a hollow muscular organ of a somewhat conical form
lies between the lungs in the middle mediastinum and is enclosed in the pericardium
placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages; projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane.
Size.—The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the broadest part, and 6 cm. in thickness.
Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. It continues to increase in weight and size up to an advanced period of life; the increase more marked in men than in women.
- a conical fibro-serous sac , in which the heart and the roots of the great vessels are contained.
- placed behind the sternum and the cartilages of the 3 rd – 7th ribs of the left side, in the mediastinal cavity.
- In front, it is separated from the anterior wall of the thorax, in the greater part of its extent, by the lungs and pleuræ; but a small area, somewhat variable in size, comes into direct relationship with the chest wall, called the bare area of the pericardium .
It is the outermost layer of the pericardial membranes around the heart. It is a tough, collagenous sheet that is superficial to the parietal layer of the serous pericardium. The two are separated by a thin layer of amorphous connective tissue.
The serous pericardium of the heart is a sheet of mesothelial cells which lines, and so demarcates, the pericardial cavity. During development, where the layer has been invaginated by the heart, it comes to be divided into two:
the potential space formed between the two layers of serous pericardium around the heart. Normally, it contains a small amount of serous fluid that acts to reduce surface tension and lubricate. Therefore, the cavity facilitates the free movement of the heart.
Both layers secrete the serous fluid which serves to lubricate the surface of the pericardial cavity.
There may be a small fold of serous pericardium joining the left pulmonary artery to the superior left pulmonary vein within the pericardial cavity. This is the fold of the left vena cava.
The attachment of this visceral layer to the parietal layer presents the shape of an inverted U. The cul-de-sac enclosed between the limbs of the U lies behind the left atrium and is known as the oblique sinus , while the passage between the aorta and pulmonary artery in front and the atria behind—is termed the transverse sinus .
Within the pericardial cavity a probe can be placed into the transverse sinus running posterior to the aorta and pulmonary trunk on the left but anterior to the left atrium and superior vena cava on the right.
Component Parts.—The heart is subdivided by septa into R and L halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium , the lower the ventricle . The heart therefore consists of 4 chambers, viz., right and left atria, and right and left ventricles.
Surfaces of the Heart Base: directed upward, backward, and to the right : separated from the 5th - 8th thoracic vertebræ by the esophagus, aorta, and thoracic duct : formed mainly by the left atrium , and, to a small extent, by the back part of the right atrium : somewhat quadrilateral in form
The Apex: is directed downward, forward, and to the left, and is overlapped by the left lung and pleura: it lies behind the fifth left intercostal space , 8 to 9 cm. from the mid-sternal line, or about 4 cm. below and 2 mm. to the medial side of the left mammary papilla
The sternocostal surface is directed forward, upward, and to the left. Its lower part is convex, formed chiefly by the right ventricle, and traversed near its left margin by the anterior longitudinal sulcus.
Its upper part is separated from the lower by the coronary sulcus, and is formed by the atria; it presents a deep concavity , occupied by the ascending aorta and the pulmonary artery
The Diaphragmatic surface , directed downward and slightly backward, is formed by the ventricles, and rests upon the central tendon and a small part of the left muscular portion of the diaphragm. It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus.
The separation of the auricula from the sinus venarum is indicated externally by a groove: the terminal sulcus that extends from the front of the superior vena cava to the front of the inferior vena cava
On the inner wall of the atrium the separation is marked by a vertical, smooth, muscula ridge, the terminal crest.
Behind the crest the internal surface of the atrium is smooth, while in front of it the muscular fibers of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati .
The blood entering the atrium through the superior vena cava is directed downward and forward, i.e., toward the atrioventricular orifice, while that entering through the inferior vena cava is directed upward and backward, toward the atrial septum. This is the normal direction of the two currents in fetal life.
~ the greater portion is thick and muscular and constitutes the muscular ventricular septum.
~ its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum .
An abnormal communication may exist between the ventricles at this part owing to defective development of the membranous septum.
_The lymphatics end in the thoracic and right lymphatic ducts.
_The nerves are derived from the cardiac plexus , which are formed partly from the vagi, and partly from the sympathetic trunks. They are freely distributed both on the surface and in the substance of the heart.
: longer and larger than the left, runs horizontally to the right, behind the ascending aorta and superior vena cava and in front of the right bronchus , to the root of the right lung, where it divides into two branches . The lower and larger of these goes to the middle and lower lobes of the lung; the upper and smaller is distributed to the upper lobe .
: shorter and somewhat smaller than the right, passes horizontally in front of the descending aorta and left bronchus to the root of the left lung, where it divides into two branches , one for each lobe of the lung.
: connected above to the concavity of the aortic arch by the ligamentum arteriosum
~ the main trunk of a series of vessels which convey the oxygenated blood to the tissues of the body.
~ described in several portions, viz., the ascending aorta , the arch of the aorta , and the descending aorta , which last is again divided into the thoracic and abdominal aortæ.
- commences at the upper part of the base of the L ventricle, passes obliquely upward, forward, and to the right, in the direction of the heart’s axis, describing a slight curve in its course, and being situated, about 6 cm. behind the posterior surface of the sternum.
: at the union of the ascending aorta with the aortic arch the caliber of the vessel is increased, owing to a bulging of its right wall. This dilatation is termed the bulb of the aorta
~ the only branches of the ascending aorta are the two coronary arteries which supply the heart.
: passes at first between the conus arteriosus and the right auricle and then runs in the right portion of the coronary sulcus
: continued to the apex of the heart as the posterior descending branch
: gives off a large marginal branch which follows the acute margin of the heart and supplies branches to both surfaces of the right ventricle . It also gives twigs to the right atrium and to the part of the left ventricle which adjoins the posterior longitudinal sulcus.
: begins at the level of the upper border of the 2nd R costal cartilage , and runs at first upward, backward, and to the left in front of the trachea and finally passes downward on the left side of the body of the 4th thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta.
Sure, you know how to steal hearts, win hearts, and break hearts. But how much do you really know about your heart and how it works? Read on to your heart's content!
Put your hand on your heart. Did you place your hand on the left side of your chest? Many people do, but the heart is actually located almost in the center of the chest, between the lungs. It's tipped slightly so that a part of it sticks out and taps against the left side of the chest, which is what makes it seem as though it is located there.
Hold out your hand and make a fist. If you're a kid, your heart is about the same size as your fist, and if you're an adult, it's about the same size as two fists.
Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.
Give a tennis ball a good, hard squeeze. You're using about the same amount of force your heart uses to pump blood out to the body. Even at rest, the muscles of the heart work hard--twice as hard as the leg muscles of a person sprinting.
Feel your pulse by placing two fingers at pulse points on your neck or wrists. The pulse you feel is blood stopping and starting as it moves through your arteries. As a kid, your resting pulse might range from 90 to 120 beats per minute. As an adult, your pulse rate slows to an average of 72 beats per minute.
The aorta, the largest artery in the body, is almost the diameter of a garden hose. Capillaries, on the other hand, are so small that it takes ten of them to equal the thickness of a human hair.
Your body has about 5.6 liters (6 quarts) of blood. This 5.6 liters of blood circulates through the body three times every minute. In one day, the blood travels a total of 19,000 km (12,000 miles)--that's four times the distance across the US from coast to coast.
The heart pumps about 1 million barrels of blood during an average lifetime--that's enough to fill more than 3 super tankers.
lub-DUB, lub-DUB, lub-DUB. Sound familiar? If you listen to your heart beat, you'll hear two sounds. These "lub" and "DUB" sounds are made by the heart valves as they open and close.