Digestive enzymes

Starch

Proteins PROTEASE

Lipids/ Fats

AMYLASE

LIPASE fatty acids &

glycerol

amino acids

maltose

identify and describe the main regions of alimentary

canal describe the functions of the

parts of the human gut and the associated organs

Pathway of Digestion in Alimentary Canal

Mouth ↓

Oesophagus↓

Stomach↓

Small Intestines↓

Large Intestines↓

Rectum↓

Anus

• Digestion is the process of breaking down complex, large molecules (food) into simple, soluble and diffusible molecules so that it can be absorbed by the body and be used to build and nourish cells and to provide energy.

Functions of digestive system:

(1) Ingestion: taking food into the body.(2) Digestion: breakdown of food materials

into smaller amounts (i) Mechanical digestion (ii) Chemical digestion

(3) Absorption(4) Assimilation(5) Egestion

Types of digestion:(i) Mechanical digestion• Break down particles into smaller pieces so as

to increase the surface area for the action of enzymes.

(ii) Chemical digestion• Involves enzymatic reactions which digest the

food into simpler chemical forms.• Hydrolysis splits the large molecules by addition

of water.

How is Food Digested? Mouth • Ingestion is the process of taking food

into the body. • The tongue rolls and lubricates food with

mucus and saliva. • Chemical digestion of starch starts here

by salivary amylase.

Oesophagus• It takes food down from the throat and

into the stomach. Moving food by waves of muscle contraction called peristalsis.

The oesophagus

Circular muscles contract to push the food ball down.

Circular muscles relax, and the tube widens for food to move.

The partially digested food is pushed to the stomach by wave-like contractions known as

peristalsis.

The stomach

stomach

Stomach• The stomach lining produces mucus and gastric juices

which contains:i) hydrochloric acid (acidic medium of pH 2 for

enzymes and kills micro-organisms in food)ii) Pepsin: hydrolyze protein to polypeptides.iii) Rennin: hydrolyze milk caseinogen to casein.

Quick Revision: What is the function of hydrochloric acid?

1) Provides an acidic medium for activation of gastric enzymes.

Inactive formsProrennin HCl RenninPepsinogen HCl Pepsin

2) Kills germs and potential parasites.3) Stop the action of salivary amylase.

Active forms

Dr. Jones, I am suffering from stomach cancer & half of my stomach was

removed. What should I do?

You should:• take multiple small meal at regular intervals, • take less protein per meal• clean and cook the food thoroughly……

Oh dear….i feel that my chest is burning after

having a heavy dinner.

What could have gone wrong?

Inflamed oesophagus This condition is due to

the irritation of the oesophagus that is

caused by too much stomach acid.

The Liver & Gall Bladder

A small pear-shaped organ that is greenish-yellow in colour.

Temporarily stores bile secreted by liver.

QUESTION:

Will bile secretion be hindered if the gall bladder is removed?

Liver and Gall Bladder

Pancreas

Small intestines

Large Intestines

Rectum and Anus

THE STRUCTURE & FUNCTIONS OF …

LIVER:

Largest gland in the body.

Lies below diaphragm, on right side of body.

Secretes bile.

QUESTION: Can bile digest food?

Bile is not an enzyme, so it cannot digest food but it aids in digestion of lipids.

Emulsification

Bile

Large oil drop

Small oil droplets

The Pancreas

Connected to duodenum by pancreatic duct

Secretes pancreatic juice that contains digestive enzymes.

• Major site of chemical digestion of all remaining food (carbohydrates, fats and proteins).

• Also, main site of absorption of nutrients occur here.

Small Intestines (Duodenum, jejunum and ileum)

The Large Intestine

Contains undigested food material.

Main function is to absorb water and mineral salts.

Rectum temporarily stores faeces that are egested through the anus.