THE DIGESTIVE

SYSTEM

Biology and Geology 3rd ESO – Unit 4 (I)

© I.E.S. “Luis de Góngora” .Córdoba. Spain

Dept. Biology and Geology

Juan Manuel Barroso Fernández

ORGAN SYSTEMS RELATED TO

THE PROCESS OF NUTRITION

DIGESTIVE

SYSTEM

RESPIRATORY

SYSTEM

CIRCULATORY

SYSTEM

EXCRETORY

SYSTEM

Remember:

Nutrition is the process through which

organisms obtain, use and transform

nutrients to keep on living.

urine

ORGAN SYSTEMS RELATED TO

THE PROCESS OF NUTRITION

Faeces

nutrients

Cellular activity DIGESTIVE

SYSTEM

RESPIRATORY

SYSTEM

CIRCULATORY

SYSTEM

EXCRETORY

SYSTEM

DIGESTIVE SYSTEM

FUNCTION:

To obtain nutrients from food

To absorb them into the circulatory system.

STRUCTURE:

A tube: the Gastrointestinal Tract

A set of glands secreting into the digestive

tract

Accessory Glands Alimentary canal or

gastrointestinal tract

Mouth

Pharynx

Oesophagus

Stomach

- Cecum

- Colon

- Rectum

Large

intestine

- Duodenum

- Jejunum

- Ileum

Small

intestine

Salivary glands

Gastric glands

Intestinal glands

Pancreras

Liver

Lips

Isthmus of the fauces

Upper oesophageal sphincter

Lower oesophageal sphincter

Pyloric sphincter

Ileocecal sphincter

Anus

Large intestine

Small intestine

Stomach

Oesophagus

Pharynx

Mouth

Intestinal glands

Pancreas

Liver

Salivary glands

Click on each arrow to

learn its name

- BLUE arrows: Accesory Glands

- GREEN arrows: Parts of the

Digestive Tract

Pharynx

Oesophagus

Stomach

Small intestine

Large intestine

Salivary glands

Liver

Pancreas

Intestinal glands

Mouth

Click on each arrow to show

further information

Egestion of non-digested substances (faeces) out of the body (defecation).

PROCESSES:

Absorption of the small

nutrients obtained through

digestion from food.

Chemical breaking down

(chemical digestion) using

enzymes, released by the

accessory glands.

Mechanical breaking down

of food.

Ingestion of food.

Deglutition.

Preparing the Digestive Process

1. INGESTION Food is taken into the digestive tract (mouth)

2. MECHANICAL BREAKING DOWN OF FOOD Mastication (chewing)

Food is broken down into small pieces thanks to the teeth and the tongue. Teeth are small, hard structures that can be classified as: Incisors (for cutting)

Canines (for tearing)

Premolars (for grinding)

Molars (for grinding)

Salivation Saliva has three functions:

It lubricates the bolus.

It kills some bacteria.

(It starts the chemical digestion of starch).

This way the bolus is formed.

Voluntarily, the tongue pushes the bolus into the pharynx and oesophagus.

Involuntary contractions of the oesophafus (peristalsis) drags the bolus along the tube until it reaches the stomach.

3. Deglutition

(swallowing)

4. CHEMICAL DIGESTION

The chemical breakdown of food takes place in:

Mouth: by saliva

Stomach (Gastric glands): by gastric juice

Liver: by bile* (* it only emulsifies fats, without any chemical effect)

Pancreas: by pancreatic juice

Intestinal glands: by intestinal juice

starch Digestive

enzymes

glucose

Stomach digestion

Gastric glands secrete gastric juice, which contains:

An enzyme: pepsin, which starts the breakdown of proteins.

Hydrochloric acid, devoted to three actions:

It activates pepsin.

It dissolves the food fibres.

It kills the bacteria that might still remain within the bolus.

When food enters into the stomach: - The stomach muscles start to contract.

- The bolus is mixed up with gastric juice for 1:30 h (carbohydrates)

3 h (proteins)

4 h (fats)

- Once the stomach digestion is finished, the mixture becomes a fluid paste called “chyme”.

Liver and Pancreas

Liver: It produces bile, which emulsifies fats.

Pancreas: It has a double function:

It acts as an inner gland, secreting insulin.

It acts as a digestive gland, secreting pancreatic juice, which contains enzymes to digest carbohydrates, fats and proteins. It also contains sodium bicarbonate to neutralise the acidity of chyme.

Chyme passes from the stomach to the duodene, where it is mixed up with three different substances secreted by:

Intestinal glands

They are microscopic glands located on the intestinal

mucouse, producing intestinal juice able to produce

enzymes to digest all the different types of biomolecules.

As a result, chyme becomes a white liquid: chyle.

Chyle contains simple molecules that are used as

nutrients by the body cells:

Monosaccharides, obtained from complex carbohydrates.

Glycerol and fatty acids, obtained from fats.

Amino acids, that have been obtained from proteins.

Intestinal

digestion CHYLE Gastric

digestion CHYME

The digestive process

Mechanical

breakdown BOLUS

MOUTH STOMACH SMALL INTESTINE

Teeth

Tonge

Saliva

Gastric juice Bile

Pancreatic juice

Intestinal juice

Chemical digestion:

SALIVA GASTRIC

JUICE

BILE PANCREATIC

JUICE

INTESTINAL JUICE

CARBO-

HYDRATES Starch →

Maltose

Starch →

Maltose

Disaccharides→

Monosaccharides

PROTEINS Proteins→

Polypetides

Polypeptides→

Peptides

Peptides→

Amino acids

FATS

(Bile

emulsifies

fats)

Fats →

Glycedrol, fatty

acids

Fats → Glycedrol,

fatty acids

Certain nutrients, such as water, mineral salts, alcohol and vitamins are direclty

absorbed without prior chemical digestion.

5. Absorption of nutrients

Once the digestive process is finished, nutrients pass from the intestine to the blood, which carries them through the circulatory system to the cells.

In the small intestine that substances, except water, are absorbed. The digestive mucose is folded forming wrinkles called villi. In turn, the cell membrane of the cells of the mucous membrane is folded forming microvilli. This way the absorption surface increases up to 400 m2. Glycerol and fatty acids are not directly delivered to the blood but to lacteals from which, in turn, pass them to the blood.

In the large intestine, water absorption takes place, giving way to the faeces, which are released out of the body through the anus. Faeces contain food remains, cells of the intestinal mucose and bacteria.

6. Egestion (defecation)

Main processes (click on each arrow to show the process)

Mouth Large int. Small int. Stomach Oesophaus Pharynx

Egestion

Absorption

Chemical breakdown

Deglutition

Mechanical breakdown

Ingestion 1

2

3

4

5

6

Web pages:

http://classes.midlandstech.com/carterp/Courses/bio211/chap23/chap23.htm

http://www.ahealthyme.com/Imagebank/digestive.swf

http://www.biographixmedia.com/stew/sbir/digestive.swf

http://hopkins-gi.nts.jhu.edu/images/shared/home/database/DigestiveSystem.swf

http://www.open2.net/everwonderedfood/interactives/digestive_system.swf

http://www.firstresponder.emszone.com/swf/CH04_Fig14.swf

http://www.giassoc.org/anatomy1.swf

http://www.upa.pdx.edu/IMS/currentprojects/TAH_Old%20Backup/Tester/MOD_3_DIGESTION.swf

http://mistupid.com/health/teeth.swf

http://www.tutorvista.com/content/biology/biology-iv/animal-nutrition/digestive-system-animation.php