Topic 10

Question 1

Sodium most abundant ion in extracellular fluid. What is its range and average

Answer 1

Range 140 to 145 mEq/Liter

Average 142 mEq/Liter

Question 2

Osmolarities range and average is?

Answer 2

Range 291 to 309 mOsm/Liter

Average 300 mOsm/Liter

Question 3

why is precise control of sodium and osmolarity important?

Answer 3

they control distribution of water between intracellular and extracellular compartments

Question 4

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

Answer 4

94%

Question 5

Glucose and urea contribute ____% of total osmolarity

Answer 5

3 to 5%

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

Question 6

Sodium not very permeable so it has a big effect on fluid movement between what compartments?

Answer 6

extracellular and intracellular compartments

Question 7

Plasma osmolarity = [formula]

Answer 7

(2.1) x (Plasma Na+ concentration)

Question 8

what 2 systems control / regulate extracellular osmolarity and sodium concentration?

Answer 8

Osmoreceptor – ADH system

Thirst mechanism

Question 9

Osmoreceptor Cells are Located in?

Answer 9

anterior hypothalamus

Question 10

describe Osmoreceptor Cells mechanism (5 steps)

KNOW

Answer 10

1. Cells shrink in response to increased ECF [Na+] (i.e. increased osmolarity)
2. As cells shrink, impulses are sent to other nerve cells in supraoptic nuclei
3. Impulses passed to posterior pituitary
4. Impulses stimulate release of AHD stored in secretory granules within nerve endings
5. Increased [ADH] of blood stimulates increased water permeability in late distal tubules, cortical collecting tubules, and medullary collecting tubules

Question 11

Increased osmolarity results in increased water permeability which allows water to be reabsorbed (conserved) while sodium does what?

Answer 11

continues to be excreted at normal rate

Question 12

What happens after a WATER DEFICIT:
\_\_\_Extracellular osmolarity
\_\_\_ADH Secretion
\_\_\_Plasma ADH
\_\_\_Water permeability in distal tubules/collecting ducts
\_\_\_Water reabsorption
\_\_\_Water excreted

Answer 12

INCREASE Extracellular osmolarity
INCREASE ADH Secretion
INCREASE Plasma ADH
INCREASE Water permeability in distal tubules/collecting ducts
INCREASE Water reabsorption
deCREASE Water excreted

Question 13

ADH release is tied into what 2 other systems?

Answer 13

1. arterial baroreceptor reflexes (which respond to changes in blood pressure)
2. cardiopulmonary reflexes (which respond to changes in blood volume)
   - -Reflex pathways tied into hypothalamic nuclei that control ADH production and release

Question 14

A Decreased blood pressure and/or decreased blood volume results in an increase or decrease in ADH release?

Answer 14

increase

Question 15

A Small increase in osmolarity of only __% will trigger increase [ADH]

Answer 15

1%

Question 16

Circulating volume must decrease approximately __% before appreciable change in [ADH]

Answer 16

10%

Question 17

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

Answer 17

15 to 20%

Question 18

What 6 things increase ADH release

Answer 18

Increased plasma osmolarity
Decreased blood volume
Decreased blood pressure
Nausea
Hypoxia
Morphine, Nicotine, Cyclophosphamide

Question 19

What 4 things decrease ADH release

Answer 19

Decreased plasma osmolarity
Increased blood volume
Increased blood pressure
Alcohol, Clonidine (antihypertensive), Haloperidol (dopamine blocker)

Question 20

Thirst Mechanism controls what?

Answer 20

fluid intake

Question 21

Thirst center is located in what 2 spots?

Answer 21

1. Anteroventricular region of third cerebral ventricle (AV3V region) (Also promotes ADH release)
2. Anterolaterally in preoptic nucleus

Question 22

The portion of the thirst center in the AV3V region: what does the upper and inferior portion contain?

Answer 22

Upper portion contains subfornical organ

Inferior portion contains organum vasculosum of the lamina terminalis

Question 23

when the thirst mechanism is stimulated, what happens?

Answer 23

causes immediate drive to drink

–Neurons within area respond to changes in osmolarity (function like osmoreceptors)

Question 24

the thirst mechanism is Stimulated by sodium concentration of?

Answer 24

2 mEq/Liter higher than normal

–Threshold for drinking

Question 25

what 5 things increase thirst

Answer 25

``` Increased plasma osmolarity Decreased blood volume Decreased blood pressure Increased angiotensin II Dryness of mouth ```

Question 26

what 5 things decrease thirst

Answer 26

``` Decreased plasma osmolarity Increased blood volume Increased blood pressure Decreased angiotensin II Gastric distention ```

Question 27

describe the mechanism for increased thirst inregards to Decreased blood volume and blood pressure

Answer 27

driven by neural input from the baroreceptor and cardiopulmonary reflexes since circulating volume and blood pressure can change without changes in osmolarity

Question 28

describe the mechanism for increased thirst inregards to Increased angiotensin II

Answer 28

acts on organum vasculosum of lamina terminalis

Question 29

how long does it take to absorb and distribute ingested fluid?

Answer 29

30-60min

Question 30

what would happen if the thirst drive wasn’t suppressed

Answer 30

we would be driven to continue our fluid ingestion until osmolarity was returned to normal which would result in over hydration

Question 31

With both osmoreceptor-ADH and thirst mechanism intake, we are able to prevent ______ in sodium concentration even if sodium intake increases 6-fold

Answer 31

large changes

Question 32

What happens if either the osmoreceptor-ADH or thirst mechanism intake fail?

Answer 32

Even if one system is not functional, other system still maintain the sodium concentration

Question 33

What happens if both the osmoreceptor-ADH and thirst mechanism intake fail?

Answer 33

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

Question 34

Angiotensin II and aldosterone play an important role controlling what?

Answer 34

SODIUM REABSORPTION

Question 35

Angiotensin II and aldosterone DO NOT play a role in controlling what?

Answer 35

SODIUM CONCENTRATION

Question 36

Increased levels of angiotensin II and aldosterone will increase what?

Answer 36

sodium reabsorption AND water reabsorption | --(Change in total amount of sodium and total amount of water, but no change in concentration)

Question 37

Extremely high levels of aldosterone will only produce an increase in sodium concentration of?

Answer 37

3 to 5 mEq/Liter

Question 38

Complete loss of aldosterone secretion can lead to a significant decrease in? Because?

Answer 38

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