Blood Composition and Functions

Plasma and Formed Elements

The blood is a specialized connective tissue composed of plasma and formed elements. Plasma is the liquid matrix, while formed elements include red blood cells (RBCs), white blood cells (WBCs), and platelets.

• Plasma: Makes up about 55% of blood volume. Contains water, proteins, electrolytes, nutrients, hormones, and waste products.

• Formed Elements: Include erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets).

• Functions: Transport of gases, nutrients, hormones, waste; regulation of pH and temperature; protection against pathogens; clotting.

Hematocrit

Hematocrit is the percentage of blood volume occupied by red blood cells.

• Normal adult values: ~40-54% for males, ~37-47% for females.

• Measured by centrifuging blood and calculating the ratio of RBC volume to total blood volume.

Major Plasma Proteins

Plasma contains several important proteins, each with specific functions:

• Albumin: Maintains osmotic pressure and transports substances.

• Globulins: Include antibodies (immunoglobulins) and transport proteins.

• Fibrinogen: Essential for blood clotting.

Blood Cells: Structure, Origin, and Function

Scientific/Medical Names and Origins

• Red Blood Cells (Erythrocytes): Transport oxygen and carbon dioxide.

• White Blood Cells (Leukocytes): Defend against infection.

• Platelets (Thrombocytes): Involved in clotting.

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

Erythropoiesis

Erythropoiesis is the process of RBC formation.

• Occurs in red bone marrow.

• Regulated by the hormone erythropoietin (EPO), produced by the kidneys in response to low oxygen levels.

• Rate is controlled by tissue oxygen demand and EPO levels.

Anemia

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

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

• Symptoms: Fatigue, pallor, shortness of breath.

White Blood Cells: Types and Functions

Granular and Agranular Leukocytes

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

• Granular Leukocytes:

  • Neutrophils: Phagocytosis of bacteria.

  • Eosinophils: Combat parasites and modulate allergic responses.

  • Basophils: Release histamine in inflammatory reactions.

• Agranular Leukocytes:

  • Lymphocytes: Include B cells (produce antibodies) and T cells (cell-mediated immunity).

  • Monocytes: Differentiate into macrophages for phagocytosis.

Antibody Production

• B lymphocytes (B cells): Responsible for producing antibodies.

Hemoglobin and Oxygen Transport

Hemoglobin Molecules in RBCs

Hemoglobin is the oxygen-carrying protein in RBCs.

• Each RBC contains about 250 million hemoglobin molecules.

• Iron is the essential element for oxygen binding in hemoglobin.

Blood Types and Transfusion

ABO Blood Types

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

• Type A: A antigen, anti-B antibody.

• Type B: B antigen, anti-A antibody.

• Type AB: Both A and B antigens, no anti-A or anti-B antibodies.

• Type O: No antigens, both anti-A and anti-B antibodies.

Transfusing the wrong blood type can cause a severe immune reaction (hemolysis).

Hemostasis and Blood Clotting

Hemostasis

Hemostasis is the process that stops bleeding at the site of an injury.

• Involves vascular spasm, platelet plug formation, and coagulation.

• Platelets: Stick to damaged vessel walls and release chemicals to recruit more platelets.

• Prostacyclin: Inhibits platelet aggregation in healthy vessels.

• Collagen: Exposure triggers platelet activation.

Fibrin and Clot Formation

Fibrin is a protein that forms the meshwork of a blood clot.

• Formed from fibrinogen by the action of the enzyme thrombin.

• Triggers for formation include exposure of blood to tissue factors and collagen.

Equation:

Intrinsic and Extrinsic Pathways of Coagulation

Blood clotting involves two main 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.

• Both pathways lead to activation of Factor X, which converts prothrombin to thrombin, leading to fibrin formation.

Equation:

Summary Table: Blood Cell Types and Functions

Additional info:

• Normal RBC count: ~4.5-6 million cells/μL in males, ~4-5.5 million cells/μL in females.

• Blood volume in adults: ~5 liters.

• Hemoglobin normal values: ~13-18 g/dL in males, ~12-16 g/dL in females.