THE BLOOD

[Pages:197]THE BLOOD

BLOOD

? One of the largest organs of the body. ? An average 70 kg man has almost 5L

blood (5.5 kg). ? Blood circulates throughout the body

and supports the functions of all other body tissues.

Blood integrates tissues and organs

and provide a special means of communications.

THE FUNCTIONS OF BLOOD

? Respiration: transport of O2 and CO2. ? Transport: hormone, nutrients, metabolic waste. ? Excretion of metabolic wastes to the kidney, lungs

and skin. ? Regulation of body temperature by distribution of

body heat. ? Defense against infections (WBCs, antibodies). ? Maintenance of acid-base balance. ? Nutrition: transport of absorbed food material.

PHYSICAL PROPERTIES OF BLOOD

? Specific gravity:

- Whole blood:

1.055 - 1.065

- Plasma:

1.024 - 1.028

? Viscosity:

5-6 times that of water.

? Mass:

6-8% of the body weight.

? Blood volume:

~ 8% of body weight.

~ 86% ml/kg body weight.

5-6L in adults

[Infants have a larger blood volume in proportion to

body weight than adults].

? Osmotic pressure: 7-8 atmosphere at body temperature.

Composition of Blood

? Formed Elements (45%),

i- Red blood cells (erythrocytes).

ii- White blood cells (leukocytes).

iii- Platelets

(thrombocytes)

? Fluid medium i.e. the plasma (55%).

Gross composition of Plasma and Blood Cells

Constituents Water Solid Protein Specific gravity

Plasma

Red blood cells

91-95%

65%

8-9 %

35%

6-8 gm %

31-33%

1.026

Haematocrit or Packed Cell Volume (PCV)

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