Regulation of Body Fluid Osmolarity - Rao

Question 1

What secretes AVP/ADH and is considered the thirst center?

Answer 1

Hypothalamus

Question 2

What are some physical and external situations that can increase fluid intake or loss?

Answer 2

Dietary habits, climate, physical activities, hot and dry climate, exercise, diarrhea, burn injury

Question 3

If you have excessive drinking or lack of ADH, by what percentage is the GFR reduced?

Answer 3

10%

Question 4

What two types of nuclei are osmoreceptors?

Answer 4

supraoptic and paraventricular nuclei

Question 5

When osmolarity is increased, what increases in the supraoptic cell that triggers secretion of AVP?

Answer 5

Ca2+ (involved in many different secretion processes)

Question 6

When there is increased osmolarity, what do the lateral preoptic nuclei sense and trigger?

Answer 6

The lateral preoptic nucleus is the thirst center, triggering a changein behavior to drink more water

Question 7

What is the most basic function of Arginine-Vasopressin (aka ADH aka AVP aka Vasopressin)?

Answer 7

It is a vasoconstrictor

Question 8

Under physiological concentrations, what does AVP do?

Answer 8

It increases water permeability in collecting ducts for reabsorption

Question 9

Explain the mechanism of increased AQP insertion in the collecting duct as a result of vasopressin?

Answer 9

Vasopressin/ADH/AVP activates adenylate cyclase, producing more cAMP. This then triggers the insertion of the AQP2 into the collecting ducts, allowing water reabsorption.

Question 10

How is the urine osmolarity affected by AVP levels? Both low and high.

Answer 10

In high plasma AVP levels, there is going to be a massive increase in Uosm, up to 1200 mOsmolar.

In low plasma levels of AVP, there can be a massive decrease in Uosm, to 50 mOsmolar.

Question 11

When will you see a high level of AVP produced? A low?

Answer 11

You will see a high vasopressin concentration in the plasma when there is increased plasma osmolarity.

You will see a low vasopressin concentration with there is a low plasma osmolarity

Question 12

Around what plasma osmolality will you begin sensing thirst because of AVP levels affecting the lateral optic nuclei in the hypothalamus?

Answer 12

280 mOml/Kg h20

Question 13

Explain the pathway from hyperosmotic plasma to decrease of plasma osmolarity through the SUPRAOPTIC NUCLEUS OF THE HYPOTHALAMUS?

Answer 13

Hyperosmotic plasma triggers activation of osmoreceptors in the supraoptic nucleus of hypothalamus. This then increases firing of nerve fibers with endings in posterior pituitary, releasing AVP. This increases h20 permeability in the collecting duct. also causes you to then excrete hyperosmotic urine leading to a decrease of plasma osmolarity

Question 14

Explain the pathway from hyperosmotic plasma to decrease of plasma osmolarity through the OSMORECEPTORS IN HYPOTHALAMUS THIRST CENTER (LATERAL OPTIC NUCLEI)?

Answer 14

hyperosmotic plasma leads to activatino of osmoreceptors in the hypothalamus thirst center, which thenincreases desirre water water. which increases water ingestion and decreases plasma osmolarity

Question 15

When you have GI fluid loss, and a decreased plasma volume, will vasopressin increase or decrease?

Answer 15

increase

Question 16

When you have GI fluid loss and hypo or iso-osomlar plasma, will your vasopressin increase or decrease

Answer 16

decrease

Question 17

By what percentage must your ECV decrease to trigger AVP action?

Answer 17

10-15%

Question 18

T or F: AVP can override the normal response to plasma osmolarity

Answer 18

true

Question 19

why would avp increase when the plasma is hypoosmolar?

Answer 19

situations like hyponatremia due to GI fluid loss

Question 20

What are side effects of hyponatremia?

Answer 20

Lethargy, hyporeflexia, mental confusion, severe hyponatremia - 50% mortality rate

Question 21

How do you treat hyponatremia

Answer 21

infusion of isotonic saline, avoiding quick change is essentail

Question 22

What are conditions with hyponatremia but no change in ecfv?

Answer 22

heart failure, liver failure (reduce pv and stimulate hypovolemic hormone secretion).

Question 23

What is the formula for osmolar clearance?

Answer 23

UF X Uosm / Posm

Question 24

How is the relationship between Uosm and Posm important?

Answer 24

The level of Uosm in relation to Posm determines the dilution vs concentration of the Urine, and thus the plasma osmolarity.

Question 25

When solutes are reabsorbed into the interstitium, what structures pick those up for the body?

Answer 25

the peritubular capillaries

Question 26

Is the human kidney better at clearing water or conserving it?

Answer 26

clearing

Question 27

How is the high osmolarity of the interstitium maintained in the renal medulla/

Answer 27

the water that enters is quickly taken up by the vasa recta and carried away.

Question 28

What are the steps in causing hyperosmotic medullary interstitium?

Answer 28

1. 300 mosm even distribution
2. active na transport from talh
3. water transport in descending limb
4. additional flow of fluid from prox tubule to loh pushing the higher osmolar fluid to lumen of ascneding limb
5. active transport of na-new gradient
6. water transport in descending limb

Question 29

What contributes 40% of osmolarity in medullary ISF?

Answer 29

Urea

Question 30

Do the medullary capillaries wash out the hyperosomlar fluid int he medulla?

Answer 30

no

Question 31

What features contribute to preservation of medullary interstitial hyperosmolarity?

Answer 31

medullary blood flow is low

vasa recta serves as countercurrent exchanges

Question 32

What are three causes of kidney’s inability to concentrate or dilute urine?

Answer 32

defect in production or regulation of AVP

inability of collecting ducts to respond to AVP

failure to form medullary osmolarity gradient

Question 33

What is central diabetes insipidus?

Answer 33

pituitary gland fails to release AVP - rare

Question 34

What is nephrogenic diabetes insipidus?

Answer 34

Collecting ducts do not respond to AVP, v2 mutation, AQP2 mutation, drugs (lithium and tetracycline)

Question 35

What are four causes of loss of medullary hyperosmolarity?

Answer 35

1. diuretics - furosemia INH Na transport
2. excessive delivery of fluid to LOH
3. Decreased urea prodx
4. Age and renal failure