Sodium Handling - Kidneys

Question 1

What is the main output of Na?

Answer 1

Urine
Feces
Sweat

Question 2

What are the 2 hormonal systems that regulate Na handling?

Answer 2

RAAS

ANP

Question 3

What is Renin-Angiotensin-Aldosterone System?

Answer 3

Increases Na reabsorption through the production of the enzyme renin and 2 hormones (angiotensin II and aldosterone)

Question 4

What is the Atrial Natriuretic Peptide?

Answer 4

Functions to decrease Na reabsorption

Question 5

What is the connection between Na levels and BP?

Answer 5

If Na is too high, ECF volume increases, increasing BP.

Question 6

Describe the RAAS pathway and how it works?

Answer 6

Multiorgan System

• Liver is making angiotensinogen all the time, floats around the blood
• Within the kidney, juxtamedullary cells make renin when there is low Na, and is put into the blood
• Renin cuts angiotensinogen –> angiotensin I which floats around the blood as a small protein
• ACE is in endothelial cells of capillaries and cleaves angiotensin I –> angiotensin II (smaller protein that is the actual hormone)

Question 7

Name the following for Angiotensin II

• Made
• Hormone properties
• Stimulus
• Action

Answer 7

Made: by ACE cleaving angiotensin I
Properties: peptide, extracellular receptor, released into the blood
Stimulus: Renin release
Action: Cause an increase in Na reabsorption in proximal tubule

Question 8

What are the ways in which angiotensin II causes reabsorption of Na

Answer 8

• Increases activity of Na/H exchanger
• Increasing activity of Na/K ATPase
• Constricting afferent and efferent arterioles
• -> GFR decreases
• -> slowing the flow of the filtrate traveling through the tubule, giving Na a higher chance or reabsorption

Question 9

Name the following for Aldosterone

• Made
• Hormone properties
• Stimulus
• Action

Answer 9

Made: Adrenal gland
Properties: Steroid, intracellular receptors
Stimulus: Angiotensin II and K levels too high
Action: cause an increase in Na reabsorption collecting duct

Question 10

How does aldosterone stimulate Na reabsorption in the collecting duct?

Answer 10

• Increasing number of Na and K channels in luminal membrane
• Increasing Na/K ATPase activity
• Increasing expression level of Na and Na/K ATPase

Question 11

What is unique about the action of aldosterone?

Answer 11

There are fast and slow acting elements to increase Na reabsorption

Question 12

What triggers/regulates the release of renin?

Answer 12

When Na levels are low in the blood

Question 13

Name the following for Atrial Natiuretic Peptide

• Made
• Hormone properties
• Stimulus
• Action

Answer 13

Made: By atrial cardiac cells
Properties: Peptide, extracellular receptors
Stimulus: High PB
Action: Inhibit Na reabsorption

Question 14

How does ANP inhibit Na absorption?

Answer 14

• ANP inhibits aldosterone secretion by the adrenal glands
• ANP is also a vast dilator, causing dilation of afferent arterioles, causing an increase flow in the Bowmans capsule, causing Na to not have enough time in the tubule for reabsorption. therefore most of the Na goes right through and is excreted

Question 15

What is the pathway of ANP starting with High Na?

Answer 15

High Na=High ECF=High blood Pressure–> Distention of Cardiac Atria–> ANP released–>

a) Afferent arterial dilated, GFR increases
b) Aldosterone secretion decreased
- -> Increased Na secretion