• Dinner Is Served

• Remember the last time you sat down to a dinner of your favorite foods? Recall everything that you did before you swallowed your first bite.

1. Why do you cut up your food?

2. What role do your teeth play in eating?

3. Saliva is the fluid that is found in your mouth. What role do you think it plays in eating?

Chapter Chapter 38.238.2The Process of Digestion

Main Function

Helps convert foods into simpler molecules that can be absorbed and used by the cells of the body

Built around a one-way tube (alimentary canal) that runs through the body

Organs of the Digestive System

The path that food travels: Mouth pharynx esophagus

stomach small intestine large intestine rectum anus

Several major accessory structures including the salivary glands, the pancreas and the liver add secretions to the digestive system.

Digestive System

Mouth

Salivary glands

Stomach

Pancreas (behind stomach)Large intestine

Small intestine

Rectum

Gallbladder (behind liver)

Liver

Esophagus

Pharynx

The Mouth

Beginning of the digestive system

Mechanical digestion physical breakdown large pieces into smaller pieces Chewing – Teeth: cut, tear, crush food Purpose is to increase surface area of food so

that more enzymes can breakdown the molecules

The Mouth (Cont’d)

Chemical Digestion large food molecules are broke down into smaller food molecules Enzymes, acid

Salivary glands – produce saliva Moistens food Contains enzymes

Amylase breaks down starches and releases sugars

Lysozyme fights infection

Swallowing

Food is pushed to the back of the throat While chewing, the tongue pushes food up

and back Smashes food against the hard and soft

pallet Clump of food bolus

Epiglottis flap of tissue that blocks off the opening to the trachea, directing the food down the esophagus

Esophagus Food tube

Connects pharynx and the stomach

Peristalsis contractions of the smooth muscle squeeze the food through the esophagus into the stomach Fig. 38-11 page 980

Stomach

Large muscular sac Site of chemical and mechanical digestion Contracts to churn and mix stomach fluids

together

Cardiac sphincter – Ring of muscle that lets food into the stomach

and prevents acid from entering the esophagus

Heartburn painful, burning sensation, that results from the backflow of stomach acid

Stomach (cont’d)

Contains gastric glands Produce mucus – protects the stomach Produce hydrochloric acid - keeps stomach

pH acidic Produce pepsin – digests proteins

Works best in acidic conditions

Mixture of stomach fluids and food chyme

Small Intestine

3 parts: duodenum, ileum, jejunum Pyloric sphincter – separates stomach

and small intestine

Functions: Complete chemical digestion Absorb nutrients

Pancreas

Pancreas and gall bladder release enzymes/fluids into small intestine

Pancreas Produces hormones that regulate blood sugar Produces enzymes that breakdown all the

macromolecules Produces sodium bicarbonate – neutralizes

stomach acid and allows enzymes to function properly

Gall Bladder

Gall bladder releases bile into the small intestine

Bile loaded with lipids and salts Acts as a detergent to breakdown fats Produced in the liver

Villi

Villi – fingerlike projections on the inside lining of the small intestine Covered by microvilli Provides an enormous surface area for

the absorption of nutrient molecules Once food is ready to leave it is

nutrient free Only cellulose, water, and other

indigestible substances remain

Large Intestine

3 parts: ascending colon, transverse colon, descending colon

Contains bacteria that aids digestion

Functions: Transports waste Absorbs water

Enzymes in DigestionSite

Mouth

Stomach

Small intestine(from pancreas)

Small intestine

Site

Mouth

Stomach

Small intestine(from pancreas)

Small intestine

EnzymeEnzyme Role in DigestionRole in Digestion

Salivary amylase

Pepsin

Amylase

Trypsin

Lipase

Maltase, sucrase, lactase

Peptidase

Breaks down starches into disaccharides

Breaks down proteins into large peptides

Continues the breakdown of starch

Continues the breakdown of protein

Breaks down fat

Breaks down remaining disaccharides into monosaccharides

Breaks down dipeptides into amino acids.

Digestive System Disorders

Peptic ulcers Acids released by the stomach damage the

organ’s own lining, producing a hole Caused by Helicobacter pylori – bacteria

Diarrhea Not enough water is absorbed

Constipation Too much water is absorbed