Leukocytes - Circulation Systems

Inflammatory Response and Immune Cells

  • Localized Inflammation and Infection

    • Inflammation aims to isolate the area with infection to prevent spreading.

    • Greta refers to localized inflammation and infection.

  • Lymphocytes

    • Major components of the immune response, include:

    • T Cells

    • B Cells

    • Natural Killer Cells (NK cells)

    • NK cells are part of the innate immunity and can kill cancer cells.

    • T cells can kill cancer cells, virus-infected cells, and foreign cells (e.g., transplanted tissue).

  • Activation Process

    • T cells present antigens to B cells, coordinating immune responses.

    • Regulatory T Cells dampen immune responses.

    • T cells initiate and coordinate immune responses.

  • Lymphocyte Statistics

    • Lymphocytes account for 25-33% of all leukocytes, making them the second most abundant leukocyte class.

    • Named for their presence in lymphatic tissues (lymph nodes, spleen, thymus).

  • Monocytes

    • Constitute 3-8% of leukocytes and are the largest type of leukocyte.

    • They differentiate into macrophages and dendritic cells upon entering tissues.

    • Engage in phagocytosis, ingesting bacteria, debris, and pathogens (e.g., in the liver).

Blood Clot Formation

  • Blood Vessel Structure

    • Blood vessels have a smooth inside lumen to facilitate red blood cell passage and prevent clogs.

    • Prostacyclins prevent platelet activation to avoid unnecessary clots.

  • Triggering Clotting Process

    • A tear in the endothelium exposes collagen fibers, prompting platelet adhesion and activation.

    • Positive Feedback Mechanism: Activated platelets stimulate more platelets to adhere, forming a plug.

  • Platelet Activation and Function

    • Activated platelets release serotonin, causing vasoconstriction to minimize blood flow and bleeding.

    • Formation of a temporary blockage (platelet plug) is initiated, followed by coagulation.

    • Conversion of fibrinogen into fibrin creates a protein polymer, trapping cells and forming a clot.

    • Fibrin forms a web-like network that traps other cells and platelets until tissue heals.

Coagulation Pathways

  • Coagulation involves intrinsic and extrinsic mechanisms that activate clotting factors, primarily resulting in factor X activation.

  • Extrinsic Mechanism

    • Initiated by tissue damage, releasing factor III (thromboplastin) for clotting.

    • This combines with factor VII to activate factor X.

  • Intrinsic Mechanism

    • Platelet activation releases factor XII, which triggers a cascade leading to factor X activation through factors XI, IX, and VIII.

  • Conversion Process

    • Activation of factor X leads to the production of thrombin from prothrombin.

    • Thrombin further converts fibrinogen into fibrin, completing the clot formation process.

Hemostasis and Fibrinolysis

  • Hemostasis

    • Stopping of bleeding through a series of steps: platelet plug formation, coagulation (fibrin formation), and tissue repair.

  • Fibrinolysis

    • The breakdown of fibrin polymers once the tissue is healed, initiated by plasmin (activated from plasminogen) via tissue plasminogen activator (tPA).

  • Clinical implications include the importance of vitamin K in coagulation and its sources (lipid transporters in the intestine).

Vitamin K and Clotting Factor Activation

  • The liver produces most clotting factors and requires adequate vitamin K for activation.

    • Vitamin K is a fat-soluble vitamin absorbed with the help of bile.

    • Supplementation is critical in late pregnancy to prevent bleeding during delivery.

  • Blood thinners and their effect on vitamin K metabolism relate to risks of blood clots.

Clinical Aspects of Coagulation Disorders

  • Hemophilia

    • A genetic disorder affecting clotting factors, sex-linked on the X chromosome.

    • Carriers can exhibit different symptoms due to the presence of one functional allele.

    • Sons have a 50% chance of inheriting hemophilia from carrier mothers.

  • Treatments for hemophilia include administering purified clotting factors.

Cardiovascular System Overview

  • Introduction to heart anatomy, histology, and the conduction pathway in the cardiovascular system.

Pericardium and Heart Structure

  • Pericardial Sac

    • A double-wall sac encasing the heart with fluid to reduce friction during heartbeats.

    • Consists of a fibrous pericardium and a serous pericardium (visceral and parietal layers).

    • Pericarditis is an inflammation leading to increased friction during heartbeats.

  • Heart Wall Layers

    • Epicardium (visceral pericardium): Outer layer of epithelial tissue.

    • Myocardium: The muscular layer responsible for heart contractions, composed of striated cardiomyocytes. Thickness varies based on chamber function.

    • Endocardium: Smooth inner lining preventing coagulation and facilitating blood flow within heart chambers.

Myocardium and Cardiomyocytes

  • Cardiac Muscle Characteristics

    • Cardiomyocytes are short, thick, branched, striated muscle cells with intercalated discs for strength and electrical conduction.

    • These cells rely on aerobic respiration and store energy in large mitochondria.

    • They cannot perform anaerobic fermentation and are vulnerable to oxygen deprivation (e.g., through blockage).

  • Fatigue Resistance

    • Cardiomyocytes can sustain continuous contraction without fatigue, making oxygenation critical for heart function.

Blood Circulation Pathways

  • Pulmonary Circulation

    • Deoxygenated blood from the right ventricle to the lungs via pulmonary arteries for oxygenation.

    • Oxygen-rich blood returns to the left atrium through pulmonary veins.

  • Systemic Circulation

    • Oxygenated blood pumped from the left ventricle through the aorta to all body regions.

    • Importance of coronary arteries in supplying oxygen to the heart muscle.