Chapter 19 The Circulatory System: THE HEART
19.1 Overview of the Cardiovascular System 720
Cardiology – the scientific study of the heart and treatment of its disorders.
The Pulmonary and Systemic Circuits 721
Cardiovascular system - consists of the heart and the blood vessels. The heart functions as a muscular pump that keeps blood flowing through the vessels. The vessels deliver the blood to all the body’s organs and then return it to the heart (figure 19.1). (page 720)
Circulatory system – includes the blood and some authorities use it to include the lymphatic system as well (described in chapter 21) (page 720)
Pulmonary circuit – carries blood to the lungs for gas exchange and returns it to the heart. (page 721)
Systemic circuit – supplies blood to every organ of the body, including other parts of the lungs and the wall of the heart itself. (page 721)
Position, Size, and Shape of the Heart 721
Define and distinguish between the pulmonary and systemic circuits. (page 721)
The right side of the heart furnishes blood to the pulmonary circuit. It receives blood that has circulated through the body, unloaded its oxygen and nutrients, and picked up a load of carbon dioxide and other wastes. It pumps the oxygen-poor blood into a large artery called the pulmonary trunk, which immediately divides into right and left pulmonary arteries. These transport blood to the air sacs (alveoli) of the lungs, where carbon dioxide is unloaded and oxygen is picked up. The oxygen rich blood then flows by way of the pulmonary veins to the left side of the heart.
The left side of the heart supplies the systemic circuit. Blood leaves it by way of another large artery called the aorta. The aorta takes a sharp inverted U-turn called the aortic arch, and passes downward, posterior to the heart. The aortic arch gives off arteries that supply the head, neck and upper limbs. The aorta then travels through the thoracic and abdominal cavities and issues smaller arteries to the other organs before branching into the lower limbs. After circulating through the body, the now deoxygenated systemic blood returns to the right side of the heart mainly by way of two large veins called the superior vena cava (draining the upper body) and the inferior vena cava (draining everything below the diaphragm). The major arteries and veins entering and leaving the heart are called the great vessels (great arteries and veins) because of their relatively large diameters.
Describe the general location, size, and shape of the heart. (pages 721 -722)
The heart is located in the thoracic cavity in the mediastinum, between the lungs and deep to the sternum. From its superior to inferior midpoints, it is tilted toward the left, so about 2/3 of the heart lies to the left of the median plan (figure 19.2 on page 722; see also figs A.18 – A.19 on page 46). The broad superior portion of the heart is called the base and it is the point of attachment for the great vessels described previously. The inferior end tapers to a blunt point called the apex, immediately above the diaphragm. The adult heart is about 9 cm wide (or about 3.5 inches) 13 cm from base to apex (about 5 inches) and about 6 cm from anterior to posterior at its thickest point (about 2.5 inches)… roughly the size of one’s fist. It weighs about 300 grams (or about 10 0z).
The Pericardium 722
Describe the pericardial sac that encloses the heart. (page 722)
The heart is enclosed in a double-walled sac called the pericardium.
Pericardial sac (parietal pericardium) – the outer wall of the pericardium—a tough, superficial fibrous layer of dense irregular connective tissue and a deep, thin serous layer. The serous layer turns inward at the base of the heart and forms the epicardium (visceral pericardium) covering the heart surface (see figure 19.3 on page 722). The pericardial sac is anchored by ligaments to the diaphragm below...
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