Anatomy of the Heart: Structure, Circuits, and Internal Features (A&P II: Lab 3 Review)

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The Heart: Structure and Circulation

Overview of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body via two main circuits: the pulmonary and systemic circuits. It is composed of four chambers and is surrounded by protective layers collectively known as the pericardium.

The Pericardium

Layers of the Pericardium

The pericardium is a double-walled sac that encloses the heart, providing protection and reducing friction as the heart beats. The two main layers are:

Parietal Pericardium: The outer fibrous layer that anchors the heart in the thoracic cavity.
Epicardium (Visceral Pericardium): The inner serous layer that lies directly on the heart surface.

Dissection showing the parietal pericardium and epicardium

External Features of the Heart

Major Chambers and Sulci

The heart's external anatomy includes four chambers (right and left atria, right and left ventricles) and visible grooves called sulci, which mark the boundaries between chambers and house coronary vessels.

Anterior Interventricular Sulcus: Marks the boundary between the right and left ventricles on the anterior surface.
Posterior Interventricular Sulcus: Marks the boundary on the posterior surface.

Heart model showing external features and coronary vessels

Pulmonary and Systemic Circuits

Pulmonary Circuit

The pulmonary circuit carries deoxygenated blood from the right side of the heart to the lungs and returns oxygenated blood to the left side of the heart.

Right Atrium: Receives deoxygenated blood from the superior and inferior vena cava.
Tricuspid Valve: Prevents backflow into the right atrium.
Right Ventricle: Pumps blood through the pulmonary semilunar valve into the pulmonary trunk and arteries to the lungs.

Pulmonary circuit: right atrium and vena cavae

Systemic Circuit

The systemic circuit delivers oxygenated blood from the left side of the heart to the body and returns deoxygenated blood to the right side.

Left Atrium: Receives oxygenated blood from the pulmonary veins.
Bicuspid (Mitral) Valve: Prevents backflow into the left atrium.
Left Ventricle: Pumps blood through the aortic semilunar valve into the aorta and systemic arteries.

Systemic circuit: left ventricle and aorta

Major Blood Vessels Associated with the Heart

Arteries and Veins

The heart is connected to major blood vessels that facilitate blood flow to and from the body and lungs:

Aorta: The main artery carrying oxygenated blood to the systemic circuit.
Pulmonary Trunk and Arteries: Carry deoxygenated blood to the lungs.
Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.
Vena Cavae: Superior and inferior veins returning deoxygenated blood to the right atrium.

Ascending aorta, aortic arch, and descending aorta

Internal Structures of the Heart

Heart Wall Layers

The heart wall consists of three layers:

Endocardium: The innermost layer lining the heart chambers and valves.
Myocardium: The thick, muscular middle layer responsible for contraction.
Epicardium: The outermost layer, also known as the visceral pericardium.

Endocardium of the heart

Heart Valves

Valves ensure unidirectional blood flow through the heart:

Atrioventricular (AV) Valves: Tricuspid (right) and bicuspid/mitral (left) valves between atria and ventricles.
Semilunar Valves: Pulmonary (right) and aortic (left) valves at the exits of the ventricles.

Bicuspid/Mitral and Tricuspid valves

Chordae Tendineae and Papillary Muscles

These structures anchor the AV valves and prevent prolapse during ventricular contraction:

Chordae Tendineae: Tendinous cords connecting valve leaflets to papillary muscles.
Papillary Muscles: Muscular projections from the ventricular wall.

Chordae tendineae, bicuspid valve, and papillary muscle

Coronary Circulation

Supplying the Heart Muscle

The heart muscle (myocardium) receives oxygen and nutrients from the coronary arteries, which branch off the aorta. Deoxygenated blood is collected by coronary veins and returned to the right atrium via the coronary sinus.

Coronary Arteries: Supply oxygen-rich blood to the myocardium.
Coronary Sinus: Collects deoxygenated blood from the myocardium.

Coronary sinus and coronary veins

Summary Table: Heart Chambers, Valves, and Major Vessels

Chamber	Valve	Major Vessel In	Major Vessel Out
Right Atrium	Tricuspid Valve	Superior/Inferior Vena Cava	Right Ventricle
Right Ventricle	Pulmonary Semilunar Valve	Right Atrium	Pulmonary Trunk/Arteries
Left Atrium	Bicuspid (Mitral) Valve	Pulmonary Veins	Left Ventricle
Left Ventricle	Aortic Semilunar Valve	Left Atrium	Aorta

Key Equations

Cardiac Output (CO): The volume of blood pumped by each ventricle per minute.

Where HR is heart rate (beats per minute) and SV is stroke volume (mL per beat).

Additional info: The ligamentum arteriosum is a remnant of the fetal ductus arteriosus, which connects the pulmonary trunk to the aorta during fetal development. After birth, it closes and becomes a ligament.