BIOS 104 Anatomy & Physiology Summer II - Assignment: Chapter 16 and 17

Chapter 17: The Heart 1. List the functions of the heart. A: The functions of the heart are: generating blood pressure, routing blood, and regulating blood supply. 2. Define the pulmonary and systemic circulations and describe the gas exchange taking place in each of them. A: The pulmonary circulation is the flow of blood from the heart through the lungs back to the heart. This blood picks up oxygen and releases carbon dioxide in the lungs. The systemic circulation is the flow of blood from the heart through the body back to the heart. This blood delivers oxygen and picks up carbon dioxide in the body’s tissues. 3. Describe the location, shape, and approximate size of the heart. A: The heart is located in the thoracic cavity between the lungs as part of the midline partition known as the mediastinum. The heart is shaped like a blunt cone with an apex rounded point and a flat part on the opposite side as the base. It is approximately the size of a closed fist, but it can be larger in more active adults. 4. What is the pericardium? Describe its parts and their function. A: The pericardium, also known as the pericardial sac, holds the pericardial fluid which helps reduce friction as the heart moves within the sac. It consists of two layers. An outer fibrous pericardium, that is a tough and fibrous connective tissue, anchors the heart to the mediastinum. The inner serous pericardium that surrounds the heart is simple squamous epithelium overlying a layer of loose connective tissue and fat. The part in contact with the fibrous pericardium is the parietal pericardium while the part covering the heart is the visceral pericardium. In between the visceral and parietal pericardia, there is the pericardial cavity filled with a thin pericardial fluid produced by the serous pericardium that helps reduce friction. 5. Describe the three layers of the heart, and state their functions. A: The three layers of the heart are epicardium, myocardium, and endocardium. The epicardium (an interchangeable term for the structure that is also called the visceral pericardium) is a thin serous membrane that forms the smooth outer surface of the heart. It consists of simple squamous epithelium overlying a layer of loose connective tissue and fat. It is part of the inner serous pericardium surrounding the heart and is important in forming the cavity that holds the pericardial fluid which reduces friction during movement. The myocardium is the thick middle layer of the heart. It is composed of cardiac muscle cells and is responsible for contractions of the heart chambers. The endocardium is the inner surface of the heart chambers. It consists of simple squamous epithelium over a layer of connective tissue. Its smoothness allows blood to move easily over its surface through the heart. 6. Name the muscular ridges found on the interior walls of the ventricles and atrium. A: Trabeculae carneae are the ridges and columns of cardiac muscle that make up the surfaces of the interior walls of the ventricles. The pectinate muscles are smaller, muscular ridges that are found in portions of the atria. 7. Name the chambers of the heart and describe their locations as seen from the outside of the heart. A: The four chambers of the heart are two atria and two ventricles. The right and left atria are located at the base of the heart, and the right and left ventricles extend from the base of the heart toward the apex. 8. Name the major blood vessels that enter and leave the heart. Which chambers of the heart do they enter or exit. A: There are six large veins that carry blood to the heart: the superior vena cava and the inferior vena cava (carry blood from the body to the right atrium) and four pulmonary veins (carry blood from the lungs to the left atrium). Two arteries, the pulmonary trunk and the aorta, carry blood away from the heart. The pulmonary trunk arises from the right ventricle and splits into the right and left pulmonary arteries known for carrying blood to the lungs. The aorta arises from the left ventricle and carries blood to the rest of the body. 9. Describe the openings through which blood enters the atria. What structure separates the atria from each other? A: The atria receive blood from veins. The right atrium has three major openings through which blood enters: the openings from the superior vena cava and the inferior vena cava both receive blood from the body and the opening of the coronary sinus receives blood from the heart itself. The left atrium has four openings that receive blood from the four pulmonary veins from the lungs. The two atria are separated by the interatrial septum, although in the embryo and fetus there was an opening between the atria to allow blood flow and the bypass of the pulmonary circulation. 10. What are the fossa ovalis and the foramen ovale? A: The fossa ovalis is a slight, oval depression on the right side of the interatrial septum that marks the former location of the foramen ovale, an opening between the right and left atria in the embryo and fetus that allowed blood to flow from the right to the left atrium in the fetus to bypass the pulmonary circulation. 11. Describe the openings through which blood leaves the ventricles. What structure separates the ventricles form each other? A: Each ventricle receives blood from the atria and then outflow through one large, superiorly placed outflow route near the midline of the heart. The right ventricles opens into the pulmonary trunk and the left ventricle opens into the aorta. The two ventricles are separated from each other by the interventricular septum. 12. Name the heart valves, give their locations, and describe their structure. A: The heart valves are important in ensuring one-way blood flow. They allow blood to flow into and out of the ventricles while preventing backflow of blood. They are formed by folds of the endocardium that consist of a double layer of endocardium with connective tissue in between. An atrioventricular (AV) valve is located between each atrium and its ventricle. The AV valve between the right atrium and the right ventricle has three cusps and is called the tricuspid valve. The AV valve between the left atrium and the left ventricle has two cusps and is called the bicuspid valve or mitral valve. A semilunar valve is located at the base of the large blood vessels carrying blood away from the ventricles. The aortic semilunar valve is in the aorta and the pulmonary semilunar valve is in the pulmonary trunks. Each valve consists of three pocket-like semilunar cusps. 13. Describe how the heart valves operate, allowing blood to flow into and out of a ventricle, but preventing the back flow of blood. A: Each ventricle contains cone-shaped, muscular pillars called papillary muscles that are attached by thin, strong connective tissue strings called chordae tendinae to the free margins of the cusps of the AV valves. When the left ventricle, used as the example, relaxes, blood pushes the cusps of the bicuspid valve toward the ventricle, the valve opens, and blood flows into the ventricle. The chordae tendinae are slack when the valve is open. When the ventricle is relaxed, blood in the aorta flows back toward the ventricle and enters the pockets of the semilunar cusps, causing them to fill and expand. The semilunar cusps meet at the midline of the aorta and the semilunar valve closes, preventing the backflow of blood into the ventricle. When the left ventricle contracts, blood pushes the cusps of the bicuspid valve back toward the atrium. When the cusps meet, the valve is closed, preventing backflow of blood into the atrium. The papillary muscles contract and the chordae tendineae are drawn taut, preventing the cusps of the valve from moving backwards into the atria. The backflow of blood into the atrium is prevented. When the ventricle contracts, blood pushes on the cusps of the semilunar valves, pushing blood out of them. As the cusps empty, they flatten against the wall of the aorta and the semilunar valve opens.