Download Lesson 10 DIGESTION Digestion. Digestion is the breakdown of

Lesson 10
DIGESTION
Digestion.
Digestion is the breakdown of large, insoluble food molecules into small, water- soluble molecules
using mechanical and chemical processes. The nutrients can then be absorbed into the blood and
taken to the cells. Digestion begins in the mouth.
Ingestion and Egesition
 Ingestion is taking substances (e.g. food and drink) into the body through the mouth.
 Teeth are used to chew the food to break it down to smaller pieces, to create a larger
surface area, and to mix it with saliva. A food bolus is made at the back of the mouth
 Saliva has a lubricant called mucus and enzymes (amylase) that begin the breakdown
process.
 Food is swallowed by a special action that covers the windpipe when the food is swallowed.
It travels down into the oesophagus and moves through the oesophagus by peristalsis.
 Peristalsis is a wave of contraction of the circular muscle.
 At the end of the digestive process there is egestion.
 Egestion is the passing out food that has not been digested, as faeces, through the anus.
Enzymes
 Enzymes are special protein molecules that are responsible for speeding up chemical
reactions in the body.
 Each enzyme has a special shape that allows it to fit into a specific substrate molecule.
 High temperatures change the shape of the enzyme molecule, which prevents it from
functioning. We say that the enzyme has been denatured.
 Amylase is the enzyme responsible for the breaking down of starch molecules.
Teeth
 Teeth are important for digestion in the mouth. They grow from the jaw bone and each
tooth is adapted to its specific function.
 Humans have two sets of teeth; a temporary set called milk teeth and a permanent set.
Biting and chewing are carried out by the teeth, jaws and jaw muscles. There are four sets of
teeth;
1. Incisors are sharp for biting and cutting food.
2. Canines are pointed for gripping, cutting and tearing food.
3. Premolars and
4. Molars are broad and uneven for crushing, chewing and grinding food.

A tooth has the following parts:
- Enamel is the hard protective outer layer;
- Dentine is the hard inner layer;
- Pulp cavity contains the blood vessels and nerves;
- Cement holds the tooth in the bone.
Label this diagram of the tooth:
Label the different types of teeth:
Lesson 11
Causes of Tooth Decay
o Sugary food sticks to teeth.
o Bacteria feeds on sugar and produce acids. (Bacteria + food = plaque).
o Acid dissolve the enamel, which reaches dentine then pulp cavity – causing pain.
Activity:
Arrange these points in the correct order:
1. Bacteria produce acids
2. Sugary food sticks to teeth
3. Pain is felt when the acid reaches the nerve
4. Acid dissolves the enamel
5. Bacteria feeds on the food that is stuck to the teeth
6. The mixture of food and bacteria is called plaque
7. The hole in the enamel eventually reaches the dentine and pulp cavity.
Types of tooth diseases
o Bad breath – halitosis
o Calculus – hardened dental plaque or tartar
o Cavities – silver and white fillings and Caps
o Rotten teeth - Bridges, dentures
o Gingivitis, periodontitis and gum disease – red swollen gums – bone loss – teeth fall out
How to prevent tooth decay
Complete the following table:
Step:
Eat less sugary foods
Clean/floss teeth regularly
Use fluoride toothpaste
Frequent trips to the dentist
Homework:
Complete the relationship between fluoride and tooth decay task.
Reason:
Lesson 12
Digestion in the Stomach and Small Intestines
-
Swallowed food enters the stomach for storage and to turn the solid food into a liquid.
-
A meal containing fat and protein lasts longer in the stomach than food with carbohydrates –
4hrs average stay
-
Stomach walls are in constant motion – physical breakdown and mixing.
-
Gastric juice =HCl ( hydrochloric acid )
-
The pyloric sphincter prevents large pieces of food from entering the rest of alimentary canal – it
releases small amounts of liquid slowly into the duodenum.
-
In the small intestines a pancreatic juice from the pancreas contains many types of enzymes to
break down the food;
-
o
Amylase(carbohydrase) – starch to maltose;
o
protease – proteins to peptides and amino acids;
o
lipase – fats to fatty acids and glycerol
Bile (green) is made in the liver (from broken down haemoglobin) and stored in the gall bladder
and released into the duodenum via the bile duct. It emulsifies the fats to allow the enzymes to
operate e.g. like a detergent breaking up fats into small drops.

Complete the following table;
Food Broken Down
Enzyme
Starch
Products Formed
Maltose
Protein
Protease
Polypeptides
Fats
Polypeptides
Protease
Milk and Fruit Sugars
-
Glucose
Most absorption of food occurs in the ileum.
o It is very long – 7m
o The absorbing surface has circular folds covered in tiny finger-like projections called
villi (0.5mm)
o The epithelia lining is very thin and each epithelia cell has microvilli (increases
exposed surface by 20 times)
o A dense blood supply.
-
The majority of the small molecules of digested food is absorbed into the blood stream by active
transport and taken to the liver, where poisons are destroyed. Fats can enter lacteal and taken
to the lymphatic system which eventually joins the bloodstream.
-
The epithelial cells of the villi are constantly being shed and replaced by new epithelial cells from
the crypts.

Draw Fig 4.9 pg 52 of a Villus
Lesson 13
Absorption in the large intestine
-
Material passing into the large intestines consists mainly of water, which is absorbed and
undigested matter e.g. roughage, mucus and dead cells from alimentary canal. Bacteria in the
colon can make fatty acids from the fibre, which are then absorbed. Bile salts are also absorbed
in the colon and returned to the liver.
-
Faeces is a semi solid waste that is passed into the rectum by peristalsis.
-
Egestion is the passing out food that has not been digested, as faeces, through the anus
The digestive system
Label the following parts of the digestive system including functions:
Homework:
Pg 53 Q1-4