ch. While in the stomach, contractions of the muscular wall continue to break down food mechanically. Chemical digestion continues when acid and enzymes are secreted into the stomach cavity. Then the food passes through the small intestine. Here enzymes from the pancreas complete the chemical part of digestion. Fat is digested with bile. Bile is made in the liver and stored in the gall bladder. Whatever is left of the food, mostly liquid, enters the large intestine. Here most of the fluid is absorbed. Whatever is not absorbed is passed out of the body through the anus.
             The frog, unlike a human, has only a three chambered heart. The frog only has one lower chamber while a human has two, the right and left ventricle. The frog has one muscular ventricle and two thin-walled atria. Blood that leaved the ventricle enters a large blood vessel that branches into two atria's. These then divide into many smaller arteries, which then are divided into capillaries. Veins are used to return blood from the capillaries to the heart. The right and left pulmonary veins carry blood from the lungs to the left atrium. As the frog breaths using air with its lungs the blood is oxygenated. Blood from all the other parts of the body is brought back through three large veins into a thin-walled sac. Blood form the sac enters the right atrium. The right and left atria then empty blood into the ventricle. So therefore blood that is pumped out by the ventricle is a mixture of oxygenated blood that is from the left atrium and deoxygenated blood that is from the ri!
             ght atrium. Circulation in humans is a bit different. Humans have a four chambered heart. The two upper, think-walled chambers are the atria. The two lower, thick-walled chambers are the ventricles. The circulatory system consists of two major pathways. Pulmonary circulation, which is the first pathway, carries blood between the heart and the lungs. Systemic circulation, wh...