Blood Anatomy and Functions

Blood Composition

• Blood is a fluid tissue comprising 55% plasma and 45% cells.
• Cells include red blood cells (RBCs or erythrocytes), white blood cells (WBCs or leukocytes), and platelets (thrombocytes).

Blood Functions

• Respiration: Transporting oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
• Nutrition: Carrying absorbed food from the intestines to cells.
• Excretion: Transporting waste products to excretory organs (e.g., liver).
• Immunity: Transporting leukocytes and antibodies.
• Transport of hormones.
• Water balance.
• Regulation of:
  • Temperature
  • Osmotic pressure
  • Acid-base balance
  • Ionic equilibrium
  • Blood pressure

Plasma Composition

• Plasma is primarily water (90%).
• Dissolved solutes (10%) consist of:
  • Inorganic substances (55%)
  • Organic substances (45%) including nutrients, waste products, hormones, and urine.

Plasma Proteins

• Plasma proteins make up 7.1% of blood plasma.
• Albumin: 4-4.5 g/dL.
• Globulins: 2.5 g/dL.
• Blood Coagulation Factors: Fibrinogen (400 mg/dL), prothrombin, etc.
• Albumin/Globulin Ratio: 1.2 to 1.6

Decreased Plasma Albumin Level

• Liver diseases.
• Malnutrition.
• Severe burns due to albumin loss through the skin.

Increased Plasma Globulin Level

• Severe infection.

Functions of Plasma Proteins

• Nutrition: Contribute to protein metabolism.
• Blood Clotting: Fibrinogen, prothrombin, and thromboplastin are crucial for blood coagulation.
• Blood Viscosity: Maintain blood's red blood cell count.
• Osmotic Pressure: Important for water retention within capillaries.
• Carrier: Plasma proteins transport components like iron, iodine, thyroxin, and vitamin A, preventing their rapid elimination from blood.
• Capillary permeability: Plasma proteins help seal pores in capillary walls.

Haemostasis

• Definition: Stopping bleeding from injured blood vessels to prevent blood loss.
• Mechanisms:
  • Local Vascular Spasm: Injured blood vessels contract to reduce blood loss.
  • Platelet Plug Formation: Platelets adhere to exposed collagen fibers in damaged vessel walls, forming a plug.
  • Blood Clotting: Soluble fibrinogen converts into insoluble fibrin, forming a network with blood cells, trapping them in a clot.

Clot Formation

• Factors influencing clot formation:
  • Suspension of RBCs.
  • Buffering action: Proteins act as weak acids in alkaline media and weak alkali in acidic media.
  • Immunity: Due to the presence of globulins.
  • Carrier: Plasma proteins carry essential substances.
  • Capillary permeability: Plasma proteins help close pores in capillary walls.