Cardiac Anatomy & Physiology Student Version 2025 PDF

Cardiac Anatomy and Physiology January 27, 2025 Golda Widawski, PT, DPT  Objectives Accurately identify anatomy involved in circulation: mediastinum, heart, blood vessels Accurately describe the path of blood flow though the body Accurately identify blood supp...

Cardiac Anatomy and Physiology January 27, 2025 Golda Widawski, PT, DPT  Objectives Accurately identify anatomy involved in circulation: mediastinum, heart, blood vessels Accurately describe the path of blood flow though the body Accurately identify blood supply to the heart Identify the functions of the cardiovascular system Explain clearly the parts of heart’s electrical and mechanical systems and how they work Identify inherent heart rates of parts of the conduction system of the heart Identify the basic nerve supply to the heart Accurately describe the cardiac cycle and what occurs at each phase  You are working in homecare and go to see Mrs. W for an initial evaluation – She is 1 week s/p left lung UL resection via thoracotomy due to newly diagnosed lung cancer – PMH: ovarian cancer s/p resection & chemo 20 yrs ago, h/o smoking (quit 20 yrs ago), and osteoarthritis Upon taking her resting vitals, you find: – HR 140 bpm (irregularly, irregular) – BP 128/70 – RR 12 – O2Sat 97% (RA) What is your course of action? – To treat or Not To Treat HPI: Patient is a 68 year old female – per H & P, pt is a 68 year old female who presented from home s/p mechanical fall, unwitnessed, not on anticoagulation. States she fell from her couch approximately 1 week ago, has had persistent lower back pain, and therefore came to the ED. PMH/PSH: Abnormal nuclear stress test (04/2016), Breast cancer s/p mastectomy (Bilateral, 2005), CAD, CHF Diabetes mellitus, Exposure to secondhand smoke, HTN, Ischemic cardiomyopathy, Positive PPD (03/2013), Psoriasis, Second degree burn of abdomen (11/22/2016), and Thyroid nodule. s/p open coronary endarterectomy (10/2010); s/p implantation of cardiac resynchronization defibrillator, total system (04/12/2012). SUBJECTIVE: Patient Report/Complaints: Pt reports she feels cold. Pre-Treatment Pain: 0-10 (Numeric): Pt did not rate pain, but endorsed that she often has back pain but it was okay at rest. OBJECTIVE: General Observations: Patient received semi-reclined in bed with step down monitoring, medlock. NC O2 present, but was not delivering O2 - RN present and NC removed. Mentation: Alert, Oriented to name, place, year Follows Directions noted to be a little slowed with answering questions, requiring repetition of questions at time. Endurance: Poor Balance Sitting Balance: Pt requires supervision with sitting at edge of bed. Standing Balance: Pt requires rolling walker and contact guard /min A with standing activities. Range of Motion Grossly WFL x 4 extremities, except left shoulder flex/abd to ~30 (pt reports prior surgery), right shoulder flex to ~90. Manual Muscle Testing At least 3/5 x 4 extremities, w/in available ROM. Skin & Soft Tissue Not formally assessed, though pt noted to have scratches on right LE, otherwise visible skin appears grossly intact. Sensation Bilateral LE intact to light touch. Posture Pt noted to have somewhat flexed posture in sitting. Bed Mobility: ROLLING: to right with min A and cues. SUPINE to SIT: mod A and cues - transitioned via right sidelying. SIT to SUPINE: mod A and cues - transitioned via right sidelying. SCOOTING: to edge of bed in sitting with min/mod A and cues. Transfers: SIT to/from STAND: min/mod A from bed to rolling walker. Ambulation: Pt ambulated ~6-8 small side steps to the right with rolling walker and min A. Gait demonstrates flexed posture, decreased step length bilaterally, and decreased cadence.  Vital Signs Position / BP Pulse SpO2 Resp Oxygen Activity 01/07/24 0600 111/48 104 100 % 10 — — 01/07/24 0745 124/71 99 95 % 11 — — 01/07/24 0933 125/51 100 94 % — RA rest-lying 01/07/24 0955 120/109 (!) 140 97 % — RA recovery-lying 01/07/24 0958 120/104 (!) 141 99 % — RA rest-lying 01/07/24 1000 113/42 (!) 124 100 % — RA rest-lying 01/07/24 1026 127/62 (!) 123 97 % 22 — — Assessment Post-Treatment Pain: There was no change in the patient's pain level following the session. Impairments: decreased strength, decreased range of motion, decreased endurance, impaired balance, decreased mobility, orthopedic restrictions, and pain Evaluation/Treatment Tolerance: no adverse response to session, pt noted to be tachycardic (RN and Red Surg team notified) and cold (provided with warmed blanket). General Observations Post Session: Patient resting at end of session. All monitors intact. Call bell in reach. Impression: Pt is a pleasant 68 y/o woman admitted post fall with above noted injuries. Pt able to get up with PT today with assistance, though noted to be a little ?confused at times, requiring questions to be repeated - though oriented and able to describe fall to this PT. Pt with tachycardia and elevated DBP post mobility, as noted above. Team and RN aware. Pt presents with decreased strength, decreased balance, pain, and deconditioning contributing to impairments in functional mobility/transfers and ambulation and limiting pt's participation in daily activities. Pt will benefit from continued skilled PT to address functional deficits and above noted goals.  Cardiac Anatomy Structural Elements Involved In Circulation – Central Components Located in the Mediastinum Heart – pumps blood The Great Vessels – transport blood to central pulmonary and systemic circulation – Systemic Circulation Arteries and arterioles that deliver blood to the body Capillaries that allow O2, nutrient and waste exchange Veins that return blood to the heart  Mediastinum Space in thorax Structures surrounded by loose connective tissue, between right and nerves, blood and lymph left pleura vessels, lymph nodes and fat Borders Can accommodate Contains all movement and volume structures in the changes due to the thorax, except looseness of the connective tissue, combined with the _____________ elasticity of the lungs and pleura Volume changes may be due to changes in: – Venous return – Cardiac output – Ventilation – Swallowing  Pericardium Double walled fibrous sac which encloses the heart and roots of great vessels – Outer fibrous layer (fibrous pericardium) Tough, thick outer layer Attached to: – Outer layer of the great vessels – Central tendon of the diaphragm – Inner double layered sac (serous pericardium) Parietal pericardium (outer layer) Visceral pericardium (inside layer) aka epicardium  Pericardial Cavity “Potential” space between the parietal and visceral layers Contains a thin layer of serous fluid Allows the heart to beat in a frictionless environment Phrenic nerve  innervates parietal pericardium Visceral pericardium is insensitive to pain  Clinical Notes re: Pericardium Inflammation of the pericardium (pericarditis) – Presents as substernal pain and can result in pericardial effusion Pericardial rub (heard on cardiac auscultation)  Heart Muscular pump that propels blood via the blood vessels to the body Pyramidal/cone shaped Situated obliquely in the _______________ Located 2/3 to the left of the median plane Contained within the pericardial sac  Heart Apex: Base: – Found in the 5th – Formed by the 2 intercostal space atria (ICS), midclavicular – Most superior line in supine portion of heart = – Tip of the left 2nd intercostal ventricle space – Point of maximum – Aorta and impulse (PMI) pulmonary trunk – Most inferior portion exit and the of the heart superior vena cava – Lies on top of the enters the heart diaphragm here  Layers of the Heart Layers of heart: – Epicardium— outermost layer (aka: visceral pericardium) – Endocardium— innermost layer – Myocardium— middle layer  Myocardium Most myocardial fibers work to contract the heart Special fibers of myocardial muscle make up the conduction system of the heart (including SA and AV nodes, AV bundle, and Purkinje fibers) Myocardial cells are grouped in to 2 structural categories: – Mechanical cells (myocytes) – Conductive cells The metabolic processes of the myocardium are almost exclusively aerobic  Myocytes Mechanical cells (myocytes) – Tracts of striated muscle fibers – Have greater capacity for mechanical shortening to allow for pump action of heart – Pattern of actin/myosin similar to skeletal muscle – Intercalated disks Join myocytes together to form a syncytium—atria and ventricles make up the 2 syncytiums of the heart Separates the cells Support synchronized contraction  Myocardium Cells have: – AUTOMATICITY Intrinsic ability to contract in absence of stimuli – RHYTHMICITY Intrinsic ability to contract in a rhythmic manner – CONDUCTIVITY Intrinsic ability to transmit nerve impulses Also see: – EXCITABILITY Ability to respond to electrical stimulus – CONTRACTILITY Ability to stretch as single unit, then passively recoil while actively contracting Myocardial cells cannot replace injured cells  Additional Anatomic Features of the Heart Coronary sulcus or groove (aka: atrioventricular sulcus/groove) – Coronary sinus Located in the coronary sulcus It receives blood from the veins of the heart and delivers it to the right atrium Anterior interventricular sulcus  Cardiac Skeleton Made up of anulus fibrosus (fibrocartilaginous tissue) Separates the atria from the ventricles Acts as electrical insulator between atria and ventricles so impulses only move through the AV node Gives support to the valve  Blood (a review) Composed of: – Red blood cells (RBC) = erythrocytes Biconcave cells that contain hemoglobin – White blood cells (WBC) = leukocytes 5 types: neutrophils, eosinophils, basophils, monocytes, and lymphocytes – Platelets Play a major role in clotting of the blood – Plasma Liquid component of blood which suspends the RBC, WBC, and platelets Made up of gases, salts, carbohydrates, proteins, and lipids Heart Anatomy 17. 16.  Heart Anatomy 2 sides divided into 4 chambers – Right side and Left Side – 2 upper chambers (_______) – receiving areas – 2 lower chambers (_______) – discharging chambers Amount of blood in pulmonic circulation equals that in systemic circulation Pulmonary arterial pressure is 1/6th that of systemic pressures  Right Atrium Has thin muscular wall Receives venous blood (___________) from the superior and inferior vena cava and coronary sinus (during diastole) Contains the SA node Interatrial septum forms the posteromedial wall of the right atrium and contains the fossa ovale – Atrial septal defect (ASD) Why is this a problem???  Right Atrium (RA) Normal filling pressure of RA = 0-8mm Hg – Referred to as central venous pressure (CVP) Pectinate muscles – Parallel muscle bundles that compose the inner wall of the right atrium – “comb like” CLINICAL NOTE: Orthotopic heart transplants usually involve the excision of the RA (LA and great vessels are left in place) and the donor heart is then attached to the RA  Atrioventricular (AV) Valves Separate atrium and Right = TRICUSPID ventricle VALVE Allow for one way blood -3 leaflets/cusps Left = MITRAL flow VALVE Complex system of -2 leaflets/cusps structures: – Valvular orifice surrounded by an annulus – Valve leaflets/cusps – Chordae tendineae – Papillary muscles – Trabeculae carneae (aka: Rathke’s bundles) Tricuspid Valve (aka Right AV Valve) Located between the right atrium and right ventricle(4th/5th intercostal space @ left sternal border) Guards the right AV orifice Composed of 3 cusps/leaflets: anterior, posterior and septal (medial) – These are thinner than those of the mitral valve  Right Ventricle Receives blood from right atrium via tricuspid valve and pumps blood into pulmonary artery via the pulmonary valve Most anterior portion of heart beneath the sternum Crescent shaped chamber with a thin myocardial wall 2 portions: – Body of the right ventricle – Infundibulum (conus arteriosus) Septo marginal trabecula  Right Ventricle Resistance of pulmonary circulation is about 1/10th that of systemic circulation – Normal systolic pressure in the right ventricle = 15-30 mm Hg – End diastolic pressure = 0-8 mm Hg Generates less than ¼ the stroke work of the left ventricle  Semilunar Valves Have 3 leaflets/cusps – Anterior, right, and left Right = PULMONARY VALVE Left = AORTIC VALVE Prevent backflow from the pulmonary artery and aorta during diastole Open and close solely based on pressure gradient changes in the heart during the cardiac cycle  Pulmonary (Pulmonic) Valve Located at the level of the 2nd intercostal space, to the left of the sternum Contraction of the right ventricle pushes blood through the pulmonary valve into the pulmonary trunk  Left Atrium Walls are slightly thicker than right atrium— why? Collects blood from right and left pulmonary veins – Carry oxygenated blood from the lungs Forms most of the posterior surface of the heart Auricular appendage (or “dog ear”) – Represents the original heart tube and serves no function Blood flows through the left AV orifice (mitral valve) into the left ventricle Normal filling pressure = 4-12 mm Hg  Left Atrium CLINICAL NOTE: In certain cardiac conditions (ex: atrial fibrillation) a thrombus can form on the wall of the left atrium and if it breaks off, it can travel to and occlude peripheral arteries (an occlusion of the artery of the brain can result in a stroke)  Mitral Valve (aka Left AV Valve) Guards the opening between the left atrium and the left ventricle Located between the left atrium and left ventricle – Situated at level of 5th intercostal space (~midclavicular line) Composed of 2 cusps (anterior and posterior) – Also known as: bicuspid valve Projects into the left ventricle  Mitral Valve Insufficiency/Problems Can cause an increased regurgitation of blood flow from the left ventricle through the leaky mitral valve into the left atrium CLINICAL NOTE: Mitral valve is the most frequently diseased heart valve – Mitral Valve Prolapse – Mitral Valve Insufficiency or Regurgitation – Mitral Stenosis  Left Ventricle Cavity of the left ventricle is conical in shape and narrows to form the apex of the heart Receives blood from left atrium via mitral valve and pumps blood into aorta (and systemic circulation) via aortic valve Makes up nearly entire left border and surface of the heart – “inferior wall” Has a thick muscular wall that is 2-3 times as thick as the right ventricular wall  Left Ventricle 2 portions Normal systolic – A funnel shaped inflow tract pressure is 80-120 direct blood toward the apex mmHg – An outflow tract sends the Normal end-diastolic blood from apex superiorly pressure is 4-12 and right toward the aortic valve mmHg Superior and anterior portion is formed by the aortic vestibule 2 large papillary muscles give rise to chordae tendinae which attach to the cusps of the mitral valve  Ventricular Septum AKA: Interventricular Septum Wall which partitions right and left ventricles – Composed of muscular and membranous portions Contains electrical conduction tissue Provides stability to the ventricles during contraction Margins of the septum correspond with the anterior and posterior interventricular grooves  Aortic Valve Guards the aortic orifice Contraction of the left ventricle pushes blood through the aortic valve into the aorta Composed of 3 thick semilunar cusps attached to fibrous ring Located roughly at 2nd intercostal space at the right sternal border General Anatomic Location of the Valves  The Great Vessels Considered to be the “Primary Blood Vessels” Vena Cava – Superior (SVC) – Inferior (IVC) Pulmonary veins – There are 4 2 from right lung 2 from left lung Pulmonary arteries – There are 2 (one to each lung which branch off the main pulmonary artery) Aorta  Basic Design of Blood Vessels Three layers of tissue called TUNICS – Tunica Intima: innermost layer – Tunica Media: mainly smooth muscle Makes up the bulk of the arterial wall – Tunica Adventitia or Externa: contains both elastic and collagenous fibers Thickest layer in veins The CV System  Arteries Deliver oxygenated blood throughout the body, – Which arteries deliver de-oxygenated blood? Artery  arteriole  capillary beds More developed media than veins Anastamoses: connections between arterial branches providing collateral circulation to capillary beds Arterial types: – Elastic – Muscular – Arteriole  Veins Return deoxygenated blood from the body to the heart Lower pressure system Relies on a system of valves and muscular contraction to ensure blood flow back to the heart Create anastamoses more easily than arteries – Development of complex networks for drainage of blood from tissue Venous types: – Venule – Medium size – Larger  Capillaries Smallest of the blood vessels – Connect arteriole to venule Capillary walls are thin and composed of endothelium – Oxygen, CO2, nutrients, and wastes are exchanged through their thin walls The CV System  Lymphatics Similar to vascular capillaries Begin blindly in tissues and number of lymph vessels varies based on body region May form plexuses – Smaller lymphatic vessels join together and develop into larger lymphatic vessels Contain valves to ensure one way flow to the heart Pass through lymph nodes  Aorta Largest artery in the body Coronary arteries arise from its root 3 branches from its arch – Brachiocephalic or Innominate – Carotid – Subclavian Made up of – Ascending aorta – Aortic arch – Descending aorta, divides into Thoracic aorta Abdominal aorta  Aorta Aortic sinuses – An anatomic dilation of the ascending aorta – Generally there are 3 aortic sinuses Right and left sinus areas give rise to the right and left coronary arteries – AKA: Sinus of Valsalva – Prevents the cusps of the aortic valve from sticking on the wall  Route of Blood Veins (systemic) Arteries (systemic and coronary)  Circulation – Right Side of Heart Right atrium receives BLU blood from the systemic E circulation Right atrium contracts and pushes blood through the ________ valve  ________ Right ventricle contracts and – Tricuspid valve closes to prevent back flow to the right atrium AND – Blood is forced through the ________ valve into the pulmonary ______  lungs where it is oxygenated in the pulmonary circulation  Circulation – Left Side of the Heart RE Left atrium receives D ________ blood from the lungs via the 4 pulmonary _____ Left atrium contracts and blood flows through the _____ valve into the ____________ Left ventricle contracts and – Mitral valve closes to prevent back flow into the left atrium AND – Blood is forced/pumped through the _____ valve into the aorta and systemic circulation Circulation to the Heart—Arterial supply Coronary Arteries arise from ____________________ Blood is supplied to the muscle of the heart via the right coronary artery (RCA) and the left coronary artery (LCA) Travel around the heart in 2 grooves – Atrioventricular groove (aka coronary sulcus) – Interventricular groove – These 2 grooves meet at the posterior aspect of the heart = crux of the heart – Right or left coronary dominance is determined by which artery crosses the crux and supplies the AV node  Coronary Arteries Coronary arteries give rise to perforating arteries that travel deep into the myocardium Capillary network of the heart is about 1 capillary for each muscle cell  Left Coronary Artery (LCA) Supplies blood to left atria and most of the left ventricle, parts of the right ventricle as well as the interventricular septum LCA (or Left Main) divides into 2 main branches – Left Anterior Descending (LAD) or Anterior Interventricular Artery – Left Circumflex (LCX) LEFT ANTERIOR DESCENDING (LAD) – Travels in the anterior interventricular groove – Anastomoses with the posterior branches of the RCA – Supplies blood to: Anterior two-thirds of the interventricular septum Anterior, lateral, and apical wall of left ventricle Most of right and left bundle branches Collateral circulation to anterior right ventricle and posterior part of the interventricular septum – It is the most commonly occluded coronary artery  “widow maker” Causes impairment/blockage of the conduction system of the heart  Left Coronary Artery Left Circumflex (LCX) – Follows the coronary groove around the left border of the heart and ends in the region of the posterior interventricular groove – Commonly anastomoses with the distal RCA – Gives off marginal branches The terminal branch is usually the largest of these branches – Supplies blood to: Most of the left atrium Posterior and lateral walls of left ventricle – May continue through AV sulcus to provide blood to the posterior wall of the left ventricle with the RCA  Right Coronary Artery Travels from the aorta Gives off a variable into the AV groove  number of branches to curves around to the the right atrium and posterior surface of the right ventricle as it heart to make a bend travels inferiorly at the crux  then continues downward in – Right marginal branch— the posterior runs down the right interventricular sulcus margin of the heart (posterior coronary supplying the right ventricle groove) to give off the posterior – Posterior descending interventricular branch artery—supplies to the inferior wall of the left Terminal portion of the ventricle and inferior portion of the RCA descends towards interventricular septum the apex of the heart  Right Coronary Artery Supplies blood to the right atrium, right ventricle, interventricular septum, and inferior wall of the left ventricle Supplies blood to the SA and AV nodes – SA Nodal Artery—branches off of the RCA at the crux of the heart to pass anteriorly along base of atrial septum to supply to AV node Occurs in ~55% of hearts In the other 45% it comes from a branch of the LCX – AV Nodal Artery—usually branches off of the distal RCA Occurs in ~85-90% of hearts In the other 10-15% it comes from a branch of the LCX  Venous Drainage of the Heart Coronary veins tend to follow coronary arteries Collect de-oxygenated blood from the myocardium Coronary sinus is the main vein of the heart – Located in the posterior portion of the coronary groove on the posterior surface of the heart – Empties directly into the right atrium – Receives drainage from: Great cardiac vein Middle cardiac vein Small cardiac vein – Thebesian veins are the smallest of the cardiac veins  Function of The Heart and Cardiovascular System Deliver O2 and nutrients to all tissues in the body and remove CO2 and waste products, via the blood Transport of heat to maintain body temp Transport of WBCs to fight infection Transport of hormones  The Heart as A Pump 2 systems of the heart – Electrical System Impulses that trigger the heart muscle – Mechanical System Made up of cardiac muscle, chambers and valves that function to contract pump blood to the lungs and to the rest of the body Conduction Video – http://www.youtube.com/watch?v=fZT9vlbL 2uA  Electrical System Resting cardiac muscle (myocardium) – Heart muscle cells called _________ are polarized, negatively charged, at rest Depolarization – When the myocytes become positive they contract – Moves as a wave through the myocardium Repolarization (relaxation) – Recovery phase following depolarization – Myocardial cells return to resting negative charge inside – Muscle relaxes  Electrocardiogram (EKG) Records the electrical activity of the heart Give information about heart’s function and structure (does NOT measure heart function) Records the depolarization and repolarization of the myocardium – P wave – atrial depolarization – QRS – ventricle depolarization – T wave – ventricular repolarization  Conduction System of Heart Sinoatrial (SA) Node Internodal Conduction Pathways Atrioventricular (AV) node Bundle of His Bundle branches Purkinje fibers  Sinoatrial (SA) NODE “Pacemaker of the heart” (normally) with the innate rate of impulse generation of 60-100 bpm (sinus rhythm) Located at the junction of the superior vena cava and the RA Initiate the cardiac cycle when action potentials that arise in the SA node cause a wave of depolarization that spreads thru the atria Travels to AV Node via internodal tracts  Atrioventricular (AV) NODE AV node is located in the right atrial septal wall near the tricuspid valve Receives the electrical impulses originated at the SA node and conducts it to the Bundle of His In a normal heart the only way that the electrical impulse can spread from the atria to the ventricles is via the AV node 2 functions of AV NODE: – When impulse arrives at AV Node depolarization slows causing a delay of.04 sec to allow the ventricles to fill with blood from the atria—“atrial kick” – Controls the number of impulses going to the ventricles Inherent rate of 40-60 bpm  Bundle of His The cardiac impulse travels from the AV Node to the Bundle of His Divides into right and left bundle branches Inherent firing rate of 20 to 40 bpm Terminates into Purkinje fibers – Continuous with cardiac muscle in the ventricles – Stimulate ventricular contraction  Heart Rate (pacemaker) SA Node “pacemaker” = 60 - 100 bpm AV Node = 40 - 60 bpm Bundle of His/Purkinje Fibers = 20 - 40 bpm Clinical Notes: – Abnormalities in the conduction system will present in abnormalities in rate and abnormalities in ECG – Myocardial infarction in the interventricular  Conduction System of heart Chambers are isolated both electrically and physically 4 Properties of myocardial cells: – Automaticity: Ability to initiate own depolarization, to contract in the absence of stimuli, w/o direct stimulation needed from a nerve – Rhythmicity: Ability to contract in a regular, rhythmic manner – Conductivity: Ability to spread impulses to adjoining cells quickly – Excitability: The cells transmit nerve impulses  Innervation of CV System The heart is controlled by 2 opposing divisions of the autonomic nervous system (ANS) – Usually balanced to create a steady state – SYMPATHETIC NERVOUS SYSTEM: Dominates during stressful situations leading to tachycardia, increased cardiac output (CO) and increased O2 demand “adrenergic” nerve cells of ANS that use norepinephrine as neurotransmitter – PARASYMPATHETIC NERVOUS SYSTEM: Dominates during relaxed states  leading to resting HR, baseline CO, and decreased O2 demand of the heart Controls heart through the vagus nerve (CN X) and the release of acetylcholine “cholinergic”  The Cardiac Plexus Nerve tissue of the heart Located anterior to the tracheal bifurcation Consists of both sympathetic and parasympathetic nerves Serves as a conduit for neurotransmitters (ex: norepinephrine and acetylcholine) to reach target receptors in the heart  Nerve Supply (summary) Sympathetic Parasympathetic (adrenergic): (cholinergic): – Also monitors SA node – Monitors SA, AV node – Slows cardiac activity – Accelerates cardiac – Increase vagal tone: activity HR slows (sleep) Increase HR – Decrease vagal tone: Increase speed of HR increases (walking) contraction “Vaso-vagal event” Increase force of – Syncope or fainting due contraction to a trigger that increases – “fight or flight” vagal tone leading to decrease in HR and BP  Cardiac Reflexes What are they? Neural mechanism that automatically increases or reduces the heart rate Stimulation of stretch receptors in the right side of the heart by increased venous return  increases the heart rate – Bainbridge Reflex Increased arterial blood pressure stimulates nerve endings in the carotid sinus and aortic arch  reduces the heart rate.  Cardiac Reflexes Baroreceptors Chemoreceptors – Sense changes in BP – Sense chemical and “report” characteristics of abnormal BP to the blood (ie carbon CNS  – High BP or arterial dioxide) to help regulate function baroreceptors Respond to high BP – Ventilatory and very quickly by cardiac responses lowering rate and These nerves detect blood vessel levels of oxygen, pH resistance and carbon dioxide – Low pressure in the blood to baroreceptors determine when Regulate blood someone needs to volume in the body increase HR or RR  Mechanical System of the Heart Cardiac Cycle: The period from the beginning of one heartbeat to the beginning of the next 2 phases – Diastole – (ventricular) relaxation – Systole – (ventricular) contraction http://www.youtube.com/watch?v=jLT dgrhpDCg  Cardiac Cycle—5 Phases Period from the beginning of one heart beat to the beginning of the next Mid Diastole – Ventricles receive blood from the atria – AV valves are open and Semilunars are closed – Pressure in Atria > Ventricles – 80% of blood to ventricles Late Diastole – Remaining 20% of volume comes into ventricles – Atrial contraction “atrial kick” – SA Node has fired  Cardiac Cycle Continued Early Systole – Impulse through AV Node  Ventricles – Ventricles contract – AV Valves are closed – ventricular pressure rises – Isovolumetric contraction – S1 = LUB Late Systole – Aortic and Pulmonic Valves are open – Ventricular ejection (rapid) – Blood flow aorta and lungs – Only part is ejected = ejection fraction – End systolic volume = volume of blood remaining after ejection  Cardiac Cycle Continued Early Diastole – S2 = DUB – Pulmonic and aortic valves are shut – AV valves open – Repolarization occurs – Isovolumetric relaxation TIMING of the Cardiac Cycle – Each cycle lasts ~0.8 sec Atrial systole: ~0.1 sec Atrial diastole: ~0.7 sec Ventricle systole: ~0.3 sec Ventricle diastole: ~0.5 sec  Blood Flow (Q) Q = CO = HR x SV Cardiac output (CO): Amount of blood ejected by left ventricle into aorta/min Venous return: Amount of blood returned to right atria/ min Heart Rate (HR) = number of beats/min Stroke Volume (SV) = amount of blood ejected by each ventricle during one contraction / systolic period / min – Affected by three things Preload—amount of tension on the muscle before it contracts (ventricular filling) Contractility—contractile force Afterload—the load against which the muscle exerts its contraction  Preload LVEDP (LV End Diastolic Pressure) and EDV (End Diastolic Volume) – Pressure in LV before it contracts – Amount of muscle fiber stretch at end of diastole – Amount of volume in the ventricle at this phase – “pulling back the rubber band” Compliance (normal) – High volume creates small change in pressure Non Compliance (diseased) – Small change in volume creates high change in pressure  Contractility The integrity of muscle fibers and effectiveness of force and rate of contraction If muscle becomes too hypertrophied or rate is >120 bpm, the effectiveness of the heart decreases – Decreased ventricular filling times – Less volume per beat – Less efficient  Afterload The resistance, impedance, pressure that the ventricle works against to eject blood Aka: total peripheral resistance (TPR) Dependent on – Volume and mass of blood ejected – Size and wall thickness of ventricle – Impedance of vasculature Inverse relationship to stroke volume – Resistance increases  SV decreases  Frank-Starling Mechanism Examines relationship between ventricular filling pressure (EDV—end diastolic volume) and ventricular mechanical activity SV=CO/HR SV is dependent on diastolic muscle fiber length and contractility Found an optimal range of LV filling pressures – Increase pressure, increase stretch of muscle fibers – Can actually decrease performance if too high or low Frank-Starling Graph  Heart Cycle Summary Videos https://www.youtube.com/watch?v=vh LNQqszg-o&pbjreload=10 https://www.youtube.com/watch?v=5t UWOF6wEnk