Write a note on the venous system of frog.

VENOUS SYSTEM OF FROG.

 The blood vessels which carry blood from different parts of the body towards heart are called veins. Veins contain deoxygenated blood except the pulmonary veins. The system consisting of veins is called the venous system. In frog, the venous system consists of the following veins.

Pulmonary Veins:

 Blood from right and left lungs come to the left auricle / atrium of the heart through pulmonary veins. Only pulmonary veins have oxygenated blood while all the other venis have deoxygenated blood. 

Right and Left Precavals:

 Each precaval is formed by the union of three veins which bring blood from tongue, lower jaw, head, shoulders, forelimbs and skin.

Post Caval:

 Blood from the lower parts of the body such as the stomach, intestine, liver, pancreas, genital organs, muscles, hind limbs, kidneys, etc is collected through veins including five or six pairs of renal veins. genital veins.,two hepatic veins.All these veins join together to form one major vein called the post cavai, 
Both the precavals and the post caval open into the sinus venosus from where the blood is pumped into the right auricle/atrium of the heart. 

Abdominal Vein:

 Pelvic veins of both sides unite to form abdominal vein which divides into two before entering the liver. Here it divides into capillaries. 

Portal System:

 Set of veins which collect the blood from one organ and discharges it into another organ are called protal veins. The set of veins draining their blood into liver are called hepatic protal whereas the set opening into the kidneys are called renal portal system. 

Hepatic Portal System:

 The blood vessels from various parts of the digestive system, e.g. stomach, duodenum, ileum, rectum, pancreas and spleen collectively fuse to form a large vein called hepatic portal vein. In the liver it unites with the abdominal vein and then divides and redivides into capillaries to allow transfer of some of the digested food into the liver for storage. From the liver, it finally enters the post caval which carries blood to the sinus venosus. 

Renal Portal System:

 The alternate route of blood from the hind limbs is by way of a renal protal vein. These veins begin in capillaries in the hind limbs and break up into capillaries in the kidneys.