Composition of Blood MCQ - NEET Practice Questions with Answers

Blood  

• Blood refers to a mobile connective tissue which mainly is a composition of a fluid called plasma and floating cells called blood corpuscles or formed elements
• Blood is a slightly alkaline fluid which forms about 30-35 % of the extracellular fluid.

Blood plasma

• Blood plasma is a slightly alkaline nonliving intercellular substance. It is pale yellow but transparent and clear fluid. It constitutes 55% of the blood
• Plasma contains minerals (Na, Ca, Mg, etc), nutrients ( glucose, amino acids, lipids etc.), proteins ( albumin, globulin, fibrinogens etc ), defence compound ( immunoglobulins, lysozyme, properdin ), excretory substances, dissolved gases, anticoagulants (heparin), hormones, vitamins, blood clotting factors etc. 
• Plasma without blood clotting factors is called serum.
• The proteins present in blood plasma performs following function:

                  1. Prevention of blood loss (Fibrinogen and prothrombin play a role in blood clotting)
                  2. Retention of fluid in the blood (albumin and globulins retain water in blood plasma) 
                  3. Body immunity  (Some immunoglobulins act as antibodies)
                  4. Maintenance of pH
                  5. Transport of certain materials
                  6. Distribution of heat
                  7. As enzymes

Formed elements ( blood corpuscles) 

• Formed elements or blood cells constitute 45% of the blood.
• Blood corpuscles are of three types i.e. leukocytes (white blood cells), erythrocytes (red blood cells) and thrombocytes (blood platelets). 
• The functions of RBC include transport of O2 and CO2, maintenance of pH etc.
• The function of leukocytes in the defence against microbes and foreign particles
• The function of thrombocytes is in blood clotting.

NOTE : Platelets are formed from Megakaryocytes by a process called as Fragmentation and hence Platelets are known as Fragments 

Lets understand the components 

A) ERYTHROCYTES

1. Most abundant

2. 5 million to 5.5 million of RBCs per cu.mm

3. Biconcave and without nuclei

4. Has carbonic anhydrase

5. 12-16 gms of Hb in every 100mL

6. Formation is Erythropoiesis Occurs in red bone marrow in adults

7. Fetal erythropoiesis takes place first in the mesenchymal tissues and subsequently in the liver and spleen. The production of red blood cells in the bone marrow gradually starts during the second trimester. This is the main site of production at the time of birth even in preterm newborns.

8. Spleen is the graveyard. Life span is 120 days

B) LEUCOCYTES

1. Colourless, have nuclei and other organelles

2. Shows diapedesis and phagocytosis

3. 2 types : Granular and Agranular

4. Agranulocytes are Lymphocytes and Monocytes

5. Lymphocytes : 20-25 %. Numerous. Small cells with round nuclei. 2 forms B and T

6. Monocytes : Largest. Have kidney or horseshoe shaped nuclei. Some monocytes enter the tissues and these are Macrophages

7. Granulocytes are Eosinophils, Basophils and Neutrophils

8. Eosinophils : 2-3%. Nucleus with two lobes. Coarse granules which have hydrolytic enzymes and peroxidases. Eosinophils resist infections and associated with allergies. Similar to lysosomes 

9. Basophils : least abundant. 0.5-1%. Nucleus is three lobed. Cells secrete serotonin, heparin and histamine

10. Neutrophils : Most abundant Phagocytic cells 

11. Formation in bone marrow

C) PLATELETS

1. Thrombocytes

2. Smallest 

3. Life span is about a week

4. These are fragments

5. Important for blood clotting

6. Reduction is Thrombocytopenia