Human Digestion

Junior Science

True or False

• The word stomach comes from the Greek meaning “Throat”.

• Butterflies in the stomach have nothing to do with the stomach.

• It is possible to live without your stomach.

• You can burst your stomach by eating too much.

• Ice cream freezes your stomach.

• Your stomach stops moving when you sleep.

• Your stomach can produce an acid which will dissolve bone.

Digestion

Digestion is the process of

breaking down food into

molecules small enough for the body to absorb.

Food and Nutrition

• Nutrition is the taking in, breaking down and use of food to provide energy and help in growth and repair.

• Food is any substances which provide energy and enable, growth and repair in the body’s cells.

• Nutrients are chemical compounds found in food – carbohydrates, proteins, fats, vitamins and minerals

Food Facts

Food is any substance (solid or liquid) which provides one or more of the following:

• Promotes Growth

• Prevents Disease

• Provides Energy

• Maintains Normal Body Processes

Nutrients

The components of food which have these functions are called NUTRIENTS these include:

Carbo- hydrates

Minerals

Vitamins

Fiber

Water Protein

Fats

Food Pyramid

Balanced Diet

A habit of eating which supplies all the

essential nutrients in the correct proportion for the needs of the body.

This is not static and will change in accordance with the circumstances of the individual

The Digestive System

The functions carried out by the

digestive system include:

• INGESTION • DIGESTION • ABSORPTION • ASSIMILATION • EGESTION

Ingestion – The Mouth

• Ingestion takes place in the mouth.

• The food is physically broken down by the teeth

• The enzyme Salivary Amylase begins the chemical digestion of Starch.

• Enzymes are a class of protein which act as a

catalyst to speed up various chemical and

biochemical reactions without being changed themselves.

Ingestion – The Oesophagus

Food moves from the mouth to the stomach via the oesophagus by a wave like motion

called PERISTALSIS.

Mechanical Digestion – The physical break down of food into smaller units

Peristalsis – Muscle Action

Mastication – Chewing

Chemical Digestion – The chemical break down of food using enzymes

Enzymes – Chemical Catalysts

Digestion - The Stomach

The stomach is a muscular storage tank.

It can hold approximately 4 litres of food.

Food stays in the stomach approximately 4-6 hrs

Peristalsis mixes the food with gastric juice to form a watery paste called CHYME.

Gastric Juice

HCl inactivates salivary

amylase and kills most bacteria.

PEPSIN begins the digestion of

protein into PEPTIDES.

RENNIN (only in infants)

curdles milk.

Mucus helps protect the lining of the

stomach from the HCl.

Produced by glands in the stomach wall gastric juice contains:

The Liver

• Produces bile which is stored in the gall bladder and aids in the fat digestion

• Removes toxins from the blood.

• Helps to generate body heat. • Stores essential vitamins such

as Vitamin K (used to aid blood clotting)

• Converts stored glycogen into glucose for energy

The liver is a very important organ

The Pancreas

The pancreas has two functions: The secretion of digestive enzymes which breakdown protein, fats and carbohydrates. The production of insulin which balances blood sugar levels.

Absorption - The small Intestine

• The main function is to complete digestion and enable the absorption of nutrients into the blood and lymph systems for assimilation on a cellular level.

• It is approximately 7-9m in length.

• Food remains here for approximately 2-4hrs.

The Small lntestine – The villi

Absorption - The Large Intestine

• The main function is to re-absorb water into the body and eliminate waste products (faeces).

• The large intestine is approximately 1.5m in length.

• Undigested food (faeces) remains here for approximately 24-48 hours

• Faeces contain – undigested food (cellulose) and dead

bacteria

– mucus and dead cells from the gut wall.

– excess bile and other secretions

Flatulence

• The removal of excess gases from the digestive tract.

• The odour is produced by bacteria feeding on protein (Indole/Skatole) which produces hydrogen sulphide.