Question

Long answer question:

Describe human blood and give its functions.

Answer 1

Human blood consists of plasma and blood corpuscles or blood cells

Plasma: It is a straw-coloured, slightly alkaline, viscous fluid. It constitutes 55% of the blood. Plasma consists of water, proteins (albumin, globulin, properdin, prothrombin, fibrinogen), inorganic salts (Na, K, Mg, Ca, Fe, Mn and Cl^-, `"HCO"_3^-` and `"PO"_4^(3-)`), food (glucose, amino acids, fatty acids, triglycerides), wastes (urea, uric acid and creatinine), regulators (hormones, enzymes, vitamins), anticoagulants (heparin), cholesterol and antibodies, dissolved gases (O₂, CO₂, N₂) Plasma contains 90% water, 7-8% proteins, inorganic salts – 1% and other substances 1-2%.

Blood Corpuscles: It constitutes 44% of the blood. Blood corpuscles are of three types as given below:

1. RBC (Red Blood Corpuscles) or Erythrocytes:

a. Erythrocytes are the most abundant cells in the human body.

b. They are circular, biconcave and enucleated (in camel and llama they are nucleated).

c. The red colour or RBCs is due to an oxygen-carrying pigment, the haemoglobin, in their cytoplasm.

d. In males, the RBC count is about 5.1–5.8 million/mm³ (per μL) and in females about 4.3–5.2 million/mm³.

e. The average life span of RBCs is 120 days.

f. The process of formation of RBCs is called erythropoiesis.

g. RBCs are produced from haemocytoblasts/reticulocytes.

h. The erythropoeitic organ of the foetus is the liver and spleen and in the adult, it is mainly the red bone marrow.

i. Vitamin B₁₂, folic acid and heme protein are required for the production of RBCs. The old and worn-out RBCs are destroyed in the liver and spleen (graveyard of RBCs).

j. Polycythemia is the condition in which the number of RBCs increase and erythrocytopenia is a decrease in the number of RBCs.

k. The hormone erythropoietin produced by the kidney cells stimulates the bone marrow for production of RBCs.

l. Mature erythrocyte is devoid of nucleus, mitochondria or other membrane-bound cell organelles. Its cytoplasm (stroma) is rich in haemoglobin and O₂ carrying proteinaceous pigment that gives the red colour to the RBCs and blood. It also contains an enzyme, carbonic anhydrase.

m. Erythrocytes are responsible for the transport of respiratory gases O₂ and CO₂, maintaining pH and viscosity of blood. They also contribute in the process of blood clotting.

n. The ratio of the volume of RBCs to the total blood volume of blood is hematocrit. It is different for men and women.

2. WBC (White Blood Corpuscles) or Leucocytes:

a. Leucocytes are colorless, nucleated, and amoeboid cells larger than RBCs.

b. These are colourless, irregular nucleated cells and show polymorphism (exist in variable forms)

c. Due to their amoeboid movement they can move out of the capillary walls by a process called diapedesis.

d. A normal adult has on average, 5000-11000 WBCs per mm3 of blood.

e. Decrease in the number of WBCs (<4000) is called leucopenia (common in HIV, AIDS, and TB patients or those exposed to radiations, shock, etc.). A temporary increase in the number of WBCs is called leucocytosis. It is due to infection. It also occurs during pregnancy and in newborn babies. An uncontrolled increase in the number of WBCs is a type of blood cancer called leukemia. WBCs are mainly concerned with defense mechanisms i.e. protection.

3. Blood Platelets or Thrombocytes:

a. Thrombocytes are cellular fragments formed from the large cells called megakaryocytes.

b. These are produced in the bone marrow. They are very small, oval-shaped cell fragments without a nucleus.

c. Normal count of thrombocytes in human blood is about 2.5 – 4.5 lakh / mm³ of blood. If the number of thrombocytes decreases than normal, the condition is called as thrombocytopenia. This condition causes internal bleeding (haemorrhage).

4. Platelets secrete platelet factors which are essential in blood clotting. They also seal the ruptured blood vessels by the formation of platelet plug/ thrombus. They secrete serotonin a local vasoconstrictor.

5. Functions of Blood: Blood perform various functions like transport, homeostasis, and protection.