Mechanical and Chemical DigestionGrade 8 Semester 1Year 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 bitingCanine-holding and cuttingPremolars-chewing and crushingMolars-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.

Region of gut

Digestive juice

Enzymes Substrate Products Other substances

Function of other

substances

Mouth Saliva Salivary amylase

Starch Maltose Hydrogencarbonate

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 amylaseTrypsinLipase

None

Starch

PeptidesFats

-

Maltose

Amino acidsFatty Acids & Glycerol-

Hydrogencarbonate

Bile salts

Alkaline environment for enzymes

Converts globulets to smaller droplets

Small intestine (ileum)

Intestinal juice

Maltase Maltose 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

Epithelialcells

Key

Nutrientabsorption

Vein carrying blood to hepatic portal vessel

Villi

Largecircularfolds

Intestinal wallVilli

Epithelial cells

Vein

Bloodcapillaries

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• 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

Liver

Bile

Acid chyme

Stomach

Pancreatic juice

Pancreas

Intestinaljuice

Duodenum of small intestine

Gall-bladder

•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.