Blood: Structure and Functions

Functions of Blood

Blood is a vital connective tissue that performs several essential functions in the human body:

• Transport: Carries oxygen, carbon dioxide, nutrients, hormones, and waste products throughout the body.

• Regulation: Maintains body temperature, pH balance, and fluid volume.

• Protection: Defends against infection (immune cells) and prevents blood loss (clotting).

Composition of Blood

Blood consists of formed elements (cells) and plasma, each with distinct roles:

• Formed Elements (Blood Cells):

  • Red Blood Cells (Erythrocytes): Carry oxygen.

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

  • Platelets (Thrombocytes): Help with clotting.

• Plasma: The liquid part of blood (~55% of blood volume).

  • Electrolytes: Na+, K+, Ca2+, Cl-, etc.

  • Plasma Proteins:

    • Albumin: Maintains osmotic pressure.

    • Globulins: Transport and immune functions (antibodies).

    • Clotting Proteins: Fibrinogen, prothrombin.

  • Other: Gases (O2, CO2), nutrients (glucose, amino acids), nitrogenous wastes (urea, creatinine).

General Characteristics of Red Blood Cells (RBCs)

Red blood cells are specialized for oxygen transport:

• Biconcave shape for increased surface area.

• No nucleus or organelles in mature cells.

• Contain hemoglobin for oxygen transport.

• Live about 120 days.

Types of White Blood Cells (WBCs)

White blood cells are classified based on the presence or absence of granules:

• Granulocytes:

  • Neutrophils: Phagocytize bacteria.

  • Eosinophils: Attack parasites, involved in allergies.

  • Basophils: Release histamine (inflammation).

• Agranulocytes:

  • Lymphocytes: Immune response (B cells, T cells).

  • Monocytes: Become macrophages, phagocytize debris.

Blood Plasma Components

Main Components

• Formed Elements: RBCs, WBCs, platelets.

• Plasma Fluid: Water (about 90%).

• Plasma Proteins: Albumin, globulins, clotting proteins.

• Gases & Nutrients: O2, CO2, glucose, amino acids, lipids.

• Electrolytes: Na+, K+, Ca2+, Cl-, HCO3-.

• Nitrogenous Wastes: Urea, uric acid, creatinine.

Hemopoiesis (Blood Cell Formation)

Process Overview

• Occurs in red bone marrow.

• Hemocytoblasts (Hematopoietic Stem Cells): Give rise to all blood cells.

• Erythroblasts: Immature RBCs, develop from stem cells.

• Reticulocyte: Young RBC, enters bloodstream before maturing.

• Erythropoietin (EPO): Hormone from kidneys that stimulates RBC production.

Dietary Factors Affecting RBC Production

• Iron (for hemoglobin synthesis).

• Vitamin B12 and folic acid (for DNA synthesis).

• Protein (for cell structure).

RBC Destruction & Pigments

• Old RBCs are broken down in the spleen and liver.

• Hemoglobin splits into heme and globin.

• Heme is converted to biliverdin (green pigment), then to bilirubin (yellow pigment), which is excreted in bile.

Blood Groups and Transfusion

ABO Blood Group

• Antigens: Proteins on RBC surface (A, B).

• Antibodies: In plasma, react with foreign antigens.

• Universal Donor: Type O (no A/B antigens).

• Universal Recipient: Type AB (no anti-A/B antibodies).

Agglutination vs. Clotting

• Agglutination: Clumping of RBCs due to antibody-antigen reaction (e.g., wrong blood type transfusion).

• Clotting (Coagulation): Formation of a fibrin mesh to stop bleeding; involves platelets and clotting factors.

Rh Incompatibility & Erythroblastosis Fetalis

• If Rh- mother carries Rh+ fetus, she may develop anti-Rh antibodies.

• In later pregnancies, these antibodies can attack fetal RBCs, causing erythroblastosis fetalis (hemolytic disease of the newborn).

Blood Clotting Process

Steps in Clotting

1. Vasospasm: Vessel constricts to reduce blood flow.

2. Platelet Plug: Platelets stick to injury site.

3. Coagulation:

   • Prothrombin (inactive) → Thrombin (active, with Ca2+ & Vit. K).

   • Thrombin converts Fibrinogen → Fibrin (forms mesh).

4. Factors promoting clotting: Prothrombin, thrombin, fibrinogen, Ca2+, Vit. K, platelet plug.

5. Factors inhibiting clotting: Antithrombin, heparin.

Key Equations:

Thrombus vs. Embolus

• Thrombus: A stationary blood clot.

• Embolus: A clot or fragment that travels in the bloodstream.

Extrinsic vs. Intrinsic Clotting Mechanisms

• Extrinsic: Triggered by tissue damage outside the vessel (tissue factor).

• Intrinsic: Triggered by damage inside the vessel (contact with collagen).

Cardiovascular System: Heart Structure and Function

Functions of the Heart

• Transport oxygen, nutrients, hormones, and waste products throughout the body.

• Regulate body temperature, pH, and fluid balance.

• Protect against blood loss and infection.

Heart Location

• The heart is located in the mediastinum, between the lungs, behind the sternum, and above the diaphragm.

Coverings of the Heart

• Fibrous Pericardium: Tough outer layer, protects and anchors the heart.

• Parietal Pericardium: Lines the inner surface of the fibrous pericardium.

• Visceral Pericardium (Epicardium): Covers the heart's surface.

• The pericardial cavity is the space between the parietal and visceral layers, filled with fluid to reduce friction.

Layers of the Heart Wall

• Epicardium: Outer layer, also the visceral pericardium.

• Myocardium: Middle, muscular layer responsible for contraction.

• Endocardium: Inner layer lining the heart chambers and valves.

Anatomy & Function of Heart Parts

• Right Atrium: Receives deoxygenated blood from the body (via superior & inferior vena cava).

• Right Ventricle: Pumps blood to the lungs (via pulmonary trunk/arteries).

• Left Atrium: Receives oxygenated blood from the lungs (via pulmonary veins).

• Left Ventricle: Pumps oxygenated blood to the body (via aorta).

• Atrioventricular Valves:

  • Tricuspid Valve: Between right atrium & right ventricle.

  • Bicuspid/Mitral Valve: Between left atrium & left ventricle.

Table: Comparison of Blood Cell Types

Table: ABO Blood Group Compatibility

Additional info:

• Immunology and lymphatic system topics (e.g., lymphocytes, antibodies, immune responses) are referenced in the original notes but not fully detailed in the provided images. For a complete study guide, students should review the roles of B cells, T cells, antigen-presenting cells, and the major histocompatibility complex (MHC).

• Blood pressure, cardiac output, and vascular resistance are mentioned in the handwritten notes but not expanded in the images. These are important for understanding cardiovascular physiology.