Nutrition is the process in which an organism obtains there materials from the environment. Nutrition has to do with the human digestive system because in order for you to get nutrition you have to be able to digest it, to get it across the cell membrane to distributed threw out your body.

There are two types of digestion mechanical and chemical. Mechanical digestion is the breakdown of without altering the chemical composition . In order to digest a material the food has to go through many organs .

The order in which it goes is the mouth ( oral cavity), pharynx (throat), esophagus, stomach, small intestines, large intestines, rectum , and the anus. The mouth and pharynx is where ingestion takes place. In the mouth there are salivary glands. Salivary glands secrete salvia, and they also contain an enzyme called salivary amylase. When the food is sufficiently chewed the tongue pushes it to the back of the throat which triggers the swallowing reflex.In the pharynx , the epiglottis which is a flap of tissue that closes the trachea to force food down the esophagus.

The esophagus is a long tube that carries food from the pharynx to the stomach, the food is moved through by a series of contractions and relaxations of the muscle tissue called peristalsis, there is not a lot if food digestion in the esophagus . A sphincter controls the movement into the stomach. The stomach is a thick walled muscular sac. , and can expand up to 2 litters of food and water.

Both mechanical and chemical digestion occurs here.The stomach contains two types of glands: a) one secretes a mucus material that covers the lining and protects it from being eroded by the acids. b) The other types are gastric acids that secrete gastric juice, gastric juices contain enzymes called pepsin for protein digestion. When the stomach is done with digesting the food it goes to the small intestine. The small intestine is a coiled tube 6. 5 meter long. Most of the chemical digestion and almost all of the absorption occurs here. The fluids are mostly alkaline.

The small intestine contains enzymes necessary to complete digestion.Peristalsis of small intestine is in constant motion when food is present the movements are:1) squeeze food through intestines2) mix food with digestive enzymes3) breakdown food particles mechanically4) speed up absorption of nutrients.Bile breaks down fats into tiny droplets. This process is know as emulsification, proteins are broken down into amino acids the into carbohydrates then into fats into fatty aids and glycerol. All of these things are absorbed through the wall into the bloodstream. For better absorption small intestines are very long, lining has many folds, lining is covered with villi ( hair-like), and villi has microvilli.The large intestine is a storage are for all the undigested and ingestible material that passes through the small intestine.

The large intestine is 1. 5 meters long and 6 centimeters in diameter, no digestion occurs here. The functions of the large intestine is to absorb the water that was added to the material during digestion, they also absorb vitamins( these are absorbed with the water ), and the large intestine also eliminates undigested and indigested material from the digestive system. As water passes through the large intestines and becomes the feces.