ANATOMY & PHYSIOLOGY OF THE HEART Unit 12 Chapter 20

HEART FACTS  A hollow muscular organ  Tipped slightly so that the part of it stick out and taps against the left side of the chest (apex), which is what makes it seem as though it is located there  During an average lifetime, the human heart will beat more than 2.5 million times  Beats over 100,000 times/day and 35 million times/year to pump blood around the body’s 60,000 miles of blood vessels  5 pints of blood pump through your entire body with one single heart beat

THE HEART The heart is responsible for the circulation of the blood The heart is actually TWO pumps in one:  One part propels blood through the pulmonary circulation  To the lungs where the blood releases carbon dioxide and receives oxygen  The second part propels blood through the systemic circulation  To all remaining tissues of the body

EXTERNAL STRUCTURE OF THE HEART Layers  Edocardium  Inner layer  Epicardium  Outer layer  Myocardium  Middle layer Pericardium  Protective membrane surrounding the heart Coronary Arteries  Supply blood to the outside of the heart

ANATOMY OF THE HEART Located in the thoracic cavity between the lungs in a space within the mediastinum called the pericardial cavity The blunt end of the cone is called the apex The flat top is the base The heart is a muscular pump consisting of 4 chambers  2 atria  2 ventricles APEX BASE

ANATOMY OF THE HEART

INTERNAL STRUCTURE Atria contract while the ventricles relax Ventricles contract while the atria relax Atrioventricular (AV) Valves  Bicuspid (Mitral) Valve  Between left atria and ventricle  Tricuspid Valve  Between right atria and ventricle Semilunar (SL) Valves  Pulmonary SL Valve  Between right ventricle and pulmonary artery  Aortic SL Valve  Between left ventricle and aorta

PERICARDIUM The pericardium or pericardial sac is a double-layered closed sac that surrounds the heart Fibrous Pericardium  Tough, fibrous connective tissue  Outer layer that prevents over-distension of the heart  Anchors heart to the mediastinum Pericardial Cavity  Between the visceral and parietal pericardia  Filled with a thin layer of serous pericardial fluid that helps to reduce friction

PERICARDIUM Serous Pericardium  Thin, transparent inner layer of simple squamous epithelium Parietal Pericardium  Portion of the serous pericardium lining the fibrous pericardium Visceral Pericardium or Epicardium  Portion covering the heart surface The parietal and visceral portions of the serous pericardium are continuous with each other where the great vessels enter or leave the heart

CARDIAC MUSCLE ONLY LOCATED IN THE HEART!!! Intercalated Disks  Has cell-to-cell special contacts Desmosomes  Hold cells close together Gap Junctions  Low electric resistance between cells = greater conductivity Therefore, cardiac cells act as a single unit electrically!

THE CARDIAC CYCLE Events are associated with 1 heartbeat A single cardiac cycle lasts 0.8 seconds Described as the contraction and relaxation of the 4 heart chambers  During relaxation, chambers will with blood (diastole)  During contraction, chambers expel blood (systole)

CONDUCTING SYSTEM PROCESS Sinoatrial (SA) Node  Pacemaker of the heart  Generates action potentials with greater frequency  0.04 faster than surrounding muscle Atrioventrical (AV) Node  Slow to transmit action potential and allows completion of atrial contraction AV Bundle of His  Fast

CONDUCTING SYSTEM PROCESS Bundle Branches  Right and left 1.IV Septum 2.Rt Ventrical Apex 3.Lt Ventrical Apex Perkinje Fibers  Large diameter cardiac muscle  Transmits singal to apex of ventricles  A lot of intercalated disks Myocardium in apex contracts in a wringing action

AUTORHYMICITY OF CARDIAC MUSCLE Action potentials in heart without external stimuli 1.After each action potential, the muscle potential returns to its resting membrane potential 2.Unstable slow ion channels open and cause depolarization 3.This causes fast channels to open and increase depolarization 4.When depolarization reaches threshold, the action potential happens more often in SA node because more slow channels Plateau Phase  Prolonged period of depolarization  Separates contractions in the heart Heart has long action potential so the heart will rest between contractions and not tetanic contractions Absolute refractory period  Cell membrane insensitive to further stimuli

ELECTROKARDIOGRAM (EKG) EKG  Device to record the action potential of cardiac muscle summation  Cannot detect force of contraction  Cannot detect blood pressure  Can detect abnormal heart rates/rhythms  Can detect abnormal conduction pathways  Can detect hypertrophy and atrophy and relative position of damage

EKG P Wave  Action potential depolarization of atrial myocardium  Causes atrial contraction QRS Complex  Ventricular depolarization  Causes onset of ventricular contraction  Also atrial repolarization masked by QRS signal T Wave  Repolarization before ventricular relaxation PQ/PR Interval  0.16 second in which atria contract and relax QT Interval  0.3 second in which ventricles contract and relax 1 Cardiac Cycle  From onset of one muscle contraction to the onset of the next muscle contraction

HEART SOUNDS First Heart Sound  “LUBB”  Ventricles contact and both AV valves close Second Heart Sound  “DUPP”  Semilunar valves close at end of ventrical systole Systole is between the first and second sounds Diastole is between second and first sounds

BLOOD PRESSURE Systolic  To contract Diastolic  To dilate Refers to ventricles 120 systolic/80 diastolic Normal BP 72 beats/min x 70 ml/beat 5,040 ml/min = 5 L/min Exercise BP 120 beats/min x 200 ml/beat 24,000 ml/min = 24 L/min

SYSTOLE 1.Isometric Contractions  Contraction of the ventricle causes A-V valves to close and pressure to build in the heart 2.Ejection  Ventricular pressure exceeds the pressure in the pulmonary trunk and aorta and the semilunar valves open to expel the blood 3.At around 80 mm Hg (pressure), aortic SVL opens and goes up to 120 mm Hg 4.At the end of systole, ventricular volume drops because the heart runs out of blood

DIASTOLE Isometric Relaxations 1.Back flow of blood closes semilunar valves 2.Pressure drops and AV valves open 3.Blood rushes into ventricles from atria 4.Cardiac reserve  Difference between cardiac output at rest and during exercise

HOW TO GET BLOOD PRESSURE 1.Center the bladder over the Brachial Artery just medial to the biceps tendon. Apply snugly and securely 2.Check the palpatory systolic pressure first 3.Inflate to 20 to 30 mm Hg above the palpatory systolic 4.Place bell of stethoscope over the brachial artery 5.Deflate the cuff slowly (2 to 3 mm Hg per sec.) and note the points where the following occurs: 6.Two consecutive beats are heard typically crisps sounding (indicates systolic pressure)…recorded as auscultatory systolic pressure 7.A muffling of the pulse sounds recorded as mid-diastolic point. The point at which the sounds begin to fade away. 8.The sound disappears- (indicates peripheral resistance of arteries)…recorded as end-diastolic pressure.

HEART PROBLEMS Myocardial Infarction  An area of heart tissue in which cardiac cells have died  Generally the result of an ischemia  Ischemia  Lack of an adequate blood supply to the heart may lead to fibrillation Abnormalities in the shape of the waves and changes in their timing send signals that something may be wrong with the intrinsic conduction system or may indicate a myocardial infarct (present or past) Heart Block  Any damage to the AV node can partially or totally release the ventricles from the control of the SA node  The ventricles begin to beat at their own rate which is much slower some or all of the time

HEART PROBLEMS Heart Rate Anomalies  Tachycardia is a rapid heart rate (over 100 beats/min)  Bradycardia is a heart rate that is substantially slower than normal (less than 60 beats/min)  Neither condition is pathological but prolonged tachycardia may progress to fibrillation Fibrillation  Rapid uncoordinated shuddering of the heart muscle  Makes the heart totally useless as a pump and is a major cause of death from heart attacks in adults  During fibrillation, the normal pattern of the ECG is totally lost and the heart ceases to act as a functioning pump