Ch. 17 Day 3 Flashcards
Renal control of electrolyte and acid-base balance
Kidneys match electrolyte (Na+, K+, Cl-, bicarbonate, phosphate) excretion to ingestion
- -a) control of Na+ levels important in BP and blood volume
- -b) control of K+ levels important in healthy skeletal and cardiac muscle activity
- -c) aldosterone plays role in Na+ and K+ balance
Role of aldosterone in Na+/K+ balance
- About 90% of filtered Na+ and K+ is reabsorbed early in the nephron - not regulated
- An assessment of what the body needs is made, and aldosterone controls additional reabsorption of Na+ and secretion of K+ in the distal tubule and collecting duct
K+ secretion
Aldosterone Independent Response: increase in blood K+ triggers increase in the number of K+ channels in the cortical collecting duct. When blood K+ levels drop, these chemicals are removed.
Aldosterone Dependent Response: increase in blood K+ triggers adrenal cortex to release aldosterone –> increase K+ secretion in the distal tubule and collecting duct
Na+ and K+
1) Increase in Na+ absorption drives extra K+ secretion
2) Due to:
- -a) potential difference created by Na+ reabsorption driving K+ through K+ channels
- -b) stimulation of renin-angiotensin-aldosterone system by water and Na+ in filtrate
- -c) increased flow rates bend cilia on the cells of the distal tubule, resulting in activation of K+ channels
Control of Aldosterone Secretion
a) a rise in blood K+ directly stimulates production of aldosterone in the adrenal cortex
b) fall in blood K+ indirectly stimulates production of aldosterone via the renin-angiotensin-aldosterone system (juxtaglomerular feedback)
Juxtaglomerular Apparatus
Located where afferent arteriole contacts distal tubule
A decrease in plasma Na+ results in a fall in blood volume
- a) sensed by juxtaglomerular apparatus
- b) granular cells secrete renin into afferent arteriole
- c) this converts angiotensinogen into angiotensin I
- d) angiotensin-converting enzyme (ACE) converts this into angiotensin II
- e) angiotensin II –> aldosterone –> increased Na+ reabsorption/K+ secretion by cortical collecting duct, increase blood volume and BP
Regulation of Renin Secretion
a) Low salt levels result in lower blood volume and BP
- -1) decreased pressure in renal artery –> decreased NaCl and water in renal filtrate
- -2) juxtaglomerular apparatus senses the changes in filtrate composition –> signals to granular cells in afferent arterioles to secrete renin
b) reduced blood volume is detected directly by granular cells in afferent arteriole that act as baroreceptors –> also increase renin secretion
c) juxtaglomerular cells also stimulated by sympathetic signals triggered by a fall in blood volume/pressure –> also increase renin secretion
Macula Densa
a) part of distal tubule that forms juxtaglomerular apparatus
b) sensor for tubuloglomerular feedback needed for regulation of glomerular filtration rate
- -1) when there is more Na+ and H2O in the filtrate, a signal is sent to the afferent arteriole to constrict limiting filtration rate
- -2) controlled via negative feedback
c) when there is more Na+ and H2O in filtrate, signal sent to afferent arteriole to inhibit production of renin
- -1) results in less reabsorption of Na+, allowing more to be excreted
- -2) helps lower Na+ in blood
Whatever happens to Na+, the ____ usually happens to K+.
Opposite
Decrease in blood volume…
increased renin secretion
increase angiotensin II production
increased aldosterone secretion
Increase in blood volume…
decreased renin secretion
decrease angiotensin II production
decreased aldosterone secretion
Increase in K+…
no effect on renin secretion
no change in angiotensin II production
increased aldosterone secretion
Increase in sympathetic nerve activity…
increased renin secretion
increased angiotensin II production
increased aldosterone secretion
Atrial Natriuretic Peptide
released when BP increases
- increase in blood volume also increase release of atrial natriuretic peptide hormone form atria of heart when atrial walls are stretched
- stimulates kidneys to excrete more salt and therefore more water
- decreases blood volume and BP
basically opposite of renin angiotensin-II secretion
Relationship between Na+, K+, and H+
- Reabsorption of Na+ stimulates secretion of other positive ions; K+ and h+ compete
- Acidosis stimulates secretion of H+ and inhibits secretion of K+ ions; acidosis can lead to hyperkalemia
- Alkalosis stimulates secretion and excretion of more K+
- Primary hyperkalemia stimulates the secretion of K+ and inhibits secretion of H+; can lead to acidosis
