Tubular function 1

Question 1

What is gout and how can it be caused by kidneys?

Answer 1

High level of uric acid in plasma forms crystals = for inflammatory deposits (frequently in joints)
overproduction or uric acid or dec in renal excretion of uric acid (inc reabsorption/dec secretion urate in PCT)

Question 2

Epithelial cells are joined at the base by?

Answer 2

Tight junctions

Question 3

What does the lumen contain?

Answer 3

tubular fluid

Question 4

What is the base of the nephron made of? 2 parts.

Answer 4

Peritubular fluid and peritbular capillary

Question 5

What are the 2 types of movement through cells? Explain them.

Answer 5

Transcellular transport - moves through cells

Paracellular - movement of substances between the cells

Question 6

Where is the Na+/K+ ATPase exclusively located in the nephron?

Answer 6

Located exclusively in basolateral membrane

is the primary active transport mechanism

Question 7

What direction does Na+ and K+ move in?

Answer 7

Na+ pushed into peritubular fluid. K+ absorbed into epithelial cell

Question 8

Which Na+ conc is lower? Intra or extracellular?

Answer 8

Extracellular has a higher Na+ (hence active transport and setting up a conc gradient)

Question 9

What is the result of having a low intracellular Na+ in terms of reabsorption?

Answer 9

conc gradient set up

reabsorption of nearly all organic solutes, ions and water coupled with Na+ reabsorption

Question 10

What is reabsorbed at the proximal tubule? What % of Na+?

Answer 10

bulk reabsorption

~60% load of Na+, water, Cl-, K+, all glucose and amino acids.

Question 11

Why is the PT highly permeable to water? What is the effect of this?

Answer 11

Because of leaky tight junctions and aquaporin-1 (AQP1). Prevents build up of significant osmotic gradients. Tubular fluid is isosmostic with plasma

Question 12

What are the 4 mechanisms that Na+ is transported in the PCT? Which is the dominant one?

Answer 12

Na+/H+ exchanger
Na+ entry coupled with other solutes
Na+ enters cells alone
Na+ moves passively through tight junctions and into lateral space

Question 13

What % of bicarbonate ions are reabsorbed in the PCT?

Answer 13

~90%

Question 14

Which membrane is impermeable to HCO3?

Answer 14

Apical membrane is impermeable.

Question 15

Explain reabsorption of the bicarb ions

Answer 15

Indirect method needed. Involves carbonic anhydrase (CA)

Reabsorption depends on H+ secretion in exchange for Na+ ions

Question 16

Why can’t acidosis be corrected by the kidneys by bicarbonate transport alone?

Answer 16

For each filtered HCO3- removed from tubular lumen, one HCO3- appears in peritubular blood. Thus it doesn’t correct acidosis. But in alkalosis reabsorption of filtered HCO3- can be reduced to help correct alkalosis

Question 17

How can alkalosis be corrected by the kidneys?

Answer 17

excrete more filtered HCO3-

Question 18

What is type 2 renal tubular acidosis?

Answer 18

Failure of bicarbonate reabsorption

Question 19

What 2 things cause H2O reabsorption in the PCT?

Answer 19

Osmotic pressure gradient (generated by Na+)

Increased oncotic pressure in peritubular capillaries and low hydrostatic pressure

Question 20

Explain transport of K+
C-
Urea
bulk reabsorption for each

Answer 20

K+ = paracellular transport. Active inwards, passive outwards
C- = electrochemical gradient: passive: paracellular transport, transcellular transport 
urea = reabsorption of Na+ and thus water conc urea in luminal fluid and moves passively down conc gradient. Paracellular and transcellular.