Topic 10 COntrol of EC Osmolarity and Na Concent

Question 1

most abundant ion in extracellular fluid?

Answer 1

SODIUM
Range 140 to 145 mEq/Liter
Average 142 mEq/Liter

Question 2

Osmolarity - Average / Corrected

Answer 2

Osmolarity
Average 300 mOsm/Liter [282 mOsm/Liter
–corrected for interionic attraction]
-Range 291 to 309 mOsm/Liter [±2%to 3%]

Question 3

Sodium and associated anions (chloride and bicarbonate) account for what % of all extracellular solute

Answer 3

94%

Sodium not very permeable so has big effect on fluid movement between extracellular and intracellular compartments

Question 4

Glucose and urea contribute what % of total osmolarity

Answer 4

3 to 5%

Urea able to permeate cells easily so exerts little effective osmotic force

Question 5

Plasma osmolarity = equation

Answer 5

(2.1) x (Plasma concentration sodium)

Posm= (2.1) x (142 mEq/L) = 298 mOsm/L

Question 6

Two systems control / regulate extracellular

osmolarity and sodium concentration?

Answer 6

Osmoreceptor-ADH system

Thirst mechanism

Question 7

Osmoreceptor Cells - Located where?

Answer 7

anterior hypothalamus

Question 8

Osmoreceptor Cells shrink in response to what? and do what?

Answer 8

increased ECF [Na+] (i.e.increased osmolarity)

As cells shrink, number of impulses sent to other nerve cells in supraoptic nuclei

Question 9

Osmoreceptor Cells - when shrink send nerve impulses to nerve cells in supraoptic nuclei which than do send them where? which do what?

Answer 9

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

Question 10

Osmoreceptor Cells:
Increased osmolarity results in increased _____ which allows water to be _____ while sodium continues to be excreted at _____

Answer 10

water permeability
reabsorbed (conserved)
normal rate

Question 11

ADH release is tied into what two reflexes?

What are these reflex pathways tied into?

Answer 11

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

Question 12

An increase in ADH release is cause by?

Answer 12

Decreased blood pressure and/or decreased blood volume

Question 13

Circulating volume must decrease approx what % before appreciable change in [ADH]

Answer 13

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)

Question 14

what % reduction in circulating volume produces a HUGE increase in [ADH]

Answer 14

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)

Question 15

Small increase in osmolarity what % will

trigger increase [ADH]?

Answer 15

(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)

Question 16

Increased ADH release caused by what ? (5 factors)

Answer 16

Nausea
Hypoxia
Morphine, Nicotine, Cyclophosphamide
Decreased BP, BV
Increased Plasma Osmolarity

Question 17

DECREASED ADH release caused by what ? (5 factors)

Answer 17

Alcohol, Clonidine (antihypertensive),
Haloperidol (dopamine blocker)
Increased BV, BP
Decreased Osmolarity

Question 18

Thirst center controls what?

Answer 18

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

Question 19

Thirst center located where? two main loacations

upper and lower portions contain what?

Answer 19

–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

Question 20

Thirst center stimulated by changes in what? at what concentration?

Answer 20

Neurons within area respond to changes in osmolarity (function like osmoreceptors)
Stimulated by sodium concentration 2mEq/Liter higher than normal
Threshold for drinking

Question 21

Increased Thirst caused by ?

Answer 21

Decreased BP, BV
Increased Plasma Osmolarity, ATII
Dry mouth

Question 22

Decreased Thirst caused by?

Answer 22

Increased BP, BV
Decreased Plasma Osmolarity & AT II
GI distension

Question 23

How long does it take to absorb and distribute ingested fluid? bc of this time what happens to help?

Answer 23

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

Question 24

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?

Answer 24

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)

Question 25

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?

Answer 25

6-fold

Question 26

ngiotensin II and aldosterone play an

important role controlling SODIUM?

Answer 26

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)

Question 27

Angiotensin II and aldosterone DO NOT play a role in controlling SODIUM

Answer 27

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)

Question 28

Extremely high levels of aldosterone will only produce an increase in sodium
concentration of what? mEq/L

Answer 28

3 to 5 mEq/Liter

Question 29

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?

Answer 29

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