Tag: transportation - the circulatory system

Blood vascular system of prawn is 'open type'. It lacks capillaries and veins. The heart pumps pure blood in arteries, which divide and redivide  into very small branches of arteries and open freely in haemocoel. The blood flows through these sinuses or blood lacunae into the entire body. All blood sinuses open into a pair of long but indistinct ventral sinus. Afferent branchial channels carry impure blood from ventral sinuses to gills, where it is purified (oxygen dissolved in water inside gills is taken in blood by diffusion and carbon dioxide present in blood is diffused out in water). The pure blood from each side of gills is conveyed to pericardial sinus by efferent branchial channels and is then returned to the heart. Thus, the heart always contains oxygenated blood, though the arteries contain mixed blood.

The lymph hearts in frog which carry lymph are two pairs located on dorsal side of frog's body. The front pair is situated below the shoulder blades. The posterior pair is on either side of a long, rod-like bone called as a urostyle. The anterior pair opens into the subclavian vein and the posterior pair into the femoral vein. The pair near the third vertebra pumps lymph into the jugular vein. The other pair at the end of the vertebral column pump lymph into the iliac vein in the legs.

Since in frogs larva changes into adult by undergoing metamorphosis and for this gills are lost. Thus with the loss of gills, first, second and fifth aortic arches also disappear and only three aortic arches remain functional- carotid arch, systemic arch and pulmonary arch. 

Vertebrates have evolved a muscular heart to pump blood to body parts. Fishes have two chambered heart. Birds and mammals have four chambered heart, having two auricles and two ventricles. Reptiles, except crocodile, have three chambered heart. Crocodiles have four chambered heart. Thus Dolphin being a mammal has four chambered heart. Salamander being an amphibian has a three chambered heart.

Fish have 2 chambers, one atrium and one ventricle. Fish hearts draw in deoxygenated blood in a single atrium, and pump it out through a ventricle. This type of system is known as "single circulation type", as blood enters the heart, gets pumped through the gills and out to the body. Thus, the correct answer is option A.

The chordae tendinae are strong, fibrous strings attached to the leaflets (or cusps) of the heart on the ventricular side i.e., the lower chamber. These strings originate from small mounds of muscle tissue, the papillary muscles, which project inward from the walls of the ventricle. When the cusps close, the chordae tendinae prevent them from swinging back into the atrium cavity (the upper chamber).

The heart of a crocodile is different from other reptiles in that it has four chambers just like birds and mammals. Blood is sent to the lungs for gas exchange from the right and from the left ventricle it is pumped to the body. Thus, the two types of blood do not mix in the heart. However, blood is mixed as soon as it leaves the heart via a valve placed in between the right and left aorta. 

Sinus venosus and conus arteriosus are not found in rabbit but they are present in the frog. In rabbits, sinus venosus is formed in the embryo, but later becomes a part of the right wall of the auricle. In rabbits, conus arteriosus forms a part of the upper wall of the right ventricle in which the pulmonary artery originates. 

In animals, rate of heart beat is connected with the size of animal. In mammals, smaller animals have higher heart beat. For example, 200 beats per minute in rabbit, 500 beats per minute in sparrow, 28 beats per minute in elephant. In frog, rate of heart beat is 64 per minute. In mammals, maximum heart beat is observed in shrew (800 per minute) and minimum in blue whale (25 per minute).

Fishes have a 2-chambered heart, with an atrium and a ventricle. In fishes, the heart pumps out deoxygenated blood, which is oxygenated by the gills and supplied to the body parts from where deoxygenated blood is returned to the heart. It is called as single circulation.