Download How Important is Your Teeth?

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.
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
Pancreatic
amylase
Trypsin
Lipase
Starch
Maltose
Hydrogen
carbonate
Peptides
Fats
Bile
None
-
Amino acids
Fatty Acids &
Glycerol
-
Alkaline
environment
for enzymes
Bile salts
Converts
globulets to
smaller
droplets
Intestinal
juice
Maltase
Maltose
Glucose
-
-
Small
intestine
(ileum)
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
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Blood
capillaries
Epithelial
cells
Muscle layers
Villi
Epithelial cells
Large
circular
folds
Lacteal
Vein
Key
Nutrient
absorption
Intestinal wall
Villi
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
•
•
•
•
Bile
Liver
Gallbladder
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
Stomach
Acid chyme
Intestinal
juice
Duodenum of
small intestine
Pancreatic juice
Pancreas
• 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.