Body fluids

BODY FLUIDS

Daily Intake of Water

(1) it is ingested in the form of liquids or water in the food, about 2100 ml/day
(2) it is synthesized in the body as a result of oxidation of carbohydrates, adding about 200 ml/day.
total water intake
of about 2300 ml/day
Daily Loss of Body Water
Insensible Water Loss. evaporation from the respiratory tract and diffusion through the skin, which about 700ml/day
Sweating about 100 ml/day.
Water Loss in Feces about 100ml/day).
urine excretion by the kidneys about 1400ml/day
total water loss
of about 2300 ml/day

Body Fluid Compartments

average 70-kilogram man
body fluid 42 liters( 60%of body weight)
Intravascular 3 liters(1/4)
Interstitial 10 liters(3/4)
Transcellular
1 liters
Intracellular
28 liters (40 % of the (total body weight
Extracellular 14 liters(20 % of the body weight)


Blood Volume

The average blood volume of adults is about 7% of body weight, ( about 5 liters).

Blood contains both extracellular fluid (plasma) and intracellular fluid (the fluid in the red blood cells).
About 60% of the blood is plasma(about 3 liters) and 40 % is red blood cells

Constituents of Extracellular Fluid Plasma and Interstitial Fluids

Ionic Composition Is Similar Because they are separated by highly permeable membranes
Contains large amounts of sodium,chloride and bicarbonate ions.
Small quantities of potassium, calcium, magnesium, phosphate, and organic acid ions.
The most important difference is the higher concentration of protein in the plasma

Constituents of the Intracellular Fluid

contains small quantities of sodium and chloride ions and almost no calcium ions. Instead, it contains large amounts of potassium and phosphate ions plus moderate quantities of magnesium and sulfate ions. Also, cells contain large amounts of protein

contents of Body Fluid in different Compartments

Ion Plasma (mmol/L) ICF (mmol/L )
Na+ 142 14
K+ 4.2 140
Ca2+ 1.3 0
Mg2+ 0.8 20
Cl- 108 4
HCO3- 24 10
Sulfate- 0.4 19
Proteinate- 1.2 4


Measurement of Fluid Volumes in the Different Body Fluid Compartments
Dilution Principle
Example: if 25 mg of glucose are added to an unknown volume of distilled water and the final concentration of glucose after mixing is 0.05 mg/ml, then the volume of solvent is

Markers for measurement must share following qualities

1-They are measurable
2-They remain in the compartment being measured
3-They are not toxic
-TBW is measured by triated water (tritium oxide)
-ECF volume is measured by inulin that is distributed between plasma volume and interstitial volume
-Plasma volume can be measured by radioactive albumin. These substances neither leave the vascular system nor penetrate the erythrocytes

the interstitial =ECF volume - plasma volume

The ICF volume = TBW - ECF volume


Relation Between Moles and Osmoles
osmole refers to the number of osmotically active particles in a solution
Therefore, a solution containing 1 mole of glucose in each liter has a concentration of 1 osm/L.
sodium chloride ionizing to give chloride and sodium ions(giving two particles), , then a solution containing 1 mol/L will have an osmolar concentration of 2 osm/L.
1 mole of sodium sulfate (Na2SO4) dissociates into three ions, will contain 3 osm/L
milliosmole (mOsm), which equals 1/1000 osmole

Osmolality and Osmolarity

Osmolarity – refers to the number of solute particles per liter of solution
Osmolality – refers to the number of solute particles per kg of water
The normal osmolality of the extracellular and intracellular fluids is about 300 milliosmoles per kilogram of water

Osmotic Pressure

Pulling pressure because it pulls water.
The higher the osmotic pressure of a solution means the higher the solute concentration of the solution ( lower water content)
The osmotic pressure of a solution is directly proportional to the osmolarity.

In order to visualize this effect, imagine a U-shaped tube with equal amounts of water on each side, separated by a water-permeable membrane. Sugar has been added to the water on one side. The height of the liquid column on that side will then rise (and that on the other side will drop).

according to van’t Hoff’s law, osmotic pressure (p) can be calculated as p = CRT

where C is the concentration of solutes in osmoles per liter,
R is the ideal gas constant,
and T is the absolute temperature in degrees kelvin (273° + centigrade°).
p is expressed in millimeters of mercury (mm Hg)

Isotonic, Hypotonic, and Hypertonic Fluids

Tonicity of a solution is related to the effect of the concentration of the solution on the volume of a cell (e.g. erythrocytes)

solution does not change the volume of the cell

solution causes a cell to shrink

solution causes a cell to swell

Edema
Excess Fluid in the Tissues
extracellular or intracellular
Intracellular Edema
lack of adequate nutrition to the cells,the cell membrane ionic pumps become depressed. When this occurs sodium ions can no longer be pumped out of the cells, and the excess sodium ions inside the cells cause osmosis of water into the cells.
Intracellular edema can also occur in inflamed
tissues.

Extracellular Edema

causes of extracellular edema:
(1)abnormal leakage of fluid from the plasma to the interstitial spaces(Increase Capillary Filtration)

(2) failure of the lymphatics to return fluid from the interstitium back into the blood.

The rise in protein concentration raises the colloid osmotic pressure of the interstitial fluid, which draws even more fluid out of the capillaries

Fluids in the “Potential Spaces”

pleural cavity, pericardial cavity, peritoneal cavity, and synovial cavities all these potential spaces have surfaces that almost touch each other, with only a thin layer of fluid in between.
Edema Fluid in the Potential Spaces Is Called “Effusion” its due to lymphatic obstruction

The general clinical terms for volume abnormalities are dehydration and over hydration. Both conditions are associated with a change in ECF volume