Anatomy of the Heart

• The cardiovascular system includes the heart, blood, and blood vessels
• The heart beats about 100,000 times daily
• Daily, the heart pumps around 8000 liters of blood

Anatomy of the Heart

• Pulmonary circuit carries blood to/from gas exchange surfaces of the lungs
• Systemic circuit carries blood to/from the rest of the body
• Arteries carry blood away from the heart
• Veins return blood to the heart
• Capillaries interconnect smallest arteries and veins, facilitating exchange between blood and tissues
• The heart has four chambers: right and left atria, right and left ventricles
• The right atrium receives blood from the systemic circuit
• The left atrium receives blood from the pulmonary circuit
• The right ventricle pumps blood into the pulmonary circuit
• The left ventricle pumps blood into the systemic circuit
• Great vessels connect at the base (superior) of the heart
• The pointed tip is called the apex (inferior)
• The heart sits between two pleural cavities in the mediastinum
• The pericardium surrounds the heart

Pericardium Layers

• Outer fibrous pericardium
• Inner serous pericardium, with parietal and visceral (epicardium) layers
• The pericardial cavity lies between the parietal and visceral layers with pericardial fluid
• Pericarditis involves pathogens in the pericardium
• This causes inflammation of pericardial surfaces rubbing which produces scratching sounds
• Cardiac tamponade may be a result of pericarditis, due to restricted heart movement from excess pericardial cavity fluid

Heart Surface Anatomy

• Two thin-walled atria, each with an expandable outer auricle
• Sulci contain fat and blood vessels
• The coronary sulcus marks the border between atria and ventricles
• Anterior and posterior interventricular sulci mark the boundary between left/right ventricles
• The heart wall has three layers: the epicardium, myocardium, and endocardium
• The Visceral layer of serous pericardium is also known as Epicardium
• Visceral Layer/Epicardium covers the surface of the heart and is covered by the parietal layer of serous pericardium
• Myocardium consists of cardiac muscle tissue, which is supported by connective tissues
• Endocardium covers the heart's inner surfaces with simple squamous epithelium
• The Cardiac skeleton is made of 4 dense bands of elastic tissue that encircle heart valves and bases of aorta/pulmonary trunk
• The cardiac skeleton Stabilizes heart valve positions and electrically insulates ventricular cells from atrial cells

Heart Interior Anatomy

• The Interatrial septum separates atria
• Interventricular septum separates ventricles and is thicker than the interatrial septum
• The atrioventricular (AV) valves include the tricuspid and mitral valves which permit blood flow in one direction
• The semilunar valves include the pulmonary and aortic valves that prevent backflow into ventricles
• The right atrium receives blood from the superior and inferior vena cavae
• The superior vena cava drains head, neck, upper limbs, and chest
• The inferior vena cava drains the trunk, viscera, and lower limbs

Blood Flow, Heart Valves and Features

• The Foramen ovale, in the fetal heart, connects the two atria and closes at birth, forming the fossa ovalis
• The Pectinate muscles are prominent muscular ridges on the anterior atrial wall and inner auricle surface
• The Tricuspid valve has three cusps and prevents backflow from the right atrium to right ventricle
• Chordae tendineae attach free valve edges to papillary muscles of the ventricle to prevent backward opening
• Trabeculae carneae are muscular ridges on the internal surfaces of the ventricles
• Moderator band is an internal muscular ridge delivering stimulus for contraction to papillary muscles
• Conus arteriosus is at the superior end of right ventricle terminating at pulmonary valve
• The pulmonary valve has three semilunar cusps and leads to the pulmonary trunk, which divides the left/right pulmonary arteries
• The left atrium receives blood from the left and right pulmonary veins
• The Mitral valve (bicuspid) has two cusps where blood passes into the left ventricle
• Blood leaves the left ventricle through the aortic valve into the ascending aorta
• Aortic sinuses are saclike expansions at base of ascending aorta
• The ascending aorta turns becoming the aortic arch, and then it descends
• Compared to the left ventricle, the right ventricle Holds and pumps the same blood amount but has thinner walls, it develops less pressure, and is more pouch-shaped
• Heart valves prevent the backward flow of blood
• Atrioventricular valves are between atria and ventricles, blood pressure closes when ventricles contract
• Papillary muscles contract and tense chordae tendineae which prevents regurgitation into atria.
• The pulmonary and aortic valves prevent backflow into ventricles with no braces
• Valvular heart disease (VHD) deteriorates valve function and can occur after carditis from rheumatic fever due to streptococcal bacteria

Coronary Circulation

• Coronary Circulation supplies blood to the cardiac muscle tissue
• Coronary arteries originate at aortic sinuses and elevated blood pressure maintains blood flood through
• The right coronary artery supplies right atrium, portions of both ventricles, and parts of heart's electrical conducting system
• The marginal and posterior interventricular arteries branch from the right coronary artery
• The left coronary artery supplies left ventricle, left atrium, and interventricular septum
• The circumflex and anterior interventricular arteries branch from left coronary artery
• The Arterial anastomoses interconnect anterior and posterior interventricular arteries sustaining constant blood supply.
• The Great cardiac vein drains the region supplied by the anterior interventricular artery and returns blood to the coronary sinus which opens to right atrium
• The Posterior vein of left ventricle, middle, and small cardiac veins empty into great cardiac vein/coronary sinus
• Anterior cardiac veins empty directly into the right atrium
• Coronary artery disease (CAD) causes partial/complete artery blockage
• Cardiac muscle cells need constant oxygen/nutrients & reduced blood flow decreases cardiac performance
• Coronary ischemia is the reduced circulatory supply from partial/complete blockage
• Formation of a fatty deposit (atherosclerotic plaque) in artery walls is the usual cause and may narrow/reduce blood flow
• Angina pectoris is a common symptom which causes temporary ischemia that develops when the heart's workload increases
• Myocardial infarction (MI), or heart attack, occurs when circulation gets blocked and causes cells to die where affect tissue becomes an infarct
• Coronary thrombosis is the most common cause of MI from thrombus development at a plaque
• Approximately 25% of MI patients die before receiving medical assistance
• Around 65% of MI deaths among people under age 50 occur within an hour

CAD and MI Treatments

• Risk factor modification
• Stopping smoking
• Treating high blood pressure
• Adjusting diet
• Reducing stress
• Increase physical activity
• Drug treatments
• Reduce coagulation
• Block sympathetic stimulation
• Cause vasodilation
• Block calcium ion movement
• Relieve pain and dissolve clots
• Noninvasive surgery
• Atherectomy long catheter to remove plaque
• Balloon angioplasty- tip which has inflated balloon used to press plaque against vessel walls and a stent can hold vessel open
• Coronary artery bypass graft (CABG)
• Graft using Small vessel sections to bypass obstructed potion with up to four arteries

The Conducting System

• Heartbeat is a single cardiac contraction where heart chambers contract in series (atria, then ventricles)
• There are two types of cardiac muscle cells autorhythmic and contractile
• Autorhythmic cells regulate the heartbeat and contractile cells propel blood.
• The conducting system consists of specialized heart muscle cells that start electrical impulses and distribute them
• Autorhythmicity means cardiac muscle contracts without neural/hormonal stimulation
• Pacemaker cells are in SA or AV node, where conducting cells are in internodal pathways/ AV bundle branches.
• The Sinoatrial (SA) node is in the wall of right atrium
• The Atrioventricular (AV) node—at junction between atria and ventricles
• Internodal pathways are of atria
• Atrioventricular (AV) bundle, bundle branches, and Purkinje fibers of ventricles
• Pacemaker potential is the gradual depolarization of pacemaker cells (unstable resting membrane potential)
• SA node depolarizes first establishing sinus rhythm, and parasympathetic stimulation slows heart rate
• SA node has 60–100 action potentials per minute
• AV node: 40-60 action potentials per minute

How Impulses Conduct Through the Heart

1. SA node activity and atrial activation begin
2. Stimulus spreads across atria and reaches AV node
3. Impulse is delayed for 100 msec at AV node
   • Atrial contraction begins
4. Impulse travels in AV bundle to left and right bundle branches in interventricular septum, onward to Purkinje fibers, and papillary muscle.
5. Purkinje fibers distribute impulse to myocardium when atrial contraction is completed, and ventricular contraction begins

Heart Rhythms

• Bradycardia is an abnormally slow heart rate
• Tachycardia is an abnormally fast heart rate
• Ectopic pacemaker generate action potentials and timing/ventricular contractions are disrupted
• An Electrocardiogram records electrical events and abnormal patterns are used to diagnosis
• ECG components:
  • P wave: Atrial depolarization
  • QRS complex: Ventricular depolarization (ventricles contract shortly after R wave)
  • T wave: Ventricular repolarization
• P-R interval measures from start of atrial depolarization to beginning of QRS complex
• Q-T interval tracks time required for ventricles to undergo a single cycle of depolarization and repolarization
• Cardiac contractile cells form the bulk of atrial and ventricular walls the, receive Purkinje signals, and have stable Resting Membrane
• Intercalated discs interconnect cardiac contractile cells transferring force contraction/ propagate actions
• Cardiac contractile cell characteristics: small, single central Intercalated discs

Action Potential and Aerobic Recovery

1. Rapid depolarization is massive influx of Na+ through fast sodium channels
2. Plateau: Extracellular Ca2+ enters cytosol through slow calcium channels
3. Repolarization involves K+ rushing out of cell through slow potassium channels

• The absolute refractory period is 200 milliseconds where contractile cells will not respond to stimulus
• The Relative refractory period is 50ms and cells only respond only to strong stimuli
• An action potential is 250-300 msec (30x longer than skeletal muscle) which prevents summation and tetany
• Calcium ions support heart contractions and give 20%
• Additional extracellular Ca2+ triggers release of additional Ca2+ from sarcoplasmic reticulum
• Cardiac muscles are sensitive to extracellular Ca2+ to prevent muscle spasms
• Cardiac contractions use aerobic energy, using the mitochondria, breaking down fatty acids, and glucose in the mitochondria
• Oxygen is delivered by circulation
• Cardiac contractile cells store oxygen in myoglobin

The Cardiac Cycle

• It starts from one heartbeat to beginning of the next with periods of relaxation
• Systole is contraction and diastole is relaxation
• Blood pressure rises and falls during the events within each chamber

Phases of the Cardiac Cycle

• Atrial systole
• Atrial diastole
• Ventricular systole
• Ventricular diastole
• Atrial contraction starts, AV valves open and atria eject blood into ventricles
• Atrial systole ends as diastole begins, which ends blood volume and begins ventricle contraction
• closing of atrioventricular (AV) valves is called end-diastolic volume (EDV)
• Ventricles build pressure or Produce isovolumetric contraction by contracting and closing AV valves
• Ventricular ejection occurs once ventricular pressure is exceeded (stroke volume-SV)
• Semilunar Valves then close
• Ventricular pressure falls and contains 40% of end -Distolic Volume
• Isovolumetric relaxation occurs where all valves are closed
• All heart valves closes and ventricular pressure is higher than atrial (blood cannot flow)
• Individuals can survive severe atrial damage and damage will lead to heart fail
• Heart sounds S1 , S2 , S3 , S4 are detected with stethoscope from valve movements

Heart Sounds Explained

• S1 Loud sound happens with AV valves closing
• S2 Loud sound happens with semilunar valves closing
• S3 and S4 soft happens from blood flowing into ventricles/ atrial contraction
• A Heart murmur happens when regurgitation through valves occurs

Cardiac Output

• Cardiac output (CO) is the volume pumped by left ventricle in 1 minute measured by HR *SV
• Stroke volume (SV) is EDV -ESV
• End-diastolic volume (EDV) Amount of blood in each ventricle at end of ventricular diastole
• End-systolic volume (ESV) is the Blood remaining in each ventricle at end of ventricular systole
• Ejection fraction is the Percentage of EDV ejected during contraction

Factors Affecting the Heart

• Heart rate depends on activity and hormones
• Autonomic innervation and cardiac centers influences the heart and Vagus nerves carry parasympathetic
• Dual Innveration to maintain heart rate
• Bainbridge reflex (atrial reflex) is the Adjustments in heart rate to increase venous return which has Amount of blood going through veins
• Hormonal effect happens: increased of Epinephrine,NE, and Thyriod Hormone
• Filling time in the ventricles affects time for filling
• preload affects The Degree of ventricular stretching during ventricular diastole which affects Muscle tension/Muscle Production
• Frank-Starling Principle As EDV increases, stroke volume increases however only has Physical limits of connective tissues