இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.
Physiology
Human Blood
Blood is the main circulatory medium in the human body.
It is a red colored fluid connective tissue.
Components of Blood:
The blood consists of two main components. The fluid plasma (fluid
matrix) and the formed elements (blood cells) which are found
suspended in the plasma.
The plasma constitutes 55% of the total blood volume. The remaining
45% is the formed elements that consist of blood cells.
The average blood volume is about 5000ml (5L) in an adult weighing 70
Kg.
Formed Elements of Blood:
Blood corpuscles are of three types
Red blood corpuscles (RBC) or Erythrocytes
White blood corpuscles (WBC) or Leucocytes
Blood platelets or Thrombocytes.
Plasma:
It is slightly alkaline, containing non-cellular substance which constitutes
about 55% of the blood.
Plasma mainly consists of water (80-92%) in which the plasma proteins,
inorganic constituents (0.9%), organic constituents (0.1%) and respiratory
gases are dissolved.
The four main types of plasma proteins synthesized in the liver are
albumin,
globulin,
prothrombin and
fibrinogen.
Albumin maintains the osmotic pressure of the blood.
Globulin facilitates the transport of ions, hormones, lipids and assists in
immune function.
Both Prothrombin and Fibrinogen are involved in blood clotting.
Organic constituents include urea, amino acids, glucose, fats and vitamins.
The inorganic constituents include chlorides, carbonates and phosphates of
potassium, sodium, calcium and magnesium.
The composition of plasma is not always constant.
The concentration of the glucose in the blood gradually falls after sometime
as most of the glucose is absorbed.
If too much of protein is consumed, the body cannot store the excess amino
acids formed from the digestion of proteins.
The liver breaks down the excess amino acids and produces urea.
Blood in the hepatic vein has a high concentration of urea than the blood in
other vessels namely, hepatic portal vein and hepatic artery.
Blood Cells:
Red blood corpuscles (Erythrocytes):
They are the most abundant cells in the human body. RBCs are formed in
the bone marrow.
The RBCs impart red colour to the blood due to presence of respiratory
pigment haemoglobin.
Matured mammalian RBCs do not have cell organelles and nucleus.
They are biconcave and disc shaped.
Their life span is about 120 days. RBC is involved in the transport of
oxygen from lungs to tissues.
White blood corpuscles (Leucocytes):
WBC’s are colourless.
They do not have haemoglobin and are nucleated cells.
It is found in the bone marrow, spleen, thymus and lymph nodes.
They are capable of amoeboid movement
The white blood corpuscles can be grouped into two categories:
Granulocytes
Agranulocytes
Granulocytes:
They contain granules in their cytoplasm.
Their nucleus is irregular or lobed.
The granulocytes are of three types
Neutrophils
Eosinophils
Basophils
(i) Neutrophils:
They are large in size and have a 2 – 7 lobed nucleus.
These corpuscles form 60% – 65% of the total leucocytes.
Their numbers are increased during infection and inflammation.
(ii) Eosinophils:
It has a bilobed nucleus and constitute 2% – 3% of the total leucocytes.
Their number increases during conditions of allergy and parasitic
infections.
It brings about detoxification of toxins.
(iii) Basophils:
Basophils have lobed nucleus.
They form 0.5% – 1.0% of the total leucocytes.
They release chemicals during the process of inflammation.
Agranulocytes:
Granules are not found in the cytoplasm of these cells. The agranulocytes are
of two types:
Lymphocytes
Monocytes
(i) Lymphocytes
These are about 20-25% of the total leucocytes.
They produce antibodies during bacterial and viral infections.
(ii) Monocytes
They are the largest of the leucocytes and are amoeboid in shape.
These cells form 5 – 6 % of the total leucocytes.
They are phagocytic and can engulf bacteria.
Blood Platelets or Thrombocytes
Platelets are also called thrombocytes that are produced from
megakaryocytes (special cells in bone marrow)
These are small and colourless. They do not have nucleus.
Life span of platelets is 8–10 days.
There are about 2,50,000 – 4,00,000 platelets / cubic mm of blood.
They secrete substances involved in coagulation or clotting of blood.
The reduction in platelet number can lead to clotting disorders that result in
excessive loss of blood from the body.
They play an important role in clotting of blood. Platelets form clot at the
site of injury and prevent blood loss.
Functions of blood
1. Transport of respiratory gases (Oxygen and CO2).
2. Transport of digested food materials to the different body cells.
3. Transport of hormones.
4. Transport of nitrogenous excretory products like ammonia, urea and uric
acid.
5. It is involved in protection of the body and defense against diseases.
6. It acts as buffer and also helps in regulation of pH and body temperature.
7. It maintains proper water balance in the body.
Coagulation of blood
The mechanism by which excessive blood loss is prevented by the formation
of clot is called blood coagulation or clotting of blood.
The clotting process begins when the endothelium of the blood vessel is
damaged and the connective tissue in its wall is exposed to the blood.
Platelets adhere to collagen fibres in the connective tissue and release
substances that form the platelet plug which provides emergency
protection against blood loss.
Clotting factors released from the clumped platelets or damaged cells mix
with clotting factors in the plasma.
The protein called prothrombin is converted to its active form called
thrombin in the presence of calcium and vitamin K.
Thrombin helps in the conversion of fibrinogen to fibrin threads.
The threads of fibrins become interlinked into a patch that traps blood cell
and seals the injured vessel until the wound is healed.
After sometime fibrin fibrils contract, squeezing out a straw coloured
fluid through a meshwork called serum (Plasma without fibrinogen is
called serum)
Heparin is an anticoagulant produced in small quantities by mast cells of
connective tissue which prevents coagulation in small blood vessels.
Types of Blood Group:
The concept of blood grouping was developed by Karl Landsteiner (1900).
He identified blood groups A, B and O.
AB blood group was recognized by Decastello and Steini (1902).
Human blood contains certain specific substances called agglutinogens or
antigens (Ag) and agglutinins or antibodies
(Ab).
Antigens are found on the membrane surface of RBC.
Antibodies are present in blood plasma.
Based on the presence or absence of antigen and antibodies human blood
group is classified into f our groups called A, B, AB and O.
An individual has one of the four blood groups.
1. ‘A’ group individuals: Antigen A is present on the surface of RBC and
antibody b (anti-b) is present in the plasma.
2. ‘B’ group individuals: Antigen B is present on the surface of RBC and
antibody a (anti – a) is present in the plasma.
3. ‘AB’ group individuals: Antigens A and B are present on the surface
of RBC And both the antibodies are absent in the plasma.
4. ‘O’ group individuals: Antigen A and B are absent on the surface of
RBC. However, the plasma contains both the antibodies a and b (anti a
and b).
Blood Group Antigens on
RBC
Antibodies in Plasma Can donate to Can receive from
A Antigen A anti- b A and AB A and O
B Antigen B anti- a B and AB B and O
AB Antigen A and B No antibody AB A, B, AB and O
(Universal
Recipient)
O No Antigen Both anti a and b A, B, AB and O
(Universal Donor)
O
Blood donation:
In blood transfusion one must consider the antigen and antibody
compatibility (matching) between the donor and the person receiving
blood (recipient).
When an individual receives a mismatched blood group from the donor
agglutination (clumping) of blood occurs in the body which leads to
death.
Persons with ‘AB’ blood group are called ‘Universal Recipient’ as they
can receive blood from persons with any blood group.
Persons with ‘O’ blood group are called ‘Universal Donor’ as they can
donate blood to persons with any blood group.
Rh-factor:
Rh factor is a protein (D antigen) present on the surface of the red blood
cells in majority (80%) of humans.
This protein is similar to the protein present in Rhesus monkey, hence the
term Rh.
Individuals who carry the antigen D on the surface of the red blood cells
are Rh+ (Rh positive) and the individuals who do not carry antigen D, are
Rh- (Rh negative).
Rh factor compatibility is also checked before blood transfusion.
When a pregnant women is Rh- and the foetus is Rh+ incompatibility
(Mismatch) is observed.
But during subsequent pregnancies the Rh antibodies from the mother Rh-
enters the foetal circulation and destroys the foetal RBCs.
This becomes fatal to the foetus because the child suffers from anaemia and
jaundice.
This condition is called erythroblastosis foetalis.
This condition can be avoided by administration of anti D antibodies (
Rhocum) to the mother immediately after the first child birth.
Blood Vessels
The vessels carrying the blood are of three types; they are
1. The arteries
2. Veins and
3. Capillaries.
These vessels are hollow structures and have complex walls surrounding the
lumen.
The blood vessels in humans are composed of three layers
1. Tunica intima
2. Tunica media
3. Tunica externa.
Arteries
The blood vessels that carry blood away from the heart are called arteries.
The arteries usually lie deep inside the body.
The walls of the arteries are thick, non-collapsible to withstand high
pressure.
All arteries carry oxygenated blood, except the pulmonary artery.
The largest artery, the aorta branch into smaller arteries and culminates into
the tissues as feed arteries.
Capillaries
Capillary beds are made up of fine networks of capillaries.
The capillaries are thin walled and consist of single layer of squamous
epithelium.
The capillary beds are the site for exchange of materials between blood and
tissues.
The walls of the capillaries are guarded by semilunar valves.
Mixed blood (oxygenated and deoxygenated) is present in the capillaries.
Veins
Veins have thinner walls and a larger lumen and hence can be easily
stretched.
They carry deoxygenated blood except, the pulmonary vein.
Unidirectional flow of blood in veins is due to the presence of semilunar
valves that prevents backflow of blood.
Blood samples are usually taken from the veins rather than artery because of
low pressure in the veins.
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