FUNCTIONS OF BLOOD
1.
NUTRITIVE FUNCTION
Nutritive substances
like glucose, amino acids, lipids and vitamins derived from digested food are
absorbed from gastrointestinal tract and carried by blood to different parts of
the body for growth and production of energy.
2.
RESPIRATORY FUNCTION
Transport of
respiratory gases is done by the blood. It carries oxygen from alveoli of lungs
to different tissues and carbon dioxide from tissues to alveoli.
3.
EXCRETORY FUNCTION
Waste products formed
in the tissues during various metabolic activities are removed by blood and
carried to the
excretory organs like kidney, skin, liver, etc. for excretion.
4.
TRANSPORT OF HORMONES AND ENZYMES
Hormones which are secreted
by ductless (endocrine) glands are released directly into the blood. The blood transports
these hormones to their target organs/tissues. Blood also transports enzymes.
5.
REGULATION OF WATER BALANCE
Water content of the blood
is freely interchangeable with interstitial fluid. This helps in the regulation
of water content of the body.
6.
REGULATION OF ACID-BASE BALANCE
Plasma proteins and
hemoglobin act as buffers and help in the regulation of acid-base balance.
7.
REGULATION OF BODY TEMPERATURE
Because of the high
specific heat of blood, it is responsible for maintaining the thermoregulatory
mechanism in the body, i.e. the balance between heat loss and heat gain in the
body.
8.
STORAGE FUNCTION
Water and some important
substances like proteins, glucose, sodium and potassium are constantly required
by the tissues. Blood serves as a readymade source for these substances. And,
these substances are take from blood during the conditions like starvation,
fluid loss, electrolyte loss, etc.
9.
DEFENSIVE FUNCTION
Blood plays an important
role in the defense of the body. The white blood cells are responsible for this
function. Neutrophils
and monocytes engulf the bacteria by phagocytosis. Lymphocytes are involved in
development of immunity.
Eosinophils are responsible for detoxification, disintegration and removal of
foreign proteins
PROPERTIES OF BLOOD
1. Color: Blood
is red in color. Arterial blood is scarlet red because it contains more oxygen
and venous
blood is purple red
because of more carbon dioxide.
2. Volume: Average
volume of blood in a normal adult is 5 L. In a newborn baby, the volume is 450
ml. It
increases during
growth and reaches 5 L at the time of puberty. In females, it is slightly less
and is about
4.5 L. It is about 8%
of the body weight in a normal young healthy adult, weighing about 70 kg.
3. Reaction and pH: Blood
is slightly alkaline and its pH in normal conditions is 7.4.
4. Specific
gravity:
Specific gravity of
total blood : 1.052 to 1.061
Specific gravity blood
cells : 1.092 to 1.101
Specific gravity of
plasma : 1.022 to 1.026
5. Viscosity:
Blood is five times more viscous than water. It is mainly due to red
blood cells and plasma
proteins.
BLOOD CELLS
Three types of cells
are present in the blood:
1. Red blood cells or
erythrocytes
2. White blood cells
or leukocytes
3. Platelets or
thrombocytes.
Hematocrit Value
If blood is collected
in a hematocrit tube along with a suitable anticoagulant and centrifuged for 30
minutes at a speed of 3000 revolutions per minute (rpm), the red blood cells
settle down at the bottom having a clear plasma at the top. Plasma forms 55%
and red blood cells form 45% of the total blood. Volume of red blood cells expressed
in percentage is called the hematocrit value or packed cell volume (PCV). In
between the plasma and the red blood cells, there is a thin layer of white
buffy coat. This white buffy coat is formed by the aggregation
of white blood cells and platelets.
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