Detailed Study Notes on Heart and Blood Vessels

Chapter 19-20: Heart and Blood Vessels

Objectives

  • Students will be able to:

    • Distinguish between pulmonary and systemic circuits.

    • Describe and label the parts and functions of the heart.

    • Sequence the flow of blood through the heart.

    • Explain the intrinsic conduction system of the heart.

    • Differentiate cardiac muscle from other types and describe its unique characters.

    • Differentiate between various blood vessels and their functions.

Cardiovascular System

  • Heart: Muscular pump responsible for circulating blood.

  • Vessels: Conducts blood flow to and from the heart.

  • Blood: Liquid tissue that delivers nutrients and removes waste.

19- The Pulmonary and Systemic Circuits

  • Major divisions of the circulatory system:

    • Pulmonary Circuit:

    • Right side of the heart.

    • Carries oxygen-poor blood to the lungs for gas exchange and returns oxygen-rich blood to the heart.

    • Systemic Circuit:

    • Left side of the heart.

    • Supplies oxygenated blood to all tissues of the body and returns deoxygenated blood to the heart.

Functions of Heart Sides

  • Left side of heart:

    • Receives fully oxygenated blood from lungs via pulmonary veins.

    • Pumps blood to all body organs via the aorta.

  • Right side of heart:

    • Receives oxygen-poor blood from the body via superior and inferior venae cavae.

    • Pumps blood to the lungs via pulmonary trunk.

19- Position, Size, and Shape of the Heart

  • Location: Mediastinum, between the lungs.

  • Base: Wider superior portion where large vessels attach.

  • Apex: Tapered inferior end that tilts to the left.

  • Size:

    • Weighs approximately 10 ounces (280 grams).

    • Measures about 3.5 inches wide at the base and 5 inches from base to apex.

    • At any age, roughly the size of a fist.

19- The Pericardium

  • Pericardium: Double-walled sac enclosing the heart.

    • Functions:

    • Allows the heart to beat without friction.

    • Provides room for heart expansion while resisting excessive expansion.

    • Anchors the heart to the diaphragm and sternum.

    • Parietal Pericardium:

    • Superficial fibrous layer of connective tissue.

    • Deep thin serous layer.

    • Visceral Pericardium (Epicardium): Serous membrane covering the heart.

    • Pericardial Cavity: Space containing 5 to 30 mL of pericardial fluid to reduce friction.

    • Pericarditis: Inflammation of the pericardial membranes causing pain.

19- The Heart Wall

  • Layers:

    • Epicardium (Visceral Pericardium):

    • Covers heart; may contain adipose tissue.

    • Contains coronary blood vessels.

    • Myocardium:

    • Thickest layer; made of cardiac muscle which adapts to work load.

    • Spiraled structure produces wringing motion during contraction.

    • Contains fibrous skeleton providing structural support, electrical insulation, and anchoring for valve tissue.

    • Endocardium:

    • Smooth inner lining that covers valve surfaces and interfaces with blood.

19- The Chambers of the Heart

  • Four Chambers:

    • Right Atrium: Superior chamber receiving blood from the body.

    • Left Atrium: Superior chamber receiving oxygenated blood from the lungs.

    • Right Ventricle: Pumps deoxygenated blood to the lungs.

    • Left Ventricle: Pumps oxygenated blood to the body.

  • Auricles: Expandable flaps on the exterior of the atria.

  • Interatrial Septum: Separates the right and left atria.

  • Interventricular Septum: Separates the right and left ventricles.

19- The Valves of the Heart

  • Atrioventricular (AV) Valves:

    • Control blood flow between atria and ventricles:

    • Right AV Valve (Tricuspid Valve): Three cusps.

    • Left AV Valve (Mitral Valve): Two cusps.

    • Chordae Tendineae: Cords connecting AV valves to papillary muscles; prevents backflow into the atria.

  • Semilunar Valves:

    • Open and close based on pressure flows into:

    • Pulmonary Semilunar Valve (between right ventricle and pulmonary trunk).

    • Aortic Semilunar Valve (between left ventricle and aorta).

19- Blood Flow Through the Chambers

  • Ventricular Relaxation:

    • Pressure decreases, allowing AV valves to open and blood to fill ventricles.

  • Ventricular Contraction:

    • AV valves close; semilunar valves open, allowing blood to flow into the great vessels.

  • Blood Pathway: From right atrium to lungs (pulmonary circuit), then to the body (systemic circuit).

19- The Coronary Circulation

  • Percentage of Blood Flow: 5% of blood pumped by the heart is supplied to the heart itself via coronary circulation for oxygen and nutrient delivery.

  • Volume: Approximately 250 mL of blood per minute.

19- Arterial Supply

  • Left Coronary Artery (LCA): Branches from the ascending aorta, supplying the left ventricle, left atrium, and interventricular septum.

    • Branches:

    • Anterior Interventricular Branch: Supplies both ventricles and anterior two-thirds of interventricular septum.

    • Circumflex Branch: Supplies posterior left ventricle and left atrium.

  • Right Coronary Artery (RCA): Supplies right atrium and parts of both ventricles.

    • Branches:

    • Right Marginal Branch: Supplies the lateral aspect of the right atrium and ventricle.

    • Posterior Interventricular Branch: Supplies the posterior walls of the ventricles.

19- Myocardial Infarction (Heart Attack)

  • Occurs due to the interruption of blood supply from clots or fatty deposits leading to death of cardiac cells.

  • Protection is provided by arterial anastomoses offering alternative blood flow routes.

19- Angina and Heart Attack

  • Angina Pectoris: Chest pain from partial blockage of coronary blood flow.

    • Associated with ischemia of cardiac muscle.

    • Caused by anaerobic fermentation and lactic acid buildup.

  • Myocardial Infarction: Results from long-term obstruction of coronary circulation.

    • Can present as heavy pressure or squeezing sensation, especially radiating to the left arm, and may result in cardiac arrest.

    • Approximately 27% of all deaths in the U.S. are attributed to heart attacks.

19- Structure of Cardiac Muscle

  • Cardiocytes: Striated, short, thick, branched muscle cells with central nuclei.

    • Intercalated Discs: Junctions that couple cardiocytes electrically and mechanically.

    • Features:

    • Interdigitating Folds: Increase contact surface area.

    • Mechanical Junctions: Prevent pulling apart during contraction (includes fascia adherens and desmosomes).

    • Electrical Junctions: Allow ion flow between cells for synchronous contraction.

19- Metabolism of Cardiac Muscle

  • Relies largely on aerobic respiration for ATP production; rich in myoglobin and glycogen.

  • Utilizes varying fuels; primarily fatty acids and glucose, capable of operating under diverse conditions.

  • Highly fatigue-resistant, adapting to long durations of activity without tiring.

19- The Conduction System

  • Components:

    • Sinoatrial (SA) Node: Primary pacemaker, starting heart rhythm, located in the right atrium.

    • Atrioventricular (AV) Node: Serves as electrical gateway to ventricles, preventing misfiring.

    • AV Bundle (Bundle of His): Conducts impulses into right and left bundle branches towards apex.

    • Purkinje Fibers: Distribute signals throughout ventricular myocardium enabling synchronized contraction.

19- Nerve Supply to the Heart

  • Sympathetic Nerves: Increase heart rate and contraction strength, originating from the spinal cord.

  • Parasympathetic Nerves: Reduce heart rate, sourced from vagus nerve in the medulla oblongata.

19- Heart Sounds

  • First Heart Sound (S1): Occurs with closure of AV valves, is louder and longer ("lubb").

  • Second Heart Sound (S2): Softer closing sound of semilunar valves ("dupp").

  • Additional Sounds (S3): May be detected, especially in younger individuals.

19- Phases of the Cardiac Cycle

  • Ventricular Filling: During diastole, valves open allowing blood inflow.

  • Isovolumetric Contraction: Ventricles contract but blood volume remains unchanged.

  • Ventricular Ejection: Blood is forced into the aorta and pulmonary trunk during systole.

  • Isovolumetric Relaxation: Ventricles relax as blood returns to the heart.

  • Entire cycle lasts less than one second.

19- Heart Rate

  • Pulse: The pressure surge felt through arterial palpation.

    • Normal Rates:

    • Infants: 120+ bpm.

    • Young adult females: 72-80 bpm.

    • Young adult males: 64-72 bpm.

    • Rates tend to rise in the elderly.

  • Tachycardia: Heart rate above 100 bpm due to stress, drugs, or heart disease.

  • Bradycardia: Heart rate less than 60 bpm, common during sleep and in athletes.

  • Factors influencing heart rate:

    • Positive Chronotropic Agents: Increase heart rate.

    • Negative Chronotropic Agents: Decrease heart rate.

20- General Anatomy of Blood Vessels

  • Arteries: Carry blood away from the heart.

  • Veins: Return blood to the heart.

  • Capillaries: Connect small arteries to small veins; sites of nutrient exchange.

20- The Vessel Wall

  • Layers (Tunics):

    • Tunica Interna (Tunica Intima): Inner layer, includes endothelium; selectively permeable barrier.

    • Tunica Media: Middle layer with smooth muscle; regulates vessel diameter.

    • Tunica Externa (Tunica Adventitia): Outermost layer, anchors vessels; contains vasa vasorum for blood supply to outer layers.

20- Types of Arteries

  • Conducting (Elastic/Large) Arteries:

    • Include aorta and larger branches; help maintain pressure through expansion and recoil.

  • Distributing (Muscular/Medium) Arteries: Deliver blood to specific organs, made of smooth muscle.

  • Resistance (Small) Arteries (Arterioles): Regulate blood flow to organs, with thicker tunica media.

20- Capillaries

  • Exchange Vessels: Site of nutrient, gas, and waste exchange between blood and tissues.

  • Three types based on permeability:

    • Continuous Capillaries: Found in most tissues; allow passage of small solutes.

    • Fenestrated Capillaries: Found in kidneys and intestines; have pores for rapid exchange.

    • Sinusoids (Discontinuous Capillaries): Found in liver/spleen; allow large proteins and cells to pass.

20- Capillary Beds

  • Networks of capillaries supplied by arterioles; transition to venules.

  • Regulation of blood flow through sphincters; only selective flow allowed based on demand.

20- Angina and Heart Attack

  • Angina Pectoris: Chest pain due to transient ischemia, caused by partial coronary obstruction.

  • Myocardial Infarction: Sustained ischemia leading to cardiac tissue death due to blocked coronary arteries.

  • Silent heart attacks: Often occur in diabetics and the elderly without typical pain indicators.

Conclusion

This extensive guide encapsulates the critical elements regarding the anatomy and physiology of the heart and blood vessels, integrating definitions, functions, and the implications of different cardiovascular conditions. Understanding these concepts is vital for further studies in biomedical sciences and clinical applications.