The Digestive System The 6 Processes Ingestion n

The Digestive System

The 6 Processes Ingestion n Mechanical digestion n Chemical digestion n Secretion n Absorption n Excretion n

Components Oral Cavity: Salivary glands, tongue, teeth n Esophagus n Stomach n Small and Large intestine n Pancreas n Liver and gallbladder n

Teeth/mouth Salivary gland Esophagus Liver Stomach Common Bile duct Small Intestine Pancreas Large Intestine Rectum Anus

A Trip Through the Tube

The Oral Cavity Ingestion occurs here and no where else n Mastication- mechanical breakdown of food into smaller pieces, requires tongue and teeth n Salivary Glands - secretion of mucus, enzyme amylase n ¨ help lube up the food and start chemical breakdown of starches

The Esophagus Muscle contractions of peristalsis force food from mouth to stomach n Mucus secretion moistens food and lubricates it as it moves n No absorption occurs here n

The Stomach

Movement in the Stomach n The bottom of the stomach near the pyloric sphincter does most of the mechanical breakdown through vigorous contractions of the smooth muscle

Functions Storage of food n Mechanical Breakdown of food n Begin chemical digestion by secreting enzymes and acid n Turn food into liquid chyme n

Digestion and Absorption n Digestion starts with gastric acid it kills bacteria in food and gives the stomach the low p. H needed by digestive enzymes that work in the stomach. n The main enzyme in the stomach is pepsin ¨ Pepsin breaks down proteins into smaller polypeptides

The Small Intestine n n Measures about 20 feet long Location of most digestion and absorption

Digestion in the Small Intestine n Digestion of food in the small intestine requires enzymes from the pancreas and gallbladder

Pancreatic enzymes ¨ Pancreatic Amylase: breaks down starch into simple sugars ¨ Pancreatic Lipase: breaks down lipids into glycerol ¨ Pancreatic Protease: breaks down proteins into amino acids

Gallbladder Secretions n n The gallbladder secretes bile which is both a waste product and a digestive chemical Bile helps emulsify fats and break them down into small pieces that can be digested with the enzyme lipase

Absorption ¨ Proteins, Lipids and Carbs must be broken down all the way into amino acids, glycerol and simple sugars in order to be absorbed by the small intestine

The Large Intestine

Function Compaction of feces n Absorption of water & vitamins n Storage of fecal material n

Movements, Secretion & Absorption n Slow, powerful peristalsis to move food down to the rectum Defecation reflex stimulates peristalsis to eliminate feces Absorption ¨ Vitamins ¨ Water K, biotin and B 5

The End n When eliminated feces consists of ¨ 75% Water ¨ 5% bacteria ¨ 20% indigestible material, inorganic matter and epithelial cells from the lining of the digestive tube