Regulation of Na and H20

Question 1

Factors that promote Na+ reabsorption

Answer 1

Activation of renal sympathetic nerves
Activation of renin/angiotensin system
Secretion of aldosterone

Question 2

Factors that promote Na+ excretion:

Answer 2

Release of atrial, brain natriuretic peptides (ANP, BNP)
Release of urodilatin
Intrarenal prostaglandins

Question 3

Factors that promote renin secretion

Answer 3

Renal sympathetic stimulation (due to fall in perfusion pressure through the cardiopulmonary baroreceptors): directly stimulates renin secretion via β1 receptor activation in the JG apparatus

Tubuloglomerular feedback: dec. NaCl delivery to macula densa = inc. renin secretion

Intrarenal baroreceptor (wall of afferent arteriole): afferent arteriolar vasoconstriction = dec pressure at granular cells = inc. renin secretion

Question 4

What effect would loop diuretics have on renin secretion?

Answer 4

diuress casue can’t conc/ urine= hypoperfusion renin secretion goes up =may aggravate HTN

Question 5

Angiotensin II stimulates

Answer 5

Systemic arteriolar constriction

Renal arteriolar constriction: efferent > afferent.
How would this affect GFR & RBF?
-Maintain GFR mostly, RBF goes down

Na+ reabsorption: PCT (via ↑ Na-H exchanger activity) > TAL, CCD

Thirst

ADH secretion from posterior pituitary
Aldosterone secretion from adrenal cortex

Constrict renal mesangial cells (dec. Filtration)

Question 6

RAAS responds to

Answer 6

decreased BP, RBF or release of catecholamines

Results in dec NA excreaton and inc Na reabsorption

Question 7

Aldosterone’s actions

Answer 7

in late distal convoluted tubule, collecting duct (principal cells)

Stimulates sodium reabsorption
Results in: lumen-negative potential difference
Electroneutrality maintained by: passive Cl- reabsorption & K+/H+ secretion

Stimulates potassium secretion

Stimulates H+ secretion (↑ H +-ATPase activity in intercalated cells of CCD)

Secreted any time you have hyperK ATCH or vol depletion

Question 8

What would happen to K & H excretion in a patient with hyperaldosteronism?

Answer 8

hypoK & metabolic alkalosis

Question 9

ANP

Answer 9

increases Na+, H2O excretion
increases GFR: Afferent arteriolar dilation, efferent arteriolar constriction
ANP inhibits Na+ reabsorption in medullary collecting duct
ANP suppresses renin secretion
ANP suppresses aldosterone secretion
ANP is a systemic vasodilator
ANP suppresses AVP secretion, actions

Question 10

Urodilatin

Answer 10

Endogenous renal natriuretic peptide

Secreted by DCT, collecting duct in response to increased arterial pressure and ECF volume

Urodilatin suppresses Na+ and water reabsorption by medullary collecting duct

Unlike ANP and BNP, urodilatin has no effect on systemic circulation

Question 11

Intrarenal prostaglandins (e.g. PGE2)

Answer 11

Increase GFR by dilating renal arterioles

Suppress Na+ reabsorption in thick ascending limb, cortical collecting duct-

what effect will this have on the solute concentration in the renal medullary tissue?

Net effect: increased urinary Na+ excretion

NSAIDs oppose = renal failure

Question 12

Two major stimuli for ADH release:

Answer 12

hyperosmolality
volume depletion
Hypothalamic osmoreceptors are more important than hepatic osmoreceptors