The Tubules

Question 1

What does the proximal tubule reabsorb and secrete

Answer 1

Bulk reabsorption of Na, Cl, glucose, amino acids, HCO3

Secretion of organic ions

Question 2

What is the function of the loop of henle

Answer 2

More Na reabsorption
Urinary dilution
Generation of medullary hypertonic interstitum via countercurrent multiplication

Question 3

Functions of the distal tubule

Answer 3

Fine regulation of Na, K, Ca, Pi

Separation of Na from H20

Question 4

What ion is reabsorption in the distal tubule dependent on

Answer 4

Chlorine

Question 5

Function of the collecting duct

Answer 5

Similar to the distal tubule
Secretes acid
Regulates h20 reabsorption concentrating urine

Question 6

Describe what drives the bulk reabsorption in the proximal tubule

Answer 6

Basolateral Na/K ATPase
3Na+ out and 2K+ into the cells
Energy is supplied from hydrolysis of 1 ATP molecule

Question 7

How much of primary urine volume is reabsorbed in the PCT

Answer 7

2/3

Question 8

What is HCO3- reabsorption dependent on

Answer 8

Na reabsorption and H+ secretion

Question 9

Explain glomerulotubular balance

Answer 9

more filtered load is matched by more proximal tubular reabsorption

Greater filtration fraction increases the osmotic pressure in the downstream peritubular capillaries resulting in more reabsorption
Efferent arteriolar constriction reduces peritubular capillary hydrostatic pressure

Question 10

Describe water permeability in the loop of henle

Answer 10

The descending limb is water permeable

The ascending limb is water impermeable

Question 11

In the loop of henle, where does solute reabsorption occur

Answer 11

Thick ascending limb

Question 12

What is the aim of the countercurrent multiplication

Answer 12

To generate a hypertonic medullary interstitium so that H2O can be sucked out of the tubule in impermeable distal segments thus concentrating the urine

Question 13

Explain how countercurrent multiplication works

Answer 13

Solute reabsorption in the impermeable ascending limb lowers luminal osmolality and increases medullary interstitial osmolarity

This draws H2O out of the permeable thin descending limb increasing the luminal osmolality

The continuous flow of fluid pushes the hyperosmotic fluid from end of the thin limb in to the ascending limb

Question 14

How is Na reabsorbed in the loop of henle

Answer 14

NKCC2 cotransporter

2Cl- , 1K+ and 1 Na+ brought in together

Question 15

How is Na reabsorbed in the distal tubules

Answer 15

Active Na transport via thiazide sensitive Na-Cl Co transporter

Question 16

What do thiazides inhibit

Answer 16

Na reabsorption in the distal tubule

Question 17

What is the water permeability in the collecting duct

Answer 17

Becomes Highly water permeable in the presence of vasopressin which flows out as it’s surrounded by hypertonic medullary interstitium

Question 18

What is the role of aldosterone

Answer 18

Aldosterone drives both Na reabsorption and K secretion

It increases the number of ENaC (specific Na transporter)

Question 19

Is urine hypo or hypertonic when it enters the collecting duct

Answer 19

Hypotonic

Question 20

What is the main osmolute that regulate water reabsorption

Answer 20

Urea

Question 21

What regulates the permeability of the collecting ducts

Answer 21

Anti diuretic hormone / vasopressin