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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
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•
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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 18.4e
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 18.4b
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 18.4d
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 1st 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 18.7a
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 18.7b
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
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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