Blood: Composition, Structure, and Function

Plasma Composition and Plasma Proteins

Blood plasma is the liquid matrix of blood, making up about 55% of total blood volume. It serves as a transport medium for nutrients, hormones, and waste products.

• Major Components: Water (about 90%), plasma proteins, electrolytes, nutrients, gases, and waste products.

• Major Plasma Proteins:

  • Albumin: Maintains osmotic pressure; produced by the liver.

  • Globulins: Include antibodies (immunoglobulins) and transport proteins; produced by the liver and immune cells.

  • Fibrinogen: Essential for blood clotting; produced by the liver.

Formed Elements of Blood

The formed elements include erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets).

• Erythrocytes (Red Blood Cells): Biconcave, anucleate cells specialized for oxygen transport.

• Leukocytes (White Blood Cells): Five types, each with distinct morphology and function.

• Thrombocytes (Platelets): Small, anucleate cell fragments involved in clotting.

Morphological Features of Blood Cells

• Erythrocytes: Biconcave discs, lack nuclei and organelles, uniform appearance.

• Leukocytes:

  • Granulocytes: Neutrophils (multi-lobed nucleus, pale granules), Eosinophils (bilobed nucleus, red-orange granules), Basophils (bilobed or S-shaped nucleus, dark blue granules).

  • Agranulocytes: Lymphocytes (large, round nucleus, scant cytoplasm), Monocytes (kidney-shaped nucleus, abundant cytoplasm).

• Platelets: Small, irregularly shaped cell fragments, no nucleus.

Normal Ranges for Blood Cell Counts

• Erythrocyte Count: Males: 4.7–6.1 million/μL; Females: 4.2–5.4 million/μL

• Hematocrit: Males: 42–52%; Females: 37–47%

• Total Leukocyte Count: 4,800–10,800/μL

• Platelet Count: 150,000–400,000/μL

Leukocyte Types and Classification

The five types of leukocytes, in order of prevalence, and their classification:

Structural Differences: Platelets vs. Other Formed Elements

• Platelets: Cell fragments derived from megakaryocytes; lack nuclei; contain granules with clotting factors.

• Other Formed Elements: RBCs are whole cells without nuclei; WBCs are complete cells with nuclei and organelles.

Hematopoiesis: Location and Overview

• Location: Occurs primarily in red bone marrow (e.g., flat bones, proximal epiphyses of long bones).

• Process: All formed elements arise from hematopoietic stem cells (hemocytoblasts).

Erythropoiesis and Regulation

• Erythropoiesis: The production of erythrocytes from stem cells in the bone marrow.

• Regulation: Controlled by the hormone erythropoietin (EPO), produced by the kidneys in response to hypoxia (low oxygen levels).

Equation:

Megakaryocytes and Platelet Formation

• Megakaryocytes: Large bone marrow cells that fragment to release platelets into the bloodstream.

Functions of Blood Cells

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

• Leukocytes: Immune defense (see table below).

• Platelets: Initiate blood clotting (hemostasis).

Hemoglobin: Structure, Function, and Breakdown

• Structure: Protein with four polypeptide chains, each containing a heme group with iron.

• Function: Binds and transports oxygen; also carries some carbon dioxide.

• Breakdown: In the spleen and liver, hemoglobin is broken down into heme (converted to bilirubin) and globin (broken into amino acids).

Functions of the Five Major Leukocytes

Hemostasis vs. Coagulation

• Hemostasis: The overall process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

• Coagulation: The specific process of blood clot formation via a cascade of clotting factors.

Process of Hemostasis

1. Vascular spasm (vasoconstriction)

2. Platelet plug formation

3. Coagulation (formation of fibrin mesh)

Hemostatic Disorders

Blood Groups: Surface Antigens and Antibodies

• Surface Antigens: Glycoproteins on RBC membranes determine blood group (ABO and Rh systems).

• ABO System: Type A (A antigen), Type B (B antigen), Type AB (both), Type O (neither).

• Antibodies: Plasma contains antibodies against antigens not present on one's own RBCs.

Rh Factor

• Rh Antigen (D): Presence = Rh positive; absence = Rh negative.

• Anti-Rh Antibodies: Only develop after exposure to Rh-positive blood (e.g., transfusion or pregnancy).

• Anti-A and Anti-B Antibodies: Present naturally without prior exposure.

Blood Transfusion Compatibility

• Compatible Types: Determined by matching antigens and avoiding antibodies that would attack donor RBCs.

• Transfusion Reaction: Occurs when incompatible blood is transfused, leading to agglutination and hemolysis.

• Universal Donor: Type O negative (no A, B, or Rh antigens).

• Universal Recipient: Type AB positive (has all antigens, no anti-A, anti-B, or anti-Rh antibodies).

Anemia: Types and Definitions

• Anemia: Condition of reduced oxygen-carrying capacity of blood due to low RBC count or hemoglobin.

• Types:

  • Iron-deficiency anemia: Due to insufficient iron for hemoglobin synthesis.

  • Pernicious anemia: Due to vitamin B12 deficiency.

  • Hemolytic anemia: Due to excessive RBC destruction.

  • Aplastic anemia: Due to bone marrow failure.

  • Sickle cell anemia: Due to abnormal hemoglobin S.

Other Blood Disorders

• Polycythemia: Excessive RBC production, increasing blood viscosity.

• Thrombocytopenia: Low platelet count, leading to bleeding risk.

• Leukemia: Cancer of white blood cells, leading to abnormal proliferation of immature WBCs.

• Erythroblastosis Fetalis: Hemolytic disease of the newborn due to Rh incompatibility between mother and fetus.

Additional info: Some details (e.g., specific anemia types and their mechanisms) were inferred based on standard Anatomy & Physiology curriculum.