Question

How do vertebrate circulatory systems differ in structure and efficiency? Use the amphibian, fish, and mammal system for your comparison.

Describe the structure of the human heart; explain the movement of blood flow through the heart, lungs, and body. Your answer should be specific.

Please answer in text

Answer 1

The heart of a fish is part of single circulation. The heart in fish has two chambers, one atrium and one ventricle. Two accessory chambers are also present, the sinus venous and bulbous arteriosus. The sinus venosus is a thin-walled sac that serves chiefly as a collecting chamber for venous blood it receives from all parts of the body. Deoxygenated blood from the sinus venous enters into the atrium and then blood enters the ventricle through an atrioventricular aperture guarded by valves. The anterior end of the ventricle becomes a muscular tube and known as bulbous arteriosus, it supplies blood to the gills through ventral aorta. Single circulation in fish has several disadvantages like it is less efficient as gill capillaries slow down the blood flow and body tissues  receives blood under low pressure and limiting the amount of oxygen that can be delivered, reducing the overall metabolic capacity.

Instead of the simple two-chambered heart characteristic of most fishes, heart in amphibians has two atria and a single ventricle. The right atrium receives deoxygenated blood from the sinus venosus and the left atrium receives oxygenated blood from the pulmonary veins and cutaneous veins. Both the atria pumps blood into a single ventricle. Ventricle pumps the blood away from the heart through conus arteriosus. The short conus arteriosus contains a spiral valve of tissue that differentially guides the blood from the left and right sides of the ventricle to the aortic arches. In the ventricle some mixing of oxygenated and deoxygenated blood takes place, which reduces the efficiency.

Reptiles are the first true land vertebrates, many differences between the reptilian and amphibian cardiovas- cular systems are associated with the loss of respiration through skin and gills and the need for efficient pulmonary circulation to bring blood to and from the lungs. The ventricle of reptiles other than crocodilians is incompletely divided into dorsal and ventral chambers by a horizontal septum. A small septum divides the ventricles into right and left chambers. In case of reptiles both atria open into the left ventricle and due to the incomplete interventricular septum blood can flow from the left ventricle into the right ventricle. The pulmonary trunk leaves the right ventricle and carries blood to the lungs. One aortic trunk emerges from the left side of the ventricle and leads to the third aortic arch and to the fourth aortic arch on the right side of the body. A second aortic trunk emerges from the right side of the ventricle and leads to the fourth aortic arch on the left side of the body. In case of reptiles less mixing of oxygenated and deoxygenated blood takes place in the ventricle as compare to the amphibians because the  atrioventricular valve subdivide the left ventricle into a cavum arteriosum on the left and a cavum venosum on the right.

Heart in mammals has 4 chambers, two atria and two ventricles. Right side of the heart contains only deoxygenated blood whereas left side of the heart contains oxygenated blood. Heart pumps the blood in two major circuits, pulmonary circulation to the lungs and systemic circulation to the rest of the body tissues. Double circulation and complete separation of the heart ensures efficient supply of the oxygenated blood to the body cells under high pressure.

HUMAN HEART

Human heart is present in the thoracic cavity and covered with a double walled pericardium. Human heart has four chambers, two atrium and two ventricles. Right atrium receives deoxygenated blood from the superior vena cava, inferior vena cava and coronary sinus. Right atrium pumps blood to the right ventricle and right ventricle pumps blood to the pulmonary trunk. Between the right and left atrium is present tricuspid valve. Pulmonary trunk divides into right and left pulmonary arteries, which lead to the lungs. From the lungs four pulmonary veins carry the blood towards the left atrium. Left atrium pumps the blood into the left ventricle. Left ventricle has the strongest muscle of the heart and it pumps blood into the aorta which supplies oxygenated blood to the whole body. Valves are present in the heart and they make sure unidirectional flow of the blood. Between the left atrium and left ventricle is present a bicuspid or mitral valve. Semilunar valves are present at the openings of pulmonary trunk and aorta.