Renal Physl 13

Question 1

What drives the osmotic movement of water?

Answer 1

The loop of henle and surrounding vessels like the vasa recta help to maintain high osmolarity in the renal medulla so when there is permeability to water induced by vasopressin, water can flow from the dilute tubular fluid into the more concentrated renal medullary interstitium

Question 2

What is reabsorbed in the proximal tubule?

Answer 2

Both water and solute

Question 3

Since both water and solute are absorbed at the proximal tubule what is the osmolarity of filtrate?

Answer 3

It is isosmotic relative to plasma

Question 4

How is the osmolarity of the interstitium affected as we down the descending loop of henle?

Answer 4

The osmolarity of the interstitium surround the tubules increases as we move from the cortex to the inner medulla which causes water to diffuse out and be reabsorbed

Question 5

What is the descending loop of henle permeable to?

Answer 5

Water and not solutes

Question 6

What happens to the osmolarity of the filtrate as a result of water diffusing out in the descending loop of henle?

Answer 6

The filtrate becomes more concentrated

Question 7

What is the ascending loop of henle permeable to?

Answer 7

Solute and impermeable to water

Question 8

What is reabsorbed in the ascending loop of henle?

Answer 8

Solute but not water

Question 9

What is a consequence to filtrate if only solute being reabsorbed in the ascending loop of henle?

Answer 9

The tubular filtrate become more dilute as solute is removed

Question 10

What is water permeability of the distal tubule under control of?

Answer 10

The hormone vasopressin

Question 11

What happens to the distal tubule in the absence of vasopressin?

Answer 11

The distal tubule is not permeable to water so only solute is reabsorbed

Question 12

What happens to the distal tubule in the presence of vasopressin?

Answer 12

The nephron is permeable to water and it can be reabsorbed along with solute

Question 13

What happens if water permeability of the distal tubule and the collecting duct is maximized?

Answer 13

A small volume of highly concentrated urine is excreted

Question 14

What happens if the body needs to get rid of excess volume?

Answer 14

Then a large volume of dilute urine is excreted

Question 15

What can urine osmolarity range between in humans?

Answer 15

50-1200 milliosmoles

Question 16

How do we maintain a high osmolarity of the renal medullary interstitium if we are reabsorbing solute and water?

Answer 16

The configuration of the loop of henle and the vasa recta form a countercurrent multiplier or countercurrent exchange system

Question 17

What does counter current refer to?

Answer 17

Fluid flowing in opposite directions

Question 18

Where is a counter current seen?

Answer 18

In the descending and ascending loops of henle and the vasa recta

Question 19

Where does isosmotic fluid from the proximal tubule flow?

Answer 19

Into the descending limb of the loop of henle

Question 20

How is the osmolarity of the filtrate affected as it moves up towards the cortex?

Answer 20

It is reduced

Question 21

Why doesn’t reabsorbed fluid dilute the medullary interstitium?

Answer 21

Because it is reabsorbed back into the circulation by the vasa recta

Question 22

What is the osmolarity of the blood flowing into the cortex vasa recta and moving down to the medulla?

Answer 22

It is isosmotic but as it flows into the renal medulla it picks up salt that was actively transported out of the ascending loop of henle so by the time blood reaches the tip of the vasa recta it is just as concentrated as the medulla

Question 23

What happens as blood flows up the vasa recta?

Answer 23

The high solute concentration attracts water to diffuse into the vessels and dilutes to blood as it reaches the cortex and becomes isosmotic