Body Fluids and Circulation

Composition of blood, blood groups, coagulation of blood


  • Blood is a fluid connective tissue with cells (RBC, WBC, Platelets) suspended in plasma. The volume of blood in an adult person of 70Kg weight is about 5.5 litres. pH of blood is 7.4. pH of blood in arteries is more than veins.
  • Plasma is slightly alkaline non living inner cellular substance which constitutes about 55% part of blood. It is composed of water, minerals and salt. It is transparent and clear but pale yellow in colour.
  • Plasma proteins are mainly albumin, globumin, immunoglobin, prothrombin and fibrinogen. Excretory substance include ammonia, urea, uric acid, creatine, creatinine. Various vitamins, enzymes, anticoagulant (heparin), hormones dissolved gases are present in plasma. Plasma without clotting factors are called serum.
  • Blood corpuscles (formed elements) are three types. Erythrocytes (RBC) import red colour to the blood. The colour is due to the presence of haemoglobin. Haemoglobin is a conjugate protein made of protein part (globin) and non protein part (Heme \tt Fe^{2+}) Porphyrin complex). 4 heme molecules joined with 4 globin molecules. Haemoglobin is made up of 2 alpha chains with 141 amino acids each and 2 beta chains with 146 amino acid each.
  • 100 ml of blood of a normal man contains 15g of haemoglobin and of normal man contains 13g of haemoglobin. The quantity of haemoglobin is less in women as they undergo menstruation. Less amount of Hb, leads to anemia. people live in hills have more RBC.
  • The life of an RBC is about 120 days. The worn out RBCs are destroyed in the spleen and liver. This pigment is degraded to yellowish pigment bilirubin which is excreted in bile.
  • An abnormal rise in RBC count is called as polycythemia. Decrease in RBC count is called as erythrocytopenia, which causes oxygen shortage in blood and tissue. Formation of erythrocytes is called as erythroporesis.
  • RBCs are mostly biconcave and circular but in camel it is oval. All adult mammals have enucleated  RBC. Hemocytoblasts in red bone marrow give rise to mature RBC. Vitamin B12, iron, protein, folic acid are essential for the formation of RBC.
  • Haemoglobin of RBC combines with oxygen to form oxyhaemoglobin CO2 combines with amino group of Hb, and form Carbamino - haemoglobin. Both O2 and CO2 are transported in this form
  • Leucocytes (WBC) count in human varies from 6000 - 8000 mm3. They are less in number than RBC. Ratio of WBC : RBC in human blood is 1 : 600. Formation of leuocytes is called as leukoporesis
  • Rise in WBC count is called as leucocytosis. decrease in WBC count is termed as leukopenia. Abnormal increase in WBC count leads to a particular cancer named leukemia.
  • WBCs are irregular in shape like amoeba and they are capable of amoeboid movement. This movement helps them to square out of blood capillaries into tissues. This is called as diapedesis.
  • Leucocytes are colourless and of two types namely granulocytes and agranulocytes (lymphocytes & Monocytes). The granulocytes and monocytes are formed only in bone marrow. Lymphocytes are produced mainly in lymphnode spleen, thymus, tonsils, bone marrow and peyer's patches of small intestine (SI).
  • Lymphocytes are non motile and non phagocytic. They produce antibodies to destroy microbes and their toxins and also helps in healing of injuries. They are two types namely B and T lymphocytes. 20 - 25% leucocytes are lymphocytes.
  • Monocytes are the largest of all WBC. They are motile and phagocytic in nature. so they engulf bacteria and cell debris. Monocytes are differentiated into macrophages after entering into tissues. 2 - 10%. of leucocytes are monocytes
  • Granulocytes are containing granules in their cytoplasm. According to their staining property, the granulocytes are named so. Eosinophils take acidic stains (eg : methylene blue), neutrophils are neutral in nature, which are stained weakly with both acid and basic stain.
  • Eosinophils (1-6%) has two lobed nucleus which plays important role in the immune system. Their number increases in people with allergic conditions such as asthma/hay fever. Also helps in dissolving blood clots. The coarse granules contain hydrolytic enzymes and peroxidase.
  • Basophils (0 - 1%) have three lobed nucleus. They release heparin, serotonin and histamine. Neutrophils has multilobed nucleus and they are phagocytic in nature. Certain neutrophils in female mammals posses a small spherical lobe attached to their nucleus by a stalk this lobe is called drum stick (≈ sec chromatic) or Barrbody 60 - 65% of leucocytes are neutrophils.
  • Thrombocytes (Blood platelets)(Blood dust), are about 1,50,000 - 350,000 mm3. Increase and decrease in the number of platelets is known as thrombocytosis and thrombocytopenia, respectively. They are rounded/oval disc cell fragments, which are smaller than RBC & WBC. [Flat and Non nucleated cells].
  • Formation of thrombocytes are called as thromboporesis. At the site of injury, blood platelets release certain chemicals which are platelet factors (thromboplastin), helps in the clotting of blood
  • Karl Landsteiner reported ABO blood groups for the first time. AB blood group was discovered by de costello and sreini. ABO blood groups are determined by the gene I (isoagglutinogen). IA, IB, IΦ are the alleles of the gene which forms the protein A antigen, B antigen etc.
  • 'A' blood group people have A antigen on the surface of RBC and antibodies to antigen B is present in their plasma. genotype for A, is IAIA (or) IAIO.
  • Person with B blood group have B antigen on the surface of RBC and antibodies against A antigen is present in their plasma. IBIB (or) IBIO are the allele for 'B' blood group
  • people with O blood group (universal donor) can donate blood to all the blood groups, because they don't have A and B antigen on their RBCs, but they have antibodies for both these antigens A & B in their plasma so they can receive blood only from his (her own group (genotype IoIo)
  • AB blood group (universal recipient) receive blood from any blood group because they don't have any antibodies in their plasma, but they can donate blood only to his/her own blood group as they have A antigen and B antigen. (IA IB - genotype)
  • Rh antigen (Rhesus) discovered by Landsteiner & wiener. It is present on the surface of RBCs. If Rh antigen is present then they are Rh+ individuals those who doesn't have this antigen are Rh− individuals.
  • Bleeding is stopped by the process called blood clotting or blood coagulation. When an injury is caused to blood vessel, bleeding starts and it is stopped by this, process.
  • At the site of injury, the blood platelets (thrombocytes) disintegrate and release a phospho lipid, thromboplastin (platelet factor 3) and injured tissues also release this. They both combine with Ca2+ ions and few proteins of blood plasma release thrombokinase (or) thromboplastin /prothrombinase.
  • Thrombokinase with the help of calcium ions, converts prothrombin of plasma into thrombin. It inactivates heparin. Thrombin in the presence of Ca2+ ions reacts with the soluble fibrinogen and converts it into insoluble fibrin.
  • Fibrin is thin, long and solid fiber which forms threads and mesh work at the site of wounds. This network traps blood cells (RBC, WBC, platelets) to form clot (or) thrombus.
  • The rate limiting factor is causing blood coagulation is the formation of prothrombin activator, as the terminal step normally occur rapidly to form the clot itself. The normal clotting time is 2 to 8 minutes.

Watch this video for the topic Composition of blood, blood groups, coagulation of blood from 0:49 to 46:07

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