regulation of plasma osmolarity (12)

Question 1

what is the average total in gain of water?

Answer 1

2500 mL/day

Question 2

what is the greatest source of water loss per day? how much is this?

Answer 2

urine 1500 mL/day

Question 3

what are the unregulated water losses from the body?

Answer 3

feces
skin/sweat
exhaled air

Question 4

when the U/P osmolarity =1 tell me about the osmolarity of the urine and ECF

Answer 4

the urine is isotonic and ECF osmolarity is also isotonic

Question 5

when the U/P osmolarity >1 tell me about the osmolarity of the urine and ECF

Answer 5

the urine is hypertonic and ECF osmolarity is also hypertonic

Question 6

when the U/P osmolarity < 1 tell me about the osmolarity of the urine and ECF

Answer 6

the urine is hypotonic and the ECF osmolarity is also hypotonic

Question 7

what is the typical osmolar excretion of solutes in the urine per day?

Answer 7

600 mOsmoles/day in the urine

Question 8

how high can the kidney increase the urine osmolarity to? how low?

Answer 8

can increase the osmolarity to 1200 mOsm/L or decrease osmolarity to 30 mOsm/L

Question 9

define “free water”

Answer 9

water that is not osmotically obligated to remain in the tubular fluid due to presence of solutes

Question 10

define “free water clearance”

Answer 10

the rate/time dependent ability of the kidney to take water from the tubular fluid and put in the plasma (or opposite)

Question 11

high or low plasma osmolarity will cause ADH releasE?

Answer 11

high plasma osmolarity

Question 12

what limits the positive & negative free water clearance?

Answer 12

the magnitude of solute consumed

Question 13

what will consuming a diet low in solute do to the free water clearance

Answer 13

increase the negative free water clearance and decrease the positive free water clearance

Question 14

describe the osmolarity of the tubular fluid in the proximal tubular

Answer 14

iso-osmotic

Question 15

describe the osmolarity of the tubular fluid in the loop of henle

Answer 15

hypo-osmotic

Question 16

describe what “antidiuresis” means

Answer 16

refers to restricted water intake (hydropenia) when the kidneys maximally concentrate the urine and excrete a minimal volume of urine because of increase absorption of water in excess of solutes

Question 17

describe what “diuresis” means

Answer 17

refers to ingestion of excess water when kidneys maximally dilute the urine & excrete a large volume of urine because absorption of water in excess of solutes does not occur

Question 18

describe the osmolarity of the fluid entering the distal convoluted tubule

Answer 18

relatively hypo-osmotic

Question 19

what area and factors determine the osmolarity of urine?

Answer 19

depends on whether or not water is reabsorbed in the initial and cortical collecting tubules (ICT and CCT) and the outer and inner medullary collecting ducts (OMCD and IMCD)
ADH/AVP acts on these nephron segments

Question 20

where is antidiuretic hormone synthesized?

Answer 20

paraventricular and supraoptic nuclei of the hypothalamus

Question 21

what is the half-life of ADH and why is this important?

Answer 21

18 minutes- this is important because you want to be able to quickly shut this off when the volume/osmolarity returns to normal. Gives you the timliness of the kidneys to act quickly

Question 22

what is the function of ADH?

Answer 22

increase the water permeability of the principal cells of the outer & inner medullary collecting tubules & ducts

Question 23

tell me about the binding of ADH/AVP in the distal tubule

Answer 23

binds to V2 receptors in the basolateral membrane of “principal cells” where present in the cells of the initial collecting tubule to the end of the collecting duct
these receptors are receptors are G protein coupled and stimulate adenyl cyclase to produce camp which then activates PKA

Question 24

true or false

ADH is able to act on the aquaporins located on the basalateral and the apical membrane

Answer 24

ONLY the apical membrane

the channels on the basolateral membrane are NOT regulated

Question 25

what two areas in the hypothalamus have the osmoreceptors

Answer 25

organum vasculosum of the lamina terminalis (OVLT) and the subfornical organ (SFO)

Question 26

explain how osmolarity affects the osmoreceptors to act to increase the release of ADH

Answer 26

An increase in osmolarity opens the mechano-sensitve cation channels causing depolarization of the membrane potential which will increase the frequency of APs traveling to ADH/AVP synthesizing & secreting neurons in the hypothalamus