038 Body fluid compartments

Question 1

What % of body weight is made up of total body water?

Answer 1

60%

Question 2

How much of body water is intracellular?

Answer 2

40%

Question 3

How much of extracellular fluid consists of plasma?

Answer 3

20%

Question 4

What markers can be used to measure volume of total body water?

Answer 4

3H2O (tritiated water)

Question 5

What marker can be used to measure extracellular fluid?

Answer 5

Inulin or thiosulphate

Question 6

Which marker can be used to measure plasma?

Answer 6

Evans blue, or plasma proteins labelled isotopically e.g. 125l albumin

Question 7

Why is urea solution not isotonic?

Answer 7

Urea is not an effective osmole

Question 8

What is the issue with using inulin to measure extracellular fluid?

Answer 8

It can enter the intracellular part and can also be lost in urine.

Question 9

What is the issue of using evans blue to measure intracellular fluid?

Answer 9

It has a short half life so you must measure it quickly.

Question 10

What is the difference in plasma composition between extracellular and intracellular fluid?

Answer 10

There are proteins and organic phosphates intracellularly. This gives intracellular compartments a slight negative charge which is balanced by high levels of Cl- and HCO3- extracellularly.

Question 11

What is the difference in body fluid compositions between interstitial and plasma compartments?

Answer 11

Interstitial fluids have low protein, and since half the Ca2+ in plasma is protein bound, the Ca2+ levels are lower in interstitial compartments.

Question 12

What is the osmolality of plasma?

Answer 12

295 mOsmol/kg

Question 13

Which ions contribute most to plasma osmolality?

Answer 13

Na+, K+, HCO3-, Cl-

Question 14

What will occur to body fluid composition during rapid ingestion of water?

Answer 14

Even distribution between compartments in their proportions 60% intracellular

Question 15

What occurs when there is rapid ingestion of 0.9% saline?

Answer 15

This is isotonic. Most of the water will remain in the extracellular fluid as Na+ won’t go through the membrane. (This helps increasing blood pressure without lysing cells)

Question 16

What occurs when there is IV infusion of 1L 5% albumin?

Answer 16

This will only be retained in the plasma, so plasma retains all of the water. It does not enter the interstitial fluid.

Question 17

What is elephantitis

Answer 17

Blockage in the lymphatics

Question 18

How does hemorrhage change fluid movement?

Answer 18

There is reduced capillary hydrostatic pressure. This means more fluid enters the capillary, so there is an increased blood volume at the expense of interstitial volume.

Question 19

How does congestive heart failure change fluid movement?

Answer 19

There is increased venous pressure, increasing hydrostatic pressure. It takes longer before oncotic pressure >hydrostatic pressure. This causes more fluid entering the tissues, causing oedema.

Question 20

How does liver failure change fluid movement?

Answer 20

Liver failure causes reduced plasma protein concentration This causes reduced oncotic pressure that draws fluid inwards, so hydrostatic pressure remains higher for a longer period of time along the capillary. More fluid enters tissues to cause oedema.

Question 21

What is the most abundant protein in plasma?

Answer 21

Albumin

Question 22

What is the relationship between oncotic and hydrostatic pressures in pulmonary circulation?

Answer 22

Hydrostatic pressures are lower then oncotic pressures, allowing alveoli to be clear of fluid.

Question 23

How does inflammation result in local oedema?

Answer 23

Capillary permeability to protein draws water in.

Question 24

What factors lead to ankle oedema during prolonged standing?

Answer 24

Reduced venous return due to venous hydrostatic pooling causes increased venous pressure and hence increased capillary pressure. Fluid moves out of the capillaries.

Question 25

Why does left ventricular failure often lead to pulmonary oedema? Explain the implications for respiration

Answer 25

There is increased pressure in the pulmonary capillaries causing fluid to move out rather than in. Pulmonary oedema leads to inefficent gas exchange across alveoli.

Question 26

In hypotonic solution, what occurs to the red blood cells?

Answer 26

cell lysis occurs as water moves in

Question 27

In a hypertonic solution, what occurs to the red blood cells?

Answer 27

Cells shrink as water moves out.

Question 28

Why isnt urea an effective osmole?

Answer 28

Urea is able to move into the cell along with water, causing cell to burst. Hence an iso-osmotic solution of urea is not necessarily isotonic.

Question 29

Normally, filtration at arteriole end exceeds reabsorption at venule end. Why doesnt oedema occur?

Answer 29

The difference of about 2-4L is returned to circulation via the lymphatic system and doesnt accumulate in the interstitium.

Question 30

What is transcellular fluid and give 2 examples?

Answer 30

Transcellular fluid is the portion of total body water contained within epithelial lined spaces. e.g. aqueous humor, synovial, cerebrospinal

Question 31

What is the 60:40:20 ratio?

Answer 31

Of total body weight:
60% is water (42L)
40% is intracellular (28L)
20% is extracellular (14L)