The Digestive System Functions: Ingestion = Food enters the mouth Digestion = Process that breaks food down into small molecules Mechanical digestion = Food is chewed and churned. Chemical digestion = Breaks down large food molecules into smaller molecules to be absorbed by cells

Absorption = Small molecules of food are taken into the body cells. Elimination = Wastes made of unabsorbed food molecules pass out of the body.

Organs and Structures Mouth = Digestion starts here. The tongue & teeth mechanically break food up. Saliva chemically digests food. When swallowing, the epiglottis (a small flap) automatically closes over the trachea (windpipe).

Esophagus Smooth muscles force food into esophagus. Rhythmic muscular contractions (peristalsis) push food downward.

Stomach Food undergoes mechanical digestion when stomach muscles churn the food. Chemical digestion happens when hydrochloric (HCl) and pepsin break down the complex proteins. Peristalsis pushes the food toward stomach’s exit.

Small Intestine (6 meters long) Most digestion happens here. Intestinal juice (full of enzymes) breaks down food. Digestive Helpers Liver = Bile is produced here (Bile breaks up fats) Gall bladder = Bile is stored here Pancreas = Produces pancreatic juices that are released into the small intestine to break down proteins and starches

Small Intestine (Continued) Digested food is absorbed through the villi that carry the nutrients to all parts of the body. e) When food leaves the small intestine, it is empty of all nutrients except water.

5. Large Intestine Undigested food spends 18–24 hours here, and most of the water is absorbed. Helpful bacteria living in the large intestine make vitamins K and B. Materials not absorbed form into solid waste Solid waste passes into the rectum and is stored until it is eliminated from the body through the anus.