Regulation of Body Fluid Osmolarity - Rao Flashcards
What secretes AVP/ADH and is considered the thirst center?
Hypothalamus
What are some physical and external situations that can increase fluid intake or loss?
Dietary habits, climate, physical activities, hot and dry climate, exercise, diarrhea, burn injury
If you have excessive drinking or lack of ADH, by what percentage is the GFR reduced?
10%
What two types of nuclei are osmoreceptors?
supraoptic and paraventricular nuclei
When osmolarity is increased, what increases in the supraoptic cell that triggers secretion of AVP?
Ca2+ (involved in many different secretion processes)
When there is increased osmolarity, what do the lateral preoptic nuclei sense and trigger?
The lateral preoptic nucleus is the thirst center, triggering a changein behavior to drink more water
What is the most basic function of Arginine-Vasopressin (aka ADH aka AVP aka Vasopressin)?
It is a vasoconstrictor
Under physiological concentrations, what does AVP do?
It increases water permeability in collecting ducts for reabsorption
Explain the mechanism of increased AQP insertion in the collecting duct as a result of vasopressin?
Vasopressin/ADH/AVP activates adenylate cyclase, producing more cAMP. This then triggers the insertion of the AQP2 into the collecting ducts, allowing water reabsorption.
How is the urine osmolarity affected by AVP levels? Both low and high.
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.
When will you see a high level of AVP produced? A low?
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
Around what plasma osmolality will you begin sensing thirst because of AVP levels affecting the lateral optic nuclei in the hypothalamus?
280 mOml/Kg h20
Explain the pathway from hyperosmotic plasma to decrease of plasma osmolarity through the SUPRAOPTIC NUCLEUS OF THE HYPOTHALAMUS?
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
Explain the pathway from hyperosmotic plasma to decrease of plasma osmolarity through the OSMORECEPTORS IN HYPOTHALAMUS THIRST CENTER (LATERAL OPTIC NUCLEI)?
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
When you have GI fluid loss, and a decreased plasma volume, will vasopressin increase or decrease?
increase
When you have GI fluid loss and hypo or iso-osomlar plasma, will your vasopressin increase or decrease
decrease
By what percentage must your ECV decrease to trigger AVP action?
10-15%
T or F: AVP can override the normal response to plasma osmolarity
true
why would avp increase when the plasma is hypoosmolar?
situations like hyponatremia due to GI fluid loss
What are side effects of hyponatremia?
Lethargy, hyporeflexia, mental confusion, severe hyponatremia - 50% mortality rate
How do you treat hyponatremia
infusion of isotonic saline, avoiding quick change is essentail
What are conditions with hyponatremia but no change in ecfv?
heart failure, liver failure (reduce pv and stimulate hypovolemic hormone secretion).
What is the formula for osmolar clearance?
UF X Uosm / Posm
How is the relationship between Uosm and Posm important?
The level of Uosm in relation to Posm determines the dilution vs concentration of the Urine, and thus the plasma osmolarity.
When solutes are reabsorbed into the interstitium, what structures pick those up for the body?
the peritubular capillaries
Is the human kidney better at clearing water or conserving it?
clearing
How is the high osmolarity of the interstitium maintained in the renal medulla/
the water that enters is quickly taken up by the vasa recta and carried away.
What are the steps in causing hyperosmotic medullary interstitium?
- 300 mosm even distribution
- active na transport from talh
- water transport in descending limb
- additional flow of fluid from prox tubule to loh pushing the higher osmolar fluid to lumen of ascneding limb
- active transport of na-new gradient
- water transport in descending limb
What contributes 40% of osmolarity in medullary ISF?
Urea
Do the medullary capillaries wash out the hyperosomlar fluid int he medulla?
no
What features contribute to preservation of medullary interstitial hyperosmolarity?
medullary blood flow is low
vasa recta serves as countercurrent exchanges
What are three causes of kidney’s inability to concentrate or dilute urine?
defect in production or regulation of AVP
inability of collecting ducts to respond to AVP
failure to form medullary osmolarity gradient
What is central diabetes insipidus?
pituitary gland fails to release AVP - rare
What is nephrogenic diabetes insipidus?
Collecting ducts do not respond to AVP, v2 mutation, AQP2 mutation, drugs (lithium and tetracycline)
What are four causes of loss of medullary hyperosmolarity?
- diuretics - furosemia INH Na transport
- excessive delivery of fluid to LOH
- Decreased urea prodx
- Age and renal failure
