Regulation of Salt Balance Flashcards
What is water excretion regulated by?
ECF osmolality
What is osmolality determined by?
Water and salt content
In ECF what is the major cation?
Na
What is excess Na a major factor in?
Hypertension
What can decreased Na levels result in?
Hypovolaemia and hypotension
What does decreased osmolality result in?
Water excretion
What does increased osmolality result in?
water retention and thirst
What is ECV?
Effective circulating volume - the component of blood which is perfusing the tissue
What is themodification of Na reabsorption changes in?
ECF , ECV
What is Renin?
An enzyme, synthesised and stored in the juxtaglomerular apparatus
What is the stimuli for renin release?
Increased sympathetic nerve activity via baroreceptor reflex
Why else is Renin released?
decresed wall tension in afferent arteriole, decreased Na delivery to the macula densa
What does the macula do in renin release?
releases prostaglanding I2 to stimulate granular cells to release renin into blood
How does macula densa release blood?
Through sympathetic nerves - via beta adrenergic receptors
What does Renin act on?
plasma protein - angiotensiongen to produce a decapeptide angiotensin 1
How is angiotensin 1 converted to angiotensin 2?
Plasma endothelial enzyme known as angiotensin converting enzyme ACE
What is angiotensin 2?
Primary hormone in Na regulation, octapeptide
What is angiotensin 2 broken into?
Angiotensin 3 and inactive products by plasma peptidases
What does Angiotensin 2 cause ?
Vasoconstriction - intrarenal, systematic
Increased proximal tubular sodium reabsorption
Aldosterone release from zona glomerulosa for distal tubular sodium reabosorption
Thirst
ADH for water retention
What does removal of adrenal glands cause?
Metabolic defects and death in 2 weeks
Why does removal of adrenal glands cause?
Loss of NaCL from body via urine
Extracellular Na content falls
ECF volume markedly reduced
Circulatory collapse
How can death be avoided if adrenal glands removed?
high sodium diet
administration of aldosterone
What is aldosterone synthesised and secreted by?
zona glomerulosa of adrenal gland , steroid hormones synthesised from cholesterol, mineralocorticoid
What causes aldosterone release?
Decrease in plasma Na concentration
Increase in plasma K concentration - sensitive
Decrease in ECV - angiotensin 2
What are the effects of aldosterone?
stimulates Na reaborption and K and H secretion in collecting duct and promotes Na reabsorption in gut and sweat glands
What is Atrial Natriuretic peptide?
28 aa hormone from 126 aa prohormones
Where is ANP released from?
Atrial cells in response to atrial stretch - hypervolemia
What does ANP act at?
ANP receptors in collecting duct - promotes Na loss in urine
What is ANP mechanism of action?
inhibits collecting duct NA-K-ATPase
inhibits aldosterone secretion
Reduces renin release
promotes vasodilation of afferent arterioles
What is natriuretic mean?
decrease in Na reabsorption
What is urodilatin?
Origin in kidney, identical to ANP with 4 extra aa’s, natriuretic
What is dopamine?
Synthesised in proximal tubule, inhibits Na-K-ATPase, inhibits Na-H antiport - natriuretic
What is Kinins?
Vasodilator peptides - produced from kininogens by enzyme kallikrein, counteracts ADH, natriuretic
What is adrenomedullin?
52 aa peptide synthesised in kidney, increases GFR, decreases sodium tubular reabsorption and natriuretic
