Unit 4 Ch. 20 Flashcards
What is hypotonic and hypertonic?
- hypertonic: too little water
- hypotonic: too much water
How can kidneys regulate water?
- can excrete
- can retain (Vasopressin)
- can’t reclaim water
How does urine concentration differ along the length of the nephron?
- vertical concentration gradient
- more concentrated in medulla than cortex
- urine concentration depends on needs
What is the role of the medullary countercurrent system?
- Loop of Henle establishes conc. gradient
- Countercurrent due to flow in opposite directions
- Gradient maintained by vasa recta.
What is the difference between the ascending and descending Loop of Henle?
- Descending: Water permeable, not solute
- Ascending: NaCl permeable, ALWAYS H2O impermeable.
What is countercurrent multiplication?
- Fluid leaving loop of Henle has been concentrated 4x and diluted 3x.
- Dilute urine excreted.
- 200 mOsM difference between vasa rect and ascending limb.
What is the role of the vasa recta?
- preserves concentration gradient.
- Because it follows the Loop of Henle
What is the role of Vasopressin?
Where does it bind and by what pathway?
What stimulates it?
- Stimulated by hypertonic blood (NEED WATER)
- binds to membrane receptor
- cAMP 2nd messenger pathway, releases vesicles containing aquaporins.
- Distal and collecting tubules are impermeable to H2O except with Vasopressin (ADH). bye bye watery pee
- Vasopressin leads to less watery pee.
- If I’m dying in a desert and my life sucks I will have lots of Vasopressin creating aquaporins.
What is the different in H2O reabsorption in the presence and absence of vasopressin?
- Present: Maximal ADH urine up to 1200 mOsM
- absent: minimal ADH urine down to 100 mOsM
How does Na+ load affect reabsorption?
- Proximal tubule and Loop of Henle: Na+ reabsorption constant
- Distal tubule: Na+ reabsorption subject to hormonal control. Greater load, less reabsorbed.
- Greater Na+ load, greater ECF volume, greater BP (H2O and Na are biffles)
What is the role of Renin?
- Secreted by kidney in response to dec. NaCl, ECF volume, and consequently BP.
- Granular cells stimulated by: Macula Densa, Baroreceptors, Sympathetic Innervation
What is the role of the RAAS?
-results in Na+ reabsorption and H2O retention. (Passive Cl- too)
Trace the RAAS pathway.
- Renin secreted by detection of decreased BP
- Renin (kidney) activates angiotensinogen (liver) into Angiotensin I
- ACE (lung) conveerts Angiotensin I to Angotensin II.
- Ang II stimulated secretion of aldosterone (adrenal cortex).
What is the role of Aldosterone in the RAAS?
- Increase Na+ reabsorption in distal/collecting duct (hormonal control aspect).
- More Na+ channels and K+ pumps
- Net Result: More Na+ into ECF, so more water follows.
What are the roles of angiotensin II?
- vasoconstriction
- thirst stimulating (to increase BP by volume increase from drinking)
- stimulated ADH (water retention)
What is the role of atrial natriuretic peptide?
- Opposes RAAS to increase Na+ (and water, they’re BIFFLES) excretion
- Vasodilation of glomerular afferent arterioles to increase GFR
- inhibits sympathetic activity
How does acid-base balance affect the system?
- Buffers prevent wide swings in pH
- Lungs reflexively respond to most pH disturbances
- Kidneys, secondary response, but can compensate for remaining pH disturbances.
What is the role of buffers?
What is the difference in effect of increasing H+ v. increasing bicarbonate?
- They are found within the cell and in the plasma
- Example, bicarbonate (HCO3)
- Plasma bicarbonate 60,000x more concentrated than H+ in the plasma.
- Increasing H+ has greater effect on plasma pH than increasing HCO3
What is the effect on acidosis of hypoventilation and hyperventilation?
- hyperventilation: counters acidosis
- hypoventilation: exacerbates acidosis
What is the proximal tubule role on acid/base balance?
- Kidneys secrete H+ and reabsorb HCO3 in proximal tubules
- Result: Na+ and HCO3- (to act as ECF buffer) reabsorption (inc pH) and secrete H+ (buffered in urine)
What is the role of the collecting duct on acid/base balance? Which intercalated cells function acidosis and which function in alkalosis?
- acidosis: Type A intercalated cells. H+ excreted, HCO3- and K+ reabsorbed
- alkalosis: Type B intercalated cells. H+ reabsorbed, HCO3- and K+ excreted.
