Human Heart Anatomy

Heart Structure

• The heart is about 10 cm long, weighs around 225g in women and 310g in men, and is roughly the size of a fist.
• It lies in the thoracic cavity in the mediastinum, with its apex in the left of the midline at the level of the 5th intercostal space.

Associated Organs

• Inferiorly, the apex of the heart rests on the central tendon of the diaphragm.
• Superiorly, the heart is associated with great blood vessels, including the aorta, superior vena cava, pulmonary artery, and pulmonary veins.
• Posteriorly, the heart is associated with the oesophagus, trachea, left and right bronchus, descending aorta, inferior vena cava, and thoracic vertebrae.
• Laterally, the heart is associated with the lungs, with the left lung overlapping the left side of the heart.
• Anteriorly, the heart is associated with the sternum, ribs, and intercostal muscles.

Heart Wall

• The pericardium is the outer layer of the serous membrane, consisting of the parietal pericardium (outer layer) and visceral pericardium (inner layer).
• The myocardium is composed of specialized cardiac muscle found only in the heart.
• The endocardium consists of flattened epithelial cells and is continuous with the endothelium lining the blood vessels.

Interior of the Heart

• The septum divides the heart into the right and left sides.
• The atrioventricular valve divides each side of the heart into the upper atrium and the ventricle below.
• The right atrioventricular valve (tricuspid valve) has three flaps or cusps.
• The left atrioventricular valve (mitral valve) has two cusps.

Cardiovascular System

• The cardiovascular system is divided into two main parts: the heart and blood vessels.
• The heart pumps blood into two anatomically separate systems of blood vessels: the pulmonary circulation and the systemic circulation.
• The right side of the heart pumps blood to the lungs (pulmonary circulation), while the left side of the heart pumps blood to the rest of the body (systemic circulation).

Blood Vessels

• Arteries and arterioles transport blood away from the heart and have three layers: outer fibrous tissue, middle smooth muscle and elastic tissue, and inner endothelium.
• Veins return blood to the heart at low pressure, with thinner walls than arteries, and may possess valves to prevent backflow.
• Capillaries are the site of gas exchange and nutrient exchange between blood and tissues.

Pulmonary Circulation

• Deoxygenated blood from the right ventricle flows through the pulmonary artery to the lungs, where gas exchange occurs.
• Oxygenated blood returns to the left atrium through the pulmonary veins.

Systemic Circulation

• Oxygenated blood from the left ventricle flows through the aorta and its branches to the rest of the body.
• Deoxygenated blood returns to the right atrium through the superior and inferior vena cavae.

Aorta

• The aorta is divided into three parts: ascending aorta, arch of the aorta, and descending aorta in the thorax.
• The ascending aorta gives rise to the right and left coronary arteries, which supply the myocardium.
• The arch of the aorta gives rise to the brachiocephalic artery, left common carotid artery, and left subclavian artery.

Arterial Supply to the Head and Neck

• The brachiocephalic artery branches into the right subclavian artery and right common carotid artery.
• The left common carotid artery arises directly from the arch of the aorta.
• Each common carotid artery divides into an internal carotid artery and an external carotid artery.
• The internal carotid artery supplies the brain, while the external carotid artery supplies the superficial tissues of the head and neck.

Venous Return from the Head and Neck

• Venous blood from the head and neck returns through deep and superficial veins, including the external and internal jugular veins, which empty into the subclavian vein.

Circulation to the Upper Limb

• The right subclavian artery arises from the brachiocephalic artery, while the left subclavian artery arises from the arch of the aorta.
• The axillary artery continues as the brachial artery, which divides into the radial and ulnar arteries.

Portal Circulation

• The portal vein is formed by the splenic, inferior mesenteric, superior mesenteric, gastric, and cystic veins, which drain blood from the digestive system, spleen, and pancreas to the liver.
• The portal vein then enters the general circulation via the inferior vena cava.