Essay on Human Blood Group (1960 Words)
Blood groups are created by protein molecules called antigens, present on the surface of red blood cells.
These antigens are complex chemical substances found on the surface of red blood cells and are different for each blood group.
Blood groups are the special characteristics of blood in human and related primates due to the presence of genetically controlled antigens and antibodies.
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Blood can be classified by the antibodies with which it will react, and such classification is essential for transfusion. More than 20 different blood group systems are recognized in medicine. Of these, the best known are the ABO system and the Rh system.
In 1900, Dr. Karl Landsteiner discovered the A, B and O groups, and in 1902 the fourth main type, AB was found by Decastrello and Sturli.
There are many more types of blood groups present in humans, but are clinically insignificant eg. Duffey’s blood group.
The ABO Blood Groups:
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The ABO blood groups were the first to be discovered and are the most important in assuring safe blood transfusions. The antigens of the ABO system are in integral part of the red cell membrane and of all the cells throughout the body.
They are also found in plasma and other body fluids. These soluble antigens are respectively A, B and H. The H antigen is a precursor to the A and B antigens, but is not expressed as a recognizable antigen on red blood cells.
The table shows the four ABO phenotypes (“blood groups”) present in the human population and the genotypes that give rise to them.
Blood Transfusion:
To transfuse blood from one individual to another, the blood types of both must be known to be able to mix safely, that is, to be compatible. The mixing of unsafe or incompatible blood may lead to very serious or possibly fatal transfusion reactions.
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The problem occurs when the protein outer layer of the red corpuscles of the donor becomes “sticky” when introduced into antagonistic plasma of the recipient.
The “sticky” red blood cells clump together and block the vessels of the patient. This clumping of blood cells is called Agglutination.
The plasma proteins concerned in agglutination are antibodies called agglutinins, while the proteins in the walls of the corpuscles are antigens, called agglutinogens. So,
i. Group A blood, with A antigens, can safely be given to group A people, but it can also be given to group AB people, because they have no anti-red-cell antibodies at all.
ii. Group B blood, with B antigens, is safe for group B and group AB recipients, for the same reason.
iii. Group AB blood, with both A and B antigens, can be given safely only to group AB people.
iv. Group O blood, with no antigens, can be given to anyone.
Rh factor:
There are several other proteins in the blood that may bring about agglutination under certain conditions.
The most important of these is the Rh factor, which likes the blood type, is an inherited characteristic that is 2 parents are Rh +ve, and then the children must have Rh +ve blood. The letters “Rh” are used since this factor was first studied in the rhesus monkey.
The Rhesus (Rh) system:
The Rhesus (Rh) system is the most important of the other blood group systems. It was discovered by Landsteiner and Weiner in 1940.
Their experiment was to produce an antibody to the red cells of the Rhesus monkey in rabbits and guinea pigs, but they discovered that not only did the antibody in the rodents’ serum agglutinate the Rhesus monkeys red cells; it also agglutinated the red cells of 85% of the human population.
If an individual’s red cells were agglutinated by this antiserum, they were said to have the Rhesus factor on their red cells (i.e. Rh positive). If an individual’s cells were not agglutinated by the antiserum, they were said to lack the Rhesus factor (i.e. Rh negative).
Haemolytic disease of the newborn (HDN) – The commonest cause of HDN is maternal al loimmunisation (immunity arising from the mothers body itself), possibly ABO incompatibility, but most cases of clinically severe HDN within the past 40 years have been associated with Rh incompatibility.
Rh negative blood does not usually contain rhesus antibodies in its plasma. So if the blood of Rh+ enters a rhesus negative individual the recipient responds by manufacturing Rh factor antibody.
HDN may occur when an Rh negative woman is carrying a foetus with an Rh positive genotype. A foeto-maternal bleed resulting in foetal red cells entering the mother’s circulation may cause Rh immunisation. This is because the initial immunisation results in the production of IgM class antibodies.
These are too large to cross the placenta to cause red cell destruction. A first pregnancy resulting in termination may also cause immunisation. Subsequent pregnancies resulting in immunisation lead to IgG class antibodies.
If the mother is Rh and the child is Rh+ the mother’s first pregnancy does not have drastic effect because it does not produce antibody or due to the fact that the concentration of Rh factor antibody in mother’s blood is negligible but it has minor complication like bleeding which affect the health of foetus.
However, the mother has now developed antibodies against the Rh factor. Another pregnancy, where she carries an Rh-positive child, her antibodies (which is weak or albumin type) can cross the placenta into the foetus, whose erythrocytes they attack, causing hemolysis, which is the breakdown of erythrocytes and the release of haemoglobin into the plasma.
The released haemoglobin may damage many organs, including the brain. This serious effect on the child is called erythroblastosis foetalis, a condition characterized by severe anaemia and jaundice. Preventing rhesus disease – Rhesus disease is now rare, since Rh-negative mothers who give birth to Rh-positive babies are immunised within 72 hours of giving birth.
The immunoglobulin preparation works by killing the foetal red blood cells inside the mother’s bloodstream before her immune system has time to react. Rh haemolytic disease of new born is usually preventable by avoiding sensitization of Rh- girls and women. This can be done by avoiding transfusion with Rh+ blood. Vaccines (eg. Rho GAM) are available to prevent erythroblastosis foetalis.
Arterial System:
It comprises all the arteries coming out from the heart and supplying blood to different parts of body. Two main arterial vessels are
(i) Pulmonary arch:
Arises from right ventricles and supplies deoxygenated blood to lungs for oxygenation.
(ii) Corticosystemic arch or Aorta:
Arises from left ventricle, carries oxygenated blood and gives many branches
Venous System
It comprises all the veins that bring blood to heart Main veins are two precavals and one post caval. Coronary sinus collects the deoxygenated blood from the wall of heart and opens into right atrium.
Portal System:
It is a system made of a portal vein and the capillary complex formed by it in an organ other than the one of its origin.
Portal vein is a vein which collects blood from one organ by a set of capillaries and distributes that blood, into a second organ through another set of capillaries instead of sending the blood into heart.
Types of Portal System:
Hepatic portal system:
It occurs in all vertebrates. Posterior mesenteric, anterior mesenteric, duodenal and lineogastric join to form hepatic portal vein.
It pours blood from digestive system into the liver. This blood is collected by hepatic veins and poured into post caval to be returned to the heart. This system functions as a short circuit for
(i) Removal of glucose, amino acids and other nutrients
(ii) Deamination of extra amino acids and conversion of harmful ammonia into urea.
(iii) Separation of chemical and their detoxification.
(iv) Direct pouring of liver products into venous blood.
Renal portal system:
It consists of renal portal veins that bring blood from posterior part of the body directly into kidneys for removal of waste products. It is well developed in fishes and amphibians, reduced in reptiles and birds and absent in mammals.
Hypophysial Portal System:
A hypophysial portal vein collects blood from hypothalamus to the anterior lobe of pituitary. It is a minor portal system that occurs in higher vertebrates.
LYMPH – For detail refer chapter – Animal Tissue.
Lymphoid organs – The organs which secrete lymph are called lymphoid organs. Besides the lymph nodes, tonsils, thymus gland, Peyer’s patches, liver and spleen are the other lymphoid organs which secrete lymph.
Lymphatic System -The lymphatic system has two major functions
1. It helps to maintain fluid and balance in the tissues of the body
2. It has a major role in the defence against injection.
It comprises lymphatic capillaries, lymphatic vessels, cysterna chyli, lymphatic nodes and lymphatic ducts. Lymphatic capillaries – Lie close to the blood capillaries but differ from them to the extent that they may end blindly.
Lymphatic vessels:
Formed by the union of lymphatic capillaries. They are similar to veins but with thinner walls and more numerous semilunar valves.
Cysterna chili:
The sac like structure situated in front of the upper lumbar vertebrae on the right of the abdominal aorte. It receives lymph from the legs, pelvic cavity and asdominal cavity.
Lymphatic nodes:
Are oval or reniform swellings on the lymph vessels hence occur or located at intervals along their course? They are abundant in neck, chest, armpit, etc. Fine branches of lymph nodes filters out many germs and other particles.
Lymphatic ducts – Two ducts are formed: right lymphatic duct and thoracic duct.
Right lymphatic duct is short and collects lymph from right side of head, neck, thorax and right upper limb. It drains lymph into right brachiocephalic vein at the junction of right juglar and subclavian veins.
Thoracic duct is a longer lymph vessel that develops in the abdomen from the union of cysterna chyli, a sac like dilation situated in front of first and second lumbar vertebrae. In the abdomen it receives lacteals (lymphatics present in intestine) and a few other lymph vessels.
It discharges its lymph into the right subclavian vein. Lymph moves from lymphatic capillaries to lymphatic vessels, lymphatic ducts and ultimately opens into the venous system.
Spleen:
The spleen is the largest component of the lymphatic system. The spleen is composed of red pulp (reticular tissue rich in RBCs) having small patches of white pulp (lymphatic nodules) scatted in it.
The red pulp is enclosed by capsule of white fibrous tissue. The capsule sends trabeculae into the pulp, and is surrounded by visceral peritoneum (peritoneum that surrounds the abdominal organs).
Spleen Serves Many Functions:
(i) Destruction of worn-out red corpuscles:
The worn-out red blood corpuscles are phagocytized by the free and fixed macrophaged present in the spleen. On this account, spleen is often described as the “graveyard” or “slaughter house” of the worn-out erythrocytes.
(ii) Reservoir for red corpuscles:
When the animal is at rest and needs less oxygen due to slow metabolism, some red corpuscles are withdrawn from circulation and stored in the spleen.
During active life, when the animal requires more oxygen, also in case of haemorrhage (blood loss in injury), the stored red corpuscles are released into the blood stream.
(iii) Formation of agranuocytes:
The lymphocytes and monocytes are produced in the bone marrow and spleen besides thymus and lymph nodes.
(iv) Production of antibodies:
The plasma cells present in the speen produce antibodies, the protective proteins that provide immunity.
(v) Storage of iron:
The iron feed from the haemoglobin of the worn-out red corpuscles is stored in the macrophages till it is needed for reuse in the synthesis of fresh haemoglobin.
(vi) Erythropoiesis:
In the embryo, the spleen produces new red blood corpuscles.
(viii) Disposal of foreign elements:
The macrophages of the speen engulf and destroy the foreign germs and other substances entering the blood.