year 9 – what lies within (biology) the digestive system aim: name and describe function of main...

Year 9 – What lies within (Biology)

The Digestive system

Aim: name and describe function of main organs of

digestive system


• Define term digestion.• Explain the process of digestion in simple

steps• Identify and explain function of digestive

enzymes.

By the end of this lesson we should be able to:


Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules.

Let’s take a close look at how this happens…

Open wide!


Teeth mechanically break down the food. (physical)

Saliva is added from the salivary glands – it contains an enzyme that starts digestion. (chemical )

Digestion starts in the mouth:

Amylase = starts break down of carbohydrates


Question????

• What is the difference between physical and chemical digestion?


All food enters our digestive system through the mouth and waste material leaves through the anus.

If we stretch the digestive system out, we can see that it is really one long tube with an opening at

each end. However, it is a 9m tube!

Anus

Mouth


The ball of food is squeezed down through the gullet by the contraction of muscles lining the pipe.

The process is known as Peristalsis.

swallowing

food bolus

The Oesophagus/gullet


Questions????

• What is the scientific name of the food pipe?

• What is peristalsis?


The stomach is basically a muscular bag, filled with Hydrochloric Acid (HCl) and enzymes that digest protein (proteases).

food enters from the gullet

Digested food leaves

Muscle tissue

protease enzyme mix with the food

The Stomach


Question

• Describe in detail the structure and function of the stomach?


Although it is called small, it can stretch up to 6 meters in length.

The small intestine contains all 3 enzymes to complete digestion:CarbohydraseProteaseLipase (fats)

The Small Intestine


Small Intestine

Bile DuctPancreatic duct

Gall Bladder

Pancreas and gall bladder:

Pancreas adds all 3 enzymes to the small intestine.

The gall bladder adds bile into the small int. which emulsifies fat (breaks up)/ alkali


Questions??

• Name the enzymes present in the small intestine – what do they do?

• Where do they originate from?


Summarise -The function of bile

• Bile is made in the liver and stored in the gall bladder.It is added to the small intestine (alkali) to neutralise the acid from the stomach. Enzymes in the Small Int. work best in alkali conditions.

• Bile also starts emulsifying the fat. (break up into droplets) to give a big surface area for Lipase enzymes to work on.

• The small intestine is the first point fat is digested.


Digestion is completed. Food is absorbed from the small intestine into

the blood.

A

S

B

R

O

T

P

N

O

I

BLOOD

Any indigestible food will leave the small intestine without having been absorbed


Large intestine (colon).

LARGE

INTESTINE

BLOOD

As the food enters this organ, all that is left is waste material and water. Water is reabsorbed into the blood..


Question

• What is the function of the large intestine?


Mouth

Stomach

Liver

Large Intestine

Rectum

Gullet

Pancreas

Small Intestine

Anus

Here is a diagram of the system.

year 9 – what lies within (biology) the digestive system aim: name and describe function of main...

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