Heart Anatomy Approximately the size of your fist

Heart Anatomy • Approximately the size of your fist – Wt. = 250 -300 grams • Location – In the mediastinum between the lungs – Superior surface of diaphragm – ⅔’s of it lies to the left of the midsternal line – Anterior to the vertebral column, posterior to the sternum

Heart Anatomy Figure 18. 1

Coverings of the Heart • Pericardium – a double-walled sac around the heart – Composed of: • A superficial fibrous pericardium • A deep two-layer serous pericardium – The parietal layer lines the internal surface of the fibrous pericardium – The visceral layer or epicardium lines the surface of the heart – They are separated by the fluid-filled pericardial cavity. – Protects and anchors the heart – Prevents overfilling of the heart with blood – Allows for the heart to work in a relatively friction-free environment

Pericardial Layers of the Heart Figure 18. 2

Layers of the Heart Wall • Epicardium – visceral pericardium • Myocardium – cardiac muscle layer forming the bulk of the heart • Endocardium – endothelial layer of the inner myocardial surface

Heart Anatomy • External markings – Apex - pointed inferior region – Base - upper region – Coronary sulcus • Indentation that separates atria from ventricles – Anterior and posterior interventricular sulcus • Separates right and left ventricles • Internal divisions – Atria (superior) and ventricles (inferior) – Interventricular and interatrial septa

Atria of the Heart • Atria - receiving chambers of the heart – Receive venous blood returning to heart – Separated by an interatrial septum (wall) • Foramen ovale - opening in interatrial septum in fetus • Fossa ovalis - remnant of foramen ovale • • Each atrium has a protruding auricle Pectinate muscles mark atrial walls Pump blood into ventricles Blood enters right atria from superior and inferior venae cavae and coronary sinus • Blood enters left atria from pulmonary veins

Gross Anatomy of Heart: Frontal Section Figure 18. 4 e

Ventricles of the Heart • Ventricles are the discharging chambers of the heart • Papillary muscles and trabeculae carneae muscles mark ventricular walls • Separated by an interventricular septum – Contains components of the conduction system • Right ventricle pumps blood into the pulmonary trunk • Left ventricle pumps blood into the aorta – Thicker myocardium due to greater work load • Pulmonary circulation supplied by right ventricle is a much low pressure system requiring less energy output by ventricle • Systemic circulation supplied by left ventricle is a higher pressure system and thus requires more forceful contractions

External Heart: Anterior View Figure 18. 4 b

Structure of Heart Wall • Left ventricle – three times thicker than right – Exerts more pumping force – Flattens right ventricle into a crescent shape Figure 18. 7

Heart Valves • Heart valves ensure unidirectional blood flow through the heart – Composed of an endocardium with a connective tissue core • Two major types – Atrioventricular valves – Semilunar valves • Atrioventricular (AV) valves lie between the atria and the ventricles – R-AV valve = tricuspid valve – L-AV valve = bicuspid or mitral valve • AV valves prevent backflow of blood into the atria when ventricles contract • Chordae tendineae anchor AV valves to papillary muscles of ventricle wall – Prevent prolapse of valve back into atrium

Semilunar Heart Valves • Semilunar valves prevent backflow of blood into the ventricles • Have no chordae tendinae attachments • Aortic semilunar valve lies between the left ventricle and the aorta • Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk • Heart sounds (“lub-dup”) due to valves closing – “Lub” - closing of atrioventricular valves – “Dub”- closing of semilunar valves

Fibrous Skeleton • Surrounds all four valves – Composed of dense connective tissue • Functions – Anchors valve cusps – Prevents overdilation of valve openings – Main point of insertion for cardiac muscle – Blocks direct spread of electrical impulses

Heart Valves

Conducting System • Cardiac muscle tissue has intrinsic ability to: – Generate and conduct impulses – Signal these cells to contract rhythmically • Conducting system – A series of specialized cardiac muscle cells – Sinoatrial (SA) node sets the inherent rate of contraction

Conducting System

Innervation • Heart rate is altered by external controls • Nerves to the heart include: – Visceral sensory fibers – Parasympathetic branches of the vagus nerve – Sympathetic fibers – from cervical and upper thoracic chain ganglia

External Heart: Posterior View Figure 18. 4 d

Major Vessels of the Heart • Vessels returning blood to the heart include: – Superior and inferior venae cavae • Open into the right atrium • Return deoxygenated blood from body cells – Coronary sinus • Opens into the right atrium • Returns deoxygenated blood from heart muscle (coronary veins) – Right and left pulmonary veins • Open into the left atrium • Return oxygenated blood from lungs

Major Vessels of the Heart • Vessels conveying blood away from the heart include: – Pulmonary trunk • Carries deoxygenated blood from right ventricle to lungs • Splits into right and left pulmonary arteries – Ascending aorta • Carries oxygenated blood away from left atrium to body organs • Three major branches – Brachiocephalic – Left common carotid, – Left subclavian artery

Blood Flow Through the Heart Figure 18. 6

Pathway of Blood Through the Heart and Lungs Figure 18. 5

Coronary Circulation • Coronary circulation – The functional blood supply to the heart muscle itself – R and L Coronary arteries are 1 st branches off the ascending aorta – Coronary sinus (vein) empties into R. atrium • Collateral routes ensure blood delivery to heart even if major vessels are occluded

Coronary Circulation - Arteries • Right Coronary Artery – Supplies blood to • Right atrium and posterior surface of both ventricles – Branches into the • Marginal artery - extends across surface of R. ventricle • Posterior interventricular artery – Found in posterior interventricular sulcus • Left Coronary Artery – Supplies blood to • Left atrium and left ventricle – Branches into • Circumflex artery • Anterior interventricular artery – Found in anterior interventricular sulcus – Connected with posterior interventricular artery via arterial anastomoses

Coronary Circulation: Arterial Supply Figure 18. 7 a

Coronary Circulation - Veins • Coronary sinus – Vein that empties into right atrium – Receives deoxygenated blood from: • Great cardiac vein - on anterior surface • Posterior cardiac vein – Drains area served by circumflex • Middle cardiac vein – Drains area served by posterior interventricular artery • Small cardiac vein – Drains blood from posterior surfaces of right atrium and ventricle

Coronary Circulation: Venous Supply Figure 18. 7 b

Microscopic Anatomy of Heart Muscle • Cardiac muscle cells – Short, striated, branched, and interconnected • The connective tissue endomysium acts as both tendon and insertion • Intercalated discs anchor cardiac cells together and allow free passage of ions • Heart muscle behaves as a functional syncytium • Many mitochondria (25% of total volume)

Microscopic Anatomy of Heart Muscle Figure 18. 11

Disorders of the Heart • Coronary artery disease – – – Atherosclerosis – fatty deposits Arteriosclerosis - hardening of the arteries Angina pectoris – chest pain Myocardial infarction – blocked coronary artery Silent ischemia – no pain or warning Fibrillation - irregular heart beat; may occur in either atria or ventricles