Introduction to Blood and Blood Groups

Blood

• Blood is thicker than water, flowing more slowly.
• Blood viscosity depends on the number of blood cells, primarily red blood cells (RBCs).
• Aspirin does not affect blood thickness, reducing clotting ability.
• Human blood temperature is 38°C.
• Blood pH is around 7.4 (range 7.35-7.45).
• Blood makes up 8% of total body weight.
• Average blood volume is 5-6 liters in males and 4-5 liters in females.

Blood Composition

• Blood is composed of 55% plasma and 45% formed elements.
• Formed elements are primarily 99% red blood cells (RBCs) and less than 1% white blood cells (WBCs) and platelets.
• Haematocrit is the percentage of total blood volume occupied by RBCs.
  • Values are 47% ± 5% for males and 42% ± 5% for females.

Blood Plasma

• Blood plasma is over 90% water.
• Plasma proteins make up 7% of plasma, mostly produced in the liver.
• Albumin maintains blood osmotic pressure.
• Globulins (alpha, beta, gamma) have transport and immune functions (gamma globulins are antibodies).
• Fibrinogen is crucial for blood clotting.
• Plasma contains electrolytes, nutrients, hormones, gases, waste products, etc.

Blood Cells

• Red blood cells (erythrocytes):
  • Biconcave discs, anucleate, salmon-colored, diameter 7-8 µm.
  • Transport oxygen and carbon dioxide.
• White blood cells (leukocytes):
  • Granular (eosinophils, basophils, neutrophils) and agranular (lymphocytes, monocytes) types.
  • Crucial in immune responses and other bodily functions.
• Platelets (thrombocytes):
  • Cell fragments, crucial for blood clotting.

Blood Functions

• Transportation: O2, CO2, metabolic wastes, nutrients, heat, hormones, and medications.
• Regulation: Blood regulates pH, temperature, and intracellular fluid composition.
• Protection: Blood plays a role in immunity and inflammation.

Platelet Physiology

• Platelets are disc-shaped cell fragments without a nucleus.
• Normal count is 150-400 x 10⁹/L.
• They are essential for haemostasis, stopping blood loss from damaged blood vessels through
  1. Vascular spasm (constriction of damaged blood vessel).
  2. Platelet plug formation (adhesion to damaged tissue and aggregation).
  3. Blood clotting (coagulation—formation of fibrin threads and meshwork).

Blood Clotting

• Clotting requires calcium, clotting proteins, and substances released by damaged tissues or platelets
• The clotting cascade is a series of reactions with each factor activating the next (intrinsic and extrinsic pathways)
• It results in the formation of a fibrin meshwork, trapping blood cells to form a clot.
• Both pathways result in producing thrombin and ultimately fibrin for blood clotting.

Haematopoiesis

• Blood cell formation (RBCs) occurs in red bone marrow of flat bones, ribs, skull, pelvis, ends of long bone, and lymphoid organs.
  • Stem cells are responsible for all cell types of blood.
  • It's an ongoing process, with cells dying and being continually replaced (approximately 100 billion RBCs produced per day)
  • EPO (Erythropoietin) is a crucial hormone in erythropoiesis released by the kidneys as a response to low oxygen levels.

Control of RBC Production

• Factors influencing RBC production include iron, vitamin B12, folic acid, tissue hypoxia, and anaemia.
• The production of RBCs is controlled by the hormone erythropoietin which is produced in the kidneys.

RBC Oxygen Carrying Capacity

• Haemoglobin (Hb) is the protein in RBCs that carries oxygen (binds with oxygen).
• Each Haemoglobin can carry 4 oxygen molecules.
• Blood containing haemoglobin and oxygen becomes oxyhaemoglobin.

Destruction of RBCs

• RBCs lack nuclei and have limited repair abilities.
• They are engulfed by macrophages in the spleen, liver, and bone marrow when they age/or are damaged.
  • The haemoglobin degrades into heme and globin.
  • Iron is recycled, heme is converted to biliverdin and bilirubin.
  • Bilirubin is processed by the liver and excreted in bile as stercobilin.

Blood Groups

• ABO blood types are determined by the presence or absence of A and/or B antigens on the surface of RBCs.
  • O blood type lacks both A and B antigens.
• Rh factor is another critical antigen.
• A person either has it(Rh+) ore doesn't (Rh-).
• Blood typing is essential to avoid incompatibility issues when transfusions are needed.

Haemolytic Disease of the Newborn

• HDN occurs due to Rh factor incompatibility between mother and fetus, where antibodies from the mother attack the baby's RBCs.
• Early detection and treatment (e.g., administration of anti-Rh antibodies) can drastically reduce issues.
• Several sensitising events can make a mother develop anti-D antibodies, including -Ectopic pregnancy, termination of pregnancy, miscarriage, trauma, abdominal pain and antepartum haemorrhage.

Physical characteristics of Blood

• Thicker (viscous) than water
• Blood flows more slowly than water.
• pH is in the range 7.35 to 7.45
• Blood constitutes 8% of a person's total body weight
• Blood volume: approximately 5-6 liters in males and 4-5 liters in females.

Learning Outcomes

• Understanding the basis of Blood groups and applying this knowledge towards safe transfusions

• Describe the process of haemostasis and the clotting cascade.

• Outline erythrocyte production (haematopoiesis).