Question 12

What are the consequences of basement membrane disruption?

Answer 12

Can lead to LOSS OF PROTEIN in urine (proteinuria)
THUS, loss of whole cells (haematuria)

• loss protein = decrease plasma colloid osmotic P (pie(PC))
• decrease pie(PC) reduces pull of fluids back from interstitial fluid to plasma
• leads to interstitial fluid retention, THUS ODEMA
• liver compensates by increasing lipoprotein production,
  THUS< increase circulating plasma cholesterol