ACTUALLY lecture 39 - regulation of fluid volume

Question 1

two major functions of the kidneys are

Answer 1

excretion of metabolic wastes and regulation of extracellular fluid volume and composition

Question 2

what is the most important enzymatic reaction in digestion?

Answer 2

hydrolysis

Question 3

give three reasons why water is important (vague I know)

Answer 3

• it dissolves most biologically significant compounds
• its essential for most metabolic processes
• hydrolysis for digestion

Question 4

give two examples of how water molecules are produced in the body

Answer 4

• cellular respiration
• binding of two amino acids

Question 5

what is an osmoconformer?

Answer 5

an animal that maintains internal conditions that are equal to the osmolarity of their environment

Question 6

what is an osmoregulator?

Answer 6

an animal that can maintain a constant osmolarity regardless of the environmental conditions

Question 7

what are the four major sources of water loss (ranked highest contributing to lowest)

Answer 7

Urine, insensible losses via skin and lungs, sweat, fecesw

Question 8

what are the major sources of water intake (ranked highest contributor to lowest)

Answer 8

drinking, food, metabolism

Question 9

only the ___ are capable of precise adjustment of water loss to compensate for the variation in water intake

Answer 9

kidneys

Question 10

what is the function of the countercurrent system in the kidneys?

Answer 10

to generate high osmolarity gradient in the interstital fluid of the renal medulla

Question 11

does osmolarity increase or decrease with distance from the cortex?

Answer 11

it increases, reaching a maximum in the innermost part of the medulla

Question 12

where (cortex vs medulla) is osmolarity highest?

Answer 12

medulla

Question 13

where (cortex vs medulla) is osmolarity lowest?

Answer 13

cortex

Question 14

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

Answer 14

300 in cortex, 1400 in medulla

Question 15

If a compartment has a low solute concentration, its water concentration is:

Answer 15

high

Question 16

Which is the major site of water reabsorption along the nephron?

Answer 16

the loop of Henle

Question 17

the descending limb of the loop of Henle is permeable to ____ but not ____

Answer 17

Water, not ions

Question 18

what moves out of the descending limb of the loop of henle: water or NaCl?

Answer 18

Water

Question 19

the ascending loop of Henle is permeable to ____ but not ____

Answer 19

Na/K/Cl, not water

Question 20

the ascending loop of henle is permeable to certain ions. is the transport of these ions passive or active?

Answer 20

active, via pumps.

Question 21

why does the ascending loop of Henle pump out ions?

Answer 21

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.

Question 22

the peritubular capillaries are permeable to ___ and ___

Answer 22

water and solutes

Question 23

in the descending limbs, water is drawn by osmosis from the ___ into the ____, and solute is drawn from the ____ into the _____

Answer 23

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

Question 24

in the ascending limbs, water is drawn by osmosis from the ___ to the ___, and solutes diffuse from the ____ to the ____

Answer 24

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

Question 25

is the solute concentration of blood leaving the peritubular capillaries higher or lower than the blood that was entered?

Answer 25

slightly higher

Question 26

what is the process that maintains the osmotic gradients in the nephron called?

Answer 26

countercurrent flow

Question 27

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?

Answer 27

the osmotic gradient of the renal medulla would be lost

Question 28

what are the two countercurrent systems in the kidneys?

Answer 28

the loops of Henle and the peritubular capillaries

Question 29

why is water balance important?

Answer 29

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)

Question 30

where is water first reabsorbed?

Answer 30

the proximal tubule

Question 31

where is water last reabsorbed?

Answer 31

the distal convoluted tubule and the collecting duct (because the lumen of the tubule is always hypo-osmolar to the itnerstital fluid)

Question 32

T/F: the tight junctions of the distal tubule and collecting duct is permeable to water

Answer 32

false. water has to move through water channels called aquaporins

Question 33

how does water enter the distal tubule and collecting duct?

Answer 33

aquaporin channels

Question 34

which membrane has aquaporin-3 channels, and which has aquaporin-2?

Answer 34

basolateral = aquaporin-3

apical = aquaporin-2 (when ADH is present)

Question 35

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

Answer 35

b

Question 36

in mOsmole, what is the maximum concentration of urine

Answer 36

1400, the same as the max concentration of the interstitial fluid in the innermost medulla

Question 37

T/F: Animals in arid, desert environments will need more efficient water conservation than animals in
moist, mesic environments

Answer 37

true

Question 38

t/f: Water conservation can be improved by increased salt gradient in the medulla

Answer 38

true. A greater the salt gradient in the medulla means more water is reabsorbed by the collecting ducts
and urine is concentrated

Question 39

what stimulates the synthesis of Aquaporin-2 and its insertion into the apical membranes of the distal tubule and collecting duct?

Answer 39

ADH

Question 40

when and where is ADH released?

Answer 40

from the posterior pituitary, in response to dehydration detected by osmoreceptors in hypothalamus

Question 41

If blood volume is too high, will Na be excreted or absorbed?

Answer 41

excreted, favours water loss

Question 42

if blood volume is too low, will Na be excreted or absorbed?

Answer 42

absorbed, to favour water retention

Question 43

JG cells of the afferent arteriole of each glomerulus secrete ___ in response to ____

Answer 43

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

Question 44

what are macula densa cells?

Answer 44

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)

Question 45

how do mesangial cells regulate blood flow?

Answer 45

contraction of these cells regulates the size of the capillary lumen

Question 46

how does angiotensin II increase blood/interstitial volume?

Answer 46

• promotes Na reabsorption
• stimulates aldosterone secretion, which will then also stimulate Na reabsorption
• causes vasoconstriction

Question 47

when does the tubular fluid become urine?

Answer 47

once it enters the renal pelvis