Circulatory system transports all the nutrients to the different parts of the body. They are involved in the transport of nutrients, hormones, transport oxygen to various body parts and carries the waste CO2 from the different [arts to the excretory organs.
The circulatory system of frog includes the heart, blood vessels together with the fluid blood. It distributes the digested food and oxygen to different parts of the body to release energy to carry out life activities. The heart is a chambered muscular structure that forces the blood to circulate constantly through the closed system of tubular elastic blood vessels. The heart of frog is a dark coloured conical muscular organ situated ventrally to the liver in the pericardial cavity along the mid ventral line at the level of fore limbs. It is enclosed in two membranes, an outer pericardium and an inner epicardium.Between these two membranes a pericardial fluid is found which prevents friction and keeps the heart moist.
The blood vessels which carry the oxygenated blood away from the heart to different parts of the body are called arteries. The arteries divide into the thinner arterioles which branch into extremely thin and small capillaries forming a network in all body tissues except cartilage and epithelium. From the capillaries the blood passes into thin venules which combine to form veins. Veins carry deoxygenated blood towards the heart so that it may be transported to the respiratory organs for the oxygenation. All blood does not pass through capillaries into venules but also passes through some channels and arterio venous anastomoses directly from arterioles into venules. The arteries along with their branches constitute arterial system where as the veins along with their fine tubes form the venous system.