Physiology of Erythropoiesis and Thrombopoiesis

Erythropoietin and Thrombopoietin

• Thrombopoietin is produced by the liver.
• It causes the maturation of megakaryocytes, which in turn produce platelets.
• Erythropoietin is produced by the kidneys.
• It leads to the production of red blood cells.

Red Blood Cell Shape

• Mature Red Blood Cells are biconcave and are the ideal shape for efficient transport of oxygen.
• This shape allows for an increased surface area, which enhances laminar flow and increases the speed of blood flow.

Hemoglobin

• Hemoglobin is the main component of red blood cells.
• It comprises four subunits, each featuring a heme group containing iron.
• Iron acts as a positive ion and oxygen as a negative.
• Each hemoglobin molecule can bind to four oxygen molecules.
• Each red blood cell contains approximately 260 million hemoglobin molecules.
• Healthy adults possess approximately 5 grams of iron in their bodies.
• Red blood cells have a lifespan of approximately 120 days.

Iron Metabolism

• Iron is transported from the gut lumen to the blood by DMT1, FPT, and Transferrin.
• Transferrin then binds to iron and carries it to the bone marrow.
• In the bone marrow, erythroblast cells utilize iron for hemoglobin synthesis.

Spleen and Blood Metabolism

• The spleen plays a crucial role in blood metabolism.
• It is responsible for the destruction of old red blood cells (after their 120-day lifespan).
• The spleen recycles amino acids and iron (Fe2+) from red blood cells.
• It stores red blood cells as a reserve in case of blood loss.
• The heme group from red blood cells is broken down into bilirubin.
• Bilirubin is either sent to the liver for elimination via the bile-intestinal route or to the kidneys for elimination.
• Iron (Fe2+) is stored in the liver as ferritin.

Hematopoiesis

• Hematopoiesis, which is the synthesis of blood cells, occurs in the bone marrow.
• Stem cells in the bone marrow differentiate into various blood cell types.
• Erythroblasts mature into reticulocytes, ultimately transforming into erythrocytes (red blood cells).
• Megakaryocytes are responsible for the production of platelets.
• Other blood cells produced in the bone marrow include neutrophils, monocytes, basophils, eosinophils, and lymphocytes.

The Immune System

• Cells of the immune system are specialized to detect, target, and destroy foreign antigens.
• Lymphocytes (T and B Cells), macrophages, and antigen-presenting cells are key players in the immune response.
• Helper T cells are crucial in amplifying the immune response.
• Cytotoxic T cells directly kill infected or cancerous cells.

Humoral Immunity

• Humoral immunity is a branch of the adaptive immune system, involving B cells.
• When B cells encounter a specific antigen, they become activated.
• Activated B cells differentiate into plasma cells and memory B cells.
• Plasma cells produce antibodies that bind to and neutralize antigens.
• Memory B cells remain dormant, waiting for a re
• exposure to the same antigen, enabling a more rapid response.

Innate Immunity

• Innate immunity is the body's first line of defense against pathogens.
• It relies on physical barriers, such as the skin and mucous membranes, and specialized cells, such as macrophages and neutrophils.
• The innate immune system acts rapidly and nonspecifically, meaning it responds to a broad range of pathogens.

Characteristics of Adaptive Immunity

• The adaptive immune system is characterized by specificity, diversity, and memory.
• It exhibits high specificity, recognizing and targeting specific antigens.
• It has a diverse range of receptors for antigens, allowing for the recognition of a vast array of pathogens.
• Memory cells enable a faster and more robust response to previously encountered antigens

Antigens

• Antigens are molecules that trigger a specific immune response.
• They can be components of microorganisms or other foreign substances.
• Antigens often have multiple epitopes, which are specific regions that can stimulate a distinct immune response.

Lymphocytes and Adaptive Immunity

• B and T cells are the primary cells of the adaptive immune system.
• They express specific receptors for specific antigens, allowing them to identify and target antigens of interest.
• B cells produce antibodies, while T cells directly kill infected cells.
• Lymphocytes play a crucial role in both humoral and cell-mediated immunity.