Integrative Physiology I Regulation of Extracellular Fluid Osmolarity and Na Concentration

Question 1

in what ways can water be lost

Answer 1

-insensible loss by skin and lungs
- sweat
-feces
-urine

Question 2

which does ADH effect: ECF osmolarity or plasma volume

Answer 2

both

Question 3

how does ADH effect changes in ECF osmolarity? for excess water ingested

Answer 3

• excess water ingested -> decreased body fluid osmolarity -> decreased firing by hypothalamic osmoreceptors ->decreased ADH secretion ->decreased plasma ADH -> decreased tubular permeability to water in CD -> decreased water reabsorption in CD -> increased water excretion

Question 4

how does ADH work with changes in plasma volume? for ex low plasma volume

Answer 4

• low plasma volume -> low venous, atrial, and arterial pressures -> increased ADH secretion -> increased plasma ADH -> increased tubular permeability to water in CD -> increased water reabsorption in CD -> decreased water excretion

Question 5

is ADH more sensitive to changes in osmolarity or volume

Answer 5

osmolarity

Question 6

what are the factors that increase ADH secretion

Answer 6

-increased ECF osmolarity
- decreased blood volume via low ANP
- decreased blood pressure via baroreceptor activity
- nausea
- hypoxia
- nicotine and morphine
- ANG II

Question 7

what are factors that decrease ADH secretion

Answer 7

• low ECF osmolarity
• high blood volume via high ANP
• high BP via high baroreceptor activity and indirectly via decrease in ANG II
  -ethanol
  -cold

Question 8

what is syndrome of inappropriate ADH (SIADH)

Answer 8

-excrete a concentrated urine
- too much ADH function

Question 9

when is SIADH most often seen

Answer 9

neurologic disease, head injury, lung tumors or after major surgery

Question 10

what does excessive ADH secretion cause

Answer 10

-hyponatremia
-decreased plasma osmolarity
-urine hyperosmolarity

Question 11

what does excessive ADH secretion not cause

Answer 11

-sodium handling
- only defect is in water excretion

Question 12

is there feedback inhibition of ADH

Answer 12

no

Question 13

how is SIADH treated

Answer 13

ADH inhibitor drugs like demeclocycline

Question 14

what happens in DI

Answer 14

-excrete a dilute urine
- too little ADH fcuntion

Question 15

what are the types of DI

Answer 15

-hypothalamic or central DI
- nephrogenic DI
- polydipsic DI

Question 16

what happens in hypothalamic DI

Answer 16

-defect in ADH synthesis or release
-decreased [ADH]plasma

Question 17

what happens in nephrogenic DI

Answer 17

-defect in ADH action
-failure to maintain hyperosmotic medullary gradient
-elevated [ADH]plasma

Question 18

what happens in polydipsic DI

Answer 18

-compulsive water drinking

Question 19

what are the symptoms of DI

Answer 19

-polyuria
- nocturia
- polydipsia

Question 20

what is polyuria defined as

Answer 20

greater than 3 liters urine/day

Question 21

what are the 2 factors that determine urine volume

Answer 21

-amount of solute to be excreted (OUV)
- [ADH]plasma

Question 22

what are the 3 major mechanisms of polyuria

Answer 22

• decrease in Na+ reabsorption (kidney disease, diuretics)
• reduced ADH secretion
• ADH resistance

Question 23

what can cause ADH resistance

Answer 23

-lithium and tetracyclines
-hypercalcemic nephrogenic DI

Question 24

what are the mechanisms of regulation of [Na+] ECF

Answer 24

-osmoreceptor -ADH system
- the thirst mechanism
- aldosterone and ANG II
- salt appetite

Question 25

what are the primary mechanisms that regulate [Na+] ECF

Answer 25

-osmoreceptor-ADH system - the thirst mechanism

Question 26

how do aldosterone and ANG II regulate [Na+]ECF

Answer 26

-alter Na+ mass but NOT concentration - changes in Na+ mass accompanied by volume changes (thirst, ADH)

Question 27

what are the stimuli for thirst

Answer 27

-low plasma volume (MAP and ECF volume) - increased plasma osmolarity -dry mouth

Question 28

what part of the brain responds to signals that initiate drinking

Answer 28

hypothalamic thirst center

Question 29

where does ANG II act to increase thirst

Answer 29

centrally

Question 30

what receptors detect low plasma volume for thirst response and what do they do

Answer 30

baroreceptors and cause increase in ANG II and directly stimulate thirst

Question 31

what receptors detect high plasma osmolarity for thirst response and what do they do

Answer 31

osmoreceptors and directly cause thirst

Question 32

what reduces thirst

Answer 32

metering of water intake by GI tract

Question 33

what are stimuli that increase salt appetite

Answer 33

-sodium deficits - decreased blood volume -decreased blood pressure associated with circulatory insufficiency

Question 34

what Na+ concentration do humans function normally at and what is the average consumption in the US every day

Answer 34

-function normally at 20 meq/day - average: 200 meq/day

Question 35

what is the response to increase in osmolarity but no change in volume

Answer 35

- ADH secreted -> increased renal water reabsorption -thirst -> increased water intake -> increased ECF volume and increased BP -> kidneys excrete salt and water and osmolarity and volume returns to normal AND cardiovascular reflexes lower BP to return BP and volume to normal

Question 36

what is the response to decrease in MAP without change in volume or osmolarity

Answer 36

- decreased BP -> decreased GFR -> decreased NaCl transport across macula densa of DT -> paracrines -> granular cells of afferent arteriole -> increase renin secretion - decreased BP -> cardiovascular control center -> increase sympathetic activity -> granular cells of afferent arteriole -> increase renin secretion - renin makes ANG I -> ANG II ->arterioles to vasocontrict, CV center in medulla increases CV response, hypothalamus increases ADH and thirst, adrenal cortex increases aldosterone which increases Na+ reabsorption -> all of which increase BP and volume to maintain osmolarity

Question 37

what is the response to increased blood volume and no change in osmolarity

Answer 37

- increased BV causes atrial stretch ->atrial myocardial cells stretch and release ANP -> acts on hypothalamus to decrease ADH, kidney to increase GFR and decrease renin, adrenal cortex to decrease aldosterone, and medulla to decrease BP -> all of which increase NaCl and water excretion