Archive for the ‘ Obj Ten-Body Fluid ’ Category

Obj 10-Volume & Composition of Body Fluid

Basic info about body fluid

-60% of total body weight

=in 70 kg body weight , about 42 lit body fluid

-↑ fat % , ↓ water %

=thus,women contain less water (as more fat)

Distribution of Body Fluid


Extra cellular fluid (ECF):-

It is about 14 liters:

  • Plasma 3 liters
  • Interstial fluid in spaces between cells 10 L
  • Transcellular 1-2liters.

↓→Intra ocular space

↓→Synovial , peritoneal , pericardial spaces

↓→Cerebrospinal fluid

Intra cellular fluid (ICF) :-

-Equal 28 liters.

-It is the fluid inside the cells.

-It contains high Concentration of K &less concentration of Na.

-Also it contains large amount of magnesium and phosphate


-Is to keep the internal environment constant.

-To keep the ECF constant.

-The distribution of fluid between plasma and interstial space is determined by two force across the cell membrane.

-That’s it the hydrostatic pressure and colloid osmotic pressure of plasma protein.

-The distribution of fluid between  IC &EC compartment is determined mainly by osmotic effect of solutes e.g. Na, CL and other electrolytes acting on cell membrane


-Osmosis and osmotic pressure:-

  • It is  the diffusion of water through a semi-permeable membrane.
  • The movement of water molecules from an area of high water conc to area of low water conc
  • Osmotic pressure is the pressure required to prevent osmosis.
  • Increased osmotic pressure means excess solutes and less water.
  • The average extracellular fluid osmolarity is (280-295)meq/l.
  • It is determined by its water and  electrolytes mainly Na


  • Osmotic equilibrium
  1. Isotonic solution – The water concentration in IC&ECF is equal and  solutes can not enter or leave the cell.
  2. Hypotonic solution – There are less solutes less osmotic pressure so water enter the cell and it swell.
  3. Hypertonic solution – High solutes ,high osmotic pressure so water leave the cell and cell shrink. Solution of NaCL 0.9%and glucose 5% are isotonic so it is important in clinical medicine  because the cell neither swell nor shrink.

Picture4Body water

Daily intake of water (by two main sources):

  • Ingested in the form of water or liquid which add about 2100ml/day to the body fluid
  • Synthesized as a result of metabolism and it is about 200ml/day.

Daily loss of  body   water:

  • Evaporation 700ml
  • Urine 1400 ml
  • Sweat 100 ml
  • Feces 100ml


Regulation of ECF volume

-The kidney plays a major role in the maintenance of body sodium and water content.

-Na account for more than 90%of all osmoticaly  active ECF solutes  so the amount of Na is the major determinant of the ECF volume.

-Regulation of water occurs  by:

  • Anti diuretic hormone(ADH)
  • Thirst sensation

Sodium Regulation

-Normal serum sodium 140 m Eq/L.

-1mEq of Na =23mg.

-Function of sodium:

  • Regulation of ECF so it essential to maintain blood volume and A.B.P
  • It is essential for normal tissue excitability.
  • It forms important buffer salt (NaHCO3).
  • It is important for glucose absorption.
  • cause of renal medullary hyperosmolarity.
  • It is the main extracellular cation

-Factors affecting Na Reabsorption & Excretion:

  1. Glomerular filtration rate (GFR): increased GFR will increase Na filtration and this increase the amount of Na reabsorbed leading to increase in Na excretion.
  2. ECF volume: when it increase it will lead to increase Na excretion (naturiuresis).
  3. Aldosterone hormone: -Secreted from suprarenal gland and helps reabsorption of Na and secretion of K from the distal convoluted tubules and collecting duct.
  4. Atrial naturiuretic peptide: This hormone increases sodium excretion
  5. Angiotensin: Results from angiotensinogen by the action of renin.
  6. Estrogen hormone : leads to salt and water retention in the body.
  7. Diuretic drugs.

Picture2Water Balance

-Is maintained in the body by adjusting water input and water output.

-Control of water input:Picture3

  • Stimulated by thirst sensation.
  • Thirst sensation occurs as a result of:
  1. Hypertonicity
  2. Hypovolemia

-Control of water loss

  • It is controlled by controlling the volume of urine.
  • Volume of urine is controlled by (ADH)
  • Anti- diuretic hormone (ADH):
  1. Synthesized in the hypothalamus.
  2. Stored in the posterior pituitary until it is secreted.
  3. Secretion is stimulated by hypertonicity and hypovolemia.