Guyton Chapter 25 Body Fluid Compartments

Question 1

What is insensible water loss?

Answer 1

Continuous loss of water by evaporation from the respiratory tract and through the skin

Question 2

What is the total body fluid distributed in?

Answer 2

Extracellular fluid and intracellular fluid

The extracellular fluid is divided into interstitial fluid and blood plasma

There is also a small compartment called transcellular fluid (this includes fluid in the synovial, peritoneal, pericardial and intraocular spaces as well as the cerebrospinal fluid

Question 3

How much in % of the total body weight is intracellular fluid?

Answer 3

40% in an average person

Question 4

What is extracellular fluid and how much of the body weight does this account for?

Answer 4

All the fluids outside the cell is collectively called the extracellular fluid. It accounts for 20% of the body weight!

Question 5

What makes up the two largest compartments of the extracellular fluid?

Answer 5

Interstitial fluid (75% of the ECF)
Plasma (25% of ECF)

Plasma is the non cellular part of the blood

Question 6

What kind of fluid does blood contain?

Answer 6

Extracellular fluid (fluid in the plasma)
Intracellular fluid (fluid in the red blood cells)
However, blood is considered to be a separate fluid compartment because it is contained in a chamber of its own

Question 7

What is the distribution of plasma and cells in blood?

Answer 7

About 60% is plasma and 40% is red blood cells

Question 8

What is the hematocrit?

Answer 8

The hematocrit is the fraction of the blood composed of red blood cells as determined by centrifuging blood in a hematocrit tube until the cells become tightly packed in the bottom of the tube.

Question 9

What is the most important difference between the plasma and interstitial fluid?

Answer 9

It’s a higher concentration of protein in the plasma.

Because the capillaries have a low permeability to the plasma proteins, only small amounts of proteins are leaked into the interstitial spaces in most tissues.

Question 10

What is the Donnan effect?

Answer 10

The plasma proteins have a net negative charge and therefor tend to bind cations such as Na and K ions thus holding extra amounts of these cations in the plasma along with the plasma proteins.

Question 11

What ions are found in large and small amounts in the extracellular fluid?

Answer 11

Contains large amounts of sodium and chloride ions, reasonably large amounts of bicarbonate ions but only small amounts of K, Ca, magnesium, phosphate and organic ions

Question 12

What separates intracellular fluid from extracellular fluid?

Answer 12

It’s separated by a cell membrane that is highly permeable to water but not to most of the electrolytes in the body

Question 13

What ions are found in the intracellular fluid?

Answer 13

Only small quantities of Na and Cl ions and almost no Ca ions. Contains large
amounts of potassium and phosphate ions plus moderate quantities of magnesium and sulfate ions.

Also cells contain large amounts of protein (almost 4 times as much in the plasma)

Question 14

What is the difference between ions in the interstitial fluid compared to plasma?

Answer 14

Negatively charged ions (anions) tend to have a slightly higher concentration in the interstitial fluid compared with the plasma because the negative charges of the plasma proteins repel the negatively charged ions.

Question 15

What is the equation that describes volume A and volume B and the concentrations of the solutions?

Answer 15

Volume B = (Volume A x Concentration A) / Concentration B

Question 16

How is intracellular fluid calculated?

Answer 16

Total body water - extracellular fluid volume

Question 17

How is the interstitial fluid calculated?

Answer 17

Extracellular fluid volume - plasma
volume

Question 18

How is total blood volume calculated?

Answer 18

Total blood volume = (Plasma volume)/(1-hematocrit)

Question 19

What determines how the relative amounts of extracellular fluid is distributed between the plasma and interstitial spaces?

Answer 19

It’s determined mainly by the balance of hydrostatic and colloid osmotic forces across the capillary membranes.

Question 20

How is the distribution of fluid between intracellular and extracellular compartments determined?

Answer 20

Mainly by the osmotic effect of the smaller solutes especially sodium, chloride and other electrolytes.

Question 21

What is the definition of osmosis?

Answer 21

Net diffusion of water across a selectively permeable membrane from a region of high water concentration to one that has a lower water concentration.

Question 22

What is osmoles?

Answer 22

The total number of particles in a solution.

Question 23

What is the definition of osmolality vs osmolarity?

Answer 23

Osmolality = osmoles per kg
Osmolarity = osmoses per litre of solution

Question 24

What is the effect of isotonic, hypotonic and hypertonic solutions on cell volume?

Answer 24

Isotonic - no change
Hypotonic- water will diffuse into the cell causing it to swell
Hypertonic- water will flow out of the cell causing it to shrink

Question 25

What does primary loss of sodium chloride result in and in which conditions is it seen?

Answer 25

It usually results in hyponatremia-dehydration and is associated with decreased extracellular fluid volume. Conditions that can cause hyponatremia owing to loss of sodium chloride include diarrhea and vomiting! Overuse of diuretics that inhibit the ability of the kidneys to conserve sodium and certain types of sodium-wasting kidney diseases can also cause modest degrees of hyponatremia as well as Addisons disease.

Question 26

What is hyponatremia - overhydration?

Answer 26

It’s associated with excess water retention which dilutes the sodium in the extracellular fluid. A cause is excess ADH which causes the kidneys to reabsorbed more water.

Question 27

What is hypernatremia - dehydration?

Answer 27

This occurs when there is primary loss of water from the extracellular fluid. This condition can occur from an inability to secrete ADH which is needed for the kidneys to conserve water (diabetes incipidus) causing dehydration and increased concentration of sodium chloride in the extracellular fluid.

Question 28

Which 3 conditions are especially prone to cause intracellular swelling?

Answer 28

1. Hyponatremia
2. Depression of the metabolic systems of the tissues
   3.Lack of adequate nutrition to the cells

See page 296 for explanation

Question 29

Name 2 causes of extracellular edema.

Answer 29

1. Abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries
2. Failure of the lymphatics to return fluid from the interstitium back to the blood (lymphedema)

The most common clinical cause of interstitial fluid accumulation is excessive capillary fluid filtration.

Question 30

What changes can increase the capillary filtration rate?

Answer 30

• increased capillary filtration coefficient
  -increased capillary hydrostatic pressure
  -decreased plasma colloid osmotic pressure

Question 31

Name examples of causes to increased capillary pressure that can lead to extracellular edema?

Answer 31

Excessive kidney retention of salt and water

-Acute or chronic kidney failure
-Mineralcorticoid excess

High venous pressure and venous constriction
-heart failure
-venous obstruction
-failure of venous pumps

Decreased arteriolar resistance
-Excessive body heat
-insufficiency of sympathetic nervous system
-vasodilator drugs

Question 32

Name causes of decreased plasma proteins that can lead to extracellular edema?

Answer 32

Loss of proteins in the urine (nephrotic syndrome)
Loss of protein from denuded skin areas
Failure to produce proteins (liver disease or serious protein or caloric malnutrition)

Question 33

Name some causes of increased capillary permeability that can lead to extracellular edema?

Answer 33

-immune reactions that cause release of histamine and other immune products
-toxins
-bacterial infections
-vitamin deficiency
-prolonged ischemia
-burns

Question 34

Name some causes of blockage of lymph return that could lead to extracellular edema?

Answer 34

-Cancer
-Infections
-Surgery
-Congenital absence or abnormality of lymphatic vessels

Question 35

What 3 major safety factors prevent excessive fluid accumulation in the interstitial spaces?

Answer 35

-low compliance of the interstitium when interstitial fluid pressure is in the negative pressure range

-the ability of lymph flow to increase 10-50 fold

-washdown of interstitial fluid protein concentration, which reduces interstitial fluid colloid osmotic pressure as capillary filtration increases