Lecture 25: Water and salt balance 2

Question 1

Describe what would happen if the right renal art. becomes abnormally constricted?

Answer 1

• Constriciton -> Decreased GFR, decreased afferent BP and NaCl past macula dense= Inc. renin release, increased ANG2 = Increased salt and water retention -> Increased BP BUT consequently increased perfusion of the other kidney, decreasing its renin release. Balancing act

Question 2

What stimulates aldosterone release?

Answer 2

ANG2

-> Independently high K stimulations aldosterone release

Question 3

Describe how aldosterone acts:

Answer 3

Aldosterone acts on mineral corticoid receptor and upregulated ENAC and its insertion into the membrane = Increased Na retention and consequently water drag.

= Isotonic water retention

Question 4

What may cause up to 10% of essential hypertension?

Answer 4

Hyperaldosteronism

Question 5

When spironolactone was given to hypertensives what was observed?

Answer 5

30% reduction in death risk (aldosterone antagonist), i.e can treat hypertensive with more than ANG 2 blockers

Question 6

Aldosterone is responsible for 33g in salt reabsoprtion, if adrenal function was lost would 33g of NaCl be lost indefinitely?

Answer 6

No.

Once Na becomes sufficiently low, Na retention mechansims will come into play such as lowering GFR, and altering other factors that influence tubular Na reabsoprtion to compensate at least partially for the decreased aldosterone-dependent Na reabsorption

Question 7

How is osmolality regulated?

Answer 7

• Regulated by changes in renal water handling
• TIGHTLY REGULATED (1-2%)
• Mediator: ADH

Question 8

How is ECF volume regulated?

Answer 8

• Regulated by changes in renal Na handling (NaCl)
• Varies increase and decrease all day long
• Mediators: RAS, and SNS

Question 9

Why is it important for osmolality need to be kept constant?

Answer 9

Changes in osmolality can draw water out or cause water to enter the ICF

Question 10

Describe the systems that increased Na reabsorption for decreased ECF volume?

Answer 10

Increased Na reabsoprtion:

• RAAS
• SNS
• Possibly some ADH

Question 11

Describe the systems that decrease Na reabsoprtion when ECF volume increases?

Answer 11

Decrease Na reabsorption:

• ANP
• Decrease RAA and SNS
• Dopamine
• Prostaglandins

Question 12

What stimulates ANP?

Answer 12

• Released from atria in response to increased filling pressure and increased atrial stretch
• ANP binds to receptors to increase cGMP

Question 13

What are the actions of ANP?

Answer 13

• Decreases Na reabsoprtion in DT and outer medullary CT by blocking ENac and inhibiting Na, K-ATPase
• Inhibits release of aldosterone
• Inhibits renin release
• Vasodilates afferent arteriole to increase GFR

Question 14

A 67‐year‐old woman was brought to the hospital after a fall on the stairs. She had a past medical history of high blood pressure and atrial fibrillation, for which she took a calcium channel blocker and a beta blocker. She reported climbing a flight of stairs with a glass of water in her hand. The next moment she was lying on the ground not remembering what had happened. She apparently had a normal diet with normal salt intake. She was diagnosed with syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Describe her expected ADH level, osmolality and renal excretory response to water ingestion?

Answer 14

• SIADH = High ADH
• Osmolality low b/c increased ADH = retained water and decreasing osmolality

= When 500mL water ingestion occurs this would further decrease osmolality, decreasing NaCl past macula dense, this would stimulate RAAS, increasing BP

Question 15

A 48Y/O presents with high BP, she stopped taking her ACE inhibiter, turns out she has unilateral atherosclerotic renal artery stenosis:

Describe: ANG2 level in her unmedicated state, describe why her creatinine levels might rise once her medication starts back, what would happen if the sclerotic kidney was removed?

Answer 15

• Stenosis = decreased GFR = Increasing ANG2 = Increased water/Salt retention = Increased BP and thus hyperperfusion of other kidney which may hypertrophy
• Creatinine would rise after medication started because her BP would drop quickly and her GFR would decrease and itd take take for the remaining kidney to compensate/catch up
• Removal of the atherosclerotic kidney would drop the blood pressure as theres no over ANG2 production etc. It The remaining kidney can sustain enough filtration