Digestive System description and function .ppt

Digestive System description and function

1. THE DIGESTIVE SYSTEMTHE DIGESTIVE SYSTEM
© PDST Home Economics

2. Without food, water and oxygen, human beings could Without food, water and oxygen, human beings could
not survive.not survive.
The digestive system is a set of organs which change The digestive system is a set of organs which change
what we eat into substances that can be used in the what we eat into substances that can be used in the
body.body.
These substances can be used for energy, growth and These substances can be used for energy, growth and
repair.repair.

3. 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 bloodchanged and the nourishment is taken into the blood
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

4. MouthMouth
1. 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
StomachStomach
LiverLiver
Produces Produces
bilebile for the for the
digestion of digestion of
fatsfats
Gall 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)
PancreasPancreas
Produces digestive Produces digestive
juicesjuices
Small intestineSmall intestine
1.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
RectumRectum
Stores faecesStores faecesAnusAnus

5. 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 down This is where large pieces of food are broken down
into smaller pieces of the same foodinto 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

6. MouthMouth
The food is broken down by the teeth and mixed with The food is broken down by the teeth and mixed with
saliva.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 salivary Saliva contains water, mucus and the enzyme salivary
amylase.amylase.

7. 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 on It contains the enzyme salivary amylase, which acts on
cooked starch turning some of it into maltose.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 a The ball of food that leaves the mouth is known as a
bolus.bolus.

8. 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 bitter salt, sweet, sour and bitter
chemicalschemicals 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 when us when
food, drink are off or inedible.food, drink are off or inedible.
ChewingChewing: the tongue aids chewing by moving the food : the tongue aids chewing by moving the food
around the mouth, pushing it between the teeth and around the mouth, pushing it between the teeth and
covering it with saliva, which contains enzymes that covering it with saliva, which contains enzymes that
start the digestive process.start the digestive process.
The food is turned into a partially digested mass known The food is turned into a partially digested mass known
as a 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 mouth.stomach, the tongue pushes it to the back of the mouth.

9. Tongue Taste Centres
Epiglottis
Bitter
Sour
Salt
Sweet
Taste Buds
Papillae

10. 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 down entrance to the larynx, this stops the food going down
the wrong way and prevents chokingthe wrong way and prevents choking..

11. 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 known as Food moves along it by a muscular contraction known as
peristalsis.peristalsis.
The muscle fibres contract and relax which acts like a The muscle fibres contract and relax which acts like a
wave on the tube, pushing the bolus forward.wave on the tube, pushing the bolus forward.
It’s lining secretes mucus to lubricate the passage of It’s lining secretes mucus to lubricate the passage of
food.food.

12. The Stomach
Oesophagus
Pyloric Sphincter
Duodenum
Body of Stomach
Cardiac Sphincter

13. 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 cardiac Food enters it from the oesophagus through the cardiac
sphincter.sphincter.
The cardiac sphincter, is a valve that stops back flow of The cardiac sphincter, is a valve that stops back flow of
the stomach`s contents.the stomach`s contents.
Food leaves the stomach through the pyloric sphincter Food leaves the stomach through the pyloric sphincter
into the duodenum (first part of the small intestine).into the duodenum (first part of the small intestine).

14. 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.

15. 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.

16. 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.

17. Structure of the Small Intestine
It is seven metres long.
It is divided into three parts:
The duodenum
The jejunum
The ileum
The walls has four layers:
A muscular layer
A layer containing blood vessels, lymph vessels, and
nerves.
A submucous layer,
A mucous layer.

18. 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.

19. Functions of The Small Intestine
Digestion
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.

20. 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.

21. Caecum
Transverse
Colon
Descending
Colon
Ascending
Colon
RectumAnus
Apendix

22. 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

23. 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.

24. 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 systems All chemical reactions that take place in living systems
require the action of an enzymerequire the action of an enzyme

25. ENZYMESENZYMES
Digestive enzymes break food down into smaller, more Digestive enzymes break food down into smaller, more
soluble substancessoluble substances
This allows the food to be absorbed into the bloodThis allows the food to be absorbed into the blood

26. 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

27. ENZYMESENZYMES
Amylase converts starch into a sugar called Amylase converts starch into a sugar called maltosemaltose
STARCH STARCH  MALTOSE MALTOSE

28. ENZYMESENZYMES
STARCHSTARCH
AMYLASE
MALTOSEMALTOSE

29. ENZYMESENZYMES
The substance that an enzyme works on is known as its The substance that an enzyme works on is known as its
SUBSTRATESUBSTRATE
The substance formed by the enzyme is known as its The substance formed by the enzyme is known as its
PRODUCTPRODUCT
Therefore Therefore starchstarch is the is the substratesubstrate for amylase and for amylase and
maltosemaltose is its is its productproduct

30. 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 “egestion”) of undigested food (also called “egestion”)

31. STAGES OF NUTRITIONSTAGES OF NUTRITION
Digestion changes food into a form that can enter the Digestion changes food into a form that can enter the
bloodblood
Physical (mechanical) digestion breaks food down into Physical (mechanical) digestion breaks food down into
smaller piecessmaller pieces
Chemical digestion breaks food down into different, Chemical digestion breaks food down into different,
more soluble substancesmore soluble substances

32. The contents of the alimentary canal are pushed The contents of the alimentary canal are pushed
along by a rhythmic pulsing of the muscles of the along by a rhythmic pulsing of the muscles of the
intestinesintestines
This is known as This is known as peristalsisperistalsis

33. 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 it The shape and size of the tooth varies with the job it
has to dohas to do
There are four different types of toothThere are four different types of tooth

34. TEETHTEETH
IncisorsIncisors
These These cut and bite foodcut and bite food
CaninesCanines
These These grasp and tear foodgrasp and tear food
Pre-molarsPre-molars
These These grind and chew foodgrind and chew food
MolarsMolars
These also These also grind and chew foodgrind and chew food

35. TEETHTEETH
IncisorIncisor
Pre-molarPre-molar
CanineCanine
MolarMolar

36. TEETHTEETH
The type of teeth that an animal has depends on what it The type of teeth that an animal has depends on what it
eatseats
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 large A carnivore eats other animals and needs very large
caninescanines
An omnivore (e.g. humans) eats all kinds of food and An omnivore (e.g. humans) eats all kinds of food and
needs and use all of the types of tooth equallyneeds and use all of the types of tooth equally