THE DIGESTIVE SYSTEMTHE DIGESTIVE SYSTEM

© PDST Home Economics

Without food, water and oxygen, human beings Without food, water and oxygen, human beings could not survive.could not survive.

The digestive system is a set of organs which The digestive system is a set of organs which change what we eat into substances that can be change what we eat into substances that can be used in the body.used in the body.

These substances can be used for energy, growth These substances can be used for energy, growth and repair.and repair.

THE DIGESTIVE SYSTEMTHE DIGESTIVE SYSTEM

The The alimentary canalalimentary canal is a tube that runs from the is a tube that runs from the mouth to the anusmouth to the anus

It is composed of the mouth, oesophagus, stomach, It is composed of the mouth, oesophagus, stomach, small intestine and the large intestinesmall intestine and the large intestine

As food passes through the alimentary canal it is As food passes through the alimentary canal it is changed and the nourishment is taken into the changed and the nourishment is taken into the bloodblood

Waste passes out the end of the canalWaste passes out the end of the canal Certain organs and glands add juices to the canal at Certain organs and glands add juices to the canal at

various pointsvarious points

MouthMouth1. Chemical digestion (amylase 1. Chemical digestion (amylase

converts starch to maltoseconverts starch to maltose))

2. Physical digestion (teeth break 2. Physical digestion (teeth break food down into smaller food down into smaller

pieces)pieces)

OesophagusOesophagus

Connects mouth Connects mouth to stomachto stomach

StomachStomachLiverLiverProduces Produces

bilebile for the for the digestion of digestion of

fatsfatsGall Gall

bladderbladder Stores bileStores bile

1.1. Holds the food for a whileHolds the food for a while

2.2. Physical digestion (food is Physical digestion (food is churned and mixed)churned and mixed)

3.3. Chemical digestion (assisted Chemical digestion (assisted by HCl)by HCl)

PancreasPancreasProduces digestive Produces digestive

juicesjuices

Small intestineSmall intestine1. Chemical digestion

2. Absorption of nutrients into blood

AppendixAppendix

Large intestine Large intestine (colon)(colon)

1.1. Elimination of wasteElimination of waste

2.2. Absorption of waterAbsorption of water

RectumRectumStores faecesStores faecesAnusAnus

Food can be broken down (digested) in one of two Food can be broken down (digested) in one of two ways:ways:

1.1. Physical DigestionPhysical Digestion

This is where large pieces of food are broken This is where large pieces of food are broken down into smaller pieces of the same fooddown into smaller pieces of the same food

2.2. Chemical DigestionChemical Digestion

This is where food is broken down into a different This is where food is broken down into a different substance that can easily pass into the bloodsubstance that can easily pass into the blood

MouthMouth

The food is broken down by the teeth and mixed The food is broken down by the teeth and mixed with saliva.with saliva.

Saliva is excreted by three pairs of glands:Saliva is excreted by three pairs of glands:• The parotid gland (below the ear)The parotid gland (below the ear)• The submandibular (under the tongue)The submandibular (under the tongue)• The sublingual (under the tongue)The sublingual (under the tongue) Saliva contains water, mucus and the enzyme Saliva contains water, mucus and the enzyme

salivary amylase.salivary amylase.

Functions of SalivaFunctions of Saliva

It lubricates food with mucus, making it easier to It lubricates food with mucus, making it easier to swallow.swallow.

It contains the enzyme salivary amylase, which acts It contains the enzyme salivary amylase, which acts on cooked starch turning some of it into maltose.on cooked starch turning some of it into maltose.

It keeps the mouth and teeth clean.It keeps the mouth and teeth clean. The ball of food that leaves the mouth is known as The ball of food that leaves the mouth is known as

a bolus.a bolus.

Functions of the TongueFunctions of the Tongue

TasteTaste: it is covered with thousands of : it is covered with thousands of taste budstaste buds. . These are sensitive to These are sensitive to salt, sweet, sour and salt, sweet, sour and bitter chemicalsbitter chemicals in food and drink. in food and drink.

They help us enjoy food and drink and They help us enjoy food and drink and warnwarn us us when food, drink are off or inedible.when food, drink are off or inedible.

ChewingChewing: the tongue aids chewing by moving the : the tongue aids chewing by moving the food around the mouth, pushing it between the food around the mouth, pushing it between the teeth and covering it with saliva, which contains teeth and covering it with saliva, which contains enzymes that start the digestive process.enzymes that start the digestive process.

The food is turned into a partially digested mass The food is turned into a partially digested mass known as a known as a bolusbolus..

Swallowing: when the food is ready to travel to the Swallowing: when the food is ready to travel to the stomach, the tongue pushes it to the back of the stomach, the tongue pushes it to the back of the mouth.mouth.

Tongue Taste CentresEpiglottis

Bitter

Sour

Salt

Sweet

Taste Buds

Papillae

OesophagusOesophagus

The food passes into the pharynx (a muscular tube The food passes into the pharynx (a muscular tube behind the mouth) and down the oesophagus.behind the mouth) and down the oesophagus.

The epiglottis a small flap of cartilage blocks the The epiglottis a small flap of cartilage blocks the entrance to the larynx, this stops the food going entrance to the larynx, this stops the food going down the wrong way and prevents chokingdown the wrong way and prevents choking..

Structure of the OesophagusStructure of the Oesophagus& Functions& Functions

It is a muscular tube.It is a muscular tube. It leads from the pharynx to the stomach.It leads from the pharynx to the stomach.FunctionFunction To carry chewed food from the pharynx to the To carry chewed food from the pharynx to the

stomach.stomach. Food moves along it by a muscular contraction Food moves along it by a muscular contraction

known as peristalsis.known as peristalsis. The muscle fibres contract and relax which acts like The muscle fibres contract and relax which acts like

a wave on the tube, pushing the bolus forward.a wave on the tube, pushing the bolus forward. It’s lining secretes mucus to lubricate the passage It’s lining secretes mucus to lubricate the passage

of food.of food.

The Stomach

Oesophagus

Pyloric Sphincter

Duodenum

Body of Stomach

Cardiac Sphincter

Stomach StructureStomach Structure

It is a J-shaped, elastic organ.It is a J-shaped, elastic organ. Food enters it from the oesophagus through the Food enters it from the oesophagus through the

cardiac sphincter.cardiac sphincter. The cardiac sphincter, is a valve that stops back The cardiac sphincter, is a valve that stops back

flow of the stomach`s contents.flow of the stomach`s contents. Food leaves the stomach through the pyloric Food leaves the stomach through the pyloric

sphincter into the duodenum (first part of the small sphincter into the duodenum (first part of the small intestine).intestine).

The walls of the stomach is made up of layers of The walls of the stomach is made up of layers of muscle.muscle.

It has an inner mucous membrane.It has an inner mucous membrane. This membrane has lots of folds.This membrane has lots of folds. When the stomach is full these folds stretch out, When the stomach is full these folds stretch out,

enabling it to expand, then they contract when the enabling it to expand, then they contract when the stomach empties.stomach empties.

Functions of The StomachFunctions of The Stomach

It digests protein through the action of enzymes.It digests protein through the action of enzymes. It churns food with the gastric juices.It churns food with the gastric juices. It helps lubricate the food by producing mucus.It helps lubricate the food by producing mucus. It absorbs alcohol.It absorbs alcohol. It kills bacteria by producing hydrochloric acid.It kills bacteria by producing hydrochloric acid.

Gastric Juices Hydrochloric acid neutralises bacteria and activates

pepsin. Rennin is an enzyme that curdles milk protein in

infants. Pepsin is an enzyme that breaks down proteins into

peptones.

Structure of the Small Intestine It is seven metres long. It is divided into three parts:

The duodenumThe jejunumThe ileum

The walls has four layers:A muscular layerA layer containing blood vessels, lymph vessels,

and nerves.A submucous layer,A mucous layer.

The inner wall is covered in villi, tiny hair like projections which increase the surface area for absorption.

Each villi contain blood vessels and lymph vessels.

Functions of The Small IntestineDigestion Pancreatic juice is secreted into the duodenum

and contains the following enzymes:Trypsin: converts proteins into shorter chains.Lipase: converts fats into fatty acids and

glycerol.Amylase: converts starch into disaccharides.

Bile: emulsifies fats (breaks them into smaller droplets).

Intestinal Juices have the following enzymes:Maltase, sucrase, lactase: change

disaccharides into monosaccharides.Peptidase: changes polypeptides into amino

acids.

Absorption

Digested food is absorbed through the villi walls.Fats, fatty acids and glycerol are passed into the

lymph system.Amino acids and sugars pass along the portal

vein to the liver.

Caecum

Transverse

ColonDescending

Colon

Ascending

Colon

RectumAnusApendix

What is the Large Intestine It deals with waste. It is about 1.5m long. It consists of the following: The caecum: a small pouch; the ileum empties its

contents into the caecum through the ileo-caecal valve.

The colon: ascending, transverse, descending colon.

The appendix: narrow tube attached to the caecum. The rectum. The anus

Functions Whatever remains of the food, is passed into the

large intestine To reabsorb water and vitamins left in digestive

waste. It secretes mucus to help the movement of faeces. Short term storage of faeces in the rectum. Many bacteria live in the large intestine, they are

harmless in the colon and may be useful e.g. produce Vitamin K.

Defecation: peristalsis pushes waste along the colon and then it is passed out of the body.

ENZYMESENZYMES

An enzyme is a An enzyme is a biological catalystbiological catalyst A catalyst speeds up chemical reactionsA catalyst speeds up chemical reactions Enzymes speed up biological reactionsEnzymes speed up biological reactions All chemical reactions that take place in living All chemical reactions that take place in living

systems require the action of an enzymesystems require the action of an enzyme

ENZYMESENZYMES

Digestive enzymes break food down into smaller, Digestive enzymes break food down into smaller, more soluble substancesmore soluble substances

This allows the food to be absorbed into the bloodThis allows the food to be absorbed into the blood

ENZYMESENZYMES

An example of a digestive enzyme is An example of a digestive enzyme is

amylaseamylase

Amylase is present in Amylase is present in salivasaliva

Amylase chemically Amylase chemically breaks down starchbreaks down starch

ENZYMESENZYMES

Amylase converts starch into a sugar called Amylase converts starch into a sugar called maltosemaltose

STARCH STARCH MALTOSE MALTOSE

ENZYMESENZYMES

STARCHSTARCH

AMYLASE

MALTOSEMALTOSE

ENZYMESENZYMES

The substance that an enzyme works on is known The substance that an enzyme works on is known as its as its SUBSTRATESUBSTRATE

The substance formed by the enzyme is known as The substance formed by the enzyme is known as its its PRODUCTPRODUCT

Therefore Therefore starchstarch is the is the substratesubstrate for amylase and for amylase and maltosemaltose is its is its productproduct

STAGES OF NUTRITIONSTAGES OF NUTRITION

There are four stages in human nutrition:There are four stages in human nutrition:

1.1. EatingEating (also called “ingestion”) (also called “ingestion”)

2.2. DigestionDigestion

3.3. AbsorptionAbsorption of digested food into the blood of digested food into the blood

4.4. EliminationElimination of undigested food (also called of undigested food (also called “egestion”)“egestion”)

STAGES OF NUTRITIONSTAGES OF NUTRITION

Digestion changes food into a form that can enter Digestion changes food into a form that can enter the bloodthe blood

Physical (mechanical) digestion breaks food down Physical (mechanical) digestion breaks food down into smaller piecesinto smaller pieces

Chemical digestion breaks food down into different, Chemical digestion breaks food down into different, more soluble substancesmore soluble substances

The contents of the alimentary canal are The contents of the alimentary canal are pushed along by a rhythmic pulsing of the pushed along by a rhythmic pulsing of the

muscles of the intestinesmuscles of the intestines

This is known as This is known as peristalsisperistalsis

TEETHTEETH

An adult human has 32 teeth, 16 in either jawAn adult human has 32 teeth, 16 in either jaw The shape and size of the tooth varies with the job The shape and size of the tooth varies with the job

it has to doit has to do There are four different types of toothThere are four different types of tooth

TEETHTEETH

IncisorsIncisorsThese These cut and bite foodcut and bite food

CaninesCaninesThese These grasp and tear foodgrasp and tear food

Pre-molarsPre-molarsThese These grind and chew foodgrind and chew food

MolarsMolarsThese also These also grind and chew foodgrind and chew food

TEETHTEETH

IncisorIncisor

Pre-molarPre-molar

CanineCanine

MolarMolar

TEETHTEETH

The type of teeth that an animal has depends on The type of teeth that an animal has depends on what it eatswhat it eats

A herbivore eats plant material and has very large A herbivore eats plant material and has very large incisors and molarsincisors and molars

A carnivore eats other animals and needs very A carnivore eats other animals and needs very large canineslarge canines

An omnivore (e.g. humans) eats all kinds of food An omnivore (e.g. humans) eats all kinds of food and needs and use all of the types of tooth equallyand needs and use all of the types of tooth equally