Study guide: Blood and Hematopoiesis

📋 Course Outline

1. Blood Composition and Functions
2. Plasma and Plasma Proteins
3. Blood Cell Types and Features
4. Hematopoiesis and Cell Origins
5. Red Cell Formation and Turnover
6. Granulocyte and Monocyte Formation
7. Lymphocyte and Platelet Formation
8. Hematopoietic and Lymphoid Organs
9. ABO Blood Groups and Inheritance
10. Rh Groups and Transfusion Compatibility

📖 1. Blood Composition and Functions

🔑 Key Concepts & Definitions

• Blood: A reddish liquid tissue that circulates through the blood vessels, represents about 7% of body weight, and transports substances and helps protect the body from disease.

★ Must-know

• Blood consists of plasma and blood cells suspended in the plasma.

Further detail

• An adult body contains approximately 5 litres of blood, usually between 4.5 and 6 litres, with the amount related to age, weight, sex, and height.

📖 2. Plasma and Plasma Proteins

🔑 Key Concepts & Definitions

• Plasma: The transparent, yellowish liquid part of blood, consisting mainly of water and dissolved substances.

★ Must-know

• Plasma contains approximately 70–80 g of proteins per litre of blood, including albumin, globulins, and clotting factors; these proteins contribute to clotting, transport, and defence against infection.

• Gamma globulins, also called immunoglobulins, form antibodies involved in defence against infections; the five types are IgG, IgA, IgM, IgD, and IgE.

Further detail

• Dissolved plasma substances include:
  • sugars
  • sodium, chloride and potassium ions
  • iron and calcium minerals
  • fats
  • proteins

📌 Almost all plasma proteins are formed in the liver, whereas gamma globulins are produced by lymphocytes.

• Albumin represents approximately half of plasma proteins and transports varied substances that cannot remain free in plasma; transferrin carries iron, ceruloplasmin carries copper, and transcobalamin carries vitamin B12.

📖 3. Blood Cell Types and Features

★ Must-know

• Red blood cells, also called erythrocytes or red cells, are the most numerous blood cells and transport oxygen from the lungs to body tissues using hemoglobin.

• White blood cells, or leukocytes, are nucleated cells that defend against infection; normal blood contains 4,000–10,000 leukocytes per mm3.

• The main leukocyte proportions are:

  • neutrophils 45–70%
  • bands 3–5%
  • eosinophils 1–3%
  • basophils 1% or less
  • monocytes 3–7%
  • lymphocytes 25–30%

• Platelets, or thrombocytes, are nucleus-free cell fragments measuring 1.5–2 μm in diameter, with 150,000–350,000 per mm3 of blood.

• Platelets protect vessel walls, form a platelet plug to limit bleeding at an injury, and release substances that help wounds heal.

Further detail

• Red blood cells lack a nucleus and have a biconcave disc shape; hemoglobin, which contains iron and gives blood its red colour, makes up about one-third of a red blood cell's weight.

• Normal blood contains approximately 4.5 million red blood cells per mm3, while reticulocytes, their immature forms, make up approximately 1% of red blood cells.

📌 Leukocytes are classified as mononuclear cells or polynuclear cells, which have one multilobed nucleus and are also called granulocytes.

• Monocytes are the largest blood cells, measuring 10–20 μm in diameter, while lymphocytes are the smallest leukocytes and have a large nucleus with little cytoplasm.

• Lymphocytes include B and T cells, which differ in their roles in the immune response; among circulating lymphocytes, most are T cells and 10–20% are B cells.

💡 Memory Hook

Red cells carry oxygen; white cells defend; platelets help stop bleeding.

📖 4. Hematopoiesis and Cell Origins

🔑 Key Concepts & Definitions

• Hematopoiesis: The formation of blood cells, which occurs mainly in bone marrow from pluripotent stem cells that can generate themselves and produce lineage-specific monopotent stem cells.

★ Must-know

• The blood-cell formation processes are:
  • erythropoiesis for red cells
  • granulopoiesis for granulocytes
  • lymphopoiesis for lymphocytes
  • thrombocytopoiesis for platelets

Further detail

• Blood cells age and are destroyed, so hematopoiesis must continuously regenerate them with contributions from bone marrow, hematopoietic organs, and lymphoid organs.

💡 Memory Hook

Pluripotent stem cell → monopotent stem cell → mature blood cell.

📖 5. Red Cell Formation and Turnover

🔑 Key Concepts & Definitions

• Erythropoiesis: The continuous formation of red blood cells, producing 100–250 billion cells per day to replace cells that live for about 120 days.

★ Must-know

• 🔄 Red blood cells develop through these changes:
  1. Developing cells multiply and shrink.
  2. The cells produce hemoglobin.
  3. The cells lose their nuclei and become reticulocytes.
  4. Reticulocytes mature into red blood cells.

Further detail

• One proerythroblast can generate 16 red blood cells.

• Red-cell formation in bone marrow takes 3–5 days, reticulocytes enter the blood 1–2 days later and mature there in about one day, making the total process 5–8 days.

💡 Memory Hook

Stem cell → reticulocyte → mature red cell.

📖 6. Granulocyte and Monocyte Formation

🔑 Key Concepts & Definitions

• Granulopoiesis: The formation of polynuclear leukocytes in bone marrow, taking about 9–10 days and producing approximately 30 billion granulocytes daily.

★ Must-know

• 🔄 Granulocytes develop in this order:
  1. myeloblast
  2. promyelocyte
  3. myelocyte
  4. metamielocyte
  5. band cell
  6. mature granulocyte

Further detail

• Increased need for leukocytes can cause bone marrow to release more immature cells, first bands and, if demand continues, metamielocytes and myelocytes; prolonged demand increases precursor-cell multiplication.

• Granulopoiesis is stimulated by infection and corticosteroid hormones, while granulopoietin specifically stimulates granulocyte formation although its mechanism is unknown.

• Neutrophils in blood are divided approximately equally between a circulating pool and a vessel-wall marginal pool; exercise can shift neutrophils from the marginal pool to the circulating pool.

• Neutrophils leave the blood after about 12 hours to enter tissues and do not return, while monocytes leave the blood after about 9 hours; prolonged allergy can increase blood eosinophils, a condition called eosinophilia.

💡 Memory Hook

Myeloblast → promyelocyte → myelocyte → metamielocyte → band → mature granulocyte.

📖 7. Lymphocyte and Platelet Formation

🔑 Key Concepts & Definitions

• Lymphopoiesis: The formation of lymphocytes, which begins in bone marrow when monopotent stem cells produce immature lymphoblasts.

★ Must-know

📌 During embryonic development, some immature lymphocytes mature into B cells in intestinal lymphoid tissue, whereas others mature into T cells in the thymus.

• Platelets form in bone marrow when a megakaryocyte cytoplasm fragments into membrane-bounded units that enter the blood as platelets.

Further detail

• Lymphocyte lifespan varies by type and activity, ranging from a few days to 3 months–10 years or longer.

• Each megakaryocyte can produce 4,000–5,000 platelets, which live about 10 days and are destroyed especially in the liver and spleen; thrombocytopoietin stimulates their formation.

💡 Memory Hook

B cells mature in intestinal lymphoid tissue; T cells mature in the thymus.

📖 8. Hematopoietic and Lymphoid Organs

★ Must-know

• In adults, hematopoiesis occurs mainly in bone marrow, while some lymphocytes form in lymphoid organs; if adult bone-marrow activity fails, the liver or spleen can regain blood-cell-forming activity.

📌 Red bone marrow forms blood cells, whereas yellow marrow contains abundant fat and loses hematopoietic activity in some bones after puberty; all bones are active before puberty, but only about one-quarter are active in adults.

• The thymus supports T-cell maturation, is most active during fetal life and childhood, and begins to atrophy at puberty; lymphoid follicles also occur in the intestinal lining and respiratory mucosa.

Further detail

• Adult active marrow is found in the:

  • ribs
  • sternum
  • vertebrae
  • skull
  • pelvis
  • long bones

• The spleen lies in the upper left abdomen, normally weighs about 150–200 g, destroys aged blood cells after birth, and participates in immunity.

• The body has 500–1,000 lymph nodes, each 2–25 mm in diameter; they filter germs and substances from lymph and supply lymphocytes to the blood.

📖 9. ABO Blood Groups and Inheritance

🔑 Key Concepts & Definitions

• Blood Group: A classification of human blood based on antigenic components of red blood cells, and typing is necessary before transfusion.

★ Must-know

• In the ABO system, group A red cells carry antigen A and the blood contains anti-B antibodies; group B red cells carry antigen B and the blood contains anti-A antibodies.

• Group AB red cells carry both A and B antigens and have neither antibody, whereas group O red cells carry neither antigen and the blood contains both anti-A and anti-B antibodies.

• The ABO system involves three alleles, A, B, and O: A dominates O, B dominates O, and A and B are codominant; phenotype alone cannot distinguish AA from AO or BB from BO.

Further detail

• Karl Landsteiner established the blood-group classification in 1901 and found that blood groups were inherited according to Mendelian laws.

📌 In an A-to-B transfusion, anti-A antibodies in the group B recipient destroy the donor's group A red blood cells.

💡 Memory Hook

A and B dominate O, while A and B are codominant with each other.

📖 10. Rh Groups and Transfusion Compatibility

📝 Essential Points

📌 Rh-positive red cells carry the Rh antigen, whereas Rh-negative red cells lack it and can prompt antibody production against it.

📌 An Rh-positive transfusion can trigger an immune response in an Rh-negative recipient, whereas the reverse Rh-negative-to-Rh-positive transfusion does not trigger the response described in the source.

• An Rh-negative mother can become immunized when Rh-positive fetal red cells cross the placenta; in a later pregnancy with an Rh-positive fetus, maternal antibodies can cross the placenta and cause hemolytic disease of the newborn.

💡 Memory Hook

Rh-positive fetal cells can immunize an Rh-negative mother → maternal antibodies may damage a later Rh-positive fetus.

📊 Synthesis Tables

ABO Antigens and Antibodies

Blood group	Red-cell antigens	Blood antibodies
A	A	Anti-B
B	B	Anti-A
AB	A and B	Neither
O	Neither	Anti-A and anti-B