Question

The blood contains numerous components, each with its own function:

Choose a component of the blood, and describe its role in the body.

Your response should be a minimum of 100 words,

with in-text citations and references.  In addition, please respond to at least

two other students to add information, present another point of view, or ask questions.

Answer 1

Blood has two components :plasma and cellular elements.

Plasma proteins form the major solid constituent of the
plasma.  
   Albumin (4.8 g/dL),
Globulins (2.3 g/dL) include:
– α1 globulin
– α2 globulin
– β globulin and
– γ globulin
Fibrinogen (0.3 g/dL).

1. Exert osmotic pressure. The protein molecules are unable
to pass across the capillary membrane and consequently
exert colloid osmotic pressure of about 25 mm Hg on the
capillary membrane. About 70–80% of the osmotic pres-
sure is contributed by the albumin fraction. The colloid
osmotic pressure plays an important role in exchange of
water between the blood and tissue fluid.

2. Contribution to blood viscosity. Fibrinogen and globulins
are significant contributors to blood viscosity because of
their asymmetrical shape. The blood viscosity plays an
important role in the maintenance of blood pressure by
providing resistance to flow of blood in blood vessels.

3. Role in coagulation of blood. The fibrinogen, pro-
thrombin and other coagulation proteins present in the
plasma play an important role in the coagulation of
blood.

4. Role in defence mechanism of the body. The γ globulins
are antibodies which play an important role in the immune
system meant for defence of the body against the
microorganisms.

5. Role in maintaining acid–base balance of the body.
Plasma proteins act as buffers and contribute for about
15% of the buffering capacity of blood. Because of their
amphoteric nature, plasma proteins can combine with acids
and bases as explained below:
In acidic pH, the NH2 group of the proteins acts as base
and accepts proton and is converted to NH4.
In alkaline pH, the COOH group of the proteins acts
as acid and can donate a proton and thus becomes
COO−.
At normal pH of blood, proteins act as acids and com-
bine with cations (mainly sodium)

6. Transport function. Plasma proteins combine easily with
many substances and play an essential role in their trans-
port as explained below:
Carbon dioxide is transported by the plasma proteins in
the form of carbamino compound.
Thyroxine is transported by an α globulin called thyroxine-
binding protein.
Cortisol is transported by transcortin which is a
mucoprotein.
Vitamin A, D and E are transported by the high and low
density lipoproteins (HDL and LDL).
Vitamin B12 is bound to transcobalamin for transport.
Bilirubin is associated with albumin and also with
fractions of the α globulin.
Drugs of various types are transported after combining
with the albumin.
Calcium of the plasma is partly (50%) bound to the
proteins for transport.
Copper is bound to ceruloplasmin (α2 globulin) for
transport.
Free haemoglobin in the vessels is bound by haptoglobin
and carried to reticuloendothelial system.

7. Role as reserve proteins. Plasma proteins serve as
reserve proteins and are utilized by the body tissues during
conditions like:
Fasting,
Inadequate protein intake and
Excessive catabolism of body proteins.

8. Role in suspension stability of RBCs. Suspension stability refers to the property of RBCs by virtue of which they remain uniformly suspended in the blood. Globulins and fibrinogen accelerate this property.

9. Fibrinolytic function. The enzymes of the fibrinolytic sys-
tem digest the intravascular clot (thrombus) and thus save
from the disastrous effects of thrombosis.

10. Role in genetic information. Many plasma proteins
exhibit polymorphism. Polymorphism is a Mendelian trait
that exists in the population with differing prevalence.

11. Role of nourishment of tissue cells. The plasma proteins
are utilized by the leucocytes to produce the substances
known as trephones or carrel which are essential for the
nourishment of tissue cells.