Hematology and Bilirubin Quiz

Blood Physiology

• Blood is a fluid connective tissue, vital for transporting oxygen from lungs to body parts and carbon dioxide from body parts to the lungs.
• Blood volume in a healthy adult male is approximately 5 liters, and in a healthy adult female it is slightly less at 4.5 liters. It equates to about 8% of body weight in a 70kg healthy young adult.
• Blood volume in a newborn baby is 450ml.
• Blood increases during growth and reaches 5 litres by puberty.

Blood Composition

• Blood has two primary components: plasma (55% of blood volume) and formed elements (45% of blood volume).
• Formed elements include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
• Plasma is primarily water (98%), with dissolved ions and plasma proteins (albumin, globulins, fibrinogen)
• Hematocrit is a measure of the percentage of red blood cells in whole blood. Healthy males average 47% ± 5%, healthy females average 42% ± 5%.
• Platelets = 250-400 thousand per cubic mm of blood
• White blood cells = 5-9 thousand per cubic mm of blood
• Red blood cells = 4.2-6.2 million per cubic mm of blood

Functions of Blood

• Transport: Oxygen, carbon dioxide, nutrients, hormones, waste products
• Homeostasis: Regulating body temperature and ECF pH
• Protection: White blood cells and antibodies defend against infections
• Clotting: Prevents blood loss through a complex cascade

Blood Cell Formation

• Hematopoiesis is the process of blood cell formation
• Erythropoiesis: Formation of red blood cells (RBCs) in yolk sac during early fetal stages. In the middle trimester, RBC formation moves to the liver and spleen. By the later stages of fetal development, and after birth, RBC formation is predominantly in the bone marrow.
• Leucopoiesis: Formation of white blood cells.
• Thrombopoiesis: Formation of platelets
• Hematopoiesis: The process of producing all the materials of the blood

Production of Red Blood Cells (RBCs)

• In Utero: Early weeks - yolk sac; Middle trimester - liver, spleen, and lymph nodes; Last months - bone marrow of all bones
• After Birth: Bone marrow of flat bones continue to produce RBCs; Shaft of long bones stop RBC production at puberty, while epiphyses continue

Hematopoiesis

• Yolk sac (3rd to 10th week)
• Liver (6th to 32nd week)
• Spleen (10th to 25th week)
• Bone marrow (30th week to birth and also after birth)

Active Bone Marrow Locations

• In adults, red bone marrow is primarily found in the axial skeleton, pelvic and pectoral girdles, and proximal epiphyses of the humerus and femur.

Normal Bone Marrow Conversion

• Infants - all red bone marrow
• Childhood (1-10 years) – red bone marrow remains in flat bones, shaft of long bones begin converting to yellow marrow
• Adolescent (10-20 years) – red bone marrow in ribs, skull, vertebrae, hip bones
• Adults – all areas of the skeleton convert to yellow marrow except flat bones

Bone Marrow

• Red bone marrow (active)
• Yellow bone marrow (inactive)

Regulation of RBC Production

• Erythropoiesis is stimulated by erythopoietin, a hormone from the kidney, produced in response to hypoxia (low oxygen in the bloodstream) .
• Hypoxia can be caused by low RBC count (anemia), hemorrhage, high altitude, or chronic heart/lung diseases.

Hemoglobin

• A complex protein molecule, containing four globin protein chains, each bound to a heme group.
• The heme group contains iron, which binds oxygen.
• Normal types: Hb A, Hb A2, Hb F (fetal Hb)

Iron Metabolism

• Iron is an essential component of hemoglobin and myoglobin.
• 65% of the body's iron is in hemoglobin; 4% in myoglobin and 1% in various heme compounds; 15-30% is stored as ferritin in the liver.

Erythropoiesis

• RBC development is characterized by a decrease in cell size.
• The nucleus disappears.
• Hemoglobin (Hb) appears.

Maturation Factors

• Vitamin B12, is essential for DNA synthesis, cell division and maturation of RBCs. Absorbed from small intestine in presence of an intrinsic factor from the stomach.
• Folic acid is also essential for DNA synthesis. Deficiency can lead to Megaloblastic anemia.
• Intrinsic factor is a protein produced in the stomach, necessary for the absorption of Vitamin B12

Erythrocyte Disorders

• Polycythemia: Excess red blood cells (RBCs), above 7 million/cu mm in healthy adults.
  • Primary Polycythemia (Polycythemia Vera): caused by red bone marrow malignancy. RBC count often above 14 millions/cu mm and WBC count is also increased.
  • Secondary Polycythemia: Various causes including respiratory disorders (like emphysema, TB, pneumonia), congenital heart disease, and heart disease. Also can result from increased metabolism (e.g., hormonal imbalances). Higher levels of Erythropoietin can also result from severe conditions like high altitude or profound heart/lung disease.
• Anemia: Deficiency of red blood cells, hemoglobin content or both.
  • Blood Loss Anemia (e.g. hemorrhage)
  • Due to malnutrition (iron, Vitamin B12, or protein deficiency)
  • Abnormal hemoglobin (e.g., sickle cell anemia, thalassemia)
  • Abnormal shape (e.g., hereditary spherocytosis)
  • Aplastic anemia (bone marrow dysfunction), caused by high-dose radiation, chemotherapy, toxic chemicals, autoimmune disorders

Platelet Structure and Formation

• Platelets originate from megakaryocytes in the bone marrow.
• Platelets are cell fragments, with an irregular shape and lobed nuclei.
• Platelets have a short lifespan (~8-12 days).
• Platelets are crucial for hemostasis and blood clotting. Normal counts are 150,000–450,000 per cubic mm of blood.

Platelet Plug Formation

• Exposed collagen triggers platelet adhesion and activation, releasing factors (ADP, thromboxane A2) that attract and aggregate more platelets to form a platelet plug.

Blood Coagulation

• Series of reactions transforming blood from liquid to gel.
  • Extrinsic Pathway: Activated by tissue trauma, involving Tissue factor, VIIa, and leads to thrombin formation.
  • Intrinsic Pathway: Activated by blood contact with collagen, involving XII, XI, IX, VIII, and leads to thrombin formation.
  • Common Pathway: These two pathways converge, and final steps involve conversion of Fibrinogen --> Fibrin, and formation of a clot

Anticoagulants

• Chemicals that prevent blood clotting. Examples include EDTA, Oxalate, Heparin, Sodium Citrate, Sodium Fluoride/Potassium Oxalate
• They oppose the procoagulant effect.

Other Factors Affecting Blood Clotting

• Intact endothelial cells produce substances (prostacyclins and nitric oxide) to prevent platelet aggregation.
• Damaged endothelial cells lose these and allow clotting.

Clot Retraction

• Platelets contract, pulling the fibrin threads together, strengthening the clot.
• Plasmin (from plasminogen) then degrades the fibrin, dissolving the clot after it no longer needed, allowing for wound healing.

Jaundice

• Jaundice, or bilirubinemia, is characterized by a yellowing of skin and mucous membranes due to elevated bilirubin levels in the blood. Bilirubin is a breakdown product of old red blood cells. -Prehepatic jaundice: Excessive RBC breakdown -Intrahepatic jaundice: Dysfunction of liver cells (hepatocytes) -Posthepatic jaundice: Obstruction of bile duct

Normal Bilirubin Metabolism

• Bilirubin metabolism involves unconjugated bilirubin being conjugated by the liver, and then excreted into bile, where it becomes urobilinogen and stercobilin, eliminated in the feces. A portion of urobilinogen will be reabsorbed into the bloodstream and processed by the kidneys.

Neonatal Jaundice

• Common in premature infants, caused by transient bilirubin excess, potentially causing kernicterus brain damage. Phototherapy and exchange blood transfusions can be used to control bilirubin levels. A high bilirubin level within the first 24 hours of life is abnormal and requires additional testing to identify the cause.

Test your knowledge on hematology topics including bilirubin, erythrocytes, reticulocytes, and aplastic anemia. This quiz covers essential concepts related to blood components and their functions, normal ranges, and implications of various blood conditions. Perfect for students in health sciences or medical-related courses.