1. The digestive system
1.1. The mouth
1.1.1. The food enters through the mouth then the salivary glands throw saliva that heps our teeth to chew the food.
1.2. The oesophagus and the stomach
1.2.1. Then the food passes through the oesophus to the stomach.
1.2.2. The stomach brake down the food with the gastric juices and it passes to the small intestine.
1.3. The small and large intestines
1.3.1. The small intestine take the nutrients from the food and then it passes to the large intestine.
1.3.2. In the large intestine the waste products mix with water and leaves the body through the anus.
2. The circulatory system
2.1. The circulation of the blood
2.1.1. The dioxigenated blood passes trough the right atrium to the left ventricle and then to the heart, and go to the lungs.
2.1.2. In the lungs bld release carbon dioxide and takes oxygen, and the blood goes to the heart.
2.2. The process
2.2.1. The oxigenated passes through the left atrium to the left ventricle, then it's pumps by the aorta to the rest of the body.
2.2.2. The aorta carries blood through small arteries to the capillaries ther the blood release oxygen to the cells and take carbon dioxide and others waste products
2.2.3. The deoxygenated blood passes from the capillaries to the small veins and then to the superior vena cava and the inferior vena cava. These veins carry the blood to the heart.
3. The respiratory system
3.1. The mouth and the nose
3.1.1. The air enters through the mouth and the nose that the are conected.
3.2. The pharynx and the trachea
3.2.1. Then the air goes trough the pharynx and the trachea.
3.2.2. There are two tubes called bronchi that are conected with the lungs.
3.3. The lungs
3.3.1. There are smaller tubes that are conectes with the bronchi. They have air small sacks at the final and there is were it occurs the change of gases.
4. The excretory system
4.1. The kidneys and the ureters.
4.1.1. The blood is filter by the kidneys and then the waste products from the blood are mixed with water.
4.1.2. Then the waste products gous trough the ureters to te bladder
4.2. The bladder and the urethra
4.2.1. When the bladder is half full it send signals to the brain.
4.2.2. Finally the waste products leave the body through the urethra.