Renal System 5 Renin A2 aldosteron

Question 1

What is one of the main functions of juxtaglomerular cells (JG)?

Answer 1

Release of Renin

Question 2

What are the 3 stimuli that stimulate the release of Renin?

Answer 2

1) Sympathetic NS
2) Less stretch on afferent arteriole due to less blood pressure and less blood flow -> JG is less stretched -> release of Renin
3) Signal from Macula Densa: when rate of Na Cl in Macula Densa slows down -> signal to JG to release Renin

Question 3

What are the 3 stimuli that stimulate the release of Renin?

Answer 3

1) Sympathetic NS
2) Less stretch on afferent arteriole due to less blood pressure and less blood flow -> JG is less stretched -> release of Renin
3) Signal from Macula Densa: when rate of Na Cl in Macula Densa slows down -> signal to JG to release Renin

Question 4

What are the effects of sodium and H2O loss in diarrhea?

Answer 4

Plasma volume down -> Venous pressure down

Venous pressure down -> Venous return down -> Atrial pressure down

Atrial pressure down -> ventricular EDV down -> SV (stroke volume) down -> CO down -> Arterial blood pressure down

Question 5

The sum effect of Na+ and H2O loss in diarrhea?

Answer 5

Sum: Venous, atrial, and arterial pressure goes down -> causing activity of renal sympathetic nerves

Question 6

What effect do Na and H20 loss have on the kidney?

Answer 6

-Activity of renal sympathetic nerve causes constriction of afferent renal arterioles, causing reduced blood flow -> drop in net glomerular filtration pressure

-Arterial pressure causing the net glomerular filtration pressure to drop directly

BOTH: causing drop in GFR -> Na+ and H2O ecxretion is reduced

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Question 7

Overall effect of Na+ and H2O loss?

Answer 7

Drop in GFR -> Drop in Na and water excretion

Because of increased loss, more of them should be kept by decreasing pressure glomerular capillaries -> reduce of GFR

Question 8

How is renin involved in Na and H2O loss?

Answer 8

-Reduction of pressure is a stimulus (less stretch of JG) to release Renin

-Reduced GFR will slow down the appearance of Na+ and Cl in the Macula Densa -> stimulate the JG to release Renin

Question 9

How does Renin work?

Answer 9

Renin released in the kidneys is an enzyme converting Angiotensinogen (always present in the bloodstream produced in the liver) to Angiotensin I

Question 10

What happens to Angiotensin I?

Answer 10

It gets converted to Angiotensin II by Angiotensin-converting enzyme (ACE I present in endothelial cells of lungs and kidneys)

Question 11

What are the effects of Angiotensin II?

Answer 11

-Cardiovascular system: Vasoconstriction -> increase blood pressure (Homeostatic -> more blood flow will stretch JG -> renin stops)

-stimulates Adrenal cortex to secrete aldosterone -> promotes salt and water retention

Question 12

What do water and H2O retention look like?

Answer 12

more reabsorption and less excretion of water and Na+

Question 13

How does aldosterone work?
EXAM !!!

Answer 13

Aldosterone (lipophilic) walks through the membrane of principal cells -> and acts as a transcription factor

1) for Na+ channel: more Na reabsorption from the urine back to the blood

2) for proteins responsible for the TCA cycle to produce more ATP, ATP is needed for the Na-K ATPase to pump Na back into the blood

Question 14

Different functions of Angiotensin II:

Answer 14

-direct Vasostrictor: activating vascular smooth muscles -> increases BP

-stimulates aldosterone release: Na+ and water retention -> increases BP

-stimulates vasopressin release -> increase water retention -> increase BP

-stimulates thirst: increase water intake -> increase BP

Question 15

What is a natriuretic effect?

Answer 15

Loss of sodium in the urine

Question 16

To what do atrial natriuretic peptides respond?

Answer 16

Increased blood volume
Stretch of cardiac atria -> causing ANP secretion -> inhibition of aldosterone (does the opposite of Angiotensin II)

in the Kidney:
1) Afferent arterioles dilated and efferent constricted -> increase of GFR
2) Reabsorption of Na reduced
3) Inhibits renin release

–> all those cause increased Na excretion

Question 17

What does BNP do?

Answer 17

similar to ANP
-released to respond to the stretch of the ventricular muscle
-enhance Na and water excretion
-BNP and ANP are broken down by neprilysin

Question 18

How does the body react to excess water?

Answer 18

The hypothalamic osmotic receptor will fire less -> less vasopressin in plasma -> fewer aquaporins that reabsorb H2O -> more H20 stays in urine and gets excreted

Question 19

How does the body to the reduced amount of water?

Answer 19

There will be less plasma volume and less venous, atrial, and arterial pressure -> recognized by Posterior Pituatiary (baroreceptors: increase Vasopressin secretion -> increase of water reabsorption through aquaporins -> less H2O excretion

Question 20

What other mechanism has the body to counteract reduced water amounts?

Answer 20

-sympathetic NS activation
-activation of renin/angiotensin and aldosterone

Question 21

How does the body compensate for severe sweating?

Answer 21

1) Sodium: low plasma volume will cause the decrease in GFR and activation of aldosterone

2) H2O: high plasma osmolarity (low H2O) will activate vasopressin -> activates aquaporins and reduces H2O excretion

Question 22

How is thirst stimulated?

Answer 22

1) Low plasma volume detected by Barorecptors -> activation of Angiotensin II

2) Baroreceptors itself

3) High plasma osmolarity detected by osmoreceptors

4) Dry mouth, throat

-Metering of water intake in GI reduces thirst

Question 23

Where and how does K+ reabsorption occur?

Answer 23

Loop of Henle (principal cells), though NKCC pumps

Question 24

How is K+ secretion stimulated/regulated?

Answer 24

a small increase of extracellular K+ will stimulate the Na+K-ATPase pump and cause K+ secretion into urine and excretion from the urine

Question 25

What is a major stimulus of aldosterone?

Answer 25

An increase in K+ plasma level
Aldesterone inccreases N+ reabsorption and K+ secretion + excretion

Question 26

How else is K+ secretion stimulated?

Answer 26

Number of Na+ in tubule lumen (urine) -> if it is high there it will go into the principal cell (collecting duct) -> and it forces K+ out of the cell either on the apical side (into the urine) or basolateral side

also, Aldosterone (released by the adrenal cortex) causes K+ secretion

Question 27

How does N+ get into the cell and K+ out of the cell?

Answer 27

NKCC pumps

Na+ reabsorption at the expense of K+ secretion

Question 28

How is the number of Na+ outside of the cell (tubule lumen - urine) increased?

Answer 28

Through Loop diuretics (drugs) blocking NKCC pumps

Question 29

Why must K+ be strongly regulated?

Answer 29

They affect the resting membrane potential of excitable cells

Question 30

Angiotensin II role in K+ secretion:

Answer 30

low plasma volume causes Angiotensin II release -> causing the adrenal cortex to release aldosterone -> aldosterone increases Na+ reabsorption and K+ secretion + excretion

Question 31

How is Ca and PO4 level regulated?

Answer 31

By PTH
-causes more reabsorption of Ca++ and inhibits reabsorption of PO4 in the kidney

-activates 1,25 dihydroxy Vitamin D (active Vit D) which increases absorption of Ca and PO4 in the intestine

Question 32

Where does reabsorption of Ca and PO4 occur?

Answer 32

-Proximal convoluted tubule
-Fine-tuning in distal convoluted tubule under control of PTH