Renal concentrating mechanisms and urine formation - Quiz 3 Flashcards
Where is renin synthesized?
Juxtaglomerular apparatus
What are the 4 components of the juxtaglomerular apparatus?
- modified smooth musc cells in the afferent arteriole
- Modified smooth muscle cells in the efferent arteriole
- Extraglomerular mesangial cells
- macula densa cells in the distal tubule
Most potent vasoconstrictor known
Angiotensin II
What are the actions of Angiotensin II?
- Profound vasoconstriction –> increased BP
- Increased aldosterone synthesis and release
- Increased ADH (vasopressin) release
- Increased thirst
- Feedback inhibition of renin release
How does angiotensin II work on the afferent and efferent arterioles?
How does this affect GFR?
Ag2 constricts the afferent and efferent arterioles
Ag2 also releases prostaglandins that maintain GFR inspire of the arteriolar constriction (autoregulation)
Where does aldosterone work?
distal tubule and collecting ducts
What does aldosterone do?
causes K secretion and also H in exchange for Na
What is the net effect of aldosterone?
gets rid of K and H
What is aldosterone and where is is made?
Steroid hormone
synthesized in zona glomerulosa of the adrenal cortex
3 factors that stimulate aldosterone release and synthesis
- Increased K in the ECF
- Ag2
- Decreased Na levels
What is Conn’s syndrome?
An aldosterone secreting tumor that causes:
- HTN
- HyperNa
- HypoK
What is the physiologic process of Conn’s syndrome?
The increased Na load eventually exceeds the distal tubule and collecting duct ability to reabsorb the Na But in its effort to pump all the Na back into the interstitial, it kicks all the K into the urine, causing hypoK.
What is the result of hypokalemia?
hyper polarization of nerve in muscle cells (will probably be manifested in the heart)
4 renal concentrating and diluting mechanisms
- ADH (vasopressin)
- ANP (atrial natriuretic peptide)
- Countercurrent multiplier
- Urea
Why is the ability to concentrate or dilute urine important?
In order for cells to fx, they must be bathed in ECF with a fairly stable concentration of electrolytes and solutes
What is the maximal urine concentration a human kidney can produce?
1200-1400 mOsm/L
a normal 70 kg human must excrete _____ mOsm of solute each day and therefore must excrete _____L/day
(if the concentrating ability is assumed to be 1200 mOsm/L)
600 mOsm
0.5 L/day
Where is ADH synthesized?
in the hypothalamus
FYI: it is an octapeptide
Where is ADH stored and released?
posterior pituitary
How does ADH play a major role in conserving water?
by concentrating the urine