Chapter 20: Cardiovascular System

(The Heart) Chapter 20 Cardiovascular System · includes the heart, blood, and blood vessels · 2 circuits: ↳ pulmonary circuit: blood flows from the heart to the lungs (low O2) ↳ systemic circuit: blood flows from the heart to the body (high O2) · functions of the cardiovascular system: ↳ delivers oxygen and nutrients ↳ removes CO2 and waste products Location and Orientation of the Heart · the heart is located between the lungs in the mediastinal space ↳ posterior to the sternum, slightly to the left of midline · 4 borders of the heart ↳ superior: base of heart where great vessels attach (3rd costal cartilage) ↳ Inferior: right ventricle forms inferior border ↳ right: right atrium forms border ↳ left: left ventricle and left atrium form border · fat in the sulci help protect the blood vessels that support the heart · coronary sulcus: grove between the atrium and ventricles · intraventricular sulcus: groove between the two ventricles · auricle: expandable sections in the atria where blood flows in The Pericardium · the membranes surrounding the heart · the pericardium includes an outer fibrous layer and two serous layers ↳ parietal pericardium (outermost layer) -dense fibrous layer -areolar tissue Three layers -mesothelium ↳ visceral pericardium (epicardium) -mesothelium -areolar tissue Two layers · the two layers are separated by the pericardial cavity which contains 15-20 mL of fluid to prevent friction The Heart Wall ① Epicardium: the external surface of the heart (visceral pericardium) ② Myocardium: includes cardiac muscle, connective tissue (including a fibrous skeleton), nerves → for structural support ③ Endocardium: epithelial lining that covers the inner surfaces of the heart including the heart values (simple squamous epithelium with underlying areolar tissue) What is the Cardiac Skeleton? ↳ four dense bands of tough elastic tissue that encircle the heart valves and the bases of the pulmonary trunk and aorta. Provides stability and electrical insulation. Internal Anatomy of the Heart The heart has 4 chambers: I. right atrium (RA) Pulmonary and tricuspid Aortic and mitral on the left on the right II. right ventricle (RV) III. left atrium (LA) IV. left ventricle (LV) · the chambers are separated by septa ↳ interatrial septum: separates the atria ↳ interventricular septum: separates the ventricles · the heart has 4 valves that direct the flow of blood between chambers and into vessels ↳ 2 semilunar valves: pulmonary and aortic → helps enter the vessels ↳ 2 atrioventricular valves: tricuspid and bicuspid/mitral valve → helps enter the ventricles · chordae tendinae: fibrous tissue that allows for closure of valves and ensures proper positioning · papillary muscle: skeletal type muscle that anchor the chordae tendinae · trabeculae carnae: meshwork in the ventricles that helps pump blood · pectinate muscles: line the atria to help them squeeze blood into the ventricles · ligmentum arteriosum: leftover from fetal development where both circuits were attached · the muscles of the heart are thicker on the left side · the left side is thicker because it pushes oxygenated blood through your whole body through the systemic circuit so it has to be stronger · the right side of the heart is thinner because it does not have to travel very far, just to the lungs through the pulmonary circuit Flow of Blood through the Heart RA → RV → LA → LV ① RA recieves blood from the body through the superior and inferior vena cava ↳ superior: head, neck, arms ↳ inferior: all the lower areas ② The auricle helps push blood through the tricuspid valve, into the right ventricle ③ From the RV blood passes through the pulmonary valve to the pulmonary trunk and arteries to go to the lungs ④ Blood returns to the heart from the pulmonary veins and enters the LA ⑤ From the LA, blood will pass through the mitral valve to the LV ⑥ From the LV blood is pumped to the rest of the body through the aortic valve and ascending aorta Valves · valves are one-way, and prevent backflow of blood ↳ chordae tendinae help keep them closed · regurgitation: leaky or damaged valves (some backflow) · Stanotic valve: stuck open or closed · Stenosis: not moving · Blood flow through the valves: T→ P → M → A ↳ mneumonic "toilet paper my assets" Overall Function of the Heart · the heart functions as two pumps that work simultaneously · the right side of the heart receives deoxygenated (used) blood and Arteries = away from heart Veins = towards the heart pumps it to the lungs to be oxygenated · the left side of the heart receives oxygenated blood and pumps it to the entire body as well as the coronary arteries Coronary Blood Supply · the heart pumps blood around the body so it needs its own blood supply ↳ blood is supplied to the heart by coronary circulation ↳ the heart does NOT receive blood when it pumps the blood · Coronary arteries ↳ originate within the aortic sinus at the base of the ascending aorta ↳ two major coronary arteries: ① Right coronary artery: supplies oxygenated blood to RA, RV, part of LA, part of LV, interatrial septum, part of intraventricular septum, and part of conducting system ② Left coronary artery: supplies oxygenated blood to LA, LV, part of RV, part of interventricular septum · Coronary veins ↳ collects wastes from cardiac muscle ↳ drains deoxygenated blood into the coronary sinus (large vein) on posterior surface of heart; coronary sinus empties into RA Conduction of Impulses in the Heart (heartbeat) · cardiac muscle tissue contracts in response to electrical impulses originating within the muscle tissue itself (autorhythmicity) ↳ contraction without stimulation of the nervous or endocrine systems · 2 types of cells involved with contraction: ↳ specialized autorhythmic cells (pacemaker and conducting cells) ↳ contractile cells Conducting cells are in AV bundle and intermodal pathway and connect the SA and AV nodes · Pacemaker cells (nodal cells) are responsible for establishing HR ↳ sinoatrial (SA) node ↳ atrioventricular (AV) node Pacemaker Cells · don't have stable resting membrane potentials ↳ sodium slowly creeps in (pacemaker potential) · Sinoatrial (SA) node ↳ located in posterior wall of right atrium ↳ "Cardiac pacemaker" where electrical impulses are generated (sets the rate of heart beat) ↳ generates action potentials at a rate of 60-100 per minute · Atrioventricular (AV) node ↳ located at the junction between the atria and the ventricles ↳ sends the signal generated by the SA node forward to the rest of the heart ↳ generates action potentials at a rate of 40-60 per minute Pacemaker Potential · pacemaker cells do not have a stable resting membrane potential, there is a potential drift toward threshold · Na+ slowly leaks into the cell continuously · When threshold is met (-40mv) depolarization occurs and calcium channels open · calcium rushes in, causing the rising phase (depolarization) · at peak, K+ channels open and K leaves the cell · rapid repolarization caused by inactivation of Ca+ channels and https://youtu.be/v7Q9BrNfIpQ?si=yLrPMeJ2exCasTOK activation of K+ channels Electrical Activity of the Heart · atria contract as a single unit followed after brief delay by a synchronized ventricular contraction · action potentials of cardiac contractile cells exhibit prolonged positive phase (plateau) accompanied by prolonged period of contraction ↳ ensures adequate ejection time, and time for blood to flow in ↳ plateau primarily due to activation of Slow L-type Ca2+ channels · because long refractory period occurs in conjunction with prolonged plateau, summation and tetanus of cardiac muscle is impossible ↳ ensures alternate periods of contraction and relaxation which are essential for pumping blood · Ca influx lengthens the action potential · As a result, cardiac muscle has a long refractory period because of prolonged action potential Brachycardia: heart rate is slower than normal <60 Tachycardia: heart rate is faster than normal >100 (Normal HR is 60-100bpm) Electrocardiogram (ECG) · a reading of electrical currents generated by depolarization and repolarization of cardiac muscle · each part of the ECG responds to a specific cardiac event Memorize! P wave: atrial depolarization (atria contract) PR segment: AV nodal delay QRS complex: ventricular depolarization ST segment: ventricles contract and eject blood T wave: ventricular repolarization QT interval: ventricular depolarization and repolarization TP interval: ventricles are relaxing and filling heart rate: how much your heart beats per minute heart rhythm: the regularity or spacing of ECG waves ↳ arrhythmias are when your heart rhythm has weird spacing Contractile Cells · purkinje fibers send the stimulus to contractile cells for contraction · contractile cells are connected by intercalculated discs (gap junctions) ↳ allows for functional synctium · energy for contraction: ↳ aerobic metabolism in mitochondria ↳ oxygen obtained from coronary circulation and O2 on myoglobin ↳ supply of calcium from sarcoplasmic reticulum (SR) · long contractile plateau and refractory period ↳ summation and tetanus not possible Cardiac Cycle · cycles between periods of contraction and relaxation · cardiac cycle: the period from the start of one contraction to the start of the next ↳ one cardiac cycle = one complete heartbeat · caused by rhythmic changes in cardiac electrical activity and pressure · divided into systole and diastole ↳ Systole (contraction): when a chamber contracts and blood is pushed into the next chamber ↳ Diastole (relaxation): when chambers fill with blood between contractions · fluids move from an area of high pressure to low pressure ↳ pressure rises with systole and falls with diastole ① Atrial Systole · pressure increases in the atria and blood is pushed into the ventricles through open AV valve · the amount of blood in the ventricles at this point is End-Diastolic Volume (EDV) ② Ventricular Systole · pressure rises in the ventricles and pushes AV values closed (S1 sound) · at this point all valves are closed = isovolumetric contraction · pressure continues to increase and semilunar valves open allowing for ventricular ejection ↳ the amount of blood that leaves the ventricle is the Stroke Volume (SV) ↳ the amount of blood left in the ventricle following ejection is the End-Systolic Volume (ESV) ③ Ventricular Diastole · ventricular pressure decreases and blood from vessels pushes semilunar valves closed (S2 sound) · at this point all valves are closed = isovolumetric relaxation ④ When pressure of ventricles drops below the pressure in the atria, the AV valves open and the cycle repeats Terms to know: · End-Diastolic Volume (EDV): the amount of blood held in one cardiac cycle (typically 130mL) · End-Systolic Volume (ESV): the amount of blood remaining in the ventricle after ejection · Ejection Fraction: the percentage of ESV that is ejected (typically 60% ) · Stroke volume: the amount of blood ejected from the ventricles (70-80mL) · Isovolumetric Contraction: When all the valves close in ventricular systole · Isovolumetric Relaxation: when all the valves close in ventricular diastole · Cardiac Output (CO): the amount of blood pumped from the left ventricle in one minute Preload. Afterload, & Contractility → affects stroke volume Preload ↳ the degree of stretch in ventricles during diastole ↳ directly proportional to EDV (↑volume↑preload) ↳ amount of blood to be ejected, dependent on venous return · Afterload ↳ the pressure that the heart must pump against, the tension needed in the ventricle to open the semilunar valves and push blood out ↳ anything that increases resistance in peripheral blood flow will increase afterload (↑resistance↑afterload) Eg. Blood clots · Contractility ↳ Frank Starling Law → the greater the heart muscle is stretched during filling, the greater the force of contraction and the greater the quantity of blood pumped into the aorta Heart Sounds · heard with a stethoscope · sounds of heartbeat are from turbulence in blood flow when the valves close ↳ S1 (lubb) heard when atrioventricular valves close ↳ S2 (dubb) heard when semilunar valves close Control of Cardiac Activity · controlled by ANS ↳ heart and greater vessels are highly innervated by cardiac plexus ↳ autonomic tone - SNS → norepinephrine and epinephrine - PNS → acetylcholine ↳ vagus nerve is responsible for most PNS innervation ↳ innervates SA & AV nodes · chemoreceptors in cardiac center of medulla senses O2 and CO2 levels · baroreceptors in aortic & carotid sinuses senses BP · atrial stretch (Bainbridge reflex) → increased HR when increased venous return · thyroid hormones increase HR and demands on heart etc. Heart failure: when heart muscles unable to pump enough blood through the heart to meet the demands of the body ↳ doesn't pump properly