The Digestive System Guts, teeth and glands! Images from:

Why Guts? Multicellular animals must have specialized structures for obtaining and breaking down their food. There are two processes: feeding and digestion. Animals are heterotrophs, they must absorb nutrients or ingest food sources.

How to dine... Ingestive eaters (us). Absorptive feeders (tapeworm) Filter feeders (clam) Substrate feeders (earthworms) Fluid feeders (mosquito)

Vertebrate Digestion The digestive system uses mechanical and chemical digestion to breakdown food.

Tube in a tube Vertebrates have a tube-within-a-tube system. digestion occurs in the lumen with the nutrient molecules being transferred to the blood.

Stages of digestion Movement of food Secretion of digestive juices Digestion of food into molecules Absorption of molecules Elimination of undigested food and wastes

The Digestive System Mouth, pharynx, esophagus, stomach small intestine large intestine anus salivary glands pancreas liver and gall bladder

The Start In the mouth, teeth, jaws and the tongue begin the mechanical breakdown of food. Chemical breakdown of starch by amylase Mucus moistens food and lubricates the esophagus. The chewed food and saliva is then pushed into the pharynx and esophagus. The esophagus uses peristalsis to send the food to the stomach.

Move the food Food is chewed and passed to the stomach through the esophagus. The name of the movement is peristalsis. (see video)

The Stomach Holds 1 to 2L (folds) The stomach secretes mucus, hydrochloric acid and pepsin. HCl lowers pH of the stomach to activate pepsin. Pepsin hydrolysis of proteins into peptides. The stomach also mechanically churns the food. Chyme, leaves the stomach and enters the small intestine. Ulcers occur when mucus lining is reduced.

The Small Intestine 3 m long tube with coils and folding plus villi. Very large surface area! Final digestion of all food and absorbtion. Villi produce enzymes which complete the digestion of peptides and sugars. The absorption process in the villi.

Villi Sugars and amino acids go into the bloodstream via capillaries in each villus. Glycerol and fatty acids go into the lymphatic system. Absorption is an active transport, requiring cellular energy.

Duodenum - busy place Secretions from the liver and pancreas are used for digestion in the duodenum. The pancreas secretes digestive enzymes and stomach acid-neutralizing bicarbonate. The liver produces bile, which is stored in the gall bladder before entering the bile duct into the duodenum.

Small intestine - more Digestion of carbohydrates, proteins, and fats continues in the small intestine. See table in text - page 166. Bile emulsifies fats so that lipases can completely digested lipids. Most absorption occurs in the ileum and jejeunum (second third of the small intestine).

Liver and Gall Bladder The liver produces bile and helps to detoxify of blood synthesis of blood proteins destruction of old erythrocytes storage of glucose as glycogen De-amination amino groups and ammonia. (this produces urea, less toxic)

Glycogen-Glucose Low glucose levels in the blood cause glucagon to stimulate breakdown of glycogen into glucose. Insulin helps store glucose and glycogen in the liver (see page 929) When no glucose or glycogen is available, amino acids are converted into glucose in the liver.

The Large Intestine what to do with left overs! The large intestine produces an alkaline mucus that neutralizes acids produced by bacterial metabolism. Water, salts, and vitamins are absorbed, the remaining contents in the lumen form feces (mostly cellulose, bacteria, bilirubin). Bacteria in the large intestine, such as E. coli, produce vitamins (including vitamin K) that are absorbed.

Nutrition See the basics of nutrition in your text. Have a hand out!