The Digestive System

The Digestive System

The next body system we will look at is the Digestive system.

The diagram below shows the main features of the Digestive system:-

Digestion is the breakdown of large, insoluble molecules of food into small, soluble ones which can be absorbed by the body.

After we swallow, our food passes through these organs in turn:

  1. Oesophagus - A muscular tube connecting the Mouth to the Stomach.

  2. Stomach - In the Stomach, food is mixed with Stomach acid, killing microorganisms and starting the breakdown process.

  3. Small Intestine - Digested food is absorbed into the bloodstream in the Small Intestine.

  4. Large Intestine - Water is absorbed into the bloodstream in the Large Intestine. Any undigested food passes out of the anus.

The videos below show an overview of the Digestive System (one in animation and one in endoc:-


In order to survive and grow, Humans require a range of Nutrients. These nutrients must also be in the right 'balance' for a healthy body.

The Nutrients are split up into 5 food groups (+Water):-

  1. Carbohydrates

  2. Protein

  3. Fats

  4. Vitamins & Minerals

  5. Fibre


Found in:

  • Dairy - Milk, yogurt, and ice cream.

  • Fruit - Whole fruit and fruit juice.

  • Grains - Bread, rice, crackers, and cereal.

  • Legumes - Beans and peas.

  • Starchy Vegetables - Corn and Potatoes.

  • Sugary Sweets - Chocolate, drinks, biscuits etc.


Found in:

  • Lean meats – beef, lamb, veal, pork.

  • Poultry – chicken, turkey, duck, goose.

  • Fish and seafood – fish, prawns, crab, lobster, mussels, oysters, scallops, clams.

  • Eggs.

  • Dairy products – milk, yoghurt (especially Greek yoghurt), cheese (especially cottage cheese)


Found in:

  • Red meat (beef, lamb, pork)

  • Chicken skin.

  • Whole-fat dairy products (milk, cream, cheese)

  • Butter.

  • Cream.

  • Oils such as olive, coconut and palm oil.

Vitamins & Minerals

Found in mainly:

  • Fruit and vegetables.

  • Nuts.

Also found in:

  • Meats.

  • Cereals.

  • Oily Fish.

  • Milk and dairy foods.


Found in:

  • Wholegrain breakfast cereals, wholewheat pasta, wholegrain bread and oats, barley and rye.

  • Fruit such as berries, pears, melon and oranges.

  • Vegetables such as broccoli, carrots and sweetcorn.

  • Peas, beans and pulses.

  • Nuts and seeds.

  • Potatoes with skin.

Healthy Eating

A healthy diet must include not just the nutrients listed above, but the right quantities of these nutrients.

Eating a healthy, well balanced and varied diet is important for good health and well being and can help you manage your weight.

It can also help reduce the risk of developing health conditions such as heart disease, high blood pressure, diabetes, strokes and certain cancers.

The Eatwell guide below shows what proportion of each Nutrient group should make up a healthy diet:-

Click the link below to view a range of meal ideas for eating a well balanced diet:-


As a Dietician, you would explain to people which foods are better for their physical and mental health. You’d motivate them to change their eating habits and lifestyles. You’d assess and treat people with a wide range of medical problems.

You could work for the National Health Service (NHS), based at a hospital or in the community.

Your role could be to develop new products and calculate their nutritional value. You might create scientifically accurate promotional literature about a food product or represent a manufacturer's point of view in the media.


Working as a Dietician

A Career as a Dietician

Salary: from £21,000 to £36,000 per year

Dietician working hours: 37.5 hours a week, which could include weekends. Part-time work may also be available.

Typical entry requirements: You would need an honours degree in dietetics or human nutrition and dietetics (SCQF level 10) which is approved by the Health and Care Professions Council (HCPC).

Or a degree in a biological subject, such as biochemistry and human physiology, (SCQF 9/10) and then a postgraduate qualification in dietetics (SCQF level 11).

Entry to a degree (SCQF level 9/10) usually requires National 5 qualifications and a minimum of three Highers including two science subjects, or a relevant HNC/HND.

To enter a postgraduate MSc in dietetics (SCQF level 11) you will require a relevant honours degree.

Skills required:

  • Supporting

  • Verbal communication

  • Creative

  • Researching

  • Empathising

  • Developing a plan

  • Taking initiative

  • Time management

  • Coaching

  • Motivating others

The Oesophagus

The Oesophagus (American sp. : Esophagus) is a long muscular tube that connects the Mouth to the Stomach. The muscles that make up its walls move food towards the Stomach by Peristalsis.

The video below shows the process of Peristalsis:-

The Stomach

The diagram shows the main parts of the stomach:-


  1. Oesophagus - Muscular Tube which connects the Stomach to the Mouth.

  2. Stomach - Large Muscular chamber containing Stomach Acid.

  3. Diaphragm - Flat Muscle that assists with breathing.

  4. Esophageal Sphincter - Valve which opens to allow Food to enter the Stomach.

  5. Pylorus - The Pyloric Valve opens to allow Food to enter the Small Intestine.

Stomach Acid

Hydrochloric Acid is found naturally within our stomachs. This Acid helps with the breakdown of food into smaller soluble parts before they are passed into the small intestine. The Acid also assists in preventing infections, by killing most microorganisms within the food. The stomach is protected from this Acid by a layer of mucus.

When the stomach is working normally, the two valves work together to keep the Acid within the stomach. If the esophageal sphincter does not close properly, however, it can allow stomach Acid to enter the esophagus, causing a burning sensation. This is normally known as Acid indigestion, or Acid reflux.

We can treat the effects of indigestion easily at home by taking a indigestion remedy such as Milk of Magnesia or Gaviscon. These indigestion remedies are bases.

When the indigestion tablet is taken, it releases a base into the stomach Acid, neutralising the Acid. This reduces the effect of the Acid indigestion.

The Small Intestine

The small intestine is between 2-4 metres long and is the region where food is digested and absorbed.

Enzymes break down nutrients into small, soluble molecules that can be absorbed. For example, amylase causes the breakdown of starch into simple sugars. These enzymes are produced and stored in three organs, the Liver, the Pancreas and the Gall Bladder:-

Absorption of Nutrients in the Small Intestine

Absorption is the movement of digested food molecules through the wall of the intestine into the blood. Absorption across a surface happens quickly and efficiently if:

  1. The surface is thin.

  2. Its area is large.

Some nutrients such as simple sugars, water, vitamins and minerals are small enough to pass through the walls of the Small Intestine and enter the Bloodstream. Larger molecules, such as complex Carbohydrates, Fats and Proteins must be broken down first, before they can pass through the walls:-

1.Large insoluble Starch

2.Broken down by Enzymes

3.absorption of soluble sugars

The diagrams below show which enzymes break down which nutrients:-





The inner wall of the small intestine is adapted so that substances pass across it quickly and efficiently as:-

  1. Its walls are very thin (only one cell thick).

  2. It has many tiny Villi to giving a huge surface area.

The villi are structures that stick out from the walls, increasing the surface area. They also contain a lot of blood capillaries to carry away the absorbed food molecules.

The video below shows the Villi within the Small Intestine as part of a Colonoscopy:-