INTERNATIONAL UNIVERSITY

Location and General Description of Heart

Dr. Sam Nang

• The hollow, four-chambered, muscular heart is roughly the size of a clenched fist.

• It averages 255 grams in adult females and 310 grams in adult males.

• The heart contracts an estimated 42 million times a year, pumping 700,000 gallons of blood.

• The heart is located in the thoracic cavity between the lungs in the mediastinum.

• About two-thirds of the heart is located left of the midline, with its apex, or cone shaped end, pointing downward and resting on the diaphragm.

• The base of the heart is the broad superior end, where the large vessels attach.

• The parietal pericardium encloses and protects the heart.

• It separates the heart from the other thoracic organs and forms the wall of the pericardial cavity, which contains a watery, lubricating pericardial fluid .

• The parietal pericardium is actually composed of an outer fibrous pericardium and an inner serous pericardium.

• It is the serous pericardium that produces the lubricating pericardial fluid that allows the heart to beat in a kind of friction-less bath

The wall of the heart is composed of three distinct layers.

• The outer layer is the epicardium, also called the visceral pericardium.

*The space between this layer and the parieral pericardium is the pericardial cavity, just described.

• The thick middle layer of the heart wall is

called the myocardium.

Heart Wall

Heart Wall

Myocardium :

• It is composed of cardiac muscle tissue and arranged in such a way that the contraction of the muscle bundles results in squeezing or wringing of the heart chambers.

Heart Wall

• The thickness of the myocardium varies in accordance with the force needed to eject blood from the particular chamber.

• Thus, the thickest portion of the myocardium surrounds the left ventricle and the atrial walls are relatively thin.

Heart Wall

The inner layer of the wall, endocardium • the endocardium, is continuous with the

endothelium of blood vessels.

• The endocardium also covers the valves of the heart.

• Inflammation of the endocardium is called endocarditis.

Chambers and Valves

Chambers and Valves

• The interior of the heart is divided into four chambers:

*upper right and left atria (singular atrium)

* lower right and left ventricles.

• The atria contract and empty simultaneously into the ventricles, which also contract in unison.

• Each atrium has an ear-shaped, expandable appendage called an auricle (or'i-kul).

Chambers and Valves

• The atria are separated from each other by the thin, muscular interatrial septum;

• the ventricles are separated from each other by the thick, muscular interventricular septum.

Chambers and Valves

• Atrioventricular valves (AV valves) lie between the atria and ventricles, and

• semilunar valves are located at the bases of the two large vessels leaving the heart.

• Heart valves maintain a one-way flow of blood.

Chambers and Valves

• Grooved depressions on the surface of the heart indicate the partitions between the chambers and also contain cardiac vessels that supply blood to the muscular wall of the heart.

Chambers and Valves

• The most prominent groove is the coronary sulcus that encircles the heart and marks the division between the atria and ventricles.

• The partition between the right and left ventricles is denoted by two (anterior and posterior) interventricular sulci.

Chambers and Valves

• The following discussion follows the sequence in which blood flows through the atria, ventricles, and valves .

• It is important to keep in mind that the right side of the heart (right atrium and right ventricle) receives deoxygenated blood (blood low in oxygen) and pumps it to the lungs.

Chambers and Valves

• The left side of the heart (left atrium and left ventricle) receives oxygenated blood (blood rich in oxygen) from the lungs and pumps it throughout the body.

Right Atrium

• The right atrium receives systemic venous blood from the superior vena cava, which drain the upper portion of the body, and from the inferior vena cava, which drains the lower portion.

Right Atrium• The coronary

sinus is an additional opening into the right atrium that receives venous blood from the myocardium of the heart itself.

Right Ventricle

• Blood from the right atrium passes through the right atrioventricular (AV) valve (also called the tricuspid valve) to fill the right ventricle.

• The right AV valve is characterized by three valve leaflets, or cusps.

• Each cusp is held in position by strong tendinous cords called chordae tendineae (kor de ten-dine-e).

Right Ventricle

• The chordae tendineae are secured to the ventricular wall by cone-shaped papillary muscles.

• These structures prevent the valves from everting, like an umbrella in a strong wind, when the ventricles contract and the ventricular pressure increases.

Right Ventricle

• Ventricular contraction causes the right AV valve to close and the blood to leave the right ventricle through the pulmonary trunk and to enter the capillaries of the lungs via the right and left pulmonary arteries.

Right Ventricle

• The pulmonary valve (also called the pulmonary semilunar valve) lies at the base of the pulmonary trunk, where it prevents the backflow of ejected blood into the right ventricle.

Left Atrium

• After gas exchange has occurred within the capillaries of the lungs, oxygenated blood is transported to the left atrium through two right and two left pulmonary veins.

Left Ventricle

• The left ventricle receives blood from the left atrium. These two chambers are separated by the left atrioventricular (AV) valve (also called the bicuspid valve or mitral valve).

• When the left ventricle is relaxed, the valve is open, allowing blood to flow from the atrium into the ventricle; when the left ventricle contracts, the valve closes.

Left Ventricle

• Closing of the valve during ventricular contraction prevents the backflow of blood into the atrium.

• The walls of the left ventricle are thicker than those of the right ventricle because the left ventricle bears a greater work load, pumping blood through the entire body.

Left Ventricle

• The endocardium of both ventricles is characterized by distinct ridges called trabeculae carneae (tra-bek'yu-le kar'ne-e)

• Oxygenated blood leaves the left ventricle through the ascending portion of the aorta.

Left Ventricle• The aortic valve (also called the

aortic semilunar valve), located at the base of the ascending portion of the aorta, closes as a result of the pressure of the blood when the left ventricle relaxes, and thus prevents the backflow of blood into the relaxed ventricle.

THE END