Anatomy of the Heart

Heart Structure

• The heart is a triangular-shaped organ, broad at the superior surface and tapering to the apex.
• It is made up of four chambers: two upper chambers (left atrium and right atrium) and two lower chambers (left and right ventricles).
• The heart has four valves: the tricuspid, pulmonary, mitral, and aortic valves.

Heart Layers

• The heart wall is divided into three layers: epicardium, myocardium, and endocardium.
• These layers are embryologically equivalent to the three layers of blood vessels: tunica adventitia, tunica media, and tunica intima.

Coronary Arteries

• Coronary arteries are the arterial blood vessels of the coronary circulation.
• They are named as such because they encircle the heart, like a crown.
• The two main coronary arteries are the left coronary artery (LCA) and the right coronary artery (RCA).
• The left coronary artery supplies blood to the left heart muscle (left ventricle and left atrium).
• The right coronary artery supplies blood to the right side, S.A. node, A.V. node, and bundle of heart between ventricle.

Coronary Artery Branches

• The left coronary artery branches to yield the left anterior descending (LAD) artery, also called the anterior interventricular artery.
• The LCA also gives off the left marginal artery (LMA) and the left circumflex artery (Cx).
• In 20-25% of individuals, the left circumflex artery contributes to the posterior interventricular artery (PIv).
• The right coronary artery branches to form the right marginal artery (RMA) anteriorly.
• In 80-85% of individuals, it also branches into the posterior interventricular artery (PIv) posteriorly.

Heart Size and Weight

• The heart length, width, and thickness are 12 cm, 8.5 cm, and 6 cm, respectively.
• The mean weight of the heart is 280-340 g in males and 230-280 g in females.

Heart Function

• The heart pumps blood throughout the body by heart muscle contraction.
• It controls heart rate and maintains blood pressure by signal electrical production via autogenerating in the right atrium SA node.
• The SA node, also known as the sinus node, initiates the electrical impulses to stimulate contraction.
• The heart rate depends on the rate at which the sinoatrial node produces action potentials.
• At rest, the heart rate is between 60 and 100 beats per minute.

Blood Vessels

• There are five types of blood vessels: arteries, arterioles, capillaries, venules, and veins.
• Arteries carry blood away from the heart.
• Capillaries are where the exchange of water and chemicals between the blood and tissues occurs.
• Veins carry blood from the capillaries back towards the heart.

Circulatory System

• The circulatory system is divided into two separate loops: the pulmonary circuit and the systemic circuit.
• The pulmonary circuit exchanges blood between the heart and the lungs for oxygenation.
• The systemic circuit distributes blood throughout all other systems and tissues of the body.
• Both circuits begin and end in the heart.