When one takes in food in the mouth,it is crushed into soluble particles by the teeth.The tongue also rolls the food into bollus to ease the movement of the food mass along the alimentary canal.Note that it is only in the mouth where machanical digestion takes place.This is because there the food is worked upon by both the tongue and the teeth.The tongue then pushes the food rolled into bollus down the oesophagus.In the oesophagus the food moves by peristalsis a process by which food moves down the alimentary canal.It is because of peristalsis that food does not just fall through the food track but moves rhythmically.The engest then falls into the stomach where germs that entered through food are killed by the hydrochloric acid.The hydrochloric acid also dissolves fats if Incase food eaten contained fats or a fatty meat.in the stomach,also digestion of proteins takes place due to the presence of trypsin that catalyzes the break down of proteins to polypeptides.The food continues to the duodenum where fats are broken down to lipids by the bile realized into the ingest through the bile duct from the pancreases where it is manufactured.Also,the starch present in the ingest is further broken down to maltose due to the presence of pancreatic amylase.The ingest continues to the illeum (small intestine)where lipids are broken down into fatty acids and glycerols due to the presence of enzymes lipase.Also,the maltose is further broken down to glucose due to the presence of enzymes maltase in the illeum.The polypeptides are also broken down to amino acids due to the presence of enzymes peptidase in the illeum.All the enzymes in the illeum are contained in a digestive juice saccus entericus which is produced by the illeum.The undigested food (feaces) is then passed out of the body through the anus.How is the food eaten made useful by and to the body?well,in the illeum,an important process called absorption takes place.The illeum's wall is rough due to the presence of the fingurelike structure called the villi which creates a suitable surface area for absorption to take place.The villi are the ones that absorb the food values obtained from the food eaten by the help of The enzymes in the small intestine.The food values difuse into the villi and also difuse into the blood capillaries in the villi and then are(the food values)carried to the hepatic portal vein that fixes small blood vessel in the walls of the small intestine and connects to the liver where deamination takes place.In the liver,a required amount of amino acids is retained and the excess amino acids are converted to ammonia which continues with the blood to the kidney for filtration.The blood then continues to the kidney where Filtration occurs.How does the kidney filter the blood and also retains it's valuable contents?well,the kidney contains special structures billions of them called the nephrons.The blood enters a knot called the glomerulus through the afferent arteriole.Due to much pressure caused by the narrowing of afferent arteriole into many small capillaries,the small substances in the blood are pushed out the blood and are all collected in a cuplike structure called the bowman's capsule.The blood and it's original contents or red blood cells,white blood cells and others continues to the efferent arteriole and collects back the valuable materials back into the blood.The filtrate in the bowman's capsule (water,glucose,ammonia,salt)moves down to the proximal convoluted tubule where all glucose is returned into the blood.The rest of the filtrate continues down the descending limb of the loop of Henle where at the U-curve of the loop of Henle salt is returned to the blood.The filtrate continues up the ascending limb of the loop of Henle to the distal convoluted tubule where water needed in the body is also taken back into the blood.The ammonia and the water left exits the nephron and is called urine.This is called urine formation.The glucose is the transported into the body tissues and is stored as ATP(Adenosine triphosphate phosphate).Incase energy is required,the ATP is broken t ADP(Adenosine diphosphate)by the process of respiration and much energy is released.That is how food is taken in,absorbedand assimilated by the body 


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