The Heart

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$\color{#3D99F6}{\textbf{THE HEART}}$

$\bullet$ The heart has a triangular shape

$\bullet$ Its pointed end is called the apex, located on the inferior margin.

$\bullet$ In most people, the heart is about the same size as the clenched fist, ~14 cm long and 9 cm wide.

$\color{#3D99F6}{\textbf{COVERINGS OF THE HEART}}$

$\bullet$ The heart and the major blood vessels that attach to it are enclosed within a double-layered serous membrane called the pericardium.

$\bullet$ The outer sac is called the parietal pericardium or pericardial sac.

$\bullet$ The inner layer is called the visceral pericardium, or epicardium.Between the epicardium and the parietal pericardium is a potential space called the pericardial cavity. It contains a small amount of fluid that is secreted by serous cells of the pericardium. The fluid acts as a lubricant that reduces friction between the membranes as they glide against each other during heart activity.

$\bullet$ If the pericardium becomes swollen, such as in the disease pericarditis, fluid production is inhibited. This decline in lubrication causes the membranes to stick together, thereby leading to severe chest pain and possibly impeding heart activity.

$\color{#3D99F6}{\textbf{HEART WALL}}$

$\bullet$ The wall of the heart is composed of three layers: the outermost epicardium, the middle myocardium, and the inner endocardium.

$\bullet$ The epicardium serves as a thin protective barrier for the heart. It is a serous membrane that is firmly attached to the heart. It contains fat deposits.

$\bullet$ The myocardium makes up the bulk of the It is composed of cardiac muscle tissue and is the layer that actually contracts to provide the propulsion of blood.

$\bullet$ The endocardium is a smooth, white membrane forming the inner layer of the heart wall.It lines the internal spaces of the heart (the heart chambers) and covers the heart valves.

This inner heart membrane, which is also found lining the inner walls of the blood vessels, is generally known as endothelium.

$\color{#3D99F6}{\textbf{HEART CHAMBERS}}$

$\bullet$ The heart has four internal spaces, called chambers.

$\bullet$ The two superior chambers are the atria (right and left), and the two inferior chambers are the ventricles (right and left ).

ATRIA :-

$\bullet$ The right and left atria (singular form is atrium) function as receiving chambers for blood entering the heart.

$\bullet$ They simply push blood “next door” into the ventricles.

$\bullet$ Their walls, are quite thin and have little myocardium.

$\bullet$ Attached to the atria are small, ear like hollow appendages, known as auricles.

$\bullet$ The endocardium lining the atrial walls is smooth in texture, except for ridges formed by parallel bundles of underlying muscle.

$\bullet$ The ridges are called pectinate muscles, after their similarity in appearance to the teeth of a comb.

$\bullet$ The right and left atria are internally separated by a partition, called the interatrial septum. This partition is complete in healthy hearts.

$\bullet$ On the posterior wall of the septum of the right atrium is an oval depression, the fossa ovalis. This is what remains of an opening that was once present in the fetal heart, in which blood was shunted from the right atrium to the left atrium in order to bypass the lungs.

In the fetus this opening is called the foramen ovale.

$\bullet$ The right atrium collects incoming blood from the superior vena cava, which drains blood from the regions above the heart from the inferior vena cava, which drains blood from regions below the heart and from the coronary sinus, which comes from the heart wall.The left atrium collects blood from the four pulmonary veins, which drain blood from the lungs.

VENTRICLES - The right and left ventricles provide the force necessary to push blood out of the heart and into the body’s circulatory network.

$\bullet$ Of the two ventricles, the left contains the thickest wall.

$\bullet$ The right ventricle pushes blood to the lungs.The right and left ventricles are internally separated by a thick muscular partition called the interventricular septum.

$\bullet$ Its position can be determined externally, for it parallels a groove in the outer surface of the heart known as the interventricular sulcus.The right ventricle pumps blood into the pulmonary trunk, which carries it to the lungs.

$\bullet$ The left ventricle pumps blood into the aorta, whose branches deliver blood to all remaining areas of the body.

$\color{#3D99F6}{\textbf{HEART VALVES}}$ The valves of the heart permit blood to flow in one direction only. two types of valves in the heart: atrioventricular and semilunar.

$\bullet$ The atrioventricular (AV) valves are located between the atria and the ventricles. The AV valve between the right atrium and the right ventricle is called the tricuspid valve.The AV valve

$\bullet$ Between the left atrium and left ventricle is called the bicuspid valve.

The bicuspid valve is also called the mitral valve.

Their pointed ends are attached to thin strands of connective tissue, called chordae tendineae.They permit the one-way movement of blood from the atria to the ventricles.

$\bullet$ The two semilunar valves are located between the ventricles and the two major vessels carrying blood away from the heart--the pulmonary trunk and the aorta

$\bullet$ The SL valve between the right ventricle and the pulmonary trunk is called the pulmonary valve.and the one located between the left ventricle and the aorta is called the aortic valve. The function of the SL valves is to direct one-way flow of blood from the ventricles to the pulmonary trunk and aorta.

$\color{#3D99F6}{\textbf{SUPPLY OF BLOOD TO THE HEART}}$

$\bullet$ The wall of the heart has its own supply of blood vessels to meet its vital needs. The flow of blood through these vessels is called the coronary circulation.

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The Heart

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