Control of Extracellular Osmolarity/[Na+]-Exam 4

Question 1

What is the most abundant ion in extracellular fluid?

Answer 1

Sodium

Question 2

What is the range in concentrations of sodium?

Answer 2

140-145 mEq/L

Avg: 142 mEq/L

Question 3

What is average osmolarity?

Answer 3

300 mOsm/L

Question 4

What is average osmolarity corrected for interionic attraction?

Answer 4

282 mOsm/L

Question 5

What is the range in osmolarity?

Answer 5

291-309 mOsm/L [+/- 3%]

Question 6

Why is precise control of osmolarity and sodium important?

Answer 6

They both control distribution of water between intracellular and extracellular compartments

Question 7

Sodium and associated anions account for what percent of extracellular solute? What are the associated ions?

Answer 7

94%; chloride and bicarbonate

Question 8

Glucose and urea contribute what percent of total osmolarity?

Answer 8

3 to 5%

Question 9

Why does urea exert little effective osmotic force?

Answer 9

Able to permeate cells easily

Question 10

Why does sodium have a big effect on fluid movement between extracellular and intracellular compartments?

Answer 10

Not very permeable

Question 11

Equation for Plasma Osmolarity

Answer 11

(2.1) x (Plasma concentration sodium)

Question 12

How do you calculate the plasma osmolarity of sodium?

Answer 12

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

Question 13

What two systems control/regulate extracellular osmolarity and sodium concentration?

Answer 13

1. Osmoreceptor - ADH system

2. Thirst mechanism

Question 14

Where are osmoreceptor cells located?

Answer 14

Anterior hypothalamus

Question 15

When would osmoreceptor cells shrink?

Answer 15

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

Question 16

What happens with impulses as osmoreceptor cells shrink? Where are impulses passed?

Answer 16

Number of impulses sent to other nerve cells in supraoptic nuclei; impulses passed to posterior pituitary

Question 17

What do impulses from shrunken osmoreceptor cells stimulate?

Answer 17

Release of ADH stored in secretory granules within nerve endings

Question 18

Water deficit leads to _________(increase/decerease) in extracellular osmolarity.

Answer 18

Increase

Question 19

Increased Extracellular osmolarity leads to increased secretion of what?

Answer 19

ADH secretion (posterior pituitary)

Question 20

ADH secretion leads to increased water reabsorption leading to ____________(increase/decrease) in water excreted.

Answer 20

Decrease

Question 21

ADH is tied to what reflexes?

Answer 21

Arterial baroreceptor reflexes and cardiopulmonary reflexes

Question 22

What do arterial baroreceptor reflexes response to?

Answer 22

Changes in blood pressure

Question 23

What do cardiopulmonary reflexes response to?

Answer 23

Changes in blood volume

Question 24

Reflex pathways tied to ________________ (2) that control ADH production and release.

Answer 24

Hypothalamic nuclei

Question 25

Decreased blood pressure and/or decreased blood volume results in ____________ (increased/decreased) ADH release.

Answer 25

Increased

Question 26

Small increase of what percent of osmolarity will trigger increase [ADH]?

Answer 26

1%

Question 27

Circulating volume must decrease by what percent before appreciable change in [ADH]?

Answer 27

10%

Question 28

What percent reduction in circulating volume produces a HUGE increase in [ADH]?

Answer 28

15-20%

Question 29

What causes increased ADH release?

Answer 29

``` Increased plasma osmolarity Decreased blood pressure Decreased blood volume Nausea Hypoxia ```

Question 30

What drugs cause increased ADH release?

Answer 30

Morphine, Nicotine, Cyclophophamide

Question 31

What causes decrease in ADH release?

Answer 31

Decreased plasma osmolarity Increased blood volume Increased blood pressure

Question 32

What drugs cause decreased ADH release?

Answer 32

Alcohol, Clonidine (Antihypertensive) Haloperidol (dopamine blocker)

Question 33

What mechanism controls fluid intake?

Answer 33

Thirst

Question 34

Why is the thirst mechanism important?

Answer 34

needed to replace fluid loss via sweating, breathing GI tract

Question 35

Where is the thirst center?

Answer 35

Anteroventricular region of third cerebral ventricle (AV3V region); anterolaterally in preoptic nucleus

Question 36

What does the thirst cneter also do?

Answer 36

Promotes ADH release

Question 37

Upper portion of thirst center contains what region?

Answer 37

Subfornical organ

Question 38

INferior portion of thirst center contains what?

Answer 38

Organum vasculosum of the lamina terminalis

Question 39

How long does the drive to drink continue?

Answer 39

As long as thirst center is stimulated

Question 40

Neurons within thirst center respond to changes in what? They function like what?

Answer 40

Osmolarity; function like osmoreceptors

Question 41

What is the thirst mechanism stimulated by? (threshold for drinking)

Answer 41

Sodium concentration 2mEq/L higher than normal

Question 42

What causes increased thirst?

Answer 42

``` Increased plasma osmolarity Decreased bp Decreased blood volume Increased angiotensin II dryness of mouth ```

Question 43

What causes decreased thirst?

Answer 43

``` Decreased plasma osmolarity Increased bp increased blood volume Decreased angiotensin II gastic distension ```

Question 44

What does increased angiotensin II probably act on?

Answer 44

Organum vasculosum of lamina terminalis

Question 45

How long does it take to absorb and distribute digested fluid?

Answer 45

30-60 minutes

Question 46

Why would we get overhydrated if thirst drive wasn't suppressed?

Answer 46

We would be driven to continue drinking until osmolarity was returned to normal

Question 47

With our regulatory systems, we're able to prevent large changes in sodium concentration even though sodium intake increases how much?

Answer 47

6-fold

Question 48

What would happen if one system of sodium regulation wasn't functional?

Answer 48

Other systems would still maintain the sodium concentration

Question 49

If both sodium regulation methods fail, what happens?

Answer 49

There is no other system that can regulate sodium concentration so sodium concentration will show large swings depending on sodium intake

Question 50

What two hormones play an important role in controlling sodium reabsorption?

Answer 50

Angiotensin II and aldosterone

Question 51

Angiotensin II and aldosterone do not play a role in controlling what?

Answer 51

Sodium Concentartion

Question 52

Increased levels of angiotensin II and aldosterone will result in what?

Answer 52

INcreased sodium reabsorption and water reabsorption

Question 53

How would you block the aldosterone system?

Answer 53

Removing adrenal glands and infusing aldosterone to maintain plasma concentration

Question 54

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

Answer 54

3 to 5 mEq/L

Question 55

Complete loss of aldosterone secretion can lead to what?

Answer 55

Significant decrease in sodium concentration

Question 56

Sodium depletion leads to ________ depletion.

Answer 56

Volume

Question 57

Sodium depletion leads to decreased _____________ (2), which activates the thirst reflex and cardiopulmonary reflex.

Answer 57

Blood pressure

Question 58

Increase reflex stimulation results in further decrease in _____________ (2) as volume is ingested and/or reabsorbed.

Answer 58

Sodium concentration