Tubular function 1

Question 1

What are the plasma concentrations of Na+, K+, Cl-, HCO3-, H+, and C6H12O6 like compared the concentrations in the ultra filtrate

Answer 1

Similar concentrations

Question 2

What is the plasma protein concentration like compared to the concentration in the ultra filtrate

Answer 2

It far exceeds

Question 3

In a normal 70kg person, what is the normal GFR

Answer 3

120ml/min

Question 4

IN a normal 70kg person, what is the normal RPF

Answer 4

600ml/min

Question 5

In a normal 70kg person, what is the PCV

Answer 5

40%

Question 6

In a normal 70kg person, what is renal blood flow

Answer 6

1L/min

Question 7

In a normal 70kg person, what is the cardiac output

Answer 7

5L/min

Question 8

What is between the peritubular capillary and the tubular epithelium

Answer 8

Peritubular fluid

Question 9

What is the basolateral membrane

Answer 9

The membrane closest to the peritubular fluid

Question 10

What is the membrane called closest to the lumen

Answer 10

Apical/luminal membrane

Question 11

What are the transport pathways in epithelial cells

Answer 11

Transcellular- across cells (can be bidirectional)

Paracellular-between cells

Question 12

Where are sodium pumps located in the kidney

Answer 12

Exclusively in the basolateral membrane

Question 13

What do the sodium pumps do

Answer 13

Pump sodium out of cell in exchange for potassium. Decreases intracellular Na+ conc in relation to the outside and so the Na+ wants to move across the electrochemical gradient from the tubular lumen, into the epithelium and then across into the peritubular fluid and then into the peritubular capillary

Question 14

What does the low pressure of the peritubular capillaries mean

Answer 14

Favours reabsorption

Question 15

Why is the proximal tubule highly water permeable

Answer 15

Because it has leaky tight junctions and aquaporins

Question 16

What is the water gradient like in the proximal tubule

Answer 16

Tubular Fluid is approximately isosmotic with the plasma

Question 17

What are the mechanisms for the entering of sodium ions into the tubular epithelium from the apical membrane

Answer 17

1) Sodium - Hydrogen exchange
2) sodium entry coupled with other solutes (simple mechanisms)
3) On its own through membrane channels
4) Passively via tight channels

Question 18

How do bicarbonate ions get reabsorbed into the blood (i.e. get from the tubular fluid into the peritubular capillaries)

Answer 18

• The apical membrane is impermeable to bicarbonate ions
• Bicarbonate ions combine with H+ which has entered the lumen from the Na+-H+ pump to form carbonic acid
• Carbonic anhydrase dissociates carbonic acid into co2 and water which moves into the cell
• Carbonic acid in the cell associates the co2 and water back into carbonic acid
• The H+ dissociates to form bicarbonate ions
• The H+ leaves again via the Lumen
• The bicarbonate ions leave with the Na+ into the peritubular fluid and into the peritubular capillaries

Question 19

IN an alkalosis (excess bicarbonate and too little H+), what do the kidneys do

Answer 19

Excrete more filtered bicarbonate so less get absorbed

Question 20

In an acidosis, what do the kidneys do ti help

Answer 20

You can’t turn up reabsorption because kidneys are already working at maximum so they can turn up the production of bicarbonate to compensate

Question 21

How does potassium reabsorption occur in proximal tubule

Answer 21

Paracellular transport

Question 22

How does cl- reabsorption occur

Answer 22

Transcellular transport

Paracellular transport