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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.


Formation of Hydrogen Bonds & its Importance

Formation Hydrogen Bonds

-attractive force between one electronegative atom and a hydrogen covalently bonded to another electronegative atom

-results from a dipole-dipole force with a hydrogen atom bonded to nitrogen, oxygen or fluorine (thus the name “hydrogen bond”, which must not be confused with a covalent bond to hydrogen.


How are they formed??

A hydrogen bond is formed when a charged part of a molecule having polar covalent bonds forms an electrostatic (charge, as in positive attracted to negative) interaction with a substance of opposite charge. Molecules that have non-polar covalent bond do not form hydrogen bonds.


Hydrogen bonds are classified as weak bonds because they are easily and rapidly formed and broken under normal biological conditions.

What classes of compounds can form hydrogen bonds?

Under the right environmental conditions, any compound that has polar covalent bond can form hydrogen bonds.


Hydrogen bonds are extremely important in biological systems. Thier presence explains many of the properties of water. They are used to stabilize and determine the structure of large macormolecules like proteins and nucleic acids. They are involved in the mechanism of enzyme catalysis

Obj 8-ATP as energy currency of the body


Metabolism: sum of all energy-requiring biochemical reactions

Catabolic pathways:  degradative process such as cellular respiration; releases energy

Anabolic pathways:  building process such as protein synthesis; photosynthesis; consumes energy


Energy Coupling & ATP

E coupling:  use of exergonic process to drive an endergonic one Adenosine triphosphate (ATP)

ATP hydrolysis:  release of free E

Phosphorylation (phosphorylated intermediate)~ enzymes