User:Antuma/Digestion and Absorption

Introduction
In this unit, you will learn about the digestion of food. Digestion is the process by which food is broken down into smaller particles. This makes the food more soluble. For food to pass into the blood stream and to cells where it is needed, it has to be broken down into smaller more soluble particles. The food we are referring to in this case are all the classes of food we dealt with in Unit 2.

Do you remember all the classes of food we learnt about in Unit 2?

If you dont, then please go back to Unit 2, which deals with these foods .This is because are going to deal with them in detail so it’s better if you have an understanding of what they are and also what they are composed of.

There are two types of digestion. These are physical digestion and chemical digestion. Physical digestion results in a change in the physical appearance of the food. The food is just crushed into smaller particles. This is done by the teeth. We are also going to learn about the different types of teeth, their structure and how they help in the breakdown of food.

Chemical digestion results in a complete change in the chemical constitution  or chemical make up of the food. This is achieved by chemicals called enzymes We are going to find out about enzymes, their nature and how they help in the chemical breakdown of food. After we have learned about these two different processes of breaking down of food, we are going to look at the alimentary canal, that is its structure and functions.

Unit Contents
This unit consists of 4 lessons as follows:


 * Lesson 1:	Teeth and the breakdown of food


 * Lesson 2:	Enzymes and the breakdown of food


 * Lesson 3:	The alimentary canal


 * Lesson 4:	Absorption and assimilation}}

=Lesson 1=

Introduction
Teeth help with the digestion of food. Digestion is the breakdown of food into smaller particles. The type of digestion that is done by the teeth is physical digestion.

Can you remember what physical digestion is?

Well, if you cannot, I will help you out. This is the breakdown of food into smaller particles, which results in a change in the physical or outward appearance of the food. In physical digestion the food is crushed into smaller particles.

In this lesson, we are going to look at how this takes place in humans. Since the teeth are the main structures for physical digestion, we are also going to look at their types, structure, possible defects and maintenance inside the mouth.

Lesson Contents List
1.0 Types of teeth 2.0 Structure of the tooth 3.0 Digestion of food 4.0 Dental diseases

5.0 Summary

6.0 Self-ssessment Exercise 1

1.0	Types of Teeth
One of the characteristics of mammals is that they have different types of teeth. You must have seen the teeth of different mammals at one time. The mammals we will consider in this discussion will be a human being, a goat and a dog.

What can you say about their sets of teeth? Are they similar?

If you cannot answer this question, don’t worry.

We are all guilty of not observing certain things that we have come into contact with in most of our lives. So on the basis of this, I would like you to do this activity. Feed back to this activity can be found below the space left out for your answer.

If you have done the activity, you would have realised that different mammals have different sets of teeth. The front teeth are structurally different from those on the sides and those of the the back of the mouth.

Can you think of the reason why it is like that? Well, it is because mammals have different diets and as a result, their teeth  are adopted to suit their particular diet.

Let us find out more about our teeth, that is, human teeth. Observe your teeth again using a mirror. Count the number of teeth you have.

How many are they?

Depending on your age, you should have counted 28, if you are less than 18 years of age and 32 if you are older. A person grows his/her first set of teeth when they are about 4 months old. This set is called milk teeth and they are temporary. At a certain age (say around 5 to 6 years of age ) they fall off to be gradually replaced by permanent ones.

We all have gone through this stage. I remember when my milk teeth fell off when I was a child. I used to throw them on top of the roof so that a bird called a kite (Mankgodi ) could collect them and give me a new set. Mind you, this was just a myth that was common in our Tswana culture. Nobody gets their teeth from a bird. On average, by the age of 14 years, twenty eight of the permanent teeth should appear in humans. Four more teeth called “wisdom” teeth are added in the late teens or early twenties.

How many different shapes of teeth do you have ?

I will help you identify them. We will start with the ones on the front of your mouth. They are sharp but do not have pointed ends. They are called the incisors.

Figure 1: Incisors

These are used for holding  and cutting or biting food.

The next ones are conical and have pointed ends. These ones are called the canines.

Figure 2: Canines

They are used for tearing and piercing meat. They are more developed in meat eating animals.

At the side of each jaw are slightly flat teeth called premolars. They are longer than canines and have one or two blunt points. They are used for crushing and grinding food.

Figure 3: Premolars

At the far end of each jaw are teeth, which are larger than all the types we have seen. They are called the molars.

Figure 4: Molars

Just like the premolars, molars are used to crush and grind food. Student, now you should be able to remember the different types of teeth and their jobs in our body. The following table summarises the types of teeth ,their numbers and functions in digestion.

Table 1: The teeth and their functions

Type of teeth	Description			Function			     Number

Incisors 		long, thin, sharpedge, 		cutting, gnawing one root 				holding, biting food. 8	Canines		conical, pointed 			tearing, piercing			 4 long root

Pre-molars       large surface 	 grinding and chewing            8 area, two roots

Molars              large surface area 	grinding and chewing            12 three roots Let’s now look at the structure of the tooth in detail.

2.0	Structure of the Tooth Study the next diagram carefully. After studying the diagram, you should move on with the text. As you go through the text, you will be expected to continuously go back to figure 5 and write the  letters again the words. Part A in the diagram has been done for you.

Figure 5: Structure of the tooth.

When you look at the outside appearance of any tooth you will notice that it has a white cover. This is the enamel. It can be seen appearing on top of the gum. Label A this part in your diagram. It covers the exposed part of the tooth and makes a hard biting surface. It is a non-living substance containing calcium. It is very hard and resistant to decay and wear.

The next one, labeled B, is a thick layer of hard bone-like material. It is softer than the enamel. It is called the dentine. The dentine is a living tissue, which contains cells. Now write the word dentine next to the letter B on figure 5.

The next one is a soft connective tissue, Part C, in the centre of the tooth. This is covered by the dentine and it is called the pulp cavity. It contains blood vessels, nerve fibres and pain-sensory receptors. The blood vessels transport materials to and from the cells in the tissue. Now label the part. Don’t you forget that you have to do that for all the parts marked with alphabets in the diagram.

Part D is a bone like substance called the cement. It attaches the tooth on to the jaw bone.

Part E is the visible part of the tooth. It covers the enamel, some part of the dentine and the pulp cavity. It is called the crown. This is the part of the tooth you see when somebody smiles.

F is neck of the tooth. It is found in between the crown and the root of the tooth.

The root –G, is the bottom part of the tooth. It includes the gum and parts of the jaw bone.

Now, let us summarise the parts of the tooth and their descriptions. Once again the alphabets have been placed next to the words. You should check in your diagram to see whether you have slotted the right letters next to the words. Table 2:	Parts of the tooth

Part of tooth				Description

Enamel		A		White material coverage crown.

Dentine		B		Thick layer of hard bone - like material.

Pulp cavity 	C		Centre of tooth, containing blood capillaries and nerves. Cement		D		Bone - like material.

Crown		E		Visible past outside the gum.

Neck		F		At the junction of the tooth and the gum

Root		G		 Part embedded in jaw bone.

We have described the tooth. Let us now look at its overall function. The function of the teeth is to physically digest food.

3.0 Digestion of Food Student, now we are going to find out how our teeth help in the process of physical digestion. The process of physical digestion begins in the mouth where the food is first chewed and crushed by the teeth and then  mixed with saliva. We all chew food before swallowing it. Even babies who have not yet developed teeth do attempt to chew food.

Have you ever wondered why we chew food? Why can’t we just swallow it?

Well, there are two reason why we do that. Firstly, chewing breaks down the food into small pieces, which can be swallowed.

If you bite a chunk of meat and then swallow it, what will happen ? Obviously you will be choked. This is because you have not chewed the food or broken it down into smaller particles which can easily pass through the gullet.

Secondly it also increases the surface area for the enzymes to work on the food. Enzymes help in chemical digestion. We will deal with chemical digestion later on in the course.

Our teeth are very important to our well being. It is therefore very important that we take proper care of them. This is called oral hygiene. If we don’t take proper care of the teeth, they could develop diseases which are always referred to as dental diseases.

4.0	Dental Diseases Illustration of tooth decay

Figure 6: Tooth decay

Brushing your teeth –an illustration The next diagram is a pictorial representation of the best and efficient way to brush your teeth.

Figure 7: Brushing teeth

These are procedures for proper brushing	. •	Place the tufts of the brush pointing to the junction of the teeth and gums 			at an angle of about 45 degrees to the teeth •	Vibrate the brush in a circular motion gently but firmly round the necks 			of the teeth and between them •	Brush the back of the teeth •	Brush the biting surfaces with a backward and forward rubbing movement. Note It is more important to clean everywhere or the teeth and mouth thoroughly than to worry about a particular method. This above method works for most people.

Activity 2 You should only do this activity after listening to the audio tape.

1. Name two types of dental diseases.

2. List four things you should do to take care of your teeth.

3. Explain the part played by bacteria in tooth decay.

4.What is the other name for tooth decay?

You should have answered these questions easily after listening to the tape. If you could not, go over the tape again and then do the Activity. Then compare your answers with the ones given below.

1.	Gum disease and tooth decay.

2.	•	brush teeth regularly •	don’t eat or drink too many sweet things •	use at tooth paste which contains fluoride •	go to a dentist for regular checkups.

3.	Bacteria feed on sugary food left on your teeth. They produce acids which 		then dissolve the enamel on your teeth. More bacteria enter the pulp cavity 		and the tooth decays.

4. 	Dental caries.

This brings us to the end of Lesson 1. Let’s us now briefly look at what we have been learning.

5.0	Summary In this lesson, we learnt about the teeth. Teeth help in the digestion of food. This is by breaking down food into smaller pieces. There are four different types of teeth. These have different functions. For example: we use our incisors to grip and cut the food we eat, canines pierce and tear meat whilst the premolars and molars crush and grind the food that we eat. Despite the fact that we have four different types of teeth, they all have the same internal parts, that is, in terms of structure. The parts are the enamel, dentine, pulp cavity, cement, crown, neck and the root. The root attaches the tooth, through the cement, into the jaw.

We also learnt that if we dont practise oral hygiene, we could develop some dental disease. These include dental decay and gum disease. It is therefore necessary to practice oral hygiene. This is by eating the right type of food, that is, we should avoid sweet  types of foods Another way is by cleaning our teeth everyday, especially after having a meal.

Thank you for going through this lesson with me. Can you now do the next exercise.

6.0	Self-Assessment Exercise 1 1.	Name the four types of teeth in humans. [4 marks]

2.	How many teeth are there in an adult? [1 mark]

3.	The hardest part of a human tooth is the? and 97% of it is the mineral? [2 marks]

4.	The words “tearing” and “chewing” have been used several times in this lesson. Say exactly what you think each word means. Tearing:												[4 marks]

Chewing: 											        [2 marks]

5.	What is dental decay? [2 marks]

6.	What causes toothache? [2 marks]

7.	Write any five preventive measures of tooth decay. [5marks]

TOTAL = [22 MARKS]