1. Mechanical and Chemical Digestion
Grade 8 Semester 1
Year

2. How Important is Your Teeth?

3. 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)

4. 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

5. 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.

6. 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.

7. Chemical Digestion

8. 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.

9. 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

10. 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.

11. 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

12. 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.

13. 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

14. 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.