The digestive system carries out digestion. Digestion is the process where by food is broken down into nutrients that the body
Look at the following pictures.
Describe each picture above briefly.
Predict what you are going to learn.
12.1: Functions of the digestive system
The major functions of the digestive system are digestion of food and absorption of digested food.
Activity 12.1: identify location of the digestive system
What to do:
(i) Touch your body to show how food moves along the digestive system.
(ii) Describe what happens to food from the time you take it in your mouth to the time it comes out as faeces.
(iii) Look at the wall chart in your class showing parts of the digestive system. Draw it in your notebook.
Digestion is the process by which food is broken down into smaller particles.
Absorption refers to the uptake of digested food into the body.
12.2: Parts and functions of the digestive system
The digestive system consists of the alimentary canal and digestive glands.
Activity 12.2: naming parts of the digestive system
(i) Draw the following picture in your notebook.
(ii) Use your XO laptop or books in the library to fill in the blanks on the diagram above.
(iii) Describe how food passes through the body to the anus.
(iv) Indicate on the picture where the salivary and gastric glands are located.
The alimentary canal
The alimentary canal is a tube-like passage, which runs from the mouth to the anus. Parts of the alimentary canal include, the mouth, oesophagus (gullet), stomach small intestine, large intestine
and the anus.
Digestive glands Digestive glands are glands that produce substances that are useful in the digestion process.
These glands include the salivary glands, gastric glands, the liver, gall bladder and the pancreas.
12.3: Stages of digestion
Activity 12.3: The digestion process
What to do:
(i) Observe the digestive system that you drew in your notebook.
(ii) Label the parts that you had not labelled.
(iii) Research the process of digestion.
(iv) Write short notes about digestion in your notebook.
Digestion takes places in stages. These are: ingestion, digestion, absorption and ejection.
Ingestion Ingestion refers to the intake of food in the mouth. We should ingest clean food and digestible food.
It is wrong to ingest non food materials like soil, metals and plastics.
(a) digestion in the mouth
Ask your friend to open his or her mouth. What do you see?
What are the functions of all the parts that you have seen in the mouth? The ingested food is chewed using teeth and mixed with saliva from salivary glands. Saliva is a digestive
juice that moistens the food.
The tongue rolls the food into small rounded balls called boluses. Saliva also contains digestive substances (enzymes) that break down starch into a simpler form.
The food boluses are then pushed through the oesophagus.
The oesophagus is a tube that connects the mouth to the stomach.
• Food moves through the oesophagus in continuous waves of contraction and relaxation.
These waves are called peristalsis.
• Digestion starts in the mouth and ends in the small intestines.
(b) Digestion in the stomach
From the oesophagus the food enters the stomach.
The lining of the stomach produces digestive enzymes, which help in the digestion of proteins.
The stomach lining also produces hydrochloric acid. This acid kills germs that may be present in the food.
The stomach serves as a temporary store for food. From time to time, food is released into the small
(c) Digestion in the small intestine The small intestine is divided into two parts. The upper part is known as the duodenum. The lower part is
known as the ileum.
Most digestion in the small intestine takes place in the duodenum. In the duodenum, bile and pancreatic
juices mix with food.
Bile is produced by the liver and stored in the gall bladder. Pancreatic juices help in further digestion of food.
The ileum is involved in the absorption of digested food. After digestion in the ileum, fats, proteins and carbohydrates are ready for absorption.
Absorption is also known as assimilation. The digested food is absorbed into the blood stream through the walls of the ileum.
Elimination The indigestible materials, unabsorbed food and water enter the large intestines. The large intestines
consists of the colon and the rectum.
In the colon, most of the water is absorbed into the blood stream.
The remaining food waste is passed down to the rectum. The rectum stores undigested food before passing through the anus as faeces.
The removal of the undigested food is known as egestion.
• Water and mineral salts are absorbed in the large intestines.
• Vitamins and glucose are not digested. They are absorbed directly into the blood.
12.4: Hygiene of digestion
Activity 12.4: identifying the hygiene of digestion
Match the hygiene of digestions practices shown below to their pictures.
Name 3 other practices that help to maintain the hygiene of digestion.
Project 1 Maintaining the hygiene of digestion
• Use your XO browser or books in the library to research ways to maintain a healthy digestive system. • Design a poster that encourages hygiene of the digestive system. Hang it at the back of your class. • An example of a poster is shown below:
Chewing food properly = Easy swallowing + healthy body Hurried eating = Choking + Poor digestion + Poor health Make your DS happy, chew slowly !
12.5: Identification of a balanced diet
A balanced diet contains energy giving food (carbohydrates), body building food (proteins) and protective food (vitamins).
Activity 12.5: identification of food groups
(i) The following table shows a variety of foods.
(ii) Put the foods into a group of 3 to create balanced diets.
Components of a balanced diet
Activity 12.6: Collecting various groups of food to identify them
What to do:
1. Collect the groups of food over the weekend and bring them to school.
2. Place the foods into their correct food groups.
A balanced diet is a meal that contains all the nutrients needed by the body in the right quantities.
A meal is food eaten during any occasion in the day.
What food groups should a balanced diet contain?
1. Carbohydrates Carbohydrates provide the body with energy to work. These foods also keep the body strong and warm.
Proteins are necessary for the growth and repair of body tissues.
3. vitamins These foods protect the body against diseases.
Fresh fruits and vegetables are the main sources of vitamins. There are many types of vitamins. Examples are vitamins A, B, C, D, E and K.
Cashew nuts and ground nuts are both energy giving and body building foods.
Minerals are present in many foods. They are required by the body in small quantities. Examples of minerals are calcium, phosphorus, iron, iodine, potassium, sodium and zinc. The following table shows some minerals, their uses in the body and their sources.
5. Lipids (fats and oils) Fats and oils provide the body with energy. They also make the skin shiny and healthy.
Fats and oils are eaten together with other foods. Fats exist in solid form while oils are in liquid form.
Oils are mainly obtained from plants such as avocado, sunflower, corn, sesame, coconut and ground nuts.
Some animals like fish produce oil (cod liver oil). Milk products like butter, ghee and cheese also contain oils.
The body needs water in order to stay healthy. Water performs the following functions in the body:
• Cools down the body when the weather is hot.
• Helps in digestion and transportation of food in the body.
Name other 2 functions of water.
Practice Activity 12.1
Activity 12.7: Preparing a balanced diet
Read the following story.
Paulo is a P5 pupil in Munini Primary School. On Friday last week, they held a sports day at his school.
He ran in a 400 metre race where he came first. His friends knew he would win because he is a healthy boy.
Paulo usually brings a packed lunch that contains all the three food groups.
On Monday and Thursday he brings rice, meat stew and oranges. Other days he brings posho or rice,
vegetables salad and bean stew or groundnut sauce.
Paulo’s parents work at a factory in Nyabisindu. His sister is ten months old.
Paulo’s parents come home late every Tuesday and Friday. On such days, Paulo helps their house help
to prepare dinner.
Paulo knows how to prepare posho, steamed rice, bean stew, vegetable salad and groundnut sauce.
He always prepares balanced meals for his family. He sometimes prepares fresh mango juice for the family.
But when he is tired he brings them clean boiled water.
(i) Why is it important for you to know how to prepare balanced meals?
Relate your answer to Paulo’s situation. (ii) What meals does Paulo prepare? List them in your notebook.
(iii) Paulo feeds on a balanced diet. What benefits does he get?
(iv) Write down the possible food-group menu for Paulo’s family from Monday to Friday.
(v) Make a one-week dinner menu for your family. Ensure that all the meals are balanced.
Project 2: Preparing a balanced diet
(i) Offer to cook a balanced meal at home.
(ii) Use guidance from the tables that you made in Activity 12.5 and Activity 12.6.
(iii) Take caution when using fire. You can burn yourself.
(iv) Practise good food hygiene when serving and eating your food.
12.6: Nutrition deficiency diseases
Activity 12.8: observe and discuss about children suffering from deficiency diseases
What to do:
(i) Observe wall charts and pictures showing children suffering from various deficiency diseases.
(ii) Research the disease that each child is suffering from.
Give symptoms and identify the deficiency disease e.g. the child is thin and bonny; marasmus.
(iii) Write in your notebook ways to prevent each deficiency diseases identified.
(iv) Give your notes to the teacher for marking.
Nutritional deficiency diseases are diseases caused by lack of some food nutrients in the body.
Nutritional deficiency diseases include:
Kwashiorkor is caused by lack of proteins in the diet. It mainly affects children under five years of age. It usually occurs after stopping breastfeeding.
Prevention of Kwashiorkor
1. The child should be breast fed up to 2 or 3 years. 2. Weaning foods should constitute a balanced diet with lots of proteins. 3. Children should be provided with food rich in proteins.
Marasmus Marasmus is caused by lack of enough food. Marasmus mainly affects children but it can also affect adults.
It occurs during severe famine that leads to starvation. The affected person becomes thin and weak.
Prevention of marasmus
1. Give the child or patient enough of all the food nutrients in adequate amounts.
2. During severe drought or famine, relief food should be provided to children to prevent starvation.
Rickets is caused by lack of vitamin D and calcium. Prevention of rickets
1. Children should be fed on foods rich in calcium, vitamin D and phosphorous.
2. Expose babies to morning and evening sunlight. Sunlight helps in formation of vitamin D by the skin.
Goitre is caused by lack of iodine in the diet. The deficiency is shown by visible swelling at the base of the neck. The affected person experiences difficulty in swallowing and breathing.
Prevention of goitre
1. It can be prevented by eating iodine-rich foods. Such foods include sea fish, crabs, prawns and lobsters. 2. People should use iodized salt in the diet.
Anaemia is caused by lack of adequate iron in the diet.
When one has anaemia his or her blood is unable to supply enough oxygen to the tissues.
This leads to exhaustion. Anaemia can occur in both young children and adults. It occurs commonly during pregnancy and in adolescent girls. People suffering from malaria may become anaemic.
Why do you think anaemia is common in pregnant women, adolescents and malaria patients?
Some signs and symptoms of anaemia 1. Pale skin (jaundice). The eyes, gums, palms and fingernails appear pale. 2. Loss of appetite and general body weakness. One feels very tired even after doing a small task.
3. Shortness of breath and dizziness.
Prevention of anaemia 1. Eating food rich in iron. Such foods include liver, eggs and green leafy vegetables like spinach and kales. 2. Girls and women should take foods rich in iron to replace the iron lost during their monthly period. 3. Visit a nearby health facility for check-up if you have the signs and symptoms mentioned.
Revision Activity 12
1. Explain briefly the meaning of the following:
2. Draw the parts of the digestive system.
3. Make correct sentences using the following words:
(a) Alimentary canal
(b) G all bladder
4. Name glands that produce the following juices:
(a) Gastric juice
5. Describe briefly five ways of maintaining hygiene of the digestive system.
6. Name the groups of food shown in the following pictures.
7. (a) What deficiency disease is caused by lack of proteins in the diet?
(b) Anaemia is caused by lack of adequate ................. in the diet.
8. (a) What is the following child suffering from?
(b) How can the disease be prevented?
(c) Name 4 foods that we should feed on in order to prevent goitre.
9. Show in a table 3 meals that constitute a balanced diet.
10. Why is it important for a P5 learner to know how to prepare a simple meal?
11. You have been provided with peas, cabbages and potatoes.
(a) Prepare a balanced meal from these foods. (b) Observe necessary hygiene practices during preparation and serving of the food.
1. Read the following words in pairs.
• C arbohydrates
• Protein • Egestion
• Alimentary canal
• Gall bladder
2. Spell 3 words while your friend writes them in his or her notebook. Let your friend also spell 3 other words
as you write them in your notebook.
3. Discuss with your friend the meaning of any 3 words in the word list. Refer to notes in your textbook.