The Heart PDF

The CardioVascular System The Heart By Fay Stirrat  Pulmonary and Systemic Circuits The heart is a transport system consisting of 2 side- by-side pumps: Right side Left side Receives oxygen-po...

The CardioVascular System The Heart By Fay Stirrat  Pulmonary and Systemic Circuits The heart is a transport system consisting of 2 side- by-side pumps: Right side Left side Receives oxygen-poor Receives oxygenated blood blood from tissues from the lungs Pumps blood to the lungs Pumps blood to body tissues to get rid of CO2, and via the systemic circuits pick up O2, via the pulmonary circuit 2  Heart Anatomy 11/20/2024 Sample Footer Text 3  Where does the heart live? Within the mediastinum 11/20/2024 Sample Footer Text 4  Layers of the Heart Pericardium – encloses the heart in a sac Myocardium – walls of the heart = muscle Endothelium – lines the inner layer 11/20/2024 Sample Footer Text 5 Receiving Chambers - Atria Small, thin-walled chambers that contribute little to the propulsion of blood Left atrium: Receives oxygenated blood from the lungs 4 pulmonary veins return blood from the lungs Right atrium: Receives deoxygenated blood from the body’s tissues 6  Receiving Chambers - Atria 3 veins empty into the right atrium: Superior vena cava: returns blood from the body regions above the diaphragm Coronary sinus: returns blood from the coronary veins Inferior vena cava: returns blood from the body regions below the diaphragm 7 Discharging Chambers - Ventricles Thicker walls than the atria Are the actual pumps of the heart Make up most of the volume of the heart 8  Discharging Chambers - Ventricles Pump bloo md into the aorta (largest artery in the body) Pump blood into the pulmonary trunk Posteroinferior surface Chordae tendineae: Attached to the heart valves Anterior Papillary muscle: Projects into the surface ventricular cavity Trabeculae carneae: Irregular ridges of muscle on the ventricular walls 9  Valves Stop blood from flowing backwards! Passive process and open / close based on pressure differences across the valves All fastened to muscular aspects of the heart (papillary muscles) of the ventricular walls by fibrous strands (chordae tendinae). Pulmonary and Aortic Valves Atrioventricular Valves (AV Valves) – between atrium and ventricle Tricuspid valve - right side Mitral / Bicuspid valve – left side 11/20/2024 Sample Footer Text 10 Blood Flow Through Heart 11 What about its own blood supply? Coronary Arteries Both the left and Functional blood the right coronary supply to the arteries arise heart muscle itself from the base of the aorta and Shortest supply arterial circulation in the (oxygenated) blood to the body heart. Delivered when Both encircle the the heart is heart in the relaxed coronary sulcus. Left ventricle: Branching of the receives most of coronary arteries varies among the coronary blood individuals supply 12 Cardiac Muscle Cardiac-muscle cells of the myocardium – arranged tightly and completely encircle the chambers. Skeletal and smooth muscle – striated. 1% have specialised features that are essential for heart excitation – make up a network called the conduction system of the heart. Cardiac vs. Skeletal Muscles - Differences The heart relies almost exclusively on aerobic respiration. Fewer mitochondria Cannot function without oxygen Less adaptable to other fuels More mitochondria Cannot function without oxygen More adaptable to other fuels 14  The Conduction System Helps initiate a heartbeat – impulse spreads rapidly through the heart In contact with other cardiac muscle fibres via gap junctions. 11/20/2024 Sample Footer Text 15 Intrinsic Conduction System Non-contractile cardiac cells initiate and distribute impulses through the heart (approx. 1% autorhythmic cardiac cells) Called cardiac pacemaker cells. Unstable resting potential which continuously depolarizes the cells work together to ensure the heart contracts in an orderly manner 16  The Heartbeat Action potentials spread from one cell to another Initial depolarisation in the sinoatrial (SA) node – located in the right atrium = contraction Discharge rate determines heart rate The link between atrial and ventricular depolarisation = atrioventricular (AV) node – base of right atrium – slight delay to allow for blood filling. Enters the wall between the 2 ventricles via the conduction system fibres called Bundle of His. Divides within the septum into the right and left bundle branches Finally make contact with the Purkinje fibres to trigger the impulse around much of the ventricles 11/20/2024 Sample Footer Text 17  The ECG. Tool for evaluating electrical events within the heart. ‘P’ wave – atrial depolarisation ‘QRS’ complex – ventricular depolarisation ‘T’ wave – ventricular repolarisation 11/20/2024 Sample Footer Text 18 Sinus Rhythm and Electrocardiography (ECG) Intrinsic Conduction Defects Arrhythmias – irregular heart rhythms Fibrillation – uncoordinated atrial/ventricular contractions Defibrillation required to restore regular contractions Pacemakers and ICD’s can be surgically implanted to control irregular HR and fibrillations Ectopics Defective SA node may lead to junctional rhythm taking over Area of heart becomes hyperexcitable and generates impulses faster than SA node – causing extrasystole Heart Block 19 Anatomical Differences between the Left and Right Ventricles Left ventricle walls 3 times thicker than the right ventricle; pumps with greater pressure 20 Phases of Cardiac Cycle 21  Extrinsic Innervation Autonomic nervous system modifies the heart beat Sympathetic nervous system increases rate and/or force of heart Parasympathetic slows it down Cardiac control originates in medulla oblongata Controlled by Vagus nerve (cranial nerve 10) 22  Cardiac Output Volume of blood pumped by each ventricle per minute – LPM. Volume of blood flowing through either the systemic or the pulmonary circuit per minute HR x SV = CO 11/20/2024 Sample Footer Text 23  Stroke Volume The volume of blood ejected by each ventricle during each contraction – ie a more forceful contraction can equal increase in SV. Affected by: End-diastolic volume / preload – Starlings Law Afterload 11/20/2024 Sample Footer Text 24 Physiotherapy Physical activity can help: Lower BP Strengthen heart Control weight Increase circulation Increase efficiency of cells to utilise O2 25