Blood and Lymph Composition

• All living cells require nutrients and oxygen while waste must be removed.
• Efficient mechanisms are essential for substance movement to and from cells.
• Different animal groups have evolved various transport methods.
• Simple organisms, like sponges, circulate water through body cavities for exchange.
• Complex organisms utilize special fluids like blood and lymph for transport.
• Blood is the most common body fluid in higher organisms.
• Lymph aids in transporting certain substances.
• Composition, properties of blood/lymph, and blood circulation are discussed.

Blood

• Blood is a special connective tissue comprised of plasma and formed elements.

Plasma

• Plasma: Straw-colored, viscous fluid, approximately 55% of blood volume.
• Plasma consists of 90-92% water and 6-8% proteins.
• Fibrinogen, globulins, and albumins are major plasma proteins.
• Fibrinogens are for clotting.
• Globulins are for defense.
• Albumins are for osmotic balance.
• Plasma contains minerals (Na+, Ca++), glucose, amino acids, lipids, etc. in transit.
• Clotting factors are present in inactive form.
• Plasma without clotting factors is called serum.

Formed Elements

• Erythrocytes, leukocytes, and platelets form 45% of blood.
• Erythrocytes (RBCs): Most abundant blood cells.
  • Healthy adults average 5 to 5.5 million RBCs mm⁻³ of blood.
  • RBCs form in red bone marrow (adults), lack nuclei, are biconcave.
  • Contain hemoglobin (iron-containing protein), for respiratory gas transport.
  • Hemoglobin levels in healthy individuals range from 12-16 gms per 100 ml of blood.
  • RBC lifespan averages 120 days.
  • RBCs are destroyed in the spleen (graveyard of RBCs).
• Leukocytes (WBCs): Colorless (lack hemoglobin), nucleated, less numerous than RBCs.
  • WBC numbers average 6000-8000 mm⁻³ of blood.
  • Generally short-lived.
  • Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes) exist.
    • Neutrophils most abundant (60-65%), basophils least (0.5-1%).
    • Neutrophils and monocytes are phagocytic, destroy foreign organisms.
    • Basophils secrete histamine, serotonin, heparin (inflammatory reactions).
    • Eosinophils (2-3%) resist infections, allergic reactions.
    • Lymphocytes (20-25%) are B and T forms, responsible for immune responses.
• Platelets (thrombocytes): Cell fragments from megakaryocytes (bone marrow).
  • Blood contains 150,000-350,000 platelets mm⁻³.
  • Platelets release substances for blood clotting.
  • Low platelet count can cause excessive blood loss.

Blood Groups

• Human blood differs despite similarities.
• ABO and Rh groupings are widely used.

ABO Grouping

• ABO grouping is based on A and B antigens on RBCs, and natural antibodies in plasma.
• Blood transfusion requires matching donor and recipient blood to avoid RBC destruction.
  • Group O blood can be donated to anyone (universal donors).
  • Group AB individuals can receive blood from anyone (universal recipients).

Rh Grouping

• Rh antigen (Rhesus monkey-like) is present in ~80% humans (Rh positive).
• Individuals lacking the Rh antigen are Rh negative.
• Rh-ve individuals exposed to Rh+ve blood form anti-Rh antibodies.
• Rh group matching before transfusions is essential.
• Rh incompatibility can occur in pregnant Rh-ve mothers with Rh+ve fetuses.
  • Anti-Rh antibodies given to the mother prevent erythroblastosis foetalis in subsequent pregnancies.

Coagulation of Blood

• Blood clotting prevents excessive blood loss after injury/trauma.
  • A clot or coagulum forms, consisting of a fibrin network trapping dead and damaged elements.
  • Fibrins forms from inactive fibrinogens with thrombin.
  • Thrombins are formed from prothrombin.
  • Thrombokinase is required for the reactions.
  • The process involves linked enzymic reactions/cascade.
  • Injury/trauma stimulates platelet release and coagulation mechanism activation.
  • Tissues at injury site release factors initiating coagulation.
  • Calcium ions are vital for clotting.