The Heart

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The Heart...

The Heart:

Throughout history, many functions have been attributed to the heart. Some philosophers have called it the seat of the soul. The ancient Egyptians, for instance, weighed the heart after a person's death because they believed that the weight of the heart equaled the weight of the soul. The heart has also been described as the seat of wisdom and understanding; accordingly, it thinks and makes plans. More often than not, however, history has portrayed the heart as the seat of emotions. An overly compassionate person is described as softhearted. A generous person has a heart of gold. A grief stricken person is broken-hearted. Every Valentine's day card displays hearts, hearts and more hearts. These cards celebrate love. None ever mentions the heart as an efficient pump.

STRUCTURE OF THE HEART

Location and size

The heart is a hollow, muscular organ. Its primary function is to pump and force blood through the blood vessels of the body providing every cell in the body with vital nutrients and oxygen while providing a path for metabolic waste to be re-circulated and removed. While blood is the transport medium, the heart is the organ that keeps the blood moving through the vessels. The hear pumps an average of 72 times each minute for your entire lifetime. If you live until you are 75, your heart will beat in excess of 3 billion times! What an amazing organ.

The adult heart is about the size of a closed fist. The heart sits in the chest within the mediastinum, between the two lungs. It is posterior to the sternum and anterior to the vertebral column and it rests on the diaphragm. It lies toward the left side of the body. Two thirds of the heart is located to the left of the midline of the sternum, and one third is located to the right. The upper flat portion of the heart is located at the level of the second rib. The other end of the heart is the apex. The apex is the lower and more pointed end of the heart and is located at the level of the fifth rib.

The heart lies within and is supported by a sling-like structure called the pericardium. The pericardium attaches the heart to surrounding structures, such as the diaphragm. You need to know the precise location of the heart because you will be asked to evaluate different heart sounds, accurately position electrodes for ECG readings, and provide life-saving CPR.

THE HEART'S LAYERS AND COVERINGS

The heart is enclosed in the pericardial membranes, of which there are three. The outermost is the fibrous pericardium, a loose-fitting sac of fibrous connective tissue that extends inferiorly over the diaphragm and superiorly over the bases of the large vessels that enter and leave the heart. The outer layer of the pericardium is attached to the diaphragm, and the posterior portion of the sternum. Lining the fibrous pericardium is the parietal pericardium, a serous membrane. On the surface of the heart muscle is the visceral pericardium, also called the epicardium, another serous membrane. The small potential space between the parietal and visceral layers is the pericardial cavity. Between the parietal and the visceral pericardial membranes is serous fluid, which prevents friction between the membranes as they rub against each other during heart contractions.

At times, the pericardial membranes become inflamed and secrete excess fluid into the pericardial space. This collection of fluid into the pericardial space compresses the heart externally, making it difficult for the heart to relax and fill with blood. Consequently, the heart is unable to pump a sufficient amount of blood to the body. This life-threatening condition is called cardiac tamponade. The symptoms of cardiac tamponade may be relieved by inserting a long needle into the pericardial space and aspirating the serous fluid out through the needle.

A Double Pump and Two Circulations

The myocardium enables the heart to pump blood. The heart is like a double pump, or tow pumps that beat as one. The pumps are the right heart and the left heart. The right heart receives unoxygenated blood from the superior and inferior venae cavae, large veins that collect blood from all parts of the body. The right heart is colored blue because

CHAMBERS-VESSELS AND VALVES

The walls and the four chambers of the heart fare made of cardiac muscle are called the myocardium. The chambers are lined with endocardium, simple epithelium that also covers the valves of the heart and continues into the vessels as their lining. The important physical characteristic of the endocardium is not its thinness, but rather its smoothness. This very smooth tissue prevents abnormal blood clotting, because clotting would be initiated by contact of blood with a rough surface.

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