Anatomy: Heart and Blood Vessels

Heart Structure

• The heart is a triangular organ with a broad superior surface and a tapering apex.
• It consists of four chambers: left and right atria, and left and right ventricles.
• The heart has four valves: tricuspid, pulmonary, mitral, and aortic valves.

Heart Layers

• The heart wall is composed of 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 coronary circulation.
• They originate from the root of the aorta and wrap around the entire heart, supplying oxygenated blood to the heart muscle.
• The two main coronary arteries are the left coronary artery (LCA) and the right coronary artery (RCA).
• LCA supplies blood to the left heart muscle (left ventricle and left atrium).
• RCA supplies blood to the right side, SA node, AV node, and bundle of His between the ventricles.

Coronary Artery Branches

• LCA branches into the left anterior descending artery (LAD), left marginal artery (LMA), and left circumflex artery (Cx).
• In 20-25% of individuals, the left circumflex artery contributes to the posterior interventricular artery (PIv).
• RCA branches into the right marginal artery (RMA) and, in 80-85% of individuals, the posterior interventricular artery (PIv).

Heart Size and Weight

• Heart length, width, and thickness are typically 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 contracting its muscle.
• It controls heart rate and maintains blood pressure through electrical signals produced in the SA node.

SA Node

• The SA node, also known as the sinus node, is a specialized myocardial structure that initiates electrical impulses to stimulate contraction.
• It is located in the atrial wall at the junction of the superior caval vein and the right atrium.
• The signal then passes through the AV node to the lower heart chambers (ventricles), causing them to contract or pump.

Heart Rate

• Heart rate depends on the rate at which the SA node produces action potentials.
• At rest, 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, while 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.