Heart Anatomy Overview

Overview

This lecture covers the anatomy of the heart, its chambers, major vessels, valves, and the layers making up the heart wall, with attention to key structural and functional details.

Location and Orientation of the Heart

• The heart is located in the mediastinum of the thoracic cavity, with two-thirds left of the midsternal line.
• The apex points toward the left hip; the base points toward the right shoulder.
• The heart weighs about 200–300 grams and is approximately the size of a fist.

Chambers of the Heart

• The heart has four chambers: right atrium, left atrium (top), right ventricle, and left ventricle (bottom).
• The right atrium receives blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The left atrium receives oxygenated blood from the right and left pulmonary veins.
• The fossa ovalis (remnant of fetal foramen ovale) is located in the right atrium.

Cardiac Valves and Supporting Structures

• The right atrioventricular (AV) valve is called the tricuspid valve; the left AV is the bicuspid (mitral) valve.
• Valves are made of three layers: zona fibrosa, zona spongiosa, and zona ventricularis, lined by endothelium.
• Chordae tendineae (collagen cords) anchor valve flaps to papillary muscles, preventing valve prolapse.
• Papillary muscles stabilize the valves during ventricular contraction.
• The right ventricle pumps blood through the pulmonary semilunar valve; the left ventricle pumps through the aortic semilunar valve.
• Valves ensure one-way blood flow and prevent backflow.

Septa and Great Vessels

• The interventricular septum separates the right and left ventricles; the interatrial septum separates the atria.
• The pulmonary trunk exits the right ventricle and splits into right and left pulmonary arteries.
• The aorta exits the left ventricle as the ascending aorta, then the aortic arch, giving rise to the brachiocephalic, left common carotid, and left subclavian arteries.

Layers of the Heart Wall

• The innermost layer is the endocardium (endothelial tissue).
• The middle layer is the myocardium (cardiac muscle), thickest in the left ventricle.
• The outer layer is the epicardium (visceral layer of serous pericardium).
• The pericardial cavity contains lubricating serous fluid.
• The parietal layer of the serous pericardium lines the cavity wall.
• The outermost fibrous pericardium anchors, protects, and prevents heart overfilling.

Key Terms & Definitions

• Mediastinum — central compartment of the thoracic cavity housing the heart.
• Atria — upper heart chambers receiving blood.
• Ventricles — lower heart chambers pumping blood out.
• Tricuspid valve — right AV valve separating right atrium and ventricle.
• Bicuspid (Mitral) valve — left AV valve separating left atrium and ventricle.
• Chordae tendineae — collagen fibers anchoring valve flaps to papillary muscles.
• Papillary muscles — muscles holding chordae tendineae and valves in place.
• Semilunar valves — valves at exits of ventricles (pulmonary and aortic).
• Interventricular septum — wall dividing ventricles.
• Endocardium — inner epithelial lining of the heart.
• Myocardium — thick muscular heart layer.
• Epicardium — outer heart layer (visceral serous pericardium).
• Pericardial cavity — fluid-filled space reducing friction around the heart.
• Fibrous pericardium — tough outer layer protecting and anchoring heart.

Action Items / Next Steps

• Review key diagrams of heart anatomy and the flow of blood.
• Memorize heart chamber, valve, vessel names, and directions of blood flow.
• Read textbook sections on the layers of the heart and pericardial sac.