ACTUALLY lecture 39 - regulation of fluid volume Flashcards
haha silly oopsies
two major functions of the kidneys are
excretion of metabolic wastes and regulation of extracellular fluid volume and composition
what is the most important enzymatic reaction in digestion?
hydrolysis
give three reasons why water is important (vague I know)
- it dissolves most biologically significant compounds
- its essential for most metabolic processes
- hydrolysis for digestion
give two examples of how water molecules are produced in the body
- cellular respiration
- binding of two amino acids
what is an osmoconformer?
an animal that maintains internal conditions that are equal to the osmolarity of their environment
what is an osmoregulator?
an animal that can maintain a constant osmolarity regardless of the environmental conditions
what are the four major sources of water loss (ranked highest contributing to lowest)
Urine, insensible losses via skin and lungs, sweat, fecesw
what are the major sources of water intake (ranked highest contributor to lowest)
drinking, food, metabolism
only the ___ are capable of precise adjustment of water loss to compensate for the variation in water intake
kidneys
what is the function of the countercurrent system in the kidneys?
to generate high osmolarity gradient in the interstital fluid of the renal medulla
does osmolarity increase or decrease with distance from the cortex?
it increases, reaching a maximum in the innermost part of the medulla
where (cortex vs medulla) is osmolarity highest?
medulla
where (cortex vs medulla) is osmolarity lowest?
cortex
the renal medulla has an osmotic gradient with the interstitial fluid being about ____ mOsmoles near the cortex and increasing up to ____ mOsmoles towards the innermost parts of the medulla
300 in cortex, 1400 in medulla
If a compartment has a low solute concentration, its water concentration is:
high
Which is the major site of water reabsorption along the nephron?
the loop of Henle
the descending limb of the loop of Henle is permeable to ____ but not ____
Water, not ions
what moves out of the descending limb of the loop of henle: water or NaCl?
Water
the ascending loop of Henle is permeable to ____ but not ____
Na/K/Cl, not water
the ascending loop of henle is permeable to certain ions. is the transport of these ions passive or active?
active, via pumps.
why does the ascending loop of Henle pump out ions?
because water was drawn out of the descending limb, so fluid entering into the ascending has incredibly high osmolarity. This also maintains a high solute concentration in the extracellular fluid, so that water is continuously drawn out of the descending loop.
the peritubular capillaries are permeable to ___ and ___
water and solutes
in the descending limbs, water is drawn by osmosis from the ___ into the ____, and solute is drawn from the ____ into the _____
in the descending limbs, water is drawn by osmosis from the blood into the interstitial fluid, and solute is drawn from the interstitial fluid into the blood
in the ascending limbs, water is drawn by osmosis from the ___ to the ___, and solutes diffuse from the ____ to the ____
in the ascending limbs, water is drawn by osmosis from the interstitial fluid to the blood, and solutes diffuse from the blood to the interstitial fluid
is the solute concentration of blood leaving the peritubular capillaries higher or lower than the blood that was entered?
slightly higher
what is the process that maintains the osmotic gradients in the nephron called?
countercurrent flow
what would happen to the osmotic gradient if the descending limbs of the peritubular capillaries returned directly to the renal vein instead of counterflowing into the asccending limb?
the osmotic gradient of the renal medulla would be lost
what are the two countercurrent systems in the kidneys?
the loops of Henle and the peritubular capillaries
why is water balance important?
plasma volume affects mean arterial pressure, and changes in plasma osmolarity can cause fluid to shift from one body compartment to another (affecting cellular functions)
where is water first reabsorbed?
the proximal tubule
where is water last reabsorbed?
the distal convoluted tubule and the collecting duct (because the lumen of the tubule is always hypo-osmolar to the itnerstital fluid)
T/F: the tight junctions of the distal tubule and collecting duct is permeable to water
false. water has to move through water channels called aquaporins
how does water enter the distal tubule and collecting duct?
aquaporin channels
which membrane has aquaporin-3 channels, and which has aquaporin-2?
basolateral = aquaporin-3
apical = aquaporin-2 (when ADH is present)
when aquaporin-2 channels are present in the apical membrane of the distal tubule and collecting duct, will the urine be:
a) hyperosmotic
b)isoosmotic
c)hypoosmotic
b
in mOsmole, what is the maximum concentration of urine
1400, the same as the max concentration of the interstitial fluid in the innermost medulla
T/F: Animals in arid, desert environments will need more efficient water conservation than animals in
moist, mesic environments
true
t/f: Water conservation can be improved by increased salt gradient in the medulla
true. A greater the salt gradient in the medulla means more water is reabsorbed by the collecting ducts
and urine is concentrated
what stimulates the synthesis of Aquaporin-2 and its insertion into the apical membranes of the distal tubule and collecting duct?
ADH
when and where is ADH released?
from the posterior pituitary, in response to dehydration detected by osmoreceptors in hypothalamus
If blood volume is too high, will Na be excreted or absorbed?
excreted, favours water loss
if blood volume is too low, will Na be excreted or absorbed?
absorbed, to favour water retention
JG cells of the afferent arteriole of each glomerulus secrete ___ in response to ____
JG cells of the afferent arteriole of each glomerulus are secrete renin in response to decreased blood pressure.
This activates the renin-angiotensin-aldosterone system
what are macula densa cells?
cells that monitor sodium load in the distal tubule. when sodium load is low, macula densa cells activate JG cells to secrete renin (increases BP)
how do mesangial cells regulate blood flow?
contraction of these cells regulates the size of the capillary lumen
how does angiotensin II increase blood/interstitial volume?
- promotes Na reabsorption
- stimulates aldosterone secretion, which will then also stimulate Na reabsorption
- causes vasoconstriction
when does the tubular fluid become urine?
once it enters the renal pelvis
