HSBTE DMLT, D. Pharm. Anatomy and Physiology of Heart, External Structure of Heart, Internal Structure of Heart, Histology of Heart,

1.2 Anatomy and Physiology of Heart

Position of Heart

• · The heart is present in the thorax between two lungs and behind the sternum, in the center of the thorax.

• · The heart rests on the diaphragm.

The External Structure of the Heart

• · The human heart is hollow, muscular, cone-shaped.

• · Apex is the lower part of the heart and the base is the broader upper part of the heart. Apex is slightly directed towards the left.

• · The heart is surrounded by a double-layered protective covering called pericardium.

• · The outer layer is called the parietal pericardium and the inner layer is called the visceral pericardium.

• · The space between both layers is called the pericardial cavity. It is filled with pericardial fluids.

• · Pericardium membrane and pericardial fluid protect the heart from mechanical shock and injury. The pericardial fluid keeps the heart moist. It also acts as a lubricant and facilitates the heart to beat freely.

• · The heart has four chambers, two atria, and two ventricles.

• · Atria is divided into two parts, right atria and left atria.

• · Externally, a groove is present between two atria; it is called an inter-atrial groove.

• · One oblique groove is present in between the atria and ventricle. It is called the atria-ventricle groove or coronary sulcus.

• · Groove is also present between two ventricles. It is called an interventricular groove (sulcus).

• · Coronary arteries are present in various grooves. The coronary artery supplies blood to cardiac muscles.

Internal Structure of Heart:

The heart has four chambers, two atria, and two ventricles.

Atria: There are two atria –right and left atria (Atria – Plural and atrium Singular).

• · Both atria are separated by a septum called inter atria septum.

• · The right atrium is larger than the left atrium and has a thin wall than the left atrium.

• · Three large veins superior vena cava, inferior vena cava, coronary sinus, and one small vein coronary vein open into the right atrium.

• · The left atrium is a roughly cuboidal chamber.

• · Four pulmonary veins (two pairs) open into the left atrium. This carries oxygenated blood from the lungs to the left atrium.

• · One pair of pulmonary veins (two pulmonary veins) comes from the left lung. One pair of pulmonary veins (two pulmonary veins) comes from the right lung.

• · The left-pair pulmonary vein opens in the left atrium by a common orifice while the right-pair pulmonary vein opens into the left atrium by two different openings. These openings have no valves. These openings have circular muscles that act as valves.

Ventricle: The heart has two ventricles. These are the right ventricle and left ventricle. The right ventricle is smaller than the left ventricle.

• · Both are separated by a septum called the inter-ventricular septum.

• · The Wall of the ventricle is thicker than the atrium.

• · The internal surface has muscular ridges called the columnae carneae.

• · The internal surface has also papillary muscles connected with chordae tendineae.

The right ventricle is connected with the right atrium by an opening called the right-atrioventricular aperture or right AV aperture. It is guarded by three membranous flaps called · tricuspid valves. The tricuspid valves allow the movement of blood from the atrium to the ventricles and blocks backflow.

• · The right ventricle has an opening in the upper left corner into the pulmonary aorta. This opening is guarded by three semilunar flaps called a pulmonary valve. This valve allows the movement of deoxygenated blood from the right ventricle into the pulmonary aorta. It does not allow the backflow of blood.

• · The left ventricle wall is thicker than the right ventricle wall and it is also larger than the right ventricle. These all make the left ventricle to pump more blood with more power than the right ventricle.

• · The left ventricle is connected with the left atrium by an opening called the left atrioventricular aperture left AV aperture or mitral aperture. It is guarded by two flaps called the bicuspid valve or mitral valve. The Mitral valve allows the movement of blood from the left atrium to the left ventricle and does not allow the backflow of blood.

• · The systemic aorta arises from the left ventricle through an opening guarded by 3 semilunar valves. It allows the movement of blood from the left ventricle into the systemic aorta but blocks the backflow of blood.

Histology of Heart: The heart (cardiac) wall is made of heart muscle fibers also called cardiac muscle fibers or myocardium. The cardiac wall has three layers of the epithelium. These are the outer layer visceral pericardium (Epicardium), middle layer myocardium, and inner layer endocardium. The myocardium is thick and consists of muscle fibers that provide mechanical strength.

Dr. Pramila Singh