BIOL 2304
Heart
Location of the Heart
Largest organ of the mediastinum
Located between the lungs
Apex lies to the left of the midline, pointing inferolaterally (toward left side)
Base is the broad posterior surface
Anatomy of the Heart
Pericardium – two primary layers
Fibrous pericardium
Strong layer of dense connective tissue
Serous pericardium
Formed from two layers
Parietal layer of the serous
pericardium (parietal
pericardium)
Visceral layer of the serous
pericardium (visceral
pericardium); aka epicardium
Layers of the Heart Wall
Epicardium
Visceral layer of the serous pericardium
Myocardium
Consists of cardiac muscle
Muscle arranged in circular and spiral patterns
Endocardium
Endothelium resting on a layer of connective
tissue
Lines the internal walls of the heart
Cardiac Muscle Tissue
Forms a thick layer called myocardium
Striated like skeletal muscle
Contractions pump blood through the heart and into blood vessels
Contracts by sliding filament mechanism
Cardiac Muscle Fibers (Cells)
Cardiac muscle cells are short, branching, with one or two nuclei
Cells join at intercalated discs:
Complex junctions that connect one cell to the next
Contain gap junctions that allow rapid transfer of cardiac impulses
Support synchronized contraction of cardiac tissue
Cells are separated by delicate endomysium
Binds adjacent cardiac fibers
Contains blood vessels and nerves
Gross Anatomy of the Heart
Atria – Two thin, upper chambers that receive blood
Right atrium receives oxygen poor blood from body
Left atrium receives oxygen rich blood from lungs
Auricles – Left and right atria are capped externally by large muscular folds called auricles that serve as
blood reservoirs
Ventricles – Two thick, lower chambers that pump blood
Right ventricle pumps oxygen poor blood to lungs
Left ventricle pumps oxygen rich blood to body
Interventricular septum – wall separating left and right sides of heart
Gross Anatomy of the Heart
Right Atrium
Receives oxygen poor blood from superior and inferior vena cava
Pumps blood to right ventricle through tricuspid valve
Fossa ovalis – a depression in the interatrial septum; a remnant of foramen ovale (of the fetal heart)
The foramen ovale allows blood to enter the left atrium from the right atrium in fetuses, allowing blood
to bypass the developing, nonfunctioning, fetal pulmonary circuit
Right Ventricle
Receives blood from right atrium through the tricuspid valve
Pumps blood into pulmonary circuit via pulmonary trunk
Pulmonary semilunar valve
Located at opening of right ventricle and pulmonary trunk; allows blood to be pumped into the
pulmonary circuit
Left Atrium
Makes up heart’s posterior surface
Receives oxygen-rich blood from lungs through left and right pulmonary veins
Opens into the left ventricle through mitral valve (bicuspid valve)
Left Ventricle
Forms apex of the heart
Is three times thicker than right ventricle
Exerts more pumping force
Because it requires more force to send blood to the body than to the lungs
Flattens right ventricle into a crescent shape
Pumps blood through systemic circuit via aortic semilunar valve (aortic valve)
Blood Flow Through Heart
Internal Structures of Heart
Internal walls of ventricles
Papillary muscles
Attach to mitral and tricuspid valves chordae tendinae
Contract to prevent inversion of valves beyond point of closure
Chordae tendineae – cord-like tendons that connect the papillary muscles to the mitral and tricuspid valves
Internal Structures of Heart
Heart Valves: AV valves and Semilunar Valves
Valves separating chambers from vessels;
regulate blood flow
Composed of endocardium with CT core
Atrioventricular (AV) valves
Between atria and ventricles
Mitral (bicuspid) & Tricuspid
Aortic and pulmonary semilunar valves
Cusps (flaps) are semilunar in shape – valve
flaps resemble half moon
At junction of ventricles and great arteries
(pulmonary and aortic)
Vasculature of the Heart – Coronary Arteries
Left and right coronary arteries
Two main arteries that branch into smaller coronary arteries
Originate from left side of heart, at root of the aorta
Delivery oxygen-rich blood to cardiac muscle
Vasculature of the Heart – Cardiac Veins
Cardiac veins – drain blood into the coronary sinus
Coronary sinus – delivers deoxygenated blood to the right atrium
Vasculature of the Heart
Conduction Pathway
Cardiac impulse originates at SA node
Action potential spreads throughout right and left atria
Impulse passes from atria into ventricles through AV node (only point of electrical contact between chambers)
Action potential briefly delayed at AV node (ensures atrial contraction precedes ventricular contraction to allow
complete ventricular filling)
Impulse travels rapidly down interventricular septum by means of bundle of His
Impulse rapidly disperses throughout myocardium by means of Purkinje fibers
Rest of ventricular cells activated by cell-to-cell spread of impulse through gap junctions