Topic 10 Flashcards
Sodium most abundant ion in extracellular fluid. What is its range and average
Range 140 to 145 mEq/Liter
Average 142 mEq/Liter
Osmolarities range and average is?
Range 291 to 309 mOsm/Liter
Average 300 mOsm/Liter
why is precise control of sodium and osmolarity important?
they control distribution of water between intracellular and extracellular compartments
Sodium and associated anions (chloride and bicarbonate) account for __% of all extracellular solute
94%
Glucose and urea contribute ____% of total osmolarity
3 to 5%
–Urea able to permeate cells easily so exerts little effective osmotic force
Sodium not very permeable so it has a big effect on fluid movement between what compartments?
extracellular and intracellular compartments
Plasma osmolarity = [formula]
(2.1) x (Plasma Na+ concentration)
what 2 systems control / regulate extracellular osmolarity and sodium concentration?
Osmoreceptor – ADH system
Thirst mechanism
Osmoreceptor Cells are Located in?
anterior hypothalamus
describe Osmoreceptor Cells mechanism (5 steps)
KNOW
- Cells shrink in response to increased ECF [Na+] (i.e. increased osmolarity)
- As cells shrink, impulses are sent to other nerve cells in supraoptic nuclei
- Impulses passed to posterior pituitary
- Impulses stimulate release of AHD stored in secretory granules within nerve endings
- Increased [ADH] of blood stimulates increased water permeability in late distal tubules, cortical collecting tubules, and medullary collecting tubules
Increased osmolarity results in increased water permeability which allows water to be reabsorbed (conserved) while sodium does what?
continues to be excreted at normal rate
What happens after a WATER DEFICIT: \_\_\_Extracellular osmolarity \_\_\_ADH Secretion \_\_\_Plasma ADH \_\_\_Water permeability in distal tubules/collecting ducts \_\_\_Water reabsorption \_\_\_Water excreted
INCREASE Extracellular osmolarity INCREASE ADH Secretion INCREASE Plasma ADH INCREASE Water permeability in distal tubules/collecting ducts INCREASE Water reabsorption deCREASE Water excreted
ADH release is tied into what 2 other systems?
- arterial baroreceptor reflexes (which respond to changes in blood pressure)
- cardiopulmonary reflexes (which respond to changes in blood volume)
- -Reflex pathways tied into hypothalamic nuclei that control ADH production and release
A Decreased blood pressure and/or decreased blood volume results in an increase or decrease in ADH release?
increase
A Small increase in osmolarity of only __% will trigger increase [ADH]
1%
Circulating volume must decrease approximately __% before appreciable change in [ADH]
10%
A ___% reduction in circulating volume produces a HUGE increase in [ADH]
15 to 20%
What 6 things increase ADH release
Increased plasma osmolarity Decreased blood volume Decreased blood pressure Nausea Hypoxia Morphine, Nicotine, Cyclophosphamide
What 4 things decrease ADH release
Decreased plasma osmolarity
Increased blood volume
Increased blood pressure
Alcohol, Clonidine (antihypertensive), Haloperidol (dopamine blocker)
Thirst Mechanism controls what?
fluid intake
Thirst center is located in what 2 spots?
- Anteroventricular region of third cerebral ventricle (AV3V region) (Also promotes ADH release)
- Anterolaterally in preoptic nucleus
The portion of the thirst center in the AV3V region: what does the upper and inferior portion contain?
Upper portion contains subfornical organ
Inferior portion contains organum vasculosum of the lamina terminalis
when the thirst mechanism is stimulated, what happens?
causes immediate drive to drink
–Neurons within area respond to changes in osmolarity (function like osmoreceptors)
the thirst mechanism is Stimulated by sodium concentration of?
2 mEq/Liter higher than normal
–Threshold for drinking
what 5 things increase thirst
Increased plasma osmolarity Decreased blood volume Decreased blood pressure Increased angiotensin II Dryness of mouth
what 5 things decrease thirst
Decreased plasma osmolarity Increased blood volume Increased blood pressure Decreased angiotensin II Gastric distention
describe the mechanism for increased thirst inregards to Decreased blood volume and blood pressure
driven by neural input from the baroreceptor and cardiopulmonary reflexes since circulating volume and blood pressure can change without changes in osmolarity
describe the mechanism for increased thirst inregards to Increased angiotensin II
acts on organum vasculosum of lamina terminalis
how long does it take to absorb and distribute ingested fluid?
30-60min
what would happen if the thirst drive wasn’t suppressed
we would be driven to continue our fluid ingestion until osmolarity was returned to normal which would result in over hydration
With both osmoreceptor-ADH and thirst mechanism intake, we are able to prevent ______ in sodium concentration even if sodium intake increases 6-fold
large changes
What happens if either the osmoreceptor-ADH or thirst mechanism intake fail?
Even if one system is not functional, other system still maintain the sodium concentration
What happens if both the osmoreceptor-ADH and thirst mechanism intake fail?
If both systems fail, there is no other system that can regulate sodium concentration so sodium concentration will show large swings depending on sodium intake
Angiotensin II and aldosterone play an important role controlling what?
SODIUM REABSORPTION
Angiotensin II and aldosterone DO NOT play a role in controlling what?
SODIUM CONCENTRATION
Increased levels of angiotensin II and aldosterone will increase what?
sodium reabsorption AND water reabsorption
–(Change in total amount of sodium and total amount of water, but no change in concentration)
Extremely high levels of aldosterone will only produce an increase in sodium concentration of?
3 to 5 mEq/Liter
Complete loss of aldosterone secretion can lead to a significant decrease in? Because?
sodium concentration
–Sodium depletion leads to volume depletion and decreased blood pressure which activates thirst reflex and the cardiopulmonary reflex which results in further decrease in sodium concentration as volume is ingested and/or reabsorbed
