Lecture 32

Question 1

How does osmolarity change through the nephron?

Answer 1

increases down loop of Henle, isosmotic in cortex, only water is absorbed by the descending limb (need increasing concentration to maintain osmotic gradient since inside loop, due to water leaving, fluid also becomes higher osmotic)

Question 2

How is H2O reabsorption regulated?

Answer 2

through arginine vasopression (ADH), hormone produced by neurons in hypothalamus, stored in posterior pituitary. released into the bloodstream, goes to the collecting duct, binds to V2 (a GPCR) and activates cAMP pathway, and causes insertion/modifications to aquaporin-2 in the APICAL membrane to increase water reabsorption
Released in response to high osmolarity, low blood pressure, low blood volume

Question 3

How is Na reabsorption regulated?

Answer 3

through aldosterone, released from the renal cortex. causes increased Na reabsorption and K secretion
stimulated through angiotensin II, or high [K+] in plasma
acts on principal (P) cells of distal tubule and collecting duct. steroid hormone so diffuses through, synthesizes/modulates new protein channels/pumps

Question 4

Describe the renin-angiotensis-system (RAS)

Answer 4

low blood pressure causes renin secretion from granular cells in 3 ways. Granular cells directly sense low BP, cardiovascular control center sends sympathetic activity to granular cells, or macula densa sense decreased NaCl transport and release paracrines. This renin acts as an enzyme to convert angiotensinogen released from liver into angiotensin I. angiotensin I converted to angiotensin II through ACE (angiotensin-converting enzyme) which signals lots of things

Question 5

What does angiotensin II do?

Answer 5

stimulate aldosterone release = increased Na reabsorption
hypothalamus = increased salt appetite, thirst, vasopressin release
cardiovascular center = increased CO
vasoconstriction of arterioles

Question 6

How is acid/base balanced

Answer 6

3 mechanisms

1) buffers = HCO3-, proteins, hemoglobin, phosphates
2) Regulation of ventilation = changes PCO2
3) kidneys = secretion/reabsorption

Question 7

Describe respiratory compensation

Answer 7

triggered by increased H+ or increased PCO2, sensed by carotid/aortic chemoreceptors or central chemoreceptors, triggers medulla control center and increase rate and depth of breathing (immediate change)

Question 8

Describe renal compensation

Answer 8

Finely regulated through intercalated (I) cells (between P cells) at the collecting duct that contain lots of carbonic anhydrase, generally regulated by H+ secreted and HCO3- reabsorbed in proximal tubule
two types
1) Type a = secrete H+, absorb HCO3-
2) Type b = absorb H+, secrete HCO3-