Into body
Substances
mouth
INGESTION
the taking of substances, e.g. food and drink,
into the body through the mouth
Small food
molecules and ions
blood
intestine
absorption
movement of small food molecules and ions through
the wall of the intestine into the blood
Undigested
food Out anus
egestion
passing out of food that has not been digested
or absorbed, as faeces, through the anus
No chemical
Smaller pieces change
breakdown
Mechanical digestion
breakdown of food into smaller pieces without
chemical change to the food molecules
Large,
breakdown insoluble Small soluble
digestion
breakdown of large, insoluble molecules into
small, soluble molecules
Used, part of
Digested food
cells
Into cells
assimilation
movement of digested food molecules into the
cells of the body where they are used, becoming
part of the cells
ALIMENTARY
CANAL
Oesophagus
Salivary gland
Teeth Tongue
epiglottis
oesophagus
Liver
stomach
Gall bladder/bile sac
Bile duct duodenum
pancreas
Large intestine Small intestine
Appendix
anus
Digestion
• Chemical digestion
Breakdown of large insoluble food particles
into small soluble molecules with the
action of enzymes
• Mechanical digestion
Breakdown of large pieces of food into
smaller pieces of food
particles. Without chemical change
Mechanical Digestion
• Occurs mainly in the mouth; chewing done by teeth
• Churning movement in the stomach
• Emulsification of fats @duodenum
INCREASES SURFACE AREA FOR ACTION OF ENZYMES DURING CHEMICAL
DIGESTION.
Adult teeth
8 incisors, 4 canines, 8 premolars, and 12 molars (including 4 wisdom teeth).
Tooth structure
Enamel :
hardest layer, made up of calcium
Dentine :
softer layer
Pulp :
inner structure with blood vessels and nerve
Cementum :
connective tissue that binds root of tooth to
jaw
Dental Decay
https://www.youtube.com/watch?v=zGoBFU1q4g0
Explain how tooth decay happens.
• Discuss with your partner and write it down on a piece of paper.
• This question is awarded a 5 marks answer.
ANSWER
1. Caused by bacteria
2. Feeding on sugar
3. Forms plaque
4. Respiration, produces acid
5. Acid corrodes enamel layer
How to prevent tooth decay
and how to look after
teeth?
• Avoid high intake of sugar at frequent
intervals
• Have frequent visits to dentist (every 6
months)
• Brush teeth twice a day using
toothbrush & fluoride toothpaste
• Rinsing mouth regularly with mouth
wash
• Use dental floss to remove plaque
Examples of gum diseases
• Gingivitis
Irritation, redness and swelling
(inflammation) of your gingiva, the part of
your gum
• Periodontitis
Serious gum infection that damages the
soft tissue and destroys the bone that
supports your teeth. Periodontitis can
cause teeth to loosen or lead to tooth loss.
Digestion In
the
alimentary
canal
MOUTH: Physical & Chemical Digestion
• Physical digestion → teeth; increase surface area for action of
enzymes
• Chemical digestion → Salivary amylase
Chewing mixes amylase with
food particles to form bolus
• Mucus is secreted to help lubricate; easier to swallow
• Epiglottis covers trachea opening to prevent food going into lungs
Peristalsis
• Wave-like contractions of muscles to push food forward
Stomach: Digestion of
protein
• Hydrochloric acid (pH 1-2)
To kill bacteria by denaturing enzymes in harmful micro-
organisms in food
To provide optimum pH for protease
• Mucus
To protect stomach lining from corrosive acid
• Digestive enzyme (pepsin & rennin)
Protein → amino acids
Caseinogen → casein
(milk protein)
Happens at the
stomach
Churning movement of stomach muscles mixes semi-
digested food further forming chyme
Digestion at the Small intestine: Duodenum
• The beginning part of
small intestine
• Chyme squeezes past
pyloric sphincter and
enters the duodenum
• Two types of secretions:
1. Bile juice
2. Pancreatic juice
Bile juice
• Contains hydrogencarbonate to help neutralize acid from stomach
providing optimum pH for enzymes
• Contains bile to emulsify fats, giving greater surface area for lipase to work
on
• Produced by liver
• Stored at bile sac
emulsification of fats
to increase the surface area for the chemical digestion of fat to fatty
acids and glycerol by lipase
Pancreatic Juice
Contains:
Lipase
Amylase
Trypsin
Fats → fatty acid + glycerol
Starch → maltose
Polypeptide → peptides
Happens at the stomach
Happens at the duodenum
Happens at the ileum
Digestion at the small intestine:
Ileum
Digestive Juice Enzymes Substrate Equation
Intestinal Maltase Maltose Maltose → glucose
Lactase Lactose Lactose → glucose + galactose
Juice
(from cells on villi) Sucrase Sucrose Sucrose → glucose + fructose
Absorption: At the small
intestine
What happens to the digested nutrients?
Amino acid, glucose, fatty acids & glycerol
Water, vitamins and mineral salts
Absorbed at the small intestines into blood stream
Structures in the small intestine
Adaptations of villi
• Has large number of villi
• Has large network of capillaries
• Has thin wall: one cell thick
• Has microvilli
• Has lacteal for absorption of fat-
soluble substances
Adaptations of small intestine and villus
How is digested nutrient absorbed?
• Into the blood capillaries
Water (most water absorbed here)
water-soluble substances
(amino acids, glucose, mineral salts,
Vit. C, B)
• Into lacteal
Fat soluble substances (Vit A, D, E, K)
Fatty acids and glycerol
What process is involved in
absorption?
Amino acids, glucose, mineral salts,
water soluble vitamin Diffusion & active transport
water Osmosis
Fatty acids, glycerol Diffusion
Question:
Absorption of glucose happens at the small
intestine. Describe how is glucose absorbed at the
villus into blood where its concentration is higher.
What happens to digested food inside blood stream?
ASSIMILATION
Blood Hepatic To all body
capillaries Portal Vein LIVER Heart
parts
@villus
What happens to undigested food?
• Continue journey into large intestine
• Remaining water is reabsorbed here
• Form faeces
• Egestion (defaecation) via anus
What happens when reabsorption
goes wrong at the intestines?
diarrhoea
Is the loss of watery faeces
How to treat diarrhoea?
• Oral rehydration therapy
• IV fluid
What causes diarrhoea?
CHOLERA
A disease caused by bacterium.
Bacteria produces toxins
Chloride ions secreted into small intestine
Water potential inside intestine decreases
Water movement into intestine
Causing diarrhoea, dehydration and loss of salts
from blood
Question
1. Cholera is a disease caused by a bacteria called Vibrio cholera. State 2
characteristics of bacteria.
Has cell wall made of protein
Has plasmid
2. Diarrhoea can be caused by bacterial or viral infection. Explain how
Vibrio cholera bacterium infection can lead to diarrhoea.
Vibrio cholera bacterium produces toxin. This toxin causes secretion
of chloride ions into the small intestine. Water potential in the
intestine becomes lower than blood. This causes water to move out of
blood into intestine, leading to watery stools (diarrhoea)
