Mechanical and Chemical Digestion Grade 8 Semester 1 Year 2011-2012

How Important is Your Teeth?

What happen inside our mouth? Mechanical digestion Food is cut up by the teeth and the pieces are mixed with the saliva by the tongue producing bolus. This cutting and mixing is called mastication (chewing)

Types of Tooth Adults humans typically have 32 teeth Humans have 4 types of teeth: Incisors-cutting and biting Canine-holding and cutting Premolars-chewing and crushing Molars-chewing and crushing

Tooth Structure Enamel: hardest tissue made of calcium salts. Dentine: forms the major part of the tooth. Contains a series of fine canals which extend to the pulp cavity. Pulp cavity: Contains tooth producing cells, blood vessels, nerve endings. Gum: Covers the junction between enamel and cement. Cement: helps anchor the tooth to the jaw. Periodontal membrane: Anchors the cement to jawbone. The tooth is held firmly but not rigidly.

Dental Health Eating food with a low sugar content. Regular and effective brushing of teeth (at least twice a day). Finishing a meal with a crisp vegetable or fruit followed by rinsing with water.

Chemical Digestion

Chemical Digestion Digestive Enzymes Carbohydrate digestion begins in the mouth. Protein digestion begins in the stomach. Digestion of food molecules is completed in the small intestine.

Function of other substances Region of gut Digestive juice Enzymes Substrate Products Other substances Function of other substances Mouth Saliva Salivary amylase Starch Maltose Hydrogen carbonate Alkaline environment for amylase Stomach Gastric juice Pepsin (protease) Proteins Peptides Hydrochloric acid Acidic environment for pepsin; kills bacteria Small Intestine (duodenum) Pancreatic juice Bile Pancreatic amylase Trypsin Lipase None Fats - Amino acids Fatty Acids & Glycerol Bile salts Alkaline environment for enzymes Converts globulets to smaller droplets Small intestine (ileum) Intestinal juice Maltase Glucose

Absorption Absorption is a process where digested food molecules are transported across the lining of the gut into the blood. Most absorption happens from the ileum. The surface of the ileum is highly folded into villi.

STRUCTURE OF SMALL INTESTINE Epithelial cells Key Nutrient absorption Vein carrying blood to hepatic portal vessel Villi Large circular folds Intestinal wall Vein Blood capillaries Lacteal Microvilli (brush border) Muscle layers

The liver and assimilation Digested food is absorbed into the bloodstream. The liver sorts out digested food molecules and make sure that the other tissues of the body receive what they need. The process of moving food molecules into the cells where they are used is called assimilation.

Functions of Liver Manufacture of bile Storage of glucose as glycogen Acid chyme Stomach Pancreatic juice Pancreas Intestinal juice Duodenum of small intestine Gall- bladder Manufacture of bile Storage of glucose as glycogen Interconversion of amino acids Excretion of excess amino acids and excreted in the urine as urea Breakdown of alcohol and other toxins Removal of old red blood cells from the circulation and storage of the iron they contained

Bread is made mainly of starch, protein and fat Bread is made mainly of starch, protein and fat. Describe what happens to the bread mechanically and chemically as it passes through the mouth, stomach and small intestine.