composition and function of blood

1. By-
Dr. Naushi Mujeeb
Professor, dept of physiology

2. Learning objectives-
At the end of this lecture, the learner should be able
to:-
1. Describe Composition of blood.
2. Describe the function of plasma proteins.
3. Applied aspect of this topic.
2

3. • Composition of Blood-
• Total blood volume: 5-6 lit(
8% of body weight or
80ml/kg body weight)
• Specific gravity: 1050-1060
• Viscosity: 4-5 times that of
water.
• Ph: 7.4± 0.05; alkaline

4. • If anticoagulated sample of
blood is allowed to stand in a
narrow tube, on settling it
separates out into cells and
plasma.

5. • A. Cells-
• The cellular elements of blood
represents 45% of the total
blood volume, called Packed
Cell Volume(PCV) or
Haematocrit. It includes:
• Erythrocytes or RBCs-
normal count: 5 million/µl
(5x106).

6. • Leucocytes or White Blood
Corpuscles(WBCs)-
• Normal count: 4,000-
11,000/µl
• Platelats or Thrombocytes
• Normal count: 1.5-4 lacs/µl

7. • Plasma & Plasma Proteins-
• Plasma is the clear straw coloured
fluid (with dissolved solid substances)
portion of the blood minus its cellular
elements.
• It constitutes about 55% of the blood
volume (about 5% of body weight).
• Composition-
• Plasma contains the following
constituents:
• Water. Water is the main constituent
of plasma forming 91% of it.
• Solids. The solids dissolved in the
plasma constitute a total of 9% of the
plasma.

8. • The solid constituents of
plasma are given below:
• Plasma proteins form 7% of the solids in
plasma. Their normal value ranges from
6.4 to 8.3 g/dl. They include albumin,
globulins, fibrinogen and others.
• Other organic molecules which form 1%
of the solids include the following:
• Carbohydrates, mainly glucose (100–120
mg/dl).
• Fats are neutral fats (30–150 mg/dl),
phospholipids (150–300 mg/dl) and
cholesterol (150–240 mg/dl).

9. • Non-protein nitrogenous substances (28–40 mg/dl) are ammonia
(traces), amino acids, creatine (1–2 mg/dl), creatinine (0.6–1.2
mg/dl), xanthine (traces), hypoxanthine (traces), urea (20–40 mg/dl)
and uric acid (2–4 mg/dl).
• Hormones, enzymes and antibodies.
• Inorganic substances Which constitute 1% of the solids in plasma
include sodium, potassium, calcium, magnesium, chloride, iodide,
iron, phosphates and copper.

10. • Gases- present in the plasma are oxygen, carbon dioxide and
nitrogen.
• Serum-
• Plasma from which fibrinogen and clotting factors (II, V and VIII)
have been removed is called serum.
• Serum is formed when the blood is allowed to clot in a test tube
and the clot is retracted. Serum has a higher serotonin (5HT)
content because of the breakdown of platelets during clotting.

11. • PLASMA PROTEINS-
• Classification of plasma proteins-
• Plasma proteins form the major solid constituent of the plasma. The
total plasma protein concentration is 7.4 g/dl (ranges from 6.4 to
8.3 g/dl).

12. • The important fractions of plasma
proteins are given as:
• 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).
• PROPERTIES OF PLASMA PROTEINS-
1. Molecular weight- plasma proteins are
large molecules with the following molecular
weight:
• Albumin: 69,000, globulins: from 90,000
to 1,56,000 and fibrinogen: 5,00,000.
• Thus the fibrinogen has got highest
molecular weight.

13. 2. Osmotic pressure- the plasma proteins exert an oncotic pressure of
about 25 mm hg.
3. Specific gravity- the specific gravity of plasma proteins is 1.026.
4. Isoelectric point- proteins can ionize either as acids or as bases
owing to the fact that the side chains of their constituent amino acids
contain a selection of amino group (NH2) and carboxyl groups (–
COOH).
5. Electrophoretic mobility- the proteins act as anions in alkaline
solutions and as cations in acidic solutions. Because of this property
they possess electrophoretic mobility.

14. 6. Precipitation by salts- proteins can be precipitated by different
concentrations of salts. This property of proteins is utilized for their
separation by the precipitation method.
7. Water solubility. The protein molecules are soluble in water because
of the presence of polar residues like NH2 and COOH.
8. Amphoteric nature. Protein molecules are amphoteric in nature
because of the presence of NH2 and COOH groups. By virtue of their
amphoteric nature the plasma proteins act as efficient buffers.

15. FEATURES OF INDIVIDUAL FRACTION OF PLASMA PROTEINS-
1. Albumin-
• Plasma levels are 4.8 g/dl (range 3–
5 g/dl).
• Molecular weight of prealbumin is
60,000 and of albumin is 69,000.
• Synthesized in liver.
• Half-life is about 10 days.
• Controls colloidal osmotic pressure
• It helps in transport of anions,
cations, dyes, drugs, hormones,
fatty acids, amino acids, enzymes
and bilirubin.

16. 2. Globulins-
• Plasma levels are 2.3 g/dl
(range 2 to 3 g/dl).
• Molecular weight varies from
90,000 to 156,000.
• Types include α1, α2, β1, β2
and γ globulins.

17. Forms of globulins are described below-
• Glycoproteins- consist of carbohydrates and
protein.
• Lipoproteins- consist of α2 globulin and lipids.
• It has got the following subtypes:
• – High density lipoproteins (HDL)- these are α
lipoproteins which contain 50% protein with
large amount of cholesterol and phospholipids.
HDL removes excess cholesterol from body cells
& the blood & transports it to the liver for
removal. A high HDL level is associated with
decreased risk of coronary artery diseases(cad).
For this reason HDL cholesterol is called “good
cholesterol”.

18. • – Low density lipoproteins (LDL)- these are β lipoproteins and
contain large amount of glycerides. It is used in repair of cell
membranes and synthesis of steroid hormones and bile salts. When
present in excess, it gets deposited in arteries forming fatty plagues
that increases the risks of coronary artery disease. For this reason,
LDL cholesterol is called “bad cholesterol”.
• – Very low density lipoproteins(vldl)- these are also β lipoproteins
and have higher proportion of fat in the form of triglycerides or
cholesterol.
• – Chylomicron contains 98% triglycerides and 2% protein. It is
synthesized in the intestine following a meal.

19. • HDL levels are increased in individuals
who exercise whereas they are
deceased in smokers, obese and
sedentary workers.
• In healthy individuals, proportion of
HDL is high but in coronary artery
diseases(CAD) patients, proportion of
β-lipoproteins(LDL & VLDL) increases.
• Lipoproteins are used in lipid
metabolism & increases in-
• Atherosclerosis
• Obesity and
• Liver diseases.

20. TYPES OF PLASMA PROTEINS AND THEIR
FUNCTIONS
ALBUMIN GLOBULIN FIBRINOGEN
Colloidal Osmotic Pressure Lipoproteins- HDL, LDL,
VLDL
Clotting Protein
Transferrin
Haptoglobin
Ceruloplasmin
Fetuin
Immunoglobin

21. • Transferrin-
• It has the specific property of iron binding.
• Functions-
• Regulates & controls iron absorption from GIT
• Protects against iron intoxication.
• Helps in iron transport.
•

22. • Haptoglobin-
1. It forms stable complexes with free haemoglobin.
2. Protects the kidney from damage by Hb.
Ceruloplasmin
• It binds with copper and helps in its transport and storage.
• Its deficiency causes Wilson’s disease (hepatolenticular
degeneration), in which liver and brain are damaged due to high
levels of free copper.
• Fetuin- is a growth promoting protein present in foetus and
newborns.
• Immunoglobulins(Ig)- are γ globulins which play role in
immunity.

23. 3. Fibrinogen-
Molecular weight is 500,000. Synthesized in the liver.
Chemical structure-
Protein part of the molecule is made up of six polypeptide chains
(α2, β2, γ2) joined by disulphide bonds.
Functions as a clotting protein.

24. • FUNCTIONS OF PLASMA PROTEINS-
• 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 pressure is contributed by the
albumin fraction.

25. 2. Contribution to blood viscosity- Fibrinogen and globulins are
significant contributors to blood viscosity. 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, prothrombin and
other coagulation proteins present in the plasma play an
important role in the coagulation of blood.

26. 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.

27. 6. Transport function- Plasma proteins combine easily with many
substances and play an essential role in their transport as explained
below:
a) Thyroxine is transported by an α globulin called thyroxine binding
protein.
b) Cortisol is transported by transcortin which is a mucoprotein.
c) Vitamin A, D and E are transported by the high and low density
lipoproteins (HDL and LDL).
d) Vitamin B12 is bound to transcobalamin for transport.
e) Drugs of various types are transported after combining with the
albumin.
7. Fibrinolytic function- The enzymes of the fibrinolytic system digest the
intravascular clot (thrombus) and thus save from the disastrous effects of
thrombosis.

28. • SYNTHESIS OF PLASMA PROTEINS-
• Site of synthesis-
• In embryo, the plasma proteins are synthesized by the
mesenchymal cells. First, the albumin is produced and then the
other proteins are synthesized.
• In adults, plasma proteins are synthesized as described below:
• The albumin and fibrinogen are synthesized mostly by the
reticuloendothelial cells of the liver.
• α and β globulins are synthesized by the liver, spleen and bone
marrow.
• γ globulins are synthesized by the B lymphocytes.

29. • Abnormalities of plasma protein levels-
• Hypoproteinaemia- Hypoproteinaemia refers to generalized
decrease in the levels of plasma proteins.
• Causes of hypoproteinaemia include the following:
• Dietary deficiency and starvation.
• Liver diseases like hepatitis and cirrhosis
• Renal diseases like nephrotic syndrome
• Haemorrhage and extensive burns

30. • Effects of hypoproteinaemia-
• Low levels of plasma proteins are associated with a decrease in
the plasma osmotic pressure.
• Colloidal osmotic pressure(COP) due to plasma colloids is called
oncotic pressure.
• Increased filtration occurs at the arterial end and decrease in
absorption of fluids occur at the venous end, resulting in
abnormal collection of fluids in the interstitial spaces called
Oedema.

31. • Starling forces
• COP across the capillary wall helps
to maintain the exchange of fluids
at tissue level.
• The rate of exchange of fluids at any
point along the capillary depends
upon a balance of forces called the
Starling forces, which are-
a)Hydrostatic pressure across
capillary wall-
b)COP across capillary wall-
c) Hydrostatic pressure in interstitial
fluid-
d) Osmotic pressure of interstitial
fluid.

32. • Hyperproteinaemia-
• Hyperproteinaemia, i.e. increase in the plasma protein levels, is
seen in following conditions:
• Acute inflammatory conditions are associated with increased
synthesis of the so-called acute phase proteins which include C-
reactive proteins, α antitrypsin, haptoglobin, fibrinogen and
ceruloplasmin.
• Chronic inflammation and malignancies are also associated with
raised levels of C-reactive proteins.
• Multiple myeloma is associated with increased levels of the so-
called Bence Jones proteins.

33. • Reversal of normal A/G ratio-
• The normal albumin: globulin (A/G) ratio (1.7:1) is reversed in the
following conditions:
• When the albumin synthesis is decreased as occurs in liver
diseases (globulin levels being normal because many globulins are
synthesized by the B lymphocytes).
• When the globulin levels are increased (as occurs in most of the
conditions) associated with hyperproteinaemia.

34. • SUMMARY-
This lecture consisted of discussion of –
1. Composition of blood.
2. Plasma proteins and their functions.
3. Applied aspects related to this topic.

35. • END