CFR 4 Notes

Blood Cells and Their Functions

  • Types of Blood Cells

  • The three main types of blood cells are:

    1. Leukocytes (White Blood Cells)

    2. Erythrocytes (Red Blood Cells)

    3. Thrombocytes (Platelets)

  • Leukocytes:

  • These are nucleated cells crucial for the body’s immune response and defense against pathogens.

  • Comprise about 1% of the total blood cell count, averaging around 7,000 cells per milliliter of blood.

  • Formed primarily in the red bone marrow, though some types, like lymphocytes, also develop in lymphoid tissues such as the spleen and thymus.

  • Leukocytes are classified into two categories: agranulocytes and granulocytes, based on the presence or absence of granules in their cytoplasm.

Detailed Components of Leukocytes
Agranulocytes

  1. Lymphocytes

  • These are the smallest type of leukocytes, making up approximately 30% of the white blood cell population.

  • Produced in lymphoid tissues like lymph nodes and the spleen.

  • Types include:

    • T-lymphocytes: Involved in cellular immunity, they directly attack infected cells and help coordinate the immune response.

    • B-lymphocytes: Responsible for the production of antibodies that neutralize pathogens and toxins.

  1. Monocytes

  • Monocytes are the largest leukocytes, constituting about 5% of the white blood cell count.

  • They have phagocytic capabilities, meaning they can engulf and digest cellular debris and pathogens.

  • Once they migrate into tissues, monocytes differentiate into macrophages, which are powerful phagocytes that play critical roles in immune response.

Granulocytes

  1. Neutrophils

  • Neutrophils are the most abundant type of white blood cell, constituting approximately 62% of leukocytes.

  • They are key players in the immune response, primarily engaged in phagocytizing (consuming) pathogens, cellular debris, and foreign substances.

  • Neutrophils are the primary cells in pus, a thick fluid that forms during infections.

  1. Eosinophils

  • Comprising a small percentage of leukocytes, eosinophils are particularly active in response to parasitic infections and play a role in the inflammatory response associated with allergies.

  • They have limited phagocytic ability compared to neutrophils but can release cytotoxic granules to combat larger parasites.

  1. Basophils

  • The rarest type of leukocytes, making up about 0.4% of the total white blood cell count.

  • These cells play important roles in allergic reactions and inflammatory responses by releasing histamine (which promotes vasodilation and increases blood flow to inflamed areas) and heparin (an anticoagulant that prevents blood clotting).

Erythrocytes (Red Blood Cells)

  • Erythrocytes are specialized cells primarily responsible for the transport of oxygen throughout the body.

  • Characteristics include:

  • Typically anucleate (lacking a nucleus) in mammals, which provides more space for hemoglobin, the oxygen-carrying protein.

  • They have a unique biconcave disc shape, enhancing surface area for gas exchange.

  • The average life span of erythrocytes is about 120 days; they are subsequently removed from circulation by the spleen and liver, where their breakdown products, particularly bilirubin, have significant roles, including the contribution to bile color.

  • Concentration varies: approximately 5.2 million cells per milliliter in males and about 4.7 million in females.

Haemopoiesis (Blood Cell Formation)

  • Haemopoiesis is the continuous process of blood cell formation necessary to replace cells lost through daily wear and tear and pathological conditions.

  • Key sites of haemopoiesis include:

  • Early in development, blood cells are formed in the liver, spleen, and lymph nodes.

  • In adults, the primary site is the red bone marrow, which generates all types of blood cells, including platelets.

  • Haemocytoblasts are multipotent stem cells that give rise to unipotent stem cells, which then develop into specific types of blood cells.

Thrombocytes (Platelets)

  • Platelets, or thrombocytes, are cell fragments that are critical in the process of blood clotting (haemostasis).

  • These anucleate fragments are about 2-3 micrometers in diameter and have a life span of approximately 8 days.

  • They play a vital role in hemostasis by adhering to damaged blood vessel walls and aggregating to form a temporary plug.

  • The clotting process can be initiated by either intrinsic or extrinsic pathways, both of which lead to the formation of a stable clot.

Blood Clotting Mechanism

  • The blood clotting process is complex and begins with the activation of various clotting factors.

  • Fibrinogen is converted into fibrin, which forms a mesh-like structure that stabilizes the clot and prevents further bleeding.

  • Factors inhibiting clotting include:

  • Heparin, which has anticoagulant properties that help prevent unnecessary clot formation.

  • The removal of calcium ions (Ca++) in blood banks is crucial in preventing clotting during storage.

Haemophilia

  • Haemophilia is a genetic disorder characterized by abnormal bleeding attributed to deficiencies in specific clotting factors.

  • There are two main types of haemophilia:

  • Hemophilia A: This type is caused by a deficiency of factor VIII, accounting for about 80% of cases.

  • Hemophilia B: This type results from a deficiency of factor IX and is less common, constituting about 20% of cases.

  • Common symptoms of haemophilia include excessive bleeding following injuries, spontaneous bleeding, and an increased risk of bleeding complications during surgical procedures.

Blood Cells and Their Functions – Detailed Learning Outcomes
1. Understand the Types of Blood Cells

  • Leukocytes (White Blood Cells): Critical for the immune response, leukocytes comprise about 1% of total blood cell count, averaging 7,000 cells/mL. They can be divided into two categories: agranulocytes and granulocytes based on the presence of granules in their cytoplasm.

  • Erythrocytes (Red Blood Cells): Responsible for oxygen transport, erythrocytes are anucleate in mammals and characterized by a biconcave disc shape, allowing for greater surface area for gas exchange.

  • Thrombocytes (Platelets): Essential for blood clotting, these anucleate cell fragments form temporary plugs at damaged blood vessels.

2. Describe the Role and Types of Leukocytes

  • Agranulocytes:

  • Lymphocytes (30% of WBCs): Includes T-lymphocytes that directly attack infected cells and B-lymphocytes that produce antibodies.

  • Monocytes (5% of WBCs): Largest leukocytes that become macrophages in tissues, responsible for phagocytizing cellular debris and pathogens.

  • Granulocytes:

  • Neutrophils (62% of WBCs): Most abundant leukocytes, primary responders to infections that phagocytize pathogens and contribute to pus formation.

  • Eosinophils: Fight against parasitic infections and play a role in allergic reactions, releasing cytotoxic granules.

  • Basophils (0.4% of WBCs): Release histamine and heparin during allergic reactions, contributing to inflammation and blood flow.

3. Explain the Structure and Function of Erythrocytes

  • Erythrocytes lack a nucleus, providing room for hemoglobin, which binds to oxygen. They live about 120 days and their breakdown, particularly bilirubin, is processed in the liver and spleen. Males have approximately 5.2 million cells/mL while females have about 4.7 million/mL.

4. Illustrate the Process of Haemopoiesis

  • Haemopoiesis is the formation of blood cells occurring primarily in red bone marrow in adults. Early in development, it occurs in the liver, spleen, and lymph nodes. Haemocytoblasts are multipotent stem cells that generate specific blood cell types through various differentiation pathways.

5. Discuss the Function and Importance of Thrombocytes

  • Thrombocytes, or platelets, are vital for hemostasis. Affected by adhesion to blood vessel walls, they aggregate to form temporary plugs. They measure 2-3 µm in diameter and have a lifespan of about 8 days. The clotting mechanisms include both intrinsic and extrinsic pathways.

6. Outline the Blood Clotting Mechanism

  • The activation of clotting factors initiates the clotting process. Fibrinogen is converted to fibrin to stabilize clots. Heparin acts as an anticoagulant to regulate clotting, and calcium removal is crucial in blood banks to prevent clot formation during storage.

7. Describe Haemophilia and its Types

  • Haemophilia is a genetic disorder leading to excessive bleeding due to deficiencies in clotting factors. Hemophilia A is due to factor VIII deficiency (80% of cases) and Hemophilia B is caused by factor IX deficiency (20%). Symptoms include excessive bleeding from injuries, spontaneous bleeding, and complications during surgeries.