1. Ingestion: The MOUTH- Food enters the gastrointestinal tract through the mouth.
2. Digestion:A) MOUTH – both physical (mechanical) and chemical digestion begins herev
v In the mouth, SALIVARY glands produce SALIVA which contains the enzyme AMYLASE which acts on starch, breaking it into maltose.BOLUS: the resulting ball of food in the mouth made by the actions of the teeth, tongue, and saliva PERISTALSIS: the rhythmic muscular contractions that push digested food in one direction through the gastrointestinal tract.The bolus is swallowed and travels down the esophagus into the stomach. It moves down the esophagus by peristalsis.
B. STOMACH: physical and chemical digestion.The bolus passes through the CARDIAC SPHINCTER, the top opening in the stomach.Sphincter: a muscle that controls the openingi) cardiac: esophagus & stomachii) pyloric: stomach and duodenumv
GASTRIC juice contains: a) HCl – hydrochloric acid b) pepsin – enzyme that breaks down PROTEIN, HCl: - helps breakdown fibrous tissue- kills bacteria- helps pepsin work properly (ph = 2 optimal pH for pepsin) PEPSIN: - enzyme begins to break down PROTEIN into smaller polypeptides MUCUS: - also made by stomach to protect itself from STRONG ACID. Chyme stays in stomach until adequate protein digestion has occurred. This is why you feel less hungry between meals if you have eaten some protein. The chyme is kept in the stomach by the pyloric sphincter.
C. SMALL INTESTINE-Final area where MOST digestion occurs and ABSORPTION begins.··- many enzymes from accessory glands (liver, gall bladder, pancreas) are dumped into the SI to help with digestion,The SI is also divided into three sections: a) duodenum b) jejunum c) ileum. Accessory glands:·- releases digestive enzymes: pancreatic amylase, lipaseà lipids, trypsinà polypeptides.
The liver performs a vast number of functions (500), including production of bile fromcholesterol, recycling of red blood cells, glycogen storage, storage of fat-solublevitamins, deamination of amino acids, and detoxification of poisons. Everything thatenters the body must go through the liver to be cleared.
3. ABSORPTION OF NUTRIENTS-
Absorption is greatly aided by the folded interior structure of the intestine, particularlydue to the presence of the villi and microvilli. Small molecules like vitamins, minerals, natural glucose and amino acids do not need to bedigested and are easily absorbed by the small intestine.
Stomach: - small amounts of water- alcohol- some medicines, e.g. aspirin. Small intestine: jejunum - where most of the absorption takes placeileum: where the remaining nutrients are absorbed.
Water is absorbed throughout the alimentary (GI) tract but the majority of waterabsorption occurs in the LARGE INTESTINE, also known as the COLON.
4. EGESTION OF WASTE
Egestion controlled by anal sphincter which allows feces to leave rectum through theanus. Toilet training is learning how to control the anal sphincter.