Blood Physiology: Structure, Function, and Disorders (Chapter 18 Study Notes)

Blood Physiology

White Blood Cells (Leukocytes): Types and Functions

White blood cells (WBCs), or leukocytes, are essential components of the immune system, each type having specialized functions in defending the body against pathogens.

• Neutrophils: Phagocytize bacteria and are the most abundant WBCs.

• Lymphocytes: Include B cells (produce antibodies) and T cells (destroy infected cells).

• Monocytes: Differentiate into macrophages, which phagocytize pathogens and debris.

• Eosinophils: Combat parasitic infections and are involved in allergic responses.

• Basophils: Release histamine and heparin, playing a role in inflammation and allergic reactions.

Example: Neutrophils increase in number during bacterial infections, while eosinophils are elevated in parasitic infections.

Erythropoietin: Function and Role

Erythropoietin is a hormone produced primarily by the kidneys that stimulates the production of red blood cells (erythrocytes) in the bone marrow.

• Function: Increases erythrocyte production in response to low oxygen levels (hypoxia).

• Clinical Application: Used therapeutically in anemia associated with chronic kidney disease.

Example: Athletes may misuse erythropoietin to increase oxygen-carrying capacity.

Centrifugation and Hematocrit

Centrifugation is a laboratory technique used to separate blood components based on density, allowing measurement of hematocrit (the percentage of blood volume occupied by red blood cells).

• Premise: Spinning blood in a centrifuge separates plasma, buffy coat (WBCs and platelets), and erythrocytes.

• Hematocrit Calculation: $\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100$

Example: A low hematocrit may indicate anemia.

Properties of Erythrocytes (Red Blood Cells)

Erythrocytes are specialized for oxygen transport due to their unique structure and metabolic adaptations.

• Biconcave Shape: Increases surface area for gas exchange and flexibility to pass through capillaries.

• Lack of Organelles: Mature erythrocytes lack nuclei and most organelles, maximizing space for hemoglobin.

• Anaerobic Metabolism: Generate ATP via glycolysis, preventing consumption of transported oxygen.

Example: The biconcave shape allows erythrocytes to deform and pass through narrow vessels.

Anemias: Types and Causes

Anemia is a condition characterized by a deficiency of red blood cells or hemoglobin, leading to reduced oxygen delivery to tissues.

• Sickle Cell Anemia: Caused by a genetic mutation in hemoglobin, resulting in sickle-shaped cells that obstruct blood flow.

• Pernicious Anemia: Caused by vitamin B12 deficiency due to lack of intrinsic factor, leading to impaired RBC production.

• Additional info: Other types include iron-deficiency anemia and aplastic anemia.

Example: Sickle cell anemia leads to pain crises and organ damage due to blocked vessels.

Hemoglobin Structure and Oxygen Transport

Hemoglobin is the protein in erythrocytes responsible for oxygen transport. Its structure enables efficient binding and release of oxygen.

• Structure: Composed of four polypeptide chains (globins), each with a heme group containing iron (Fe2+).

• Oxygen Binding: Each heme group binds one oxygen molecule ($O_2$).

• Total Oxygen Capacity: One hemoglobin molecule can carry up to four oxygen molecules.

Example: $\text{1 Hemoglobin} = 4 \text{O}_2$ molecules

Diapedesis: Movement of White Blood Cells

Diapedesis is the process by which white blood cells move out of blood vessels into surrounding tissues to fight infection.

• Mechanism: WBCs extend pseudopods ("feet") to squeeze through endothelial gaps.

• Importance: Enables immune cells to reach sites of infection or injury.

Example: Neutrophils undergo diapedesis during acute inflammation.

Clotting Factors and Bleeding Disorders

Blood clotting requires a series of proteins called clotting factors. Deficiency in these factors leads to bleeding disorders.

• Hemophilia: A genetic disorder resulting from lack of specific clotting factors (e.g., Factor VIII or IX).

• Clinical Consequence: Inability to form stable clots, leading to excessive bleeding even from minor injuries.

Example: Hemophilia A is caused by deficiency of Factor VIII.