11. human digestive system - e-learning

Human Digestive System

Lesson Objectives• At the end of this topic, you should be able to:

o explain the importance of the digestive systemo identify the main parts of a digestive system and how they work

together to perform a functiono describe how a digestive system helps in digestion of food and

the part played by enzymes in digestion (Only classes of enzymes such as amylase, protease and lipase are needed. Specific names of enzymes not required.)

o infer that the end products of digestion are used for cellular processes like respiration, growth and tissue repair

o show an awareness of the importance of hygiene habits and food handling practices in preventing food-borne diseases

Hungry?

Section 1: Importance of Digestive System

Why We Need To Eat?• We need food to:

o provide energy for our daily activities like walking

o grow new cells and tissueso repair worn-out or damaged tissueso maintain a healthy bodyo produce heat to maintain our body

temperature

What is in the Food We Eat?

• Food in our diet contains nutrients that are essential for our health

• The types of nutrients can be found in the food label on a food package.

• The food label lists the nutrient content of the food.

Food Labels

Main types of nutrients

• The three main types of nutrients: carbohydrates, proteins and fats.


• Carbohydrateso It is a source of energy that the body uses

first.

o It consists of the elements carbon, hydrogen and oxygen.

o It is commonly found in food containing starch and sugars.

Main types of nutrients• Carbohydrates

o Starch can be found in rice, bread, noodles and potatoes.

o Sugars such as sucrose, glucose and maltose are found in fruits like bananas and apples

o Cellulose is another type of carbohydrates, which can be found in plants. This cannot be digested by the body and it forms part of the dietary fibre (roughage) that is passed out from the body as faeces.

• Excessive intake of carbohydrates will be converted into fats and are stored in the body.


• Proteinso Proteins are very large molecules that are

made up of several small molecules called amino acids.

o Proteins are needed to:• form new cells for body growth • repair of worn-out tissues.• make more complex proteins such as enzymes that

carry essential functions in the body. o Proteins can be found in meat, fish and eggs.


• Proteinso It can also supply

energy when the body has used up all the carbohydrates and stored fats.


• Fatso Fats are large insoluble molecules that are

made up of glycerol and fatty acids.o It is a source of energy that is stored in the

body.• Fats release twice as much energy as do

carbohydrates.


• Fatso Fats are also stored under our skin to

insulate our body and prevent heat loss.o Fats are usually solid at room temperature,

melting to liquid at higher temperatures to form oil.

o Fats can be found in food like butter and cheese.

Fats are solids and

oils are liquids.

Definition of Digestion

• The breakdown of large insoluble food molecules into small soluble molecules to be absorbed into the body cells.

Why Must Food be Digested?• Remember the cell membrane?

It is a partially permeable membrane.

• We need digestion because the cell membrane has small openings (or pores) that allow small molecules to enter, but not large molecules.

• Nutrients like glucose and amino acids are such small molecules that can pass through the cell membranes easily and enter the bloodstream.

Nutrients like starch, proteins and fats, are large, complex molecules. They cannot pass through the cell membrane.

Nutrients like glucose and amino acids, are small, soluble molecules. They can pass through the cell membrane.

Checkpoint Time

a) You have just eaten a bowl of chicken noodles in soup for lunch. State the nutrients present in your meal.

Checkpoint Time

b) Suggest what should be added to the meal to make it a more balanced diet. Why ?

Section 2: Human Digestive System

Types of Digestion

• There are two types of digestion.• Physical digestion is the breakdown of food into

smaller pieces without any change to the molecules of the food.

• Chemical digestion is the breakdown of large food molecules into smaller molecules by the action of enzymes.

Physical Digestion

• Physical digestion occurs in the:o mouth, where the teeth chew the food into

smaller pieces. o stomach, where it churns to break down

food into smaller pieces.

To churn means to shake with

violence or continued motion

Physical Digestion

• Smaller pieces of food have a larger total surface area for enzymes to act on.

Physical Breakdown

PHYSICAL

Chemical DigestionOur body is able to carry out chemical

digestion by producing complex proteins called enzymes.

Chemical digestion is the breakdown of large food molecules into smaller molecules by the action of enzymes.

What are Enzymes?• Enzymes are complex proteins that speed up

the rate of chemical reactions, while remaining unchanged at the end of chemical reactions.

• Enzymes act like chemical ‘scissors’.• They break down large molecules into small

molecules to speed up the process of digestion.• The enzymes involved in digestion are called

digestive enzymes.

“Lock and key” hypothesis

• Each type of enzyme is specific. It can only bind and help to digest one type of food.

active sites

Enzyme molecule

Food molecule

Enzyme-food complex

Enzyme free to take part in next reaction.

Two products leave the enzyme.

Product X

Product Y

Types of digestive enzymes

• For example, enzymes that break down proteins cannot break down starch or fats.

Class of enzyme

Acts on Digested product(s)

Amylase Starch Maltose (a complex sugar)Maltase Maltose Glucose (simple sugar)Protease Proteins Amino acids

Lipase Fats Fatty acids and glycerol

Enzymes in Detergents?

• Special enzymes are found in detergents.

• Why do you think this is so?o To help speed up the digestion of food stains

that usually contains carbohydrates, proteins and fats which can then be washed out of the clothes.

Actions of Digestive Enzymes •Glucose, the end product of carbohydrate digestion, is used for cellular respiration to release energy.

Starch Maltose Glucose

Amylase Maltase

Actions of Digestive Enzymes • Amino acids, the end products of protein

digestion, are used for growth and repair of tissues, new cells and antibodies formation.

Proteins Amino acids

Protease

Actions of Digestive Enzymes • Fatty acids & glycerol, the end products of fat digestion,

are used for cellular respiration to release energy and for forming cell membrane.

Fats Glycerol

Lipase

Fatty acids+

The Human Digestive System• Food is digested in our body through the

digestive system.

• The digestive system is made up a long tube called the gut (or alimentary canal), which starts at the mouth and ends at the anus.

• The gut is about nine metres long. The wall of the gut is muscular, which allows food to move along its length.

The Human Digestive System• Other accessory organs are attached to

the tube, which supplies enzymes for digestion of nutrients.

• These organs are also known as glands, e.g. the salivary glands, liver and pancreas.

The Human Digestive System

salivary glandmouth cavity

oesophagus

stomach

salivary glands

pancreas

colon

rectumanus

large intestine

liver

gall bladder

small intestine

1st Stop: Mouth

1st Stop: Mouth

• Both physical and chemical digestions take place in the mouth.

• Physical digestion:o Food is chewed in the mouth with the teeth. o Chewing helps to cut and grind the food into

smaller pieces.o This increases the surface area and allows

the food to be digested faster.

1st Stop: Mouth• Chemical digestion:

o As food is chewed, salivary glands in the mouth secrete saliva.

o Saliva serves two purposes:• Wets the food, so that it is easier to swallow.• Contains enzymes (amylase) to break down starch into

maltose. o Digestion of starch:

• Starch Maltose

• There is no digestion of proteins and fats in the mouth.

amylase

1st Stop: Mouth• While chewing food, the tongue rolls the food

into small balls which are pushed to the back of the mouth and squeezed into the oesophagus. This is known as swallowing.

• Food stays in the mouth for about 20 seconds.

1st Stop: Mouth

2nd Stop: Oesophagus

2nd Stop: Oesophagus• The oesophagus is a long muscular tube leading to the

stomach.• Food moves slowly down to the stomach by process of

peristalsis (contracting and relaxing of the muscles).• This is how food moves along the rest of the gut too.

• No digestion occurs in the oesophagus. However, the digestion of starch by amylase continues as as saliva is mixed with food.

• Food stays in the oesophagus for about 10 seconds.

2nd Stop: Oesophagus

Peristalsis is the involuntary wave-like movement that pushes the food into the stomach.

3rd Stop: Stomach

3rd Stop: Stomach• The stomach is a muscular bag that lies in

the upper part of the abdomen.• Both physical and chemical digestions

take place in the stomach.• Physical digestion:

o Food is churned and mixed by muscles in stomach wall.

o This movement also mixes the food well with gastric juice for better digestion.

3rd Stop: Stomach• Chemical digestion:

o Gastric juice is secreted by glands in the stomach walls, into the stomach cavity. It contains:a) hydrochloric acid, which kills harmful bacteria

provides the acidic environment for proteases to work.b) protease which break down proteins into amino acids

o Digestion of proteins: • Protein Amino acids

• There is no digestion of carbohydrates or fats in the stomach. protease

3rd Stop: Stomach• The cells lining the stomach walls produce a

thick layer of mucus to protect the stomach from digesting itself and from the corrosive hydrochloric acid.

• A thick mass of semi-liquid called chyme is produced.

• Food stays in the stomach for 2 to 6 hours before passing into the small intestine by peristalsis.

4th Stop: Small Intestine

4th Stop: Small Intestine• The small intestine is a long muscular tube,

which is about 6 m long.• The liver and the pancreas are connected to the

small intestine.• Digestion ends in the small intestine.

4th Stop: Small IntestineChyme is mixed with 3 fluids in the small

intestine to aid digestion:Bile Pancreatic juice Intestinal juice


• Physical digestion:o The liver produces an alkaline yellowish-green fluid

called bile.o Bile is stored in the gall bladder and has a duct (a

small tube) that carries bile into the small intestine.o Bile does not contain digestive enzymes, but helps to

break up fats into smaller oil droplets in a process known as emulsification.

o This increases the surface area of the oil and allows the fats to be digested quickly by the lipases in the pancreatic and intestinal juices.


• Emulsification:


• Chemical digestion:o The pancreas produces alkaline pancreatic

juice and the intestine walls produces intestinal juice.

o The juice contains the enzymes amylase, protease and lipase.


• The digestion of food in the small intestine are as follows:o Digestion of starch:

• Starch Maltose

• Maltose Glucoseo Digestion of small protein molecules

• Protein molecules amino acidso Digestion of fats:

• Fat Fatty acids and glycerol

amylase

maltase

protease

lipase


• Absorption is the process whereby digested food molecules are taken into the body cells.

• Digested food passes through the wall of the small

intestine and into the blood vessels (capillaries) which surround it.

• Water, vitamins and minerals are also absorbed.

• Food stays in the small intestine for about 5 hours.

5th Stop: Large Intestine

5th Stop: Large IntestineThe large intestine is about 1.5 m long.

Food that cannot be digested reaches here. Undigested food is made up largely of fibres which come from cellulose cell walls of plants.

Water and mineral salts are absorbed here in the colon.

There is no enzymes or digestion here.

5th Stop: Large Intestine• The mixture of undigested food and dead

bacteria is called faeces. • Faeces are stored temporarily in the rectum.• Most of the time, the muscles in the rectum stay

contracted. • When the ring-like muscles between the rectum and

anus relax, faeces is passed out of the body through the anus.

• This is known as defaecation or egestion.• Food stays in the large intestine for up to 24 hours.

5th Stop: Large Intestine

• The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to expel faeces. (unwanted semi-solid matter).

Systems working together

• Each part of the digestive system carries out its own function and work with other parts to make sure food is digested and absorbed by the body.

• The digestive system also interacts with other systems such as the muscular and blood circulatory system.

Absorption of nutrients• Digestion ends in the small intestine.

• The final products of digestion are glucose, amino acids, fatty acids and glycerol, which are small and thus can pass through its wall and into the bloodstream.

• Large molecules like starch and proteins cannot pass through the walls of the small intestine.

Absorption of nutrients

• Food molecules pass through the intestine into the blood by diffusion.

Absorption of nutrients• To speed up the rate of absorption, the small intestine

has to increase its surface area.

• Adaptations:1. Being long

• The small intestine is about 6 m.

2. Having a wall thickness of one cell• This shortens the distance between the wall and

blood vessels, resulting in faster absorption.

Absorption of nutrients• Adaptations:

3. Having microvilli• The walls of the small intestine have many

finger-like projections called microvilli (singular: microvillus).

• The microvilli provide a large surface area for absorption of digested food molecules.

• Hence, digested food molecules can be absorbed quickly into the blood.

Absorption of nutrients• Villi

microvillus

Checkpoint Time

1. Label the parts of the Digestive System.

Part Name1.

2.

3.

4.

5.

6.

7.

Checkpoint Time

1. Label the parts of the Digestive System.

Part Name8.

9.

10.

11.

12.

13.

14.

15.

Checkpoint Time

3. State the end products that are obtained in the digestion of :

a) Proteins__________________________ b) Fats_____________________________c) Carbohydrates_____________________

Checkpoint Time

2. State the types of enzymes that help in the digestion of :


Checkpoint Time

4. State the location(s) that the following nutrients are digested in our body.


Food-Borne Diseases

• Foodborne illnesses are infections or irritations of the gastrointestinal (GI) tract caused by food that contain harmful bacteria, parasites, viruses, or chemicals. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus.

• Common symptoms of foodborne illnesses include vomiting, diarrhea, abdominal pain, fever, and chills.

Preventing Food-Borne Diseases

• Foodborne illnesses can be prevented by properly storing, cooking, cleaning, and handling foods.

• Ways to prevent food-borne diseases:o Raw and cooked perishable foods should be

refrigerated or frozen promptly. o Foods should be cooked long enough to kill the

harmful bacteria that cause illnesses.

Preventing Food-Borne Diseases

• Ways to prevent food-borne diseases:o Fruits and vegetables should be washed under

running water just before eating, cutting, or cooking. o Raw meat, poultry, seafood, and their juices should

be kept away from other foods.o Wash your hands with warm, soapy water before and

after handling raw meat, poultry, fish, shellfish or eggs. Wash your hands after using the toilet.

o Utensils and surfaces should be washed with hot, soapy water before and after they are used to prepare food.

11. human digestive system - e-learning

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