Blood Composition and Functions

Plasma and Hematocrit

The blood consists of plasma and formed elements. Plasma is the liquid component, while hematocrit refers to the percentage of blood volume occupied by red blood cells (RBCs).

• Plasma: The straw-colored fluid portion of blood, comprising about 55% of total blood volume. It contains water, proteins, electrolytes, nutrients, hormones, and waste products.

• Hematocrit: The ratio of the volume of RBCs to the total volume of blood, usually expressed as a percentage. Normal values: Men ~40-54%, Women ~37-47%.

• Function: Hematocrit is used to assess anemia, polycythemia, and overall blood health.

Major Plasma Proteins and Their Functions

Plasma proteins play vital roles in maintaining osmotic pressure, immunity, and blood clotting.

• Albumin: Maintains osmotic pressure and transports substances.

• Globulins: Includes antibodies (immunoglobulins) for immune defense.

• Fibrinogen: Essential for blood clotting.

Blood Cells: Types, Origins, and Functions

Red Blood Cells (Erythrocytes), White Blood Cells (Leukocytes), and Platelets

Blood contains three main types of formed elements, each with distinct functions and origins.

• Red Blood Cells (RBCs): Carry oxygen via hemoglobin.

• White Blood Cells (WBCs): Defend against infection. Two main categories: Granular and Agranular.

• Platelets (Thrombocytes): Cell fragments involved in clotting.

• Origin: All blood cells originate from hematopoietic stem cells in the red bone marrow.

Erythropoiesis

Erythropoiesis is the process of RBC formation, regulated by erythropoietin (EPO) produced by the kidneys in response to low oxygen levels.

• Rate Control: EPO stimulates bone marrow to increase RBC production.

Anemia

Anemia is a condition characterized by a deficiency of RBCs or hemoglobin, leading to reduced oxygen transport.

• Causes: Blood loss, decreased production, increased destruction, or nutritional deficiencies.

Leukocytes: Types and Functions

Granular and Agranular Leukocytes

Leukocytes are classified based on the presence of granules in their cytoplasm.

• Granular Leukocytes: Neutrophils, Eosinophils, Basophils

• Agranular Leukocytes: Lymphocytes, Monocytes

• Lymphocytes: Two major types: B cells (produce antibodies) and T cells (cell-mediated immunity)

Antibody Production

B lymphocytes (B cells) are responsible for producing antibodies, which are proteins that target specific antigens.

Hemoglobin and Oxygen Transport

Hemoglobin Molecules in RBCs

Hemoglobin is the oxygen-carrying protein in RBCs. Each RBC contains about 250 million hemoglobin molecules.

• Essential Element: Iron is required for hemoglobin to bind oxygen.

Blood Types and Transfusion Compatibility

ABO Blood Types

The ABO system classifies blood based on the presence of antigens (A and B) on RBC surfaces.

• Responsible for ABO Types: The presence or absence of A and B antigens.

• Importance: Transfusing incompatible blood can cause immune reactions, hemolysis, and potentially fatal complications.

Platelets and Hemostasis

Hemostasis and Platelet Function

Hemostasis is the process that stops bleeding at the site of injury. Platelets play a central role by adhering to damaged vessels and forming a plug.

• Platelets: Stick to exposed collagen in injured vessels.

• Prostacyclin: Inhibits platelet aggregation, preventing unnecessary clotting.

• Collagen: Exposure triggers platelet activation.

Platelet Adhesion and Clot Formation

Platelets adhere to injured vessel walls, aggregate, and release factors that promote clotting.

• Trigger: Exposure to collagen and other subendothelial components.

Fibrin and Blood Clotting

Fibrin is a protein that forms the meshwork of a blood clot, stabilizing the platelet plug.

• Formation: Fibrinogen is converted to fibrin by the enzyme thrombin.

$\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

Intrinsic and Extrinsic Pathways of Blood Clotting

Blood clotting involves two pathways that converge to form a stable clot.

• Intrinsic Pathway: Initiated by damage inside the vessel; involves clotting factors present in blood.

• Extrinsic Pathway: Triggered by external trauma; involves tissue factor from damaged tissue.

• Common Pathway: Both lead to activation of factor X, resulting in conversion of prothrombin to thrombin and fibrinogen to fibrin.

$\text{Prothrombin} \xrightarrow{\text{Factor X}} \text{Thrombin}$ $\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

Summary Table: Blood Cell Types and Functions

Additional info: Academic context and definitions have been expanded for clarity and completeness.