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Body Fluids and Circulation - Notes | Class 11 | Part 2: Blood & Blood Vessels

Blood

Formed of plasma (55%) & formed elements (45%).

A. Plasma

Straw-coloured, slightly alkaline (pH 7.4) viscous fluid.

Constituents of Plasma

  • Water (90-92%): It is a good solvent.
  • Plasma proteins (6-8%): Include
    • Fibrinogen: For blood coagulation.
    • Globulins: Act as antibodies (for defense of the body).
    • Albumins: For osmotic balance. Regulate blood pressure.
  • Glucose, amino acids, lipids & cholesterol.
  • Inorganic constituents: Na+, Ca2+, Mg2+, Cl-, HCO3- etc.
  • Gases like CO2, O2, N2 etc.

Plasma without clotting factors is known as Serum.


B. Formed Elements (RBC, WBC & Platelets)

Red Blood Cells (RBC) or Erythrocytes:

  • Biconcave non-nucleated cells. No mitochondria, Golgi complex etc.
  • Red colour is due to Haemoglobin (iron containing protein).
  • Normal Hb level is 12-16 g/100 ml.
  • Count: 5 - 5.5 millions/mm3.
  • Formed in: Red Bone marrow.
  • Average lifespan: 120 days. Worn-out RBCs are destroyed in spleen (graveyard of RBCs).
  • Function: CO2 and O2 transports.

White Blood Cells (WBC) or Leucocytes:

  • Colourless nucleated cells.
  • Count: 6000-8000 /mm3.
  • Formed in: Bone marrow, lymph glands, spleen.
  • Average lifespan: Generally short lived (1-15 days).
  • Function: Part of immune system.

WBCs are 2 types: Granulocytes & Agranulocytes

1. Granulocytes

They are 3 types:

  • Neutrophils: 60-65%. They are phagocytes which destroy foreign organisms.
  • Eosinophils: 2-3%. Resist infections. Cause allergic reactions.
  • Basophils: 0.5-1%. Secrete histamine, serotonin, heparin etc. Cause inflammatory reactions.

2. Agranulocytes

They are 2 types:

  • Lymphocytes: 20-25%. Includes B- lymphocytes & T- lymphocytes. Cause immune responses.
  • Monocytes: 6-8%. They are phagocytes.

Platelets (Thrombocytes):

  • Colourless non-nucleated cell fragments.
  • Count: 1.5 - 3.5 lakhs /mm3.
  • Formed in: Megakaryocytes in Bone marrow.
  • Average lifespan: 7 days.
  • Function: Blood clotting.
Formed Elements Diagram

Blood Coagulation

It is a mechanism for haemostasis (prevention of blood loss through injuries).

At the site of injury, following events occur:

Clumped platelets & tissues release thromboplastin

↓

It forms thrombokinase (Prothrombinase) enzyme

↓

Thrombokinase hydrolyses prothrombin to thrombin enzyme in presence of Ca2+

↓

Thrombin converts soluble fibrinogen to insoluble fibrin

↓

Fibrin threads trap dead & damaged blood cells to form clot (coagulum).


Blood Groups

1. ABO Grouping

  • It is based on presence or absence of 2 surface antigens (chemicals that induce immune response) on RBCs namely A & B.
  • Similarly, plasma contains 2 antibodies (proteins produced in response to antigens) namely anti-A & anti-B.
    • Blood group Antigens Antibodies Can donate blood to Can receive blood from (Donor’s group)
    A A Anti-B A & AB A, O
    B B Anti-A B & AB B, O
    AB A, B Nil AB only A, B, AB & O
    O Nil Anti-A & Anti-B A, B, AB & O O only
  • Antigen A reacts with anti-A. Antigen B reacts with anti-B.
  • If bloods with interactive antigens & antibodies are mixed together, it causes clumping (agglutination) of RBCs.
  • Persons with O Group are called Universal donors because they can donate blood to persons with any other blood group.
  • Persons with AB group are called Universal recipients because they can accept blood from all groups.

2. Rh Grouping

  • Rhesus (Rh) factor is another antigen found on RBC.
  • Rh+ve means the presence of Rh factor and Rh-ve means absence of Rh factor.
  • Nearly 80% of humans are Rh+ve.
  • Anti-Rh antibodies are not naturally found. So Rh-ve person can receive Rh+ve blood only once but it causes the development of anti-Rh antibodies in his blood. So, a second transfusion of Rh+ve blood causes agglutination. Therefore, Rh-group should be matched before transfusion.
Erythroblastosis Foetalis
  • It is a Rh incompatibility between the Rh-ve blood of a pregnant mother and Rh+ve blood of the foetus.
  • Rh antigens do not get mixed with maternal blood in first pregnancy because placenta separates the two bloods.
  • But during first delivery, the maternal blood may be exposed to small amount of foetal blood (Rh+ve). This induces the formation of Rh antibodies in maternal blood.
  • In case of her subsequent pregnancies, the Rh antibodies from the mother leak into the foetal blood (Rh+ve) and destroy the foetal RBCs. This is fatal to the foetus or cause severe anaemia and jaundice to the baby. This condition is called Erythroblastosis foetalis.
  • It can be avoided by administering anti-Rh antibodies to the mother immediately after the first delivery.

2. Blood Vessels

Blood vessels are 3 types: Arteries, Veins & Capillaries.

Arteries:

  • They carry blood from heart to other tissues.
  • They contain oxygenated blood (except pulmonary artery).
  • Their smaller branches are called arterioles.
  • Arteries are 3-layered- inner tunica intima (squamous endothelium), middle tunica media (smooth muscles & elastic fibres) and outer tunica externa (fibrous connective tissue).

Veins:

  • They carry blood towards heart.
  • They contain deoxygenated blood (except pulmonary vein).
  • Their smaller branches are called venules.
  • Veins are also 3-layered but tunica media is comparatively thin.

Capillaries:

  • In tissues, arterioles divide into thin walled and single layered vessels. They are called capillaries. They unite into venules.

Select a Topic 👇

1. Circulatory Pathways 2. Blood & Blood Vessels 3. Heart 4. Cardiac Cycle 5. Lymphatic System, Disorders of Circulatory System
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