Clinical measurements of renal function/tubule transport

Question 1

What is the sum of all the forces in the renal corpuscle called?

Answer 1

Net Filtration Pressure

Question 2

The 4 Pressures affecting glomerular filtration (HCHC)

Answer 2

• Hydrostatic pressure of glomerular capillaries
• Colloid osmotic pressure of glomerular capillaries
• Hydrostatic pressure of Bowman’s capsule
• Colloid osmotic pressure of Bowman’s capsule

Question 3

What is the hydrostatic pressure of glomerular capillaries (Pgc)?

Answer 3

• pressure cause by blood flowing into the glomerulus
• promotes filtration
  ~55mm Hg

Question 4

What is the colloid osmotic pressure of glomerular capillaries(πgc)?

Answer 4

• pressure caused by the presence of proteins in the glomerulus (in the blood)
• inhibits filtration (osmosis)
  ~ 30mm Hg

Question 5

What is the hydrostatic pressure of Bowman’s capsule (Pbc)?

Answer 5

• pressure caused by filtrate remaining in the Bowman’s capsule
• inhibits filtration
  ~ 15 mm Hg

Question 6

What is the colloid osmotic pressure of Bowman’s capsule (π bc)?

Answer 6

• pressure caused by the proteins in Bowman’s capsule
• promotes filtration
  ~ 0 mm Hg

Question 7

Net filtration pressure = ?

Answer 7

NFP = Pgc - (Pbc + πgc)
= 55 - (15 + 30)
= 10

Question 8

What is the glomerular filtration rate (GFR)?

Answer 8

• amount of fluid filtered by the kidney in a day
• average value of 180 L/day

Question 9

Factors affecting GFR

Answer 9

• NFP
• Filtration coefficient (affected by the spaces in between podocytes and integrity of basal lamina)

Question 10

Two autoregulatory mechanisms to keep GFR constant

Answer 10

• the myogenic response
• tubuloglomerular feedback

Question 11

How does the myogenic response work?

Answer 11

• afferent arteriole stretches from higher blood pressure, causing stretch sensitive ion channels to open
• smooth muscle cells depolarize and calcium channels open, causing contraction of smooth muscles and vasoconstriction of the arteriole
• blood flow decreases in glomerulus

Question 12

How does tubuloglomerular feedback work?

Answer 12

• macula densa cells sense increase in ions (Na and Cl) due to increased flow rate
• paracrine signalling (adenosine) from these cells to afferent arteriole
• afferent arteriole constricts, reducing hydrostatic pressure in glomerulus and lowering GFR

Question 13

GFR = ?

Answer 13

GFR = ([Substance] in urine x Urine Volume) / [Substance] in plasma

Question 14

What does the filtered load calculate?

Answer 14

• how much of a substance is filtered into Bowman’s capsule in a day

Question 15

True/False - Everything that gets filtered into Bowman’s capsule and enters the tubule system is excreted from the body

Answer 15

False - Reabsorption and more secretion occurs in the tubule system