III. Answer the following question in an elaborative way.
Q18. (a) Draw the diagram of human heart and label the following parts:
(i) receives deoxygenated blood from vena cava
(ii) sends deoxygenated blood to lung through pulmonary artery
(iii) receives oxygenated blood from lungs
(iv) sends oxygenated blood to all the parts of the body through aorta
(b) What is the advantage of separate channels in mammals and birds for oxygenated and deoxygenated
blood?
Answers
Answer:
he heart consists of four chambers separated into two sides. Each side contains an atria which receives blood into the heart and flows it into a ventricle, which pumps the blood out of the heart. The atria and ventricle on each side of the heart are linked together by valves that prevent backflow of blood. The wall that separates the left and right side of the heart is called the septum.
The left heart deals with systemic circulation, while the right heart deals with pulmonary circulation. The left side of the heart receives oxygenated blood from the pulmonary vein and pumps it into the aorta, while the right side of the heart receives deoxygenated blood from the vena cava and pumps it into the pulmonary vein. The pulmonary vein and aorta also have valves connecting them to their respective ventricle.
The heart has its own self-sustaining conduction system that sends nervous impulses to cardiac tissue. The sinoatrial (SA) and atrioventricular (AV) nodes are bundles of nerve fibers that form this conduction system. They are located in the left atrial wall of the heart and send nerve impulses to a large, highly specialized set of nerves called the Purkinje fibers, which in turn send those nerve impulses to the cardiac muscle tissue. These nodes can send impulses to the heart without central nervous system stimulation, but may be influenced by nervous stimulation to alter heart rate. The heart also has its own blood supply, the cardiac arteries that provide tissue oxygenation to the heart as the blood within the heart is not used for oxygenation by the heart.
Cardiac Histology
The heart is enclosed in a double-walled protective membrane called the pericardium, which is a mesothelium tissue of the thoracic cavity. The double membrane of pericardium contains pericardial fluid which nourishes the heart and prevents shock. This composite sac protects the heart, anchors it to surrounding structures, and prevents the heart from overfilling with blood.
The wall of the heart is composed of three layers of different tissues. The outer layer is called the epicardium, or visceral pericardium, since it is also the inner wall of the pericardium. The middle layer of the heart, the myocardium, and contains specialized cardiac muscle tissue responsible for contraction. Cardiac muscle tissue is distinct from skeletal or smooth muscle because it pumps involuntarily based on conduction from the AV and SA nodes. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. It also merges with the inner lining of blood vessels and covers heart valves. Cardiac tissue is permanent tissue that does not heal or regenerate when damaged. As a result, is prone to scarring and enlargement due to mechanical stress and injury.
This diagram of the heart indicates the superior vena cava, aorta, pulmonary artery, pulmonary vein, left and right atria, mitral valve, aortic valve, left and right ventricles, inferior vena cava, tricuspid valve, and pulmonary valve.
The Mammalian Heart: The position of valves ensures proper directional flow of blood through the cardiac interior. Note the difference in the thickness of the muscled walls of the atrium and the left and right ventricle.
Pericardium
The pericardium is a thick, membranous, fluid-filled sac which encloses, protects, and nourishes the heart.
Explanation: