Loop of henle, DCT and CD

Question 1

What determines the concentrating ability of the kidneys in a species?

Answer 1

• length of LOH

- number of juxtamedullary nephrons

Question 2

What happens to the ISF in the renal medulla?

Answer 2

Gets increasingly hyperosmotic

Question 3

What is the descending limb of the LOH permeable to?

Answer 3

Water but it lacks ion pumps

Question 4

What leads to osmotic transport of water out of the descending limb?

Answer 4

Active transport of ions out of the ascending limb make interstitial space hyperosmotic and draws water out of descending limb making filtrate more concentrated

Question 5

What happens as filtrate is continually produced?

Answer 5

New tubular fluid enters the descending limb and pushes the fluid at higher osmolarity down the tube

Question 6

How is the capillary network around the LOH specialised and what is this network called?

Answer 6

• Vasa recta
• supply oxygen and nutrients to the medulla
• run parallel to the limbs of the LOH
• blood flows in opposite directions

Question 7

Which hormone is mainly involved in the regulation of the reabsorption of water?

Answer 7

ADH - anti diuretic hormone

Question 8

How does ADH increased water reabsorption?

Answer 8

• Inserts aquaporins into the apical membrane of the collecting duct
• ↑ ADH causes ↑ permeability of collecting duct to water and the medullary osmotic gradients allows the movement of water from the filtrate into the medulla

Question 9

By the time the filtrate has entered the DCT what has happened to calcium and phosphorus?

Answer 9

Calcium
- 50% bound to albumin so only free 50% is filtered
- Approximately 70% reabsorbed in PCT
- Selective reabsorption of Ca 2+ in DCT and CD under hormone control
Phosphorus
- - Inorganic phosphate 100% filtered
- Reabsorption in PCT by Na+ co-transport under hormone control
- NOT reabsorbed in DCT & CD

Question 10

Which hormone is released in response to decreased calcium conc in the blood?

Answer 10

Parathyroid hormone

Question 11

What are the functions of parathyroid hormone in the kidney?

Answer 11

• Decreases reabsorption of phosphate in the proximal tubule
• Increases reabsorption of Ca2+ in the ascending loop of Henle, distal tubule, and collecting tubule

Question 12

What is the function of principle cells in the DCT and CD?

Answer 12

Allow further reabsorption of sodium and secretion of potassium

Question 13

Which hormones regulates the principle cells?

Answer 13

Aldosterone

Question 14

What % of bicarbonate ions have been reabsorbed by the time the filtrate enters the DCT?

Answer 14

80-90% in the PCT

10-20% in the LOH

Question 15

What is the function of intercalated cells?

Answer 15

Allow further regulation of H+ secretion and synthesis of bicarbonate

Question 16

Which two new players in the DCT can pump H+ against larger conc gradients?

Answer 16

• H+ ATPase - Actively pumps H+ into filtrate in DCT

* H+ K+ ATPase - Actively pushes H+ into urine in exchange for K+ in the DCT

Question 17

What are the two types of intercalated cells are found in the distal nephron?

Answer 17

Type A - alpha - that work during acidosis

Type B - beta - that work during alkalosis

Question 18

On which membranes are type A and type B cells active?

Answer 18

Type A = apical membrane

Type B = basolateral membrane