Unit 1 biology
.docx
School
West Virginia University,Parkersburg**We aren't endorsed by this school
Course
BIO 108
Subject
Anatomy
Date
Dec 16, 2024
Pages
12
Uploaded by JusticeGrasshopperPerson1247
Heart AnatomyLocation and Orientation●The heart is situated in the mediastinum, a chest compartment between the lungs, under the rib cage, to the left of the sternum, and between the lungs.●It is positioned between the third and sixth ribs, slightly tilted to the left.●The base of the heart is at the level of the third costal cartilage, while the apex is to the left of the sternum, between the fourthand fifth ribs, pointing downward towards the diaphragm.Shape and Encasement●The heart is likened to a quadrangular pyramid falling onto its side.●It is encased in the pericardium, a double-walled fibrous sac that surrounds the heart and its major blood vessels.●The pericardium has two layers: a tough outer fibrous layer and an inner serous layer with a fluid-filled space between them.Layers of the Heart Wall●Epicardium: The outermost layer, also the visceral pericardium, contains coronary arteries, veins, and nerves.●Myocardium: The thick, muscular middle layer responsible for heart contractions.●Endocardium: The innermost layer in contact with blood flow, composed of endothelial cells and connective tissue.Pericardium Structure and FunctionComponents of the Pericardium●Fibrous Pericardium: Outer layer of strong, inelastic connective tissue anchoring the heart and preventing over-expansion.●Serous Pericardium: Double-layered membrane with visceral and parietal layers, forming the pericardial cavity.●Pericardial Cavity: Space between the serous layers containing lubricating pericardial fluid.Functions of the Pericardium●Protection: Acts as a barrier against infection and blunt trauma to the heart.●Lubrication: Pericardial fluid reduces friction, allowing smooth heart movement.●Structural Support: Holds the heart in place within the chest cavity.Fibrous and Serous Pericardium●Fibrous Pericardium: Protects the heart, prevents over-expansion, and provides structural support.●Serous Pericardium: Lubricates the heart, forms a protective barrier, and limits heart expansion.Pericardial Fluid and Cavity
●Function: Minimizes friction during cardiac contractions by lubricating the heart surfaces.●Composition: Serous fluid similar to plasma, secreted by the serous layer of the pericardium.●Location: Situated between the parietal and visceral layers of the pericardium.Layers of the HeartEpicardium●The epicardium is the outermost layer of the heart, serving as the visceral layer of the pericardium.●Composed primarily of mesothelium, connective tissue, and adipose tissue.●Functions include providing a smooth surface for heart movement, protecting the heart, aiding in cardiac cell development, and responding to cell injury.ComponentDescriptionMesothelial cellsFlat cells forming the epicardiumAdipose tissueFat layer cushioning and binding the heart to the myocardiumConnective tissueThe tissue layer binding the epicardium to the myocardiumMyocardium●The myocardium is the middle layer of the heart wall, composed of cardiac muscle responsible for pumping blood.●Made up of cardiomyocytes (cardiac muscle cells) and connective tissue.●Functions by contracting and relaxing to facilitate blood circulation.ComponentDescription
Cardiac muscle cellsPrimary cells in the myocardium, responsible for heart contractionsConnective tissueIncludes interstitium with endomysial connective tissue and collagen fibersEndocardium●The innermost layer of the heart, lining chambers and covering valves, chordae tendineae, and papillary muscles.●Comprised of endothelium, subendocardial layer, and inner connective tissue layer.●Functions include material exchange control and protection against pathogens.LayerComposition and FunctionEndotheliumSpecialized endothelial cells lining the blood-filled chamberSubendocardial layerContains blood vessels, nerves, and connective tissue
Inner connective tissue layerA dense layer continuous with myocardial interstitium and valvular leafletsHeart Chambers and StructuresHeart Chambers●The heart has four chambers: right atrium, left atrium, right ventricle, and left ventricle.●Each chamber plays a specific role in managing the heartbeat and blood circulation.●Valves in each chamber ensure one-way blood flow, with the septum separating the right and left sides of the heart.ChamberFunctionRight atriumReceives blood from the body via the superior and inferior vena cavaLeft atriumReceives oxygenated blood from the lungsRight ventricleReceives blood from the right atrium and pumps it to the lungs
Left ventricleReceives blood from the left atrium and pumps it to the bodyAuricles●Ear-shaped projections of the atria, aid in blood flow regulation and stress relief.●The auricles help fill the ventricles before contraction and can relieve atrial pressure during stress.●The left auricle, also known as the left atrial appendage, is a prominent feature of the heart anatomy.RoleDescriptionBlood flowAssist in filling ventricles and relieving atrial pressureStress reliefAct as overflow vessels during stressLocationRight auricle near the sinus node, left auricle as the left atrial appendageAnatomyThe left auricle is a structural feature of the left atrium
Anterior and Posterior Interventricular Sulcus●The anterior sulcus is on the front heart surface, while the posterior sulcus is on the back.●These sulci meet below the cardiac apex, with distinct locations and functions.SulcusLocation and DescriptionAnteriorOn the sternocostal surface near the left marginPosteriorOn the diaphragmatic surface near the right margin, extending to the apexRight Atrium and VentriclesRight Atrium●Function: Receives deoxygenated blood from the body.●Wall Thickness: Thin, around 2mm.●Muscles: Pectinate muscles line the inner wall.●Notable Feature: Fossa ovalis, a remnant of the fetal foramen ovale.●Tricuspid Valve: Connects the right atrium to the right ventricle.Right Ventricle●Function: Pumps deoxygenated blood to the lungs.●Wall Thickness: Moderate, around 3-5mm.●Muscles: Trabeculae carneae, irregular muscular ridges on the inner wall.●Atrioventricular Valve: The Tricuspid valve connects to the right atrium.●Pulmonary Semilunar Valve: Located between the right ventricle and the pulmonary artery.Pulmonary Semilunar Valve●The valve has three flaps controlling blood flow: anterior, left, and right.
●Its annulus, a connective tissue ring, defines the right ventricle chamber.●The valve prevents blood backflow by closing its flaps when the right ventricle relaxes.●The cardiac fibrous skeleton anchors all heart valves in the myocardium.Left Atrium and VentricleLeft Atrium●Location: Upper left chamber of the heart.●Function: Receives oxygenated blood from the lungs via pulmonary veins.●Wall Thickness: Relatively thin, specialized for short-distance blood transfer.●Muscle Type: Atrial muscle with a slower contraction rate.●Atrioventricular Valve: The mitral valve separates the left atrium from the left ventricle.Left Ventricle●Location: Lower left chamber of the heart.●Function: Pumps oxygenated blood into systemic circulation through the aorta.●Wall Thickness: Thickest among heart chambers for powerful blood propulsion.●Muscle Type: Ventricular muscle with strong and forceful contraction.●Atrioventricular Valve: The mitral valve separates the left atrium from the left ventricle.Ligamentum Arteriosum●Definition: Remnant of the fetal ductus arteriosus.●Location: Connects the aorta to the pulmonary artery.●Function: No functional significance in adults, serves as a reminder of fetal circulation.Heart Valves and CirculationAortic Semilunar Valve●Located between the left ventricle and the aorta.●Composed of three flaps shaped like half-moons.●Prevents oxygen-rich blood from flowing back into the left ventricle.●Opens when left ventricle pressure exceeds aortic pressure, closing when pressure drops.●Contributes to the second heart sound upon closure.Pulmonary Veins and Circulation●Pulmonary veins carry oxygen-rich blood from the lungs to the left atrium.●Blood flows from the left atrium to the left ventricle through the mitral valve.●The left ventricle contracts when full, closing the mitral valve and opening the aortic valve.
●Blood is sent through the aortic valve to the aorta for distribution throughout the body.Myocardial Wall Thickness●Thicker walls generate more pressure during contraction for efficient blood pumping.●The left ventricle has the thickest walls due to high-pressure requirements for systemic circulation.●Atria have the thinnest walls as they primarily receive blood passively.Fibrous Skeleton of the HeartStructure and Location●Composed of four dense connective tissue rings surrounding the bases of atrioventricular valves and extending to the origins of the aorta and pulmonary trunk.●Situated at the base of the ventricles where the atria meet the ventricles.Functions●Valve attachment: Provides stable points of attachment for heart valve leaflets.●Electrical insulation: Prevents direct passage of electrical signals between atria and ventricles, ensuring coordinated contractions.●Structural support: Offers a robust framework for heart muscle fibers.Valve Mechanism and Blood Flow●Valves act as one-way gates, allowing blood to flow in one direction while preventing backflow.●Opening mechanism: Valves open when pressure inside a chamber increases during contraction.●Closing mechanism: Valves close when the pressure inside a chamber decreases during relaxation.●Example: Atrioventricular (AV) valves open when atria contract and close when ventricles contract to prevent backflow.Blood Flow Pathway and CircuitsPulmonary Circuit●Deoxygenated blood enters the right atrium from the body via the vena cava.●Blood moves to the right ventricle, and then to the lungs via the pulmonary artery for oxygenation.●Oxygenated blood returns to the heart through the pulmonary veins into the left atrium.Systemic Circuit●Oxygenated blood from the left atrium flows into the left ventricle, which pumps it out through the aorta to all body tissues.●Deoxygenated blood returns to the heart through the vena cava, completing the systemic circuit.
Key Points About Blood Flow Pathway●The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.●Valves ensure unidirectional blood flow.●Arteries carry blood away from the heart, while veins carry blood back to the heart.Cardiac Muscle TissueCharacteristics and Function●Characterized by striated, short, branched muscle fibers with a single centrally located nucleus.●Intercalated discs contain desmosomes for mechanical coupling and gap junctions for electrical communication.●Mitochondria provide energy for continuous pumping action.●T tubules transmit electrical signals deep into muscle fibers.●The sarcoplasmic reticulum stores calcium ions for muscle contraction.Histological Features●Intercalated discs ensure synchronized contraction of the heart muscle.●Desmosomes anchor cardiac muscle fibers together during contraction.●Gap junctions facilitate the rapid propagation of electrical impulses.●Mitochondria abundance meets high energy demand for heart function.●T tubules allow efficient delivery of electrical signals to the sarcoplasmic reticulum.Muscle Tissue Structure and ContractionMyosin and Actin Arrangement●Myosin filaments are centrally positioned and thicker, while actin filaments are thinner and anchored to Z discs at the sarcomere ends.●Actin and myosin filaments partially overlap in specific regions within the sarcomere.●Contraction occurs when myosin cross-bridges bind to actin and slide past each other.●Z discs mark sarcomere boundaries, A bands contain myosin filaments, I bands contain actin filaments, the H zone has onlymyosin, and the M line anchors myosin filaments.Muscle Contraction Mechanism●Calcium ions trigger exposure of binding sites on actin, allowing myosin to attach and initiate sliding motion.●Troponin binding with calcium causes tropomyosin to move, exposing actin-binding sites for myosin cross-bridges.●Myosin heads attach to actin binding sites, pulling filaments towards the sarcomere center, leading to muscle contraction.Importance of Calcium
●Calcium is crucial for exposing myosin binding sites on actin, essential for muscle contraction.●Without calcium, actin-myosin interaction and muscle contraction cannot occur.Cardiac Autorhythmic Fibers and Conduction PathwayPacemaker Function●Autorhythmic fibers generate electrical impulses spontaneously, setting the heart's rhythm.●These fibers are primarily located in the SA node, AV node, and bundle of His, and Purkinje fibers.Conduction System●Electrical impulses from autorhythmic fibers spread through a specialized conduction system in the heart.●SA node initiates the impulse, which travels through the atria, AV node, bundle of His, bundle branches, and Purkinje fibers.Cardiac Conduction Pathway●SA Node: Initiates the electrical impulse in the right atrium.●AV Node: Located at the atria-ventricles junction, slightly delays impulse transmission.●Bundle of His: Thick tissue bundle transmitting impulse to bundle branches.●Purkinje Fibers: Specialized fibers rapidly transmitting impulses for coordinated ventricular contraction.Cardiac Action Potential●Depolarization: Rapid upstroke due to sodium influx.●Plateau Phase: Sustained depolarization maintained by calcium influx and potassium efflux.●Repolarization: Potassium ions leave the cell, returning membrane potential to negative.Aerobic Respiration in Heart Muscle●Heart muscle primarily gains ATP through aerobic respiration.●The process involves glucose/fatty acid breakdown in the presence of oxygen to produce ATP.●Adaptations for aerobic respiration include a rich blood supply, abundant mitochondria, and myoglobin for oxygen storage.Electrocardiogram (ECG)ECG Basics●ECG is a painless test measuring the heart's electrical activity.●Commonly used to diagnose arrhythmias, coronary heart disease, and heart attacks.●Electrodes were placed on the chest, arms, and legs connected to the ECG machine.●The doctor interprets wavy lines on a graph for abnormal heart activity.●P wave (atrial contraction), QRS complex (ventricular contraction), and T wave (ventricular relaxation) are key components.
●Abnormal wave characteristics can indicate heart conditions.ECG Wave Breakdown●P wave: Represents atrial contraction.●QRS complex: Signifies ventricular contraction.●T wave: Indicates ventricular relaxation.●Abnormal wave size and shape can indicate heart issues.●For instance, a large P wave may suggest an enlarged atrium.Systole and Diastole●Systole: Heart contraction, pumping blood out, increasing blood pressure.●Diastole: Heart relaxation, allowing filling with blood.●Blood pressure is measured as systolic/diastolic pressure (e.g., 120/80 mm Hg).●Normal systolic pressure: 90–120, normal diastolic pressure: 60–80.●Monitoring blood pressure helps manage health risks.Cardiac CyclePhases of Cardiac Cycle●Diastole: The heart relaxes and fills with blood.●Systole: Heart contracts and pumps blood out.●Driven by electrical changes, pressures, and mechanical actions.●The SA node initiates the heartbeat, AV node regulates impulses.●Changes in pressure and volume move blood through the heart and body.Key Components of the Cardiac Cycle●Heart Sounds: 'Lub' (S1) and 'Dub' (S2) correspond to valve closures.●Blood Volume: Ventricles fill during diastole, and eject blood during systole.●Cardiac Output: Determined by heart rate (HR) and stroke volume (SV).●Factors Affecting Stroke Volume: Preload, afterload, and contractility.●******* Diagram: Graphical representation of cardiac cycle events.Factors Affecting Stroke Volume●Preload: Increased blood volume leads to higher ventricular filling.●Afterload: Resistance the ventricle must overcome to pump blood out.●Contractility: Strength of heart muscle contraction.●Factors affecting each include blood volume, systemic vascular resistance, and sympathetic nervous system activity.
Cardiac Output and Heart RateCardiac Output Calculation●Cardiac Output (CO): Determined by multiplying HR by SV.●Formula: CO = HR x SV.●Normal resting CO for adults: around 5–6 liters per minute.●Increases during exercise due to higher heart rate and blood pumping.●Factors affecting CO: Metabolism, age, size, and activity level.Factors Affecting Heart Rate●Exercise: Increases heart rate and maintains elevation during activity.●Stress: Anxiety can elevate heart rate.●Medications: Some drugs can lower or increase heart rate.●Body Position and Size: Influence heart rate measurement.●Environmental Factors: Temperature, humidity, smoking, alcohol, and caffeine.