Lecture 34

Question 1

What are the three key ideas of the descending and ascending limb of the hoops of henle?

Answer 1

1.) Descending limb is very impermeable to solutes, but highly permeable to H2O
2.) Ascending limb has high Na/K ATPase activity, but it is very impermeable to water.
3.) There is an osmolarity gradient in the kidney interstitial fluid, such that the fluid deep in the medulla is hyperosmotic relative to most body fluids.

Question 2

What happens to the water (and solutes) reabsorbed from the loop of Henle?

Answer 2

They are returned to circulation via bulk flow into the capillaries of the vasa recta

Question 3

What is the function of the vasa recta?

Answer 3

Takes all the reabsorbed fluid and make it into blood plasma - and carried away out of the kidney

Question 4

Describe the rates of water and solute movement into/out of the interstitium

Answer 4

the rates are matched
- The interstitial fluid volume remains steady and the osmolarity gradient is maintained (not equilibrium)

Question 5

Why is the gradient important?

Answer 5

It adjusts urine composition later, as the urine makes its final pass through the collecting ducts

Question 6

What parameters of urine can be adjusted? (semi independently)

Answer 6

• Volume produced (amount of water excreted)
• ionic concentration (principally Na+, but also K+ and Ca+)
• pH (via H+ and. HCO3- synthesis, reabsorption, and secretion)

Question 7

What are two critical regulatory mechanisms of urine composition?

Answer 7

• Reabsorption of H2O in the collecting duct, controlled by vasopressin
• Reabsorption of Na+ in the distal tubule and collecting duct controlled by RAAS system

Question 8

What if there is high vasopressin levels?

Answer 8

More H2O reabsorption
-increase in plasma volume and increase in bp

Question 9

What if there is high aldosterone signaling?

Answer 9

More Na+ reabsorption
- this indirectly causes more H20 reabsorption and thus increased in plasma volume and increased in bp

Question 10

What are two direct feedbacks to control urine parameters?

Answer 10

• Hypothalamic osmoreceptors directly monitor the osmolarity of body fluids and increase vasopressin release when osmolarity is high
• Kidney regulatory cells in the distal tubule epithelium (macula densa) directly monitor urinary Na+ and activate renin-secreting cells when it is low (leading to higher aldosterone signaling)

Question 11

What is an indirect feedback to control urine parameters?

Answer 11

cardiovascular and intrarenal baroreceptors (monitor bp) affect vasopressin and renin release to control water/Na+ reabsorption and thus regulate blood volume and pressure

Question 12

What occurs during high vasopressin conditions?

Answer 12

The interstitial osmolarity gradient favors water uptake from the urine as it passes into the renal pelvis through the collecting duct, producing concentrated urine

• When there is high vasopressin, there is more aquaporins in the membrane of collecting duct cells to help faster the process of water reabsorption to the interstitial fluid
• G- protein coupled signaling pathway leading to the shuttling of aquaporins into the apical membranes of duct epithelial cells

Question 13

What occurs during low vasopressin conditions?

Answer 13

water reabsorption is reduced, allowing the production of urine to be more diluted

Question 14

What is the function of the RAAS system?

Answer 14

Alters kidney Na+ reabsorption in response to urinary Na+ and bp

Question 15

Describe one common pathway related to the RAAS system (starting with decrease in MAP)

Answer 15

Decrease in MAP
= lower afferent arteriole pressure
= baroreceptor reflex
= decrease in GFR

• lower afferent arteriole pressure triggers increase in renin release
• Baroreceptor reflex triggers increase in sympathetic activity= increase in renin release
• decrease in GFR=decrease in Na+ and Cl- in distal tubules= increase paracrine secretion (reabsorbs more sodium)= increase in renin release

1.) Liver produces angiotensinogen (hormone thats always present)
2.) cells in kidney produce renin (enzyme) is released in the blood stream when there is increase in renin release
3.) Andiotensin I regulates cardiovascular and kidney functioning
4.) Angiotensin II acts on adrenal cortex
5.) Adosterone is produced (steroid hormone and acts on cells to reabsorb Na+)
This process causes increase in NA+ retention, Increase in H2O retention, Increase in Blood Volume, increase in MAP

Question 16

What does Aldosterone do?

Answer 16

Increases Na+ reabsorption and K+ secretion by altering transport protein densities in the membranes of the nephron epithelial cells

Question 17

What are the different homeostatic responses RAAS system is involved in?

Answer 17

• fine tunes the amount of Na+ reabsorbed by the kidneys to match day- to day functions in Na+ intake from food or to compensate for increased losses through sweating
• Activates during non-sodium regulated physiological challenges associated with blood pressure or blood volume (eg a large hemorrhage)

Question 18

What happens if there is a hemorrhage?

Answer 18

High aldosterone signaling and increased Na+ retention serve to help increase blood volume and blood pressure towards normal

Question 19

Important kidney functions

Answer 19

• voiding metabolic waste
• body fluid pH balance by adjusting urine
• production of some important hormones (ex: EPO)