Blood Biology and Composition

Blood Biology

• Blood functions: Regulation of body temperature, buffer for pH (7.4), maintaining osmotic balance. Defence against microbes, and wound healing. Transport of gases (O2, CO2), nutrients, wastes, and chemical messengers between organs and tissues. Blood also provides hydraulic force for urine production.

Blood Composition

• Two major components: Fluid (plasma) and solid matters (formed elements, including erythrocytes, leukocytes, and platelets).

• Plasma: Makes up ~55% of whole blood and the least dense component. Consists primarily of water plus proteins (albumins, globulins, fibrinogens), salts dissolved in the water, and various nutrients, gases, waste products, and hormones responsible for metabolism and various cellular activities.

• Formed elements:

  • Erythrocytes (RBCs): ~45% of whole blood. The most dense component and transport O2 from lungs to tissue and CO2 from tissue to lungs. (~6,000,000 per µL blood).
  • Leukocytes (WBCs): <1% of whole blood. Consist of granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (monocytes, lymphocytes). Crucial for immunity, by combatting infection.
  • Platelets: (<1%) also known as thrombocytes; important in preventing blood loss.

• Buffy coat: The layer that separates plasma from the erythrocytes in a centrifuged blood sample. Consists of leukocytes and platelets

Haematopoiesis

• Formation of blood cellular components.
• Red bone marrow is active, whereas yellow bone marrow is inactive.

Blood Typing: ABO and Rhesus (Rh) Blood Groups

• ABO blood group system: Determined by the presence or absence of A and B antigens on red blood cells. Blood types: A, B, AB, O.

• Rh factor: Another system of blood groups determined by the presence or absence of the Rh D antigen. Rh+ (has D antigen), and Rh- (no D antigen).

• Understanding of blood typing is critical for safe blood transfusions.

Haemolytic Disease of the Newborn (HDFN)

• Pathophysiology: Occurs when an Rh-negative mother is pregnant with an Rh-positive baby. The first pregnancy is usually unremarkable. However, during delivery some fetal blood cells enter the mother's circulation, resulting in the production of anti-Rh antibodies. If the mother becomes pregnant with another Rh-positive baby these antibodies cross the placenta and attack fetal red blood cells leading to hemolysis(destruction) of fetal RBCs.

• Prevention: Administration of Rh immune globulin (RhIG) to Rh-negative mothers during pregnancy and after delivery. This prevents the mother's body from making Rh antibodies.

Haemostasis

• Haemostasis- stopping bleeding
• Components:
  • Vasoconstriction: Vessel constriction to minimize blood loss.
  • Platelet plug formation: Platelets aggregate and adhere to damaged vessel walls to form a plug.
  • Coagulation: Conversion of blood from a liquid to a gel via a cascade of reactions. • Clotting factors (proteins) are critical for the coagulation process. Vitamin K is needed in the biosynthesis of several of these factors.
• Fibrinolysis: • This system removes unneeded clots after healing. • Conversion of plasminogen to plasmin dissolves the blood clot.
• Natural anticoagulants: Various proteins that inhibit blood clotting, including protein C, protein S, antithrombin III, and tissue factor pathway inhibitors (TFPI).

Innate and Adaptive Immunity

• Innate immunity: Immediate and non-specific response to pathogens utilizing various physical barriers (skin, mucous membranes, and chemical secretions), phagocytes, natural killer cells, cytokines, complement proteins, and inflammation.

• Adaptive immunity: A slower response focusing on specific pathogens; providing immunological memory and leading to a more potent response upon reinfection. The immune response includes a cell mediated and an antibody mediated component. Lymphocytes are the key cells in this response.

Cytokines

• Produced by various cells and regulate immune and inflammatory responses. Examples: chemokines, interferons, interleukins, and tumor necrosis factors.

Complement Proteins

• A set of proteins that can enhance both innate and adaptive immune responses by opsonization (to increase phagocytosis), chemotaxis, and cell lysis.

Inflammation

• Body's response to tissue injury. Cardinal signs: redness, heat, swelling, and pain. Promotes tissue repair by attracting phagocytes and other immune cells.

• Learning Objectives: The study guide covers the key components and functions of blood and the key systems involved in homeostasis and immunity, fulfilling the expected learning objectives.