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BSC NURSING SEM1 APPLIED ANATOMY UNIT 4 The Circulatory and lymphatic system

  • Structure of blood components, blood vessels-Arterial and Venous system

Structure of Blood Components

Blood is a specialized connective tissue that consists of two main components:

1. Plasma (55% of blood volume)

  • The liquid portion of blood.
  • Composition:
    • Water (~90%): Acts as a solvent.
    • Proteins (~7%):
      • Albumin: Maintains osmotic pressure.
      • Globulins: Includes antibodies for immune defense.
      • Fibrinogen: Essential for blood clotting.
    • Solutes (~3%): Nutrients (glucose, amino acids), electrolytes (Na⁺, K⁺, Ca²⁺), hormones, and waste products (urea, CO₂).

2. Formed Elements (45% of blood volume)

  • Red Blood Cells (RBCs/Erythrocytes):

Red Blood Cells (RBCs/Erythrocytes): Detailed Overview

Red blood cells (RBCs), also known as erythrocytes, are the most abundant cells in the blood. Their primary function is to transport oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs.

Structure of RBCs

  1. Shape:
    • Biconcave Disc: RBCs are biconcave, which increases their surface area for gas exchange and allows flexibility to pass through narrow capillaries.
  2. Size:
    • Diameter: ~7.5 µm.
    • Thickness: ~2 µm at the periphery and ~1 µm in the center.
  3. Nucleus and Organelles:
    • Mature RBCs lack a nucleus and organelles, which provides more space for hemoglobin.
    • They cannot synthesize proteins or perform aerobic respiration.
  4. Cytoplasm:
    • Filled with hemoglobin, a red-pigmented protein that binds oxygen and carbon dioxide.
  5. Membrane:
    • Composed of a lipid bilayer with embedded proteins that maintain flexibility and stability.
    • Contains specific antigens (A, B, AB, or O) that determine blood type.

Formation of RBCs (Erythropoiesis)

  1. Site of Production:
    • Occurs in the red bone marrow of flat bones (e.g., sternum, ribs, pelvis) and long bones.
  2. Stages of Development:
    • Proerythroblast → Basophilic Erythroblast → Polychromatic Erythroblast → Orthochromatic Erythroblast → Reticulocyte → Mature RBC.
    • Reticulocytes enter the bloodstream and mature into RBCs within 1–2 days.
  3. Regulation:
    • Controlled by erythropoietin (EPO), a hormone secreted by the kidneys in response to hypoxia (low oxygen levels).
  4. Nutrients Required:
    • Iron: For hemoglobin synthesis.
    • Vitamin B12 and Folate: For DNA synthesis during cell division.

Functions of RBCs

  1. Oxygen Transport:
    • Hemoglobin binds oxygen in the lungs and releases it to tissues.
    • Each hemoglobin molecule can carry four oxygen molecules.
  2. Carbon Dioxide Transport:
    • Transports CO₂ from tissues to the lungs.
    • ~20% of CO₂ binds to hemoglobin, while the rest is transported as bicarbonate ions.
  3. Buffering Role:
    • Helps maintain blood pH by buffering hydrogen ions.

Lifespan of RBCs

  • Lifespan: ~120 days in circulation.
  • Senescence:
    • Old RBCs are removed by macrophages in the spleen, liver, and bone marrow.
    • Hemoglobin is broken down into:
      • Heme: Converted to bilirubin and excreted in bile.
      • Globin: Broken down into amino acids.
      • Iron: Recycled and stored as ferritin or transported by transferrin.

Clinical Significance

Disorders of RBCs

  1. Anemia:
    • Decreased RBC count or hemoglobin levels.
    • Types:
      • Iron-Deficiency Anemia: Due to insufficient iron.
      • Megaloblastic Anemia: Caused by vitamin B12 or folate deficiency.
      • Hemolytic Anemia: Premature destruction of RBCs.
      • Sickle Cell Anemia: Genetic disorder causing abnormal hemoglobin (HbS), leading to misshapen RBCs.
      • Aplastic Anemia: Bone marrow failure to produce RBCs.
  2. Polycythemia:
    • Increased RBC count.
    • Can be primary (polycythemia vera) or secondary (due to hypoxia or EPO overproduction).
  3. Jaundice:
    • Excessive breakdown of RBCs can lead to high bilirubin levels, causing yellowing of skin and eyes.
  4. Thalassemia:
    • Genetic disorder causing abnormal hemoglobin synthesis.

Laboratory Tests

  1. Complete Blood Count (CBC):
    • Measures RBC count, hemoglobin concentration, hematocrit, and red cell indices.
  2. Peripheral Smear:
    • Examines RBC morphology under a microscope.
  3. Reticulocyte Count:
    • Assesses bone marrow activity in producing RBCs.
  4. Hemoglobin Electrophoresis:
    • Identifies abnormal hemoglobin variants.
  • White Blood Cells (WBCs/Leukocytes):
  • White Blood Cells (WBCs/Leukocytes):

White Blood Cells (WBCs/Leukocytes): Detailed Overview

White blood cells (WBCs), or leukocytes, are essential components of the immune system. They protect the body against infections, remove debris, and play a role in inflammation and immune responses.

Structure and Classification

WBCs are larger than red blood cells, have a nucleus, and are classified into two main categories based on the presence of granules in their cytoplasm:

1. Granulocytes (Polymorphonuclear Leukocytes)

Characterized by the presence of cytoplasmic granules and lobed nuclei.

  1. Neutrophils:
    • Percentage: ~50–70% of total WBCs.
    • Appearance: Multilobed nucleus (3–5 lobes); pale-staining granules.
    • Function:
      • First responders to bacterial infections.
      • Phagocytize and destroy bacteria.
    • Lifespan: ~6 hours to a few days.
  2. Eosinophils:
    • Percentage: ~1–4%.
    • Appearance: Bilobed nucleus; granules stain red with eosin.
    • Function:
      • Combat parasitic infections.
      • Involved in allergic reactions by modulating histamine release.
    • Lifespan: ~8–12 days.
  3. Basophils:
    • Percentage: ~0.5–1%.
    • Appearance: Bilobed nucleus; granules stain dark blue/purple.
    • Function:
      • Release histamine and heparin during allergic and inflammatory responses.
      • Promote vasodilation and increased vascular permeability.
    • Lifespan: A few hours to a few days.

2. Agranulocytes (Mononuclear Leukocytes)

Characterized by the absence of granules and a round or kidney-shaped nucleus.

  1. Lymphocytes:
    • Percentage: ~20–40%.
    • Appearance: Large, round nucleus occupying most of the cell.
    • Types:
      • B-cells: Produce antibodies (humoral immunity).
      • T-cells: Directly attack infected or cancerous cells (cell-mediated immunity).
      • Natural Killer (NK) Cells: Destroy infected or abnormal cells without prior sensitization.
    • Function:
      • Central role in adaptive immunity.
    • Lifespan: Varies from days to years (memory cells).
  2. Monocytes:
    • Percentage: ~2–8%.
    • Appearance: Kidney-shaped nucleus; abundant cytoplasm.
    • Function:
      • Differentiate into macrophages or dendritic cells in tissues.
      • Phagocytize pathogens, dead cells, and debris.
      • Present antigens to lymphocytes to trigger immune responses.
    • Lifespan: ~1–3 days in circulation; months to years in tissues.

Production and Regulation

  1. Site of Production:
    • WBCs are produced in the bone marrow from hematopoietic stem cells.
    • Lymphocytes also mature in lymphoid tissues (e.g., thymus, spleen, lymph nodes).
  2. Regulation:
    • Controlled by cytokines and growth factors like colony-stimulating factors (CSFs) and interleukins.
    • Infection or inflammation increases WBC production (leukocytosis).

Functions of WBCs

  1. Immune Defense:
    • Protect the body against bacteria, viruses, fungi, parasites, and toxins.
  2. Phagocytosis:
    • Neutrophils, monocytes, and macrophages engulf and destroy pathogens and debris.
  3. Antibody Production:
    • B-cells produce specific antibodies to neutralize antigens.
  4. Allergic Reactions:
    • Eosinophils and basophils mediate allergic and hypersensitivity reactions.
  5. Inflammation:
    • Basophils and mast cells release mediators (e.g., histamine) to promote inflammation.
  6. Immune Regulation:
    • T-cells regulate immune responses, including cytotoxic and helper functions.

Normal WBC Count

  • Normal Range: 4,000–11,000 cells/µL of blood.
  • Leukocytosis: Elevated WBC count (>11,000/µL), often due to infections or inflammation.
  • Leukopenia: Low WBC count (<4,000/µL), seen in conditions like bone marrow suppression or severe infections.

Clinical Significance

WBC Disorders

  1. Increased WBC Count (Leukocytosis):
    • Causes:
      • Infections (bacterial, viral, parasitic).
      • Inflammation (e.g., rheumatoid arthritis).
      • Leukemia (cancer of WBCs).
      • Stress or corticosteroid use.
  2. Decreased WBC Count (Leukopenia):
    • Causes:
      • Viral infections (e.g., HIV).
      • Bone marrow suppression (e.g., chemotherapy, radiation).
      • Autoimmune diseases (e.g., lupus).
      • Severe bacterial infections (sepsis).
  3. Leukemia:
    • Cancer of bone marrow leading to abnormal WBC production.
    • Types:
      • Acute Lymphocytic Leukemia (ALL).
      • Acute Myeloid Leukemia (AML).
      • Chronic Lymphocytic Leukemia (CLL).
      • Chronic Myeloid Leukemia (CML).
  4. Lymphomas:
    • Cancers of lymphocytes (e.g., Hodgkin’s and non-Hodgkin’s lymphoma).
  5. Eosinophilia:
    • Elevated eosinophils due to parasitic infections or allergic reactions.

Diagnostic Tests

  1. Complete Blood Count (CBC):
    • Measures WBC count and distribution of WBC types (differential count).
  2. Peripheral Blood Smear:
    • Examines the size, shape, and characteristics of WBCs under a microscope.
  3. Bone Marrow Biopsy:
    • Evaluates WBC production in the bone marrow.
  4. Flow Cytometry:
    • Identifies specific WBC populations and abnormalities.
  • Platelets (Thrombocytes):

Platelets (Thrombocytes): Detailed Overview

Platelets, or thrombocytes, are small, anucleated cell fragments derived from megakaryocytes in the bone marrow. They play a critical role in blood clotting and maintaining hemostasis.

Structure of Platelets

  1. Size:
    • Diameter: 2–3 µm.
    • Smaller than red and white blood cells.
  2. Shape:
    • Disc-shaped in their resting state.
    • Become irregular and sticky when activated.
  3. Structure:
    • Membrane:
      • Phospholipid bilayer containing glycoproteins that mediate adhesion and aggregation.
      • Contains receptors for clotting factors and von Willebrand factor (vWF).
    • Cytoplasm:
      • Filled with granules that release substances critical for clotting and vessel repair:
        • Alpha Granules: Contain clotting factors (fibrinogen, vWF) and growth factors (platelet-derived growth factor, PDGF).
        • Dense Granules: Contain ADP, ATP, serotonin, and calcium.
      • Contains microtubules and actin filaments to maintain shape and facilitate movement.
    • No Nucleus:
      • Platelets cannot divide or synthesize proteins.

Production of Platelets (Thrombopoiesis)

  1. Site:
    • Produced in the bone marrow by megakaryocytes, large cells that shed cytoplasmic fragments.
  2. Regulation:
    • Controlled by thrombopoietin (TPO), a hormone primarily produced in the liver and kidneys.
    • Low platelet count stimulates increased TPO production.
  3. Lifespan:
    • Circulate in the bloodstream for ~7–10 days.
    • Old platelets are removed by macrophages in the spleen and liver.

Functions of Platelets

  1. Hemostasis:
    • Primary Hemostasis:
      • Platelets adhere to damaged endothelium via vWF and glycoprotein receptors.
      • Form a temporary platelet plug to stop bleeding.
    • Secondary Hemostasis:
      • Platelets provide a surface for the activation of clotting factors, leading to fibrin formation and stabilization of the clot.
  2. Wound Healing:
    • Release growth factors like PDGF and vascular endothelial growth factor (VEGF), promoting tissue repair and angiogenesis.
  3. Vasoconstriction:
    • Release serotonin, which causes constriction of blood vessels at the site of injury.
  4. Immune Function:
    • Platelets interact with immune cells and participate in the inflammatory response.

Normal Platelet Count

  • Normal Range: 150,000–450,000 platelets/µL of blood.
  • Thrombocytopenia: Platelet count <150,000/µL.
  • Thrombocytosis: Platelet count >450,000/µL.

Clinical Significance

Disorders of Platelets

  1. Thrombocytopenia (Low Platelet Count):
    • Causes:
      • Decreased production (e.g., bone marrow failure, aplastic anemia).
      • Increased destruction (e.g., immune thrombocytopenia, DIC).
      • Sequestration (e.g., splenomegaly).
    • Symptoms:
      • Easy bruising.
      • Prolonged bleeding from minor cuts.
      • Petechiae (small red or purple spots on the skin).
      • Mucosal bleeding (e.g., gums, nosebleeds).
  2. Thrombocytosis (High Platelet Count):
    • Causes:
      • Primary Thrombocytosis: Due to bone marrow disorders (e.g., essential thrombocythemia).
      • Secondary Thrombocytosis: Reactive increase due to inflammation, infection, or iron deficiency.
    • Complications:
      • Increased risk of thrombosis (clot formation).
  3. Platelet Dysfunction:
    • Inherited Disorders:
      • Glanzmann thrombasthenia (defective platelet aggregation).
      • Bernard-Soulier syndrome (defective adhesion).
    • Acquired Disorders:
      • Due to medications (e.g., aspirin, clopidogrel).
      • Uremia (kidney failure).
  4. Disseminated Intravascular Coagulation (DIC):
    • Uncontrolled activation of clotting pathways leads to widespread clotting and subsequent bleeding.

Diagnostic Tests

  1. Platelet Count:
    • Measures the number of platelets in the blood.
  2. Peripheral Blood Smear:
    • Examines platelet size, shape, and distribution.
  3. Bleeding Time:
    • Assesses the time taken for blood to clot.
  4. Platelet Function Tests:
    • Evaluate aggregation and adhesion.
  5. Bone Marrow Biopsy:
    • Assesses megakaryocyte production in cases of unexplained thrombocytopenia or thrombocytosis.

Treatment Options

  1. For Thrombocytopenia:
    • Platelet transfusion in severe cases.
    • Treat underlying causes (e.g., infections, autoimmune diseases).
  2. For Thrombocytosis:
    • Medications like aspirin to reduce clotting risk.
    • Cytoreductive therapy in primary thrombocytosis.
  3. For Platelet Dysfunction:
    • Desmopressin (DDAVP) for mild bleeding.
    • Avoidance of antiplatelet drugs in inherited disorders.

Blood Vessels

Blood vessels are the channels through which blood circulates throughout the body. They include arteries, veins, and capillaries.

Arterial System

Arteries are blood vessels that carry oxygenated blood (except the pulmonary artery) away from the heart to the tissues.

  1. Structure of Arteries:
    • Tunica Intima (Inner Layer):
      • Lined with endothelium.
      • Provides a smooth surface to reduce friction.
    • Tunica Media (Middle Layer):
      • Made of smooth muscle and elastic fibers.
      • Responsible for vasoconstriction and vasodilation.
    • Tunica Externa (Adventitia):
      • Outer layer of connective tissue providing structural support.
  2. Types of Arteries:
    • Elastic Arteries:
      • Largest arteries (e.g., aorta).
      • Contain abundant elastic fibers to handle high-pressure blood flow.
    • Muscular Arteries:
      • Medium-sized arteries (e.g., radial, femoral arteries).
      • Distribute blood to specific body regions.
    • Arterioles:
      • Smallest arteries.
      • Regulate blood flow into capillaries via vasoconstriction and vasodilation.
  3. Function:
    • Transport oxygenated blood under high pressure from the heart to tissues.

Venous System

Veins are blood vessels that carry deoxygenated blood (except the pulmonary vein) from the tissues back to the heart.

  1. Structure of Veins:
    • Tunica Intima (Inner Layer):
      • Lined with endothelium.
      • May have valves to prevent backflow.
    • Tunica Media (Middle Layer):
      • Thinner than in arteries, with fewer smooth muscle fibers.
    • Tunica Externa (Adventitia):
      • Thickest layer in veins, providing strength and flexibility.
  2. Types of Veins:
    • Superficial Veins:
      • Located near the surface of the body (e.g., great saphenous vein).
    • Deep Veins:
      • Located deeper within the body, often accompanying arteries (e.g., femoral vein).
    • Venules:
      • Small veins that collect blood from capillaries.
  3. Function:
    • Transport deoxygenated blood under low pressure back to the heart.
    • Store up to 70% of the body’s blood volume at any time.

Comparison: Arteries vs. Veins

FeatureArteriesVeins
Blood DirectionAway from the heartToward the heart
OxygenationOxygenated (except pulmonary)Deoxygenated (except pulmonary)
Wall ThicknessThickThin
PressureHighLow
Lumen SizeNarrowWide
ValvesAbsent (except aorta branches)Present to prevent backflow

Capillaries

Capillaries are the smallest blood vessels, acting as sites of exchange between blood and tissues.

  1. Structure:
    • Single layer of endothelial cells.
    • Thin walls to facilitate diffusion.
  2. Types:
    • Continuous Capillaries: Least permeable, found in muscles and the brain.
    • Fenestrated Capillaries: Have small pores, found in kidneys and intestines.
    • Sinusoidal Capillaries: Most permeable, found in the liver and spleen.
  3. Function:
    • Exchange of gases (O₂ and CO₂), nutrients, and waste products.

Clinical Significance

Arterial Disorders

  • Atherosclerosis: Plaque buildup in arteries, leading to narrowing.
  • Aneurysm: Abnormal dilation of an artery.
  • Hypertension: High blood pressure damaging arterial walls.

Venous Disorders

  • Varicose Veins: Enlarged, twisted veins due to valve failure.
  • Deep Vein Thrombosis (DVT): Clot formation in deep veins.
  • Venous Insufficiency: Inadequate blood return to the heart.
  • Position of heart relative to the associated structures

Position of the Heart Relative to Associated Structures

The heart is a hollow, muscular organ located in the thoracic cavity. It is slightly tilted and lies within the mediastinum, a central compartment between the lungs, behind the sternum, and above the diaphragm.

Relative Position

  1. Location in the Thoracic Cavity:
    • Lies in the middle mediastinum.
    • Positioned between the second rib (base of the heart) and the fifth intercostal space (apex of the heart).
  2. Orientation:
    • Apex: Directed downward, forward, and to the left.
    • Base: Directed upward, backward, and to the right.

Position Relative to Key Structures

Anterior (Front):

  • Sternum and ribs (specifically the 3rd to 6th costal cartilages).
  • Thymus in children and young adults.

Posterior (Back):

  • Esophagus.
  • Descending thoracic aorta.
  • Vertebral column (T5–T8 vertebrae).

Lateral (Sides):

  • Lungs:
    • Right lung on the right side.
    • Left lung on the left side, with the heart occupying the cardiac notch of the left lung.

Superior:

  • Great vessels, including:
    • Aorta.
    • Pulmonary trunk.
    • Superior vena cava.

Inferior:

  • Diaphragm, which separates the heart from the abdominal cavity.
  • The central tendon of the diaphragm is in direct contact with the heart’s pericardium.

Chambers and Orientation

  1. Right Atrium and Right Ventricle:
    • Positioned more anteriorly.
    • Close to the sternum.
  2. Left Atrium and Left Ventricle:
    • Positioned more posteriorly.
    • The left ventricle forms the apex of the heart.

Pericardium and Surrounding Structures

  1. Fibrous Pericardium:
    • Outermost layer, attached to the diaphragm and the great vessels.
    • Protects the heart and anchors it in place.
  2. Serous Pericardium:
    • Parietal layer lines the fibrous pericardium.
    • Visceral layer (epicardium) covers the heart’s surface.
  3. Pericardial Cavity:
    • Lies between the parietal and visceral layers, containing lubricating fluid.

Clinical Relevance

  1. Cardiac Compression (Tamponade):
    • Rapid fluid accumulation in the pericardial cavity can compress the heart, affecting its position and function.
  2. Mediastinal Shift:
    • Conditions like pneumothorax can shift the heart’s position due to pressure changes.
  3. Cardiac Imaging:
    • Chest X-rays and echocardiography help visualize the heart’s position relative to other structures.
  • Chambers of heart

Chambers of the Heart: Detailed Overview

The heart consists of four chambers that work together to pump blood throughout the body. These chambers are divided into two atria (upper chambers) and two ventricles (lower chambers), separated by septa.

Anatomy of the Chambers

1. Right Atrium (RA)

  • Location:
    • Upper right chamber.
    • Forms the right border of the heart.
  • Function:
    • Receives deoxygenated blood from the body.
    • Sends blood to the right ventricle.
  • Structures:
    • Openings:
      • Superior vena cava (SVC): Brings blood from the upper body.
      • Inferior vena cava (IVC): Brings blood from the lower body.
      • Coronary sinus: Drains blood from the heart’s own circulation.
    • Right auricle: A small, ear-shaped extension that increases the atrium’s capacity.
    • Fossa ovalis: A depression in the interatrial septum, a remnant of the fetal foramen ovale.
    • Crista terminalis: A ridge that separates the smooth posterior wall from the rough anterior wall (containing pectinate muscles).

2. Right Ventricle (RV)

  • Location:
    • Lower right chamber.
    • Forms most of the anterior surface of the heart.
  • Function:
    • Pumps deoxygenated blood to the lungs via the pulmonary artery.
  • Structures:
    • Tricuspid valve:
      • Located between the right atrium and right ventricle.
      • Prevents backflow of blood into the atrium.
    • Trabeculae carneae:
      • Irregular muscular ridges lining the ventricular walls.
    • Papillary muscles:
      • Anchor the chordae tendineae, which attach to the tricuspid valve cusps.
    • Pulmonary valve:
      • Located at the opening of the pulmonary artery.
      • Prevents backflow into the right ventricle during diastole.

3. Left Atrium (LA)

  • Location:
    • Upper left chamber.
    • Forms the posterior surface of the heart.
  • Function:
    • Receives oxygenated blood from the lungs via the pulmonary veins.
    • Sends blood to the left ventricle.
  • Structures:
    • Openings:
      • Four pulmonary veins (two from each lung).
    • Left auricle:
      • A small, ear-shaped extension that increases atrial capacity.
    • Smooth walls:
      • Unlike the right atrium, most of the left atrium has smooth walls due to embryological development.

4. Left Ventricle (LV)

  • Location:
    • Lower left chamber.
    • Forms the apex and most of the inferior and left lateral surfaces of the heart.
  • Function:
    • Pumps oxygenated blood to the entire body via the aorta.
    • Performs the strongest contractions because it must overcome high systemic vascular resistance.
  • Structures:
    • Mitral (Bicuspid) Valve:
      • Located between the left atrium and left ventricle.
      • Prevents backflow into the atrium.
    • Trabeculae carneae:
      • Irregular muscular ridges on the ventricular walls.
    • Papillary muscles:
      • Anchor the chordae tendineae of the mitral valve.
    • Aortic Valve:
      • Located at the opening of the aorta.
      • Prevents backflow into the left ventricle during diastole.
    • Thicker Wall:
      • The left ventricle’s wall is 2–3 times thicker than the right ventricle to generate higher pressure.

Septa of the Heart

  1. Interatrial Septum:
    • Separates the right and left atria.
    • Contains the fossa ovalis in adults (remnant of the fetal foramen ovale).
  2. Interventricular Septum:
    • Separates the right and left ventricles.
    • Composed of a thick muscular part and a thin membranous part.

Functions of the Chambers

Right Side (Right Atrium + Right Ventricle):

  • Collects deoxygenated blood from the body and pumps it to the lungs for oxygenation.
  • Low-pressure system.

Left Side (Left Atrium + Left Ventricle):

  • Receives oxygenated blood from the lungs and pumps it to the entire body.
  • High-pressure system due to systemic circulation.

Comparison of Ventricles

FeatureRight VentricleLeft Ventricle
FunctionPumps blood to lungsPumps blood to the entire body
Wall ThicknessThinThick (2–3 times thicker)
Pressure GeneratedLow pressure (pulmonary circuit)High pressure (systemic circuit)

Clinical Significance

  1. Atrial Septal Defect (ASD):
    • Congenital defect in the interatrial septum, causing abnormal blood flow between atria.
  2. Ventricular Septal Defect (VSD):
    • Congenital defect in the interventricular septum, causing blood to flow from the left to the right ventricle.
  3. Heart Failure:
    • Left-sided: Reduces systemic blood flow; leads to pulmonary congestion.
    • Right-sided: Causes systemic venous congestion (e.g., edema).
  4. Valve Disorders:
    • Mitral or aortic valve stenosis or regurgitation affects the left heart.
    • Tricuspid or pulmonary valve disorders affect the right heart.
  • layers of heart

Layers of the Heart

The heart wall is composed of three main layers that work together to perform its vital function of pumping blood. These layers, from innermost to outermost, are the endocardium, myocardium, and epicardium.

1. Endocardium

  • Location: The innermost layer of the heart wall.
  • Composition:
    • Lined with simple squamous epithelium (endothelium) that is continuous with the lining of blood vessels.
    • Supported by a thin layer of connective tissue.
  • Features:
    • Smooth surface reduces friction as blood flows through the chambers.
    • Contains Purkinje fibers in the subendocardial layer, which are specialized for conducting electrical impulses.
  • Function:
    • Provides a smooth, non-thrombogenic surface to prevent clot formation.
    • Protects the myocardium and contributes to the heart’s electrical conduction system.

2. Myocardium

  • Location: The thick, middle layer of the heart wall.
  • Composition:
    • Made up of cardiac muscle fibers arranged in spiral and circular bundles.
    • Contains intercalated discs for synchronized contractions.
    • Highly vascularized to meet its metabolic demands.
  • Features:
    • Thicker in the left ventricle than in the right ventricle to generate higher pressure for systemic circulation.
    • Thinner in the atria compared to the ventricles.
  • Function:
    • Provides the contractile force to pump blood out of the heart.
    • Responsible for the rhythmic contractions of the heart.

3. Epicardium

  • Location: The outermost layer of the heart wall, also known as the visceral layer of the serous pericardium.
  • Composition:
    • Composed of a thin layer of simple squamous epithelium (mesothelium) and underlying connective tissue.
    • Contains fat, blood vessels, and lymphatics that supply the heart wall.
  • Features:
    • Smooth, slippery surface reduces friction as the heart beats within the pericardial sac.
  • Function:
    • Provides a protective outer covering.
    • Houses coronary arteries and veins.

Additional Structure: Pericardium

Although not part of the heart wall, the pericardium surrounds the heart and provides protection and lubrication.

  1. Fibrous Pericardium:
    • Tough, outer layer made of dense connective tissue.
    • Anchors the heart to surrounding structures (diaphragm, sternum).
  2. Serous Pericardium:
    • Double-layered membrane:
      • Parietal Layer: Lines the fibrous pericardium.
      • Visceral Layer (Epicardium): Covers the heart’s surface.
    • Pericardial Cavity:
      • Space between the layers, containing a small amount of serous fluid to reduce friction.

Clinical Significance

  1. Endocarditis:
    • Inflammation of the endocardium, often involving heart valves, caused by bacterial or fungal infection.
  2. Myocarditis:
    • Inflammation of the myocardium, often due to viral infections or autoimmune diseases.
  3. Epicarditis:
    • Often associated with pericarditis, leading to inflammation of the epicardium.
  4. Pericarditis:
    • Inflammation of the pericardium, causing chest pain and potential fluid accumulation (pericardial effusion).
  5. Cardiac Hypertrophy:
    • Thickening of the myocardium, typically due to high blood pressure or other cardiac stressors.
  • Heart valves,

Heart Valves: Detailed Overview

The heart valves are crucial structures that regulate blood flow through the heart, ensuring unidirectional flow and preventing backflow. They open and close in response to pressure changes during the cardiac cycle.

Types of Heart Valves

There are four valves in the heart, categorized into two types:

1. Atrioventricular (AV) Valves

Located between the atria and ventricles, they prevent backflow from the ventricles into the atria.

  1. Tricuspid Valve:
    • Location: Between the right atrium and right ventricle.
    • Structure: Has three cusps (anterior, posterior, and septal).
    • Function: Prevents backflow of blood into the right atrium during ventricular contraction.
  2. Mitral Valve (Bicuspid Valve):
    • Location: Between the left atrium and left ventricle.
    • Structure: Has two cusps (anterior and posterior).
    • Function: Prevents backflow of blood into the left atrium during ventricular contraction.

2. Semilunar Valves

Located at the openings of the arteries leaving the heart, they prevent backflow into the ventricles.

  1. Pulmonary Valve:
    • Location: At the junction of the right ventricle and the pulmonary artery.
    • Structure: Has three semilunar cusps.
    • Function: Prevents backflow of blood into the right ventricle after blood is ejected into the pulmonary artery.
  2. Aortic Valve:
    • Location: At the junction of the left ventricle and the aorta.
    • Structure: Has three semilunar cusps.
    • Function: Prevents backflow of blood into the left ventricle after blood is ejected into the aorta.

Structure of Heart Valves

  1. Cusps/Leaflets:
    • Made of endocardium reinforced with dense connective tissue.
    • Flexible and thin but strong enough to withstand pressure changes.
  2. Chordae Tendineae:
    • Fibrous cords attached to the cusps of the AV valves.
    • Anchored to papillary muscles in the ventricles.
    • Prevent valve prolapse during ventricular contraction.
  3. Papillary Muscles:
    • Contract with the ventricles to hold the chordae tendineae taut, ensuring proper valve closure.
  4. Annulus:
    • Fibrous ring surrounding each valve, providing structural support.

Function of Heart Valves

  1. Atrioventricular Valves:
    • Open during diastole (ventricular relaxation) to allow blood to flow from the atria to the ventricles.
    • Close during systole (ventricular contraction) to prevent backflow.
  2. Semilunar Valves:
    • Open during systole when ventricular pressure exceeds arterial pressure, allowing blood to flow into the arteries.
    • Close during diastole to prevent backflow into the ventricles.

Valve Dynamics During the Cardiac Cycle

  1. Diastole:
    • AV valves (tricuspid and mitral) are open, allowing blood to flow into the ventricles.
    • Semilunar valves (pulmonary and aortic) are closed to prevent arterial backflow.
  2. Systole:
    • AV valves are closed, preventing backflow into the atria.
    • Semilunar valves are open, allowing blood ejection into the arteries.

Clinical Significance

1. Valve Disorders

  1. Stenosis:
    • Narrowing of the valve opening, restricting blood flow.
    • Common examples:
      • Aortic Stenosis: Causes increased workload on the left ventricle.
      • Mitral Stenosis: Leads to left atrial enlargement and pulmonary congestion.
  2. Regurgitation (Insufficiency):
    • Incomplete closure of the valve, leading to backflow of blood.
    • Common examples:
      • Mitral Regurgitation: Backflow into the left atrium during systole.
      • Aortic Regurgitation: Backflow into the left ventricle during diastole.
  3. Prolapse:
    • Bulging of valve cusps into the atrium during systole.
    • Example: Mitral Valve Prolapse (MVP).

2. Diagnostic Tests

  1. Echocardiography:
    • Assesses valve structure and function in real time.
  2. Doppler Ultrasound:
    • Measures blood flow through valves to detect abnormalities.
  3. Cardiac Catheterization:
    • Provides detailed pressure and flow measurements.

3. Treatments

  1. Medical Management:
    • Medications like diuretics, anticoagulants, or beta-blockers for symptom control.
  2. Surgical Options:
    • Valve Repair: Reconstruction of a damaged valve.
    • Valve Replacement: Using mechanical or bioprosthetic valves.
  • coronary arteries

Coronary Arteries: Detailed Overview

The coronary arteries supply oxygenated blood to the heart muscle (myocardium). These arteries originate from the base of the ascending aorta and ensure the heart receives adequate oxygen and nutrients for its continuous function.

Anatomy of Coronary Arteries

1. Right Coronary Artery (RCA)

  • Origin: Arises from the right coronary sinus of the aortic root.
  • Course: Travels in the right atrioventricular (AV) groove.
  • Branches:
    1. Right Marginal Artery:
      • Supplies the right ventricle’s lateral wall.
    2. Posterior Descending Artery (PDA):
      • Also known as the posterior interventricular artery.
      • Supplies the posterior part of the interventricular septum and portions of the right and left ventricles.
    3. Sinoatrial (SA) Nodal Artery:
      • Supplies the sinoatrial node in ~60% of individuals.
    4. Atrioventricular (AV) Nodal Artery:
      • Supplies the AV node in ~85% of individuals.
  • Area Supplied:
    • Right atrium.
    • Right ventricle.
    • Inferior wall of the left ventricle (in most individuals).
    • Posterior part of the interventricular septum.

2. Left Coronary Artery (LCA)

  • Origin: Arises from the left coronary sinus of the aortic root.
  • Course: Divides into two major branches shortly after its origin.
Major Branches:
  1. Left Anterior Descending Artery (LAD):
    • Travels in the anterior interventricular groove.
    • Branches:
      • Diagonal branches: Supply the anterior wall of the left ventricle.
      • Septal branches: Supply the anterior part of the interventricular septum.
    • Area Supplied:
      • Anterior wall of the left ventricle.
      • Anterior two-thirds of the interventricular septum.
      • Apex of the heart.
  2. Circumflex Artery (LCX):
    • Travels in the left atrioventricular (AV) groove.
    • Branches:
      • Obtuse marginal branches: Supply the lateral wall of the left ventricle.
    • Area Supplied:
      • Left atrium.
      • Lateral and posterior walls of the left ventricle.
    • SA Nodal Artery:
      • Supplies the sinoatrial node in ~40% of individuals.
    • AV Nodal Artery:
      • Supplies the AV node in ~15% of individuals.

3. Coronary Circulation Variations

  • Right Dominance (~70% of people):
    • PDA arises from the right coronary artery.
  • Left Dominance (~10% of people):
    • PDA arises from the circumflex artery.
  • Co-Dominance (~20% of people):
    • PDA receives contributions from both the RCA and LCX.

Functions of Coronary Arteries

  • Deliver oxygen-rich blood to the myocardium.
  • Remove carbon dioxide and waste products from the heart tissue.
  • Adjust blood flow based on myocardial oxygen demand (e.g., during exercise or rest).

Clinical Significance

1. Coronary Artery Disease (CAD)

  • Cause: Narrowing or blockage of coronary arteries due to atherosclerosis.
  • Consequence: Reduced blood flow leads to ischemia and angina.
  • Complications:
    • Myocardial infarction (heart attack).
    • Heart failure.

2. Myocardial Infarction (MI):

  • Pathophysiology: Complete blockage of a coronary artery, leading to ischemic necrosis of myocardial tissue.
  • Common Sites of Blockage:
    1. LAD (~40–50% of cases): “Widowmaker” artery due to its critical supply areas.
    2. RCA (~30–40% of cases).
    3. LCX (~15–20% of cases).

3. Coronary Artery Spasm:

  • Temporary narrowing of the coronary arteries due to smooth muscle contraction, leading to chest pain (variant angina).

4. Diagnostic Tests:

  1. Electrocardiogram (ECG):
    • Detects ischemic changes or myocardial infarction.
  2. Stress Test:
    • Assesses blood flow to the myocardium during exercise or pharmacological stress.
  3. Coronary Angiography:
    • Visualizes coronary artery anatomy and blockages using X-rays and contrast dye.
  4. CT Coronary Angiography:
    • Non-invasive imaging of coronary arteries.
  5. Cardiac Biomarkers:
    • Troponin levels to confirm myocardial damage.

5. Treatments:

  1. Medical Management:
    • Antiplatelet agents (e.g., aspirin).
    • Statins (e.g., atorvastatin).
    • Beta-blockers and calcium channel blockers.
  2. Percutaneous Coronary Intervention (PCI):
    • Includes angioplasty and stent placement.
  3. Coronary Artery Bypass Grafting (CABG):
    • Surgical creation of a bypass around blocked arteries using grafts.
  • Nerve and blood supply to heart

Nerve and Blood Supply to the Heart

The heart’s efficient function depends on its nerve supply (autonomic regulation) and blood supply (oxygenation and nourishment of the myocardium). Below is a detailed overview:

Nerve Supply to the Heart

The heart is innervated by the autonomic nervous system (ANS), which controls the rate and strength of contractions, and some sensory innervation for reflexes and pain.

1. Sympathetic Innervation

  • Origin:
    • Arises from the thoracic spinal cord (T1–T5).
    • Preganglionic fibers synapse in the cervical and upper thoracic ganglia of the sympathetic chain.
  • Pathway:
    • Postganglionic fibers form the cardiac plexus, located near the base of the heart.
  • Functions:
    • Increases heart rate (positive chronotropic effect).
    • Increases force of contraction (positive inotropic effect).
    • Dilates coronary arteries, enhancing blood flow.
  • Effect: “Fight or flight” response.

2. Parasympathetic Innervation

  • Origin:
    • Arises from the vagus nerve (cranial nerve X).
  • Pathway:
    • Preganglionic fibers travel to the heart via the cardiac branches of the vagus nerve.
    • Synapse with postganglionic neurons within the cardiac plexus or directly in the heart wall.
  • Functions:
    • Decreases heart rate (negative chronotropic effect).
    • Reduces force of contraction (negative inotropic effect), especially in the atria.
    • Constricts coronary arteries.
  • Effect: “Rest and digest” response.

3. Cardiac Plexus

  • Located near the aortic arch and the tracheal bifurcation.
  • Contains both sympathetic and parasympathetic fibers.
  • Divided into:
    • Superficial Cardiac Plexus: Lies below the aortic arch.
    • Deep Cardiac Plexus: Lies behind the aortic arch near the tracheal bifurcation.

4. Sensory (Afferent) Innervation

  • Pain signals (e.g., from myocardial ischemia) travel via sympathetic fibers to the spinal cord segments T1–T5.
  • Reflex signals (e.g., baroreceptor and chemoreceptor activity) are carried by vagus nerve afferents.

Blood Supply to the Heart

The coronary arteries supply oxygen-rich blood to the myocardium, while the cardiac veins return deoxygenated blood to the right atrium.

1. Coronary Arteries

  • Right Coronary Artery (RCA):
    • Supplies the right atrium, right ventricle, part of the left ventricle, and the conduction system (SA node in ~60%, AV node in ~85% of individuals).
    • Key branches:
      • Right marginal artery.
      • Posterior descending artery (PDA).
  • Left Coronary Artery (LCA):
    • Divides into:
      • Left Anterior Descending (LAD):
        • Supplies the anterior left ventricle, anterior interventricular septum, and apex.
      • Circumflex Artery (LCX):
        • Supplies the lateral and posterior walls of the left ventricle, left atrium.
    • Key roles:
      • Critical for oxygenation of most of the myocardium.

2. Cardiac Veins

  • Great Cardiac Vein:
    • Runs alongside the LAD and drains the anterior myocardium.
  • Middle Cardiac Vein:
    • Runs with the PDA and drains the posterior myocardium.
  • Small Cardiac Vein:
    • Runs along the RCA and drains the right atrium and right ventricle.
  • Coronary Sinus:
    • Large venous structure on the posterior heart wall.
    • Collects blood from cardiac veins and drains into the right atrium.

Clinical Relevance

Autonomic Disorders

  1. Overactive Sympathetic Stimulation:
    • Tachycardia, hypertension.
    • Contributes to arrhythmias or stress-related cardiac events.
  2. Parasympathetic Dysfunction:
    • Can result in bradycardia or fainting (vasovagal syncope).

Coronary Artery Disease (CAD)

  • Atherosclerosis can block coronary arteries, leading to ischemia or myocardial infarction.
  • Common sites: LAD (“widowmaker”), RCA, LCX.

Angina and Referred Pain

  • Myocardial ischemia sends pain signals via sympathetic fibers, causing referred pain to the chest, shoulder, or arm (T1–T5 dermatomes).
  • Lymphatic tissue

Lymphatic Tissue: Detailed Overview

Lymphatic tissue is a specialized connective tissue essential for the immune system. It plays a key role in producing, storing, and circulating lymphocytes, which defend the body against infections and foreign invaders.

Structure and Components of Lymphatic Tissue

Lymphatic tissue consists of a network of lymphocytes, macrophages, dendritic cells, and supporting reticular fibers. It is distributed throughout the body in organized and diffuse forms.

1. Types of Lymphatic Tissue

  1. Diffuse Lymphatic Tissue:
    • Loosely arranged lymphatic cells and fibers.
    • Found beneath mucosal surfaces in areas like the gastrointestinal tract (e.g., lamina propria).
  2. Nodular Lymphatic Tissue:
    • Dense, spherical aggregates of lymphatic cells.
    • Commonly forms lymphatic nodules (follicles).

Lymphatic Organs

Lymphatic tissue is organized into primary and secondary lymphatic organs:

Primary Lymphatic Organs

  1. Bone Marrow:
    • Site of lymphocyte production (hematopoiesis).
    • B-cells mature in the bone marrow.
  2. Thymus:
    • Located in the mediastinum.
    • T-cells mature here.
    • Largest in children, shrinks with age (involution).

Secondary Lymphatic Organs

  1. Lymph Nodes:
    • Bean-shaped structures located along lymphatic vessels.
    • Contain a cortex (rich in B-cells) and a medulla (rich in macrophages and plasma cells).
    • Functions:
      • Filter lymph.
      • Trap pathogens and debris.
      • Site of lymphocyte activation.
  2. Spleen:
    • Located in the upper left abdominal quadrant.
    • Contains:
      • White Pulp: Lymphatic tissue around arterioles; rich in lymphocytes for immune response.
      • Red Pulp: Contains macrophages for the destruction of old RBCs and platelets.
    • Functions:
      • Filters blood.
      • Stores platelets and iron.
      • Immune surveillance.
  3. Mucosa-Associated Lymphoid Tissue (MALT):
    • Found in mucosal linings of the respiratory, gastrointestinal, and genitourinary tracts.
    • Includes:
      • Tonsils:
        • Palatine Tonsils: At the back of the throat.
        • Pharyngeal Tonsil (Adenoid): At the nasopharynx.
        • Lingual Tonsils: At the base of the tongue.
      • Peyer’s Patches:
        • Aggregates of lymphatic tissue in the ileum of the small intestine.
      • Appendix:
        • Contains lymphoid follicles in its wall.
  4. Lymphatic Vessels:
    • Transport lymph, returning it to the circulatory system via the thoracic duct and right lymphatic duct.

Cells of Lymphatic Tissue

  1. Lymphocytes:
    • Key immune cells.
    • Types:
      • B-Lymphocytes:
        • Differentiate into plasma cells to produce antibodies.
      • T-Lymphocytes:
        • Cytotoxic T-cells: Kill infected cells.
        • Helper T-cells: Activate other immune cells.
        • Regulatory T-cells: Suppress immune response.
      • Natural Killer (NK) Cells:
        • Destroy abnormal or infected cells.
  2. Macrophages:
    • Engulf and digest pathogens, dead cells, and debris.
    • Present antigens to lymphocytes.
  3. Dendritic Cells:
    • Specialized antigen-presenting cells (APCs) that activate T-cells.
  4. Reticular Cells:
    • Produce reticular fibers, forming a supportive framework for lymphatic tissue.

Functions of Lymphatic Tissue

  1. Immune Surveillance:
    • Detect and respond to pathogens or abnormal cells.
  2. Lymphocyte Production and Maturation:
    • Primary lymphatic organs produce and mature lymphocytes.
  3. Filtration:
    • Lymph nodes and spleen filter lymph and blood, removing pathogens and debris.
  4. Antigen Presentation:
    • APCs present antigens to lymphocytes, initiating an immune response.
  5. Return of Interstitial Fluid:
    • Lymphatic vessels return excess interstitial fluid to the bloodstream.
  6. Transport of Fats:
    • Specialized lymphatic vessels (lacteals) in the intestine transport dietary fats.

Clinical Significance

  1. Lymphadenopathy:
    • Swelling of lymph nodes due to infection, inflammation, or malignancy.
  2. Lymphedema:
    • Accumulation of lymph due to obstruction of lymphatic vessels.
  3. Splenomegaly:
    • Enlargement of the spleen, often due to infections or blood disorders.
  4. Lymphomas:
    • Cancers of lymphatic tissue, such as Hodgkin’s lymphoma and non-Hodgkin’s lymphoma.
  5. Tonsillitis:
    • Inflammation of the tonsils, typically due to infection.
  6. Thymoma:
    • Tumor of the thymus, associated with autoimmune conditions like myasthenia gravis.
  • Veins used for IV injections

Veins Commonly Used for Intravenous (IV) Injections

In clinical practice, several veins are used for intravenous (IV) injections based on accessibility, size, and ease of cannulation. Below is a detailed anatomical overview of these veins:

1. Veins of the Upper Limb

Superficial Veins

These veins are close to the surface of the skin and are the most commonly used for IV injections.

  1. Cephalic Vein:
    • Location:
      • Runs along the lateral aspect of the forearm and arm.
      • Drains into the axillary vein near the shoulder.
    • Clinical Use:
      • Often used for IV cannulation or injections due to its size and superficial location.
  2. Basilic Vein:
    • Location:
      • Runs along the medial aspect of the forearm and arm.
      • Joins the brachial vein to form the axillary vein.
    • Clinical Use:
      • Commonly used when the cephalic vein is not accessible.
  3. Median Cubital Vein:
    • Location:
      • Lies in the cubital fossa, connecting the cephalic and basilic veins.
    • Clinical Use:
      • Preferred vein for blood draws and IV injections due to its superficial location and low mobility.
  4. Dorsal Venous Network:
    • Location:
      • Found on the back of the hand.
    • Clinical Use:
      • Used for IV cannulation, especially in emergency settings.

Deep Veins

Used less commonly for IV access due to their deeper location.

  1. Brachial Veins:
    • Paired veins accompanying the brachial artery.
    • Occasionally accessed for central venous lines or deep IV access.

2. Veins of the Lower Limb

  1. Great Saphenous Vein:
    • Location:
      • Runs along the medial side of the leg and thigh.
      • Drains into the femoral vein.
    • Clinical Use:
      • Occasionally used for IV injections, particularly in infants or when upper limb veins are inaccessible.
  2. Dorsal Venous Network of the Foot:
    • Location:
      • Found on the dorsum of the foot.
    • Clinical Use:
      • Used in pediatric or emergency settings when other veins are inaccessible.

3. Veins of the Neck and Chest

  1. External Jugular Vein:
    • Location:
      • Runs diagonally across the sternocleidomastoid muscle.
    • Clinical Use:
      • Used for IV access in emergency or critical care situations.
  2. Internal Jugular Vein:
    • Location:
      • Runs deep in the neck alongside the carotid artery.
    • Clinical Use:
      • Primarily used for central venous access rather than peripheral IV injections.
  3. Subclavian Vein:
    • Location:
      • Found beneath the clavicle.
    • Clinical Use:
      • Used for central venous catheters.

4. Central Veins

These are used for central venous access in critical care or for administering irritant solutions.

  1. Superior Vena Cava:
    • Accessed indirectly via central venous catheters placed in the internal jugular or subclavian veins.
  2. Inferior Vena Cava:
    • Accessed via femoral vein cannulation.

Factors Affecting Vein Selection

  1. Accessibility:
    • Superficial veins are preferred for ease of access.
  2. Size and Mobility:
    • Larger, less mobile veins (e.g., cephalic, median cubital) are easier to cannulate.
  3. Condition of the Vein:
    • Veins that are not thrombosed, sclerotic, or inflamed are chosen.
  4. Purpose of the Injection:
    • Peripheral veins for routine injections; central veins for long-term or irritant medications.

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Categorized as BS NURSING SEM 1 ANATOMY, Uncategorised