renal 6 Flashcards
how does urea contribute to the osmolarity of the medullary interstitium?
-the high solute concentration in the medulla is only partly due to NaCl
-about half of the solute in the medulla interstitium is urea
-a large amount of urea is reabsorbed in the distal portion of the nephron and creates a recycling loop
what is the water balance summary?
what is our diet in north america and our plasma concentration?
-north american diet is high in NaCl (9g or 155 milliosmoles) of Na and 155 milliosmoles of Cl each day
-our plasma Na concentration is 135-145 milliosmoles/L, Na is distributed freely between plasma and interstitial fluid thus representing out ECF (Na)
if we ingeste enough NaCl to increase the ECF (NaCl) to 155mosmol/L how much water do we need to keep the Na at 140mosmol/L?
how would adding 155 mosmol NaCl affect osmolarity if we did not consume any water?
-it would increase total body osmolarity from 300-307 mOsM
-this would draw water from cells, disrupting normal function
how do our homeostatic mechanisms maintain mass balance?
-anything extra that enters the body is excreted
-the kidneys are responsible for most Na excretion, very little is lost during perspiration and in feces
-although we talk about ingesting and excreting NaCl, only Na absorption is regulated, Cl tends to follow through the electrochemical gradient set up by Na movement or co-transported with Na
what does the regulation of blood Na levels take place through?
-through a complicated endocrine pathway: the renin-angiotensin-aldosterone system
what is aldosterone?
-a steroid hormone responsible for altering Na reabsorption and K secretion
-targets the last third of the distal tubule and the portion of the collecting duct located in the cortex of the kidney
what is the early response of aldosterone binding?
-in early response phase to aldosterone binding receptor apical Na and K channels increase their open time through an unknown mechanism
aldosterone acts on ___________
PRINCIPAL CELLS
-aldosterone binds to cytoplasmic mineralocorticoid receptor in P cells
what is the way that aldosterone acts on p cells (modulation)?
Modulation of existing transporters: increases opening of apical Na and K channels enhancing Na reabsorption and K secretion, also insertion of pre-existing transporters
-increased Na entry to the cell, speeds up basolateral Na-K pump leading to increased Na reabsorption
-increased Na-K pump increases intracellular K leading to increased K secretion
what is the way that aldosterone acts on p cells (hormone)?
hormone ligand complex translocate into the cell nucleus, binds to hormone response elements that increase transcription of apical Na channels and K channels as well as basolateral Na/K pumps further enhancing Na absorption and K excretion
what is aldosterone secretion?
I. K acts directly on the adrenal cortex protecting the body from hyperkalemia
II. decreased blood pressure usually controls aldosterone secretion initiating a pathway that results in the production of angiotensin II which triggers aldosterone release
what are two additional modifiers of aldosterone release?
-increased osmolarity acts directly on the adrenal cortex during dehydration to inhibit release
-abnormally large drops in plasma Na can directly stimulate aldosterone secretion
what is the full graph of the renin-angiotensin-system (RAS)?
-a multi-step pathway for maintaining blood pressure
