Topic 10 COntrol of EC Osmolarity and Na Concent Flashcards
most abundant ion in extracellular fluid?
SODIUM
Range 140 to 145 mEq/Liter
Average 142 mEq/Liter
Osmolarity - Average / Corrected
Osmolarity
Average 300 mOsm/Liter [282 mOsm/Liter
–corrected for interionic attraction]
-Range 291 to 309 mOsm/Liter [±2%to 3%]
Sodium and associated anions (chloride and bicarbonate) account for what % of all extracellular solute
94%
Sodium not very permeable so has big effect on fluid movement between extracellular and intracellular compartments
Glucose and urea contribute what % of total osmolarity
3 to 5%
Urea able to permeate cells easily so exerts little effective osmotic force
Plasma osmolarity = equation
(2.1) x (Plasma concentration sodium)
Posm= (2.1) x (142 mEq/L) = 298 mOsm/L
Two systems control / regulate extracellular
osmolarity and sodium concentration?
Osmoreceptor-ADH system
Thirst mechanism
Osmoreceptor Cells - Located where?
anterior hypothalamus
Osmoreceptor Cells shrink in response to what? and do what?
increased ECF [Na+] (i.e.increased osmolarity)
As cells shrink, number of impulses sent to other nerve cells in supraoptic nuclei
Osmoreceptor Cells - when shrink send nerve impulses to nerve cells in supraoptic nuclei which than do send them where? which do what?
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
Osmoreceptor Cells:
Increased osmolarity results in increased _____ which allows water to be _____ while sodium continues to be excreted at _____
water permeability
reabsorbed (conserved)
normal rate
ADH release is tied into what two reflexes?
What are these reflex pathways tied into?
arterial baroreceptor reflexes (which respond to changes in BP) and the cardiopulmonary reflexes (which respond to changes in bld vol)
Reflex pathways tied into hypothalamic nuclei that control ADH production and release
An increase in ADH release is cause by?
Decreased blood pressure and/or decreased blood volume
Circulating volume must decrease approx what % before appreciable change in [ADH]
10%
Think of graph with white dots and black dots, this is the black dots, the graph doesnt start rising until after 10%
(No change in osmolarity, decreased circulating volume)
what % reduction in circulating volume produces a HUGE increase in [ADH]
A 15 to 20%
Think of graph with white dots and black dots, this is the black dots sky rocketing
(No change in osmolarity, decreased circulating volume)
Small increase in osmolarity what % will
trigger increase [ADH]?
(1%
)Think of graph with white dots and black dots, this is the white dots they start to rise almost immediately with increases osmolarity
(Increased osmolarity, no change in circulating volume)
Increased ADH release caused by what ? (5 factors)
Nausea Hypoxia Morphine, Nicotine, Cyclophosphamide Decreased BP, BV Increased Plasma Osmolarity
DECREASED ADH release caused by what ? (5 factors)
Alcohol, Clonidine (antihypertensive),
Haloperidol (dopamine blocker)
Increased BV, BP
Decreased Osmolarity
Thirst center controls what?
Controls fluid intake
Needed to replace fluid loss via sweating, breathing, GI tract
When stimulated causes immediate drive to drink, and continues as long as area is stimulated
Thirst center located where? two main loacations
upper and lower portions contain what?
–Anteroventricular region of third cerebral ventricle (AV3V region) (Also promotes ADH release)
(Upper portion contains subfornical organ
Inferior portion contains organum vasculosum of the lamina terminalis)
–Anterolaterally in preoptic nucleus
Thirst center stimulated by changes in what? at what concentration?
Neurons within area respond to changes in osmolarity (function like osmoreceptors)
Stimulated by sodium concentration 2mEq/Liter higher than normal
Threshold for drinking
Increased Thirst caused by ?
Decreased BP, BV
Increased Plasma Osmolarity, ATII
Dry mouth
Decreased Thirst caused by?
Increased BP, BV
Decreased Plasma Osmolarity & AT II
GI distension
How long does it take to absorb and distribute ingested fluid? bc of this time what happens to help?
30-60 minutes
Gastric distension and relief of dry mouth quench the thirst drive so ingested water has time to be processed. 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, able to prevent large changes in sodium concentration. what if one system fails? what if both fail?
Even if one system is not functional,
other system still maintain the Na concentration
If both systems fail, there is no other system that can regulate Na concentration so Na concentration will show large swings depending on sodium intake
(think of graph with blue and red line, normal- red is like straight non fluctioating, both systems blocked - blue line sky rockets up)
With both osmoreceptor -ADH and thirst mechanism intake, able to prevent large changes in Na concentration even though Na intake has increases up how much?
6-fold
ngiotensin II and aldosterone play an
important role controlling SODIUM?
REABSORPTION
Increased levels of angiotensin II and
aldosterone will increase Na reabsorption AND H2O reabsorption
(Change in total amount of Na and total amount of H2O), but no change in concentration)
Angiotensin II and aldosterone DO NOT play a role in controlling SODIUM
CONCENTRATION
Increased levels of angiotensin II and
aldosterone will increase Na reabsorption AND H2O reabsorption
(Change in total amount of Na and total amount of H2O), but no change in concentration)
Extremely high levels of aldosterone will only produce an increase in sodium
concentration of what? mEq/L
3 to 5 mEq/Liter
Complete loss of aldosterone secretion
can lead to a significant decrease in what?
which activates what 2 reflexes which in turn does what? is this good?
sodium concentration
Na depletion leads to volume depletion and decreased BP which activates thirst reflex and the cardiopulmonary reflex which results in further decrease in [Na] as volume is ingested
and/or reabsorbed
