Renal Physiology Lecture 2: Sodium Balance

Question 1

What happens in kidneys with excess sodium?

Answer 1

• increases plasma osmolarity
• drives renal water reabsorption & thirst
• Expansion of blood volume due to retention of water
  
  • increases arterial pressure

Question 2

Mechanism of salt ingestion

Answer 2

Question 3

What hormone control sodium balance

Answer 3

Aldosterone

• Synthesized in the adrenal cortex → circulates in the blood

Question 4

Where does aldosterone act?

Answer 4

at the renal distal tubule and collecting duct

• At principle cells

Question 5

Function of Aldosterone

Answer 5

• Stimulates sodium reabsorption
• Increases acitvity of Na-K-ATPase
• Increases potassium excretion

Question 6

Aldosterone process

Answer 6

• Aldosterone combines with a cytoplasmic receptor
• Hormone-receptor complex intiates trnascription in the nucleus
• Translation and protein synthesis makes new protein channels and pumps
• Aldosterone-induced proteins moldultes existing channels and pumps
• Result is increases Na reabsorption and K secretion

Question 7

What stimulates aldosterone release?

Answer 7

Plasma osmolarity & blood volume/ pressure

• Low blood volume/ pressure, high circulating potassium stimulates aldosterone release

Question 8

How does potassium stimulate aldosterone release?

Answer 8

High potassium acts directly at the adrenal cortex

• Aldosterone results in increased potassium excretion, protecting from high potassium levels

Question 9

Effect of osmolarity & blood pressure/ volume on aldosterone release

Answer 9

• Low pressure/ volume initiates mechanisms for salt/ water reabsorption by kidneys and production of Angiotensin II (Ang II) and aldosterone
• High plasma osmolarity (dehydration) suppresses aldosterone production
• decreased plasma osmolarity stimulates aldosterone production

Question 10

RAAS

Answer 10

Renin-Angiotensin-Aldosterone System

• a hormone system within the body that is essential for the regulation of blood pressure and fluid balance. The system is mainly comprised of the three hormones renin, angiotensin II and aldosterone. Primarily it is regulated by the rate of renal blood flow.

Question 11

RAAS process

Answer 11

1. Blood pressure falls which stimulates the juxta cells to secrete renin
2. Renin converts angiotensinogen to Angiotensin I
3. Angiotensin I is converted to angiotension II via angiotension converting enzyme
4. Angiotension II acts on the adrenal cortex to stimulate aldosterone release and acts acts directly to raise blood pressure
5. aldosterone released acts on kidneys to retain sodium, raising blood pressure

Question 12

What does Ang II contribute to?

Answer 12

fluid and sodium balance

Question 13

Ang II contribution at the brain

Answer 13

• Stimulates vasopressin release at the hypothalamus
  
  • increases renal water reabsorption & restores blood volume/ pressure
• Stimulates thirst and water intake
• increases sympathetic outflow
  
  • increase CO, vasoconstriction, RAAS

Question 14

Ang II contribution at vasculature

Answer 14

• Vasoconstriction
  
  • short-term increase in blood pressure

Question 15

Ang II contribution at the proximal tubule

Answer 15

• stimulates apical Na-H-Exchanger (NHE)
  
  • stimulates salt & water reabsorption

Question 16

ANP

Answer 16

Atrial Natriuretic Peptide

• Increases sodium excretion

Question 17

Where does ANP come from?

Answer 17

Family of hormones released by cardiac cells

• ANP from atria
• Brain Natriureitc Peptide (BNP) from ventricles

Question 18

How does ANP increase Na excretion?

Answer 18

• Induces natriuresis & diuresis - increase sodium and water excretion
  
  • also vasodilation
• Released in high volume conditions in response to cardiac stretch
• ANP dilates afferent arterioles & increases GFR
  
  • Also inhibits sodium reabsorption in the collecting duct
  • INhibits release of sodium/ water reabsorbing mediators