The Heart

Cardiology

Physical Characteristics Situated between the lungs in the

mediastinum About the size of a clenched fist Cone or pyramid shape, tilting to

the left Apex - inferior portion Base - superior portion

Pericardium - 3 layers Fibrous pericardium - outer layer Serous pericardium - inner layer

parietal layer visceral layer (epicardium)

Pericardial cavity - space between the parietal and visceral layers that is filled with pericardial fluid

Pericardial fluid - lubrication,reduces friction

Heart Wall Epicardium - outermost layer

visceral pericardium Myocardium - middle layer

cardiac muscle involuntary, striated, short, branched cells intercalated discs

Endocardium - inner layer lines the chambers and covers the valves simple squamous epithelium

Heart Chambers Two upper atria ; two lower ventricles Atria are the receiving chambers Ventricles are the distributing chambers Interatrial septum separates atria Interventricular septum divides

ventricles Auricles are external flaps Left ventricle very thick

Heart Valves Atrioventricular valves

tricuspid (right) bicuspid or mitral (left) chordae tendineae papillary muscle

Semilunar valves aortic semilunar pulmonary semilunar three pocketlike cusps

Valve Disorders Rheumatic Fever - group A, B-

hemolytic Streptococcus pyogenes Heart Mumur

stenosis incompetent valves Mitral valve prolapse (MVP)

Blood Flow through the Heart

The heart receives blood from the superior vena cava, inferior vena cava and the coronary sinus

Right atrium->tricuspid valve->right ventricle-> pulmonary semilunar valve-> pulmonary trunk>pulmonary arteries-> lungs-> pulmonary veins->left atrium->mitral valve->left ventricle>aortic semilunar valve -> aorta

Pulmonary & Systemic Circulation

Pulmonary circulation - refers to blood going through the right side of the heart to the lungs

Systemic circulation - involves the left heart. Oxygenated blood from the lungs flows into the left atrium, enters the left ventricle, out through the aorta into the body’s tissue, and back via systemic veins to the right atrium

Coronary Circulation The aorta

branches into the left and right coronary arteries

Blood flow through myocardium

Left coronary artery Anterior interventricular artery Circumflex artery

Right coronary artery Posterior interventricular artery Marginal artery

Arterial anastomoses

Venous Drainage Great cardiac veins Coronary sinus Right atrium

Cardiac Conduction System

Sinoatrial (SA) node Pacemaker of the heart

Atrioventricular (AV) node Atrioventricular bundle (Bundle of His) Left and right bundle branches Purkinje fibers Modification by the ANS and hormones

Cardiac Physiology

Electrocardiogram - ECG P wave - atrial depolarization QRS complex - ventricular

depolarization T wave - ventricular repolarization Atrial repolarization is masked by

the larger QRS complex

Arrhythmias Abnormal Heart Rhythms Heart block - blockage in the AV node Tachycardia - >100 beats per minute Bradycardia - <60 beats per minute Fibrillation - uncoordinated quivering Flutter - rapid contractions PVC - premature ventricular

contraction PAC - preatrial contraction

Terms Myocardial infarction (MI) - heart

attack Infarction - tissue death due to loss

of blood supply Ischemia - decreased blood flow

causing hypoxia Angina pectoralis - chest pain

related to coronary problems

Cardiac Cycle

Cardiac cycle consists of one complete cycle of contraction and relaxation

Contraction phase - systole Relaxation phase - diastole Complete cycle - 0.8 seconds Phases : relaxation period,

ventricular filling, ventricular systole Normal heart rate - 75 beats/minute

Cardiac Output CO = Stroke volume x Heart rate

Amount of blood passing through a ventricle in 1 minute

SV = Amount of blood that is pumped by a ventricle per beat (approx. 70 ml)

HR = number of beats per minute

Examples Rest - CO = 70ml/beat x 75 beats/min = 5250ml/minute =5.25 liters/minute Exercise - CO = 140ml/beat x 150 beats/min = 21,000ml/minute = 21 liters /minute

Factors influencing stroke volume

“Frank - Starling law of the heart” Critical factor = stretch of cardiac muscle Preload - how much blood enters a

ventricle during diastole Contractility - forcefulness of a contraction Afterload - pressure needed before

ventricle ejection occurs

Regulation of Heart Rate

Cardiovascular Center Medulla Sympathetic nervous

system Cardiac accelerator

nerves Parasympathetic

nervous system Vagus nerve

Baroreceptors - monitor pressure aortic arch carotid arteries

Chemoreceptors - monitor chemicals aortic/carotid

bodies Hormones, age,

fitness,gender