Physiology L8 P1

Blood Functions

• Blood performs transport, regulation, and protection functions.
• Transport: Carries oxygen (O2) and carbon dioxide (CO2), hormones, nutrients, and wastes.
• Regulation: Maintains pH balance, body temperature, fluid balance, and electrolyte balance.
• Protection: Defends against foreign substances (including microorganisms) and stops bleeding (hemostasis).

Blood Constituents

• Blood is composed of plasma and cellular elements.
• Plasma: Forms 55-60% of whole blood, primarily water (91%). Also contains inorganic components (e.g., Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, HPO4-, etc.) and organic components (e.g., proteins, hormones, vitamins, lipids, glucose, amino acids, urea, uric acid, etc.).
• Cellular elements: Erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. These account for 40-45% of whole blood.

Plasma Proteins

• Albumins: Transport various substances and contribute significantly to plasma's colloid osmotic pressure.
• Globulins (α & β): Important in blood clotting and transporting substances; gamma globulins are antibodies.
• Fibrinogen: An inactive precursor for the fibrin meshwork in blood clots.

Erythrocytes (Red Blood Cells)

• Most abundant blood cells.
• Biconcave discs, anucleated (no nucleus), and lack organelles.
• Filled with hemoglobin (Hb) for oxygen transport.
• Life Span: ~120 days.
• Average size: ~7.5 μm in diameter.
• Shape: Biconcave disc.
• Shape and flexible cell membrane are vital for efficient gas exchange.
• Removed from circulation by the spleen.
• About 5 million per mm³.

Hemoglobin (Hb)

• Hemoglobin is made up of heme and globin.
• Heme contains iron groups that bind to oxygen.
• Globin is a protein made up of four polypeptide chains(2 α and 2 β).
• Each hemoglobin molecule can carry four molecules of oxygen (O2).
• Normal Hb content: 16 g/dL in men and 14 g/dL in women.
• Transportation of oxygen is the primary function.

Oxygenated and Deoxygenated Blood

• Oxygenated blood appears red due to its iron content.
• Deoxygenated blood appears bluish.
• 98.5% of O2 is carried by hemoglobin.

Hematopoiesis (Hemopoiesis)

• Blood cell production occurs in bone marrow.
• Two types: Erythropoiesis (RBC formation) and Leukopoiesis (WBC formation).
• Hypoxia (low oxygen in the blood) stimulates the kidneys to secrete erythropoietin, a hormone that regulates RBC production.

Anemia

• Anemia results from reduced oxygen-carrying capacity of blood.
• Symptoms: Decreased RBC count and Hemoglobin levels.
• Consequences: Low oxygen delivery to tissues.
• Causes: Reduced erythropoiesis, loss of erythrocytes, low hemoglobin, or hemolysis (RBC destruction).
• Normal Hb levels: 13 g/dL in adult men, 12 g/dL in adult non-pregnant women, 11 g/dL in adult pregnant women, 12 g/dL in children above 6 years old, and 11 g/dL in children below 6 years old.

Causes of Anemia

• Decreased erythropoiesis
• Blood loss (hemorrhagic anemia)
• Low hemoglobin (nutritional anemia)
• Destruction of red blood cells (hemolytic anemia)

Blood Group Systems

• ABO system: Based on antigens (A, B) on red blood cells and corresponding antibodies (anti-A, anti-B) in plasma.
  • Blood types: A, B, AB, O
  • Universal receiver: AB
  • Universal donor: O
• Rh system: Determined by the presence or absence of the Rh antigen (D antigen) on red blood cells.
  • Blood types: Rh+, Rh-
  • Rh incompatibility can lead to serious complications in pregnancy
  • Other minor systems exist.

Cross-Matching

• Crucial procedure before blood transfusion to ensure compatibility between donor and recipient blood.
• Involves mixing donor red blood cells with recipient plasma to check for compatibility.
• No reaction (no agglutination) signifies compatibility. A reaction indicates incompatibility.