Digestive System

Science : Biology : DigestionScience : Biology : Digestion

Digestion refers to the breaking down of Digestion refers to the breaking down of large food molecules into smaller food large food molecules into smaller food

molecules in the body.molecules in the body.So that small food molecules can diffuse So that small food molecules can diffuse

through the walls and enter bloodstream. through the walls and enter bloodstream. Starch and proteins are large food Starch and proteins are large food

molecules that cannot pass through the molecules that cannot pass through the walls.walls.

NutrientsNutrientsBody needs energy to do work.Body needs energy to do work.Nutrients includeNutrients include– CarbohydratesCarbohydrates

Provide energy (growth, warmth, movement)Provide energy (growth, warmth, movement)– ProteinsProteins

For growth of cells and tissues For growth of cells and tissues Repair of damaged tissues. Repair of damaged tissues. Source of energy if carbohydrates and fats unavailableSource of energy if carbohydrates and fats unavailable

NutrientsNutrientsNutrients includeNutrients include– FatsFats

Provide energyProvide energyTwo times that of carbohydratesTwo times that of carbohydrates

Nutrients helpNutrients help– in our growth, in our growth, – by keeping us healthy, by keeping us healthy, – by repairing our cells and tissues, by repairing our cells and tissues, – by giving us energy.by giving us energy.

Enzymes : their roleEnzymes : their roleEnzymes are used to digest foodEnzymes are used to digest food– Carbohydrase / AmylaseCarbohydrase / Amylase

Carbohydrates to Simple sugarsCarbohydrates to Simple sugars– ProteaseProtease

Proteins to Amino acidsProteins to Amino acids– LipaseLipase

Fats to Glycerol and Fatty acidsFats to Glycerol and Fatty acids

Alimentary canal, organs and functionsAlimentary canal, organs and functions

Alimentary canal consists of the Alimentary canal consists of the – Mouth (20sec)Mouth (20sec)

Starch (carbohydrate) is digested to maltose by carbohydrase / Starch (carbohydrate) is digested to maltose by carbohydrase / amylaseamylase

– Oseophagus (10sec)Oseophagus (10sec)Walls of the alimentary canal are made of muscles which squeezes Walls of the alimentary canal are made of muscles which squeezes food along the canal.food along the canal.

– Stomach (2-6hrs)Stomach (2-6hrs)Produces gastric juice which mixes food when stomach churns.Produces gastric juice which mixes food when stomach churns.Protease in the juice breaks down complex proteins into simpler Protease in the juice breaks down complex proteins into simpler onesones

Organs joined to the Alimentary canalOrgans joined to the Alimentary canal

LiverLiver– Makes bileMakes bile

Greenish liquid which emulsifies fats, breaking them Greenish liquid which emulsifies fats, breaking them into smaller droplets, easier for lipase to digest it.into smaller droplets, easier for lipase to digest it.

Gall bladderGall bladder– Stores bileStores bile

PancreasPancreas– Creates pancreatic juiceCreates pancreatic juice

Flows to small intestine and contain enzymesFlows to small intestine and contain enzymes

Alimentary canal, organs and functionsAlimentary canal, organs and functions

Small intestine (5hrs)Small intestine (5hrs)– Produces intestinal juice which contains enzymesProduces intestinal juice which contains enzymes– Completes the digestion process with the help of Completes the digestion process with the help of

the organs joined to the alimentary canal.the organs joined to the alimentary canal.

Alimentary canal, organs and functionsAlimentary canal, organs and functionsDigestion ends at the small intestine:Digestion ends at the small intestine:–

– Small molecules of digested food passes through the small Small molecules of digested food passes through the small intestine wall, into the bloodstream surrounding it.intestine wall, into the bloodstream surrounding it.

Digested food enters bloodDigested food enters bloodDigested foodDigested food– Made of small food moleculesMade of small food molecules

Diffuse through walls of small intestineDiffuse through walls of small intestineInto blood vessels in wallsInto blood vessels in wallsCarried away by blood the rest of the bodyCarried away by blood the rest of the bodyCalled Called absorption of foodabsorption of food

– Blood carries the small food molecules to the cells Blood carries the small food molecules to the cells of the body where they can be used.of the body where they can be used.

Easier absorptionEasier absorptionFinger-like villiFinger-like villi– Provides large surface area Provides large surface area – Folds the cell membraneFolds the cell membrane

7 m-long small intestine7 m-long small intestine– Increases surface areaIncreases surface area

One-cell thick small intestineOne-cell thick small intestine– Shortens distance between wall and bloodstreamShortens distance between wall and bloodstream

Alimentary canal, organs and functionsAlimentary canal, organs and functions

Alimentary canal consists of theAlimentary canal consists of the– Large intestine and anus (24hrs)Large intestine and anus (24hrs)

Undigested food reaches the large intestineUndigested food reaches the large intestineLots of water is removed and taken back into the bodyLots of water is removed and taken back into the bodyPass out through anus as faecesPass out through anus as faeces

Summary : Digestion of foodsSummary : Digestion of foodsNutrients in foodsNutrients in foods– Carbohydrates and fats are used for respiration and as Carbohydrates and fats are used for respiration and as

sources of energy.sources of energy.– Proteins are used for growth and the repair of body Proteins are used for growth and the repair of body

tissues.tissues.– Starch and glucose are two kinds of carbohydrates.Starch and glucose are two kinds of carbohydrates.

Why digestion is neededWhy digestion is needed– Only small molecules are able to pass through cell Only small molecules are able to pass through cell

membranes into cells.membranes into cells.– Starch, fat and protein molecules are too large to pass Starch, fat and protein molecules are too large to pass

through.through.

Summary : Digestion of foodsSummary : Digestion of foodsMeaning of digestionMeaning of digestion– Digestion is the breaking down of large food molecules in Digestion is the breaking down of large food molecules in

the body into small food molecules.the body into small food molecules.– The small food molecules are: glucose (from starch), The small food molecules are: glucose (from starch),

amino acids (from proteins) and glycerol and fatty acids amino acids (from proteins) and glycerol and fatty acids (from fats).(from fats).

– Digestion takes place by the action of enzymes.Digestion takes place by the action of enzymes.

Summary : Digestion of foodsSummary : Digestion of foodsThe alimentary canal and digestionThe alimentary canal and digestion– MouthMouth

Digestion of starch begins here.Digestion of starch begins here.

– StomachStomachDigestion of proteins begins here.Digestion of proteins begins here.

– Small intestineSmall intestineMost digestion takes place here.Most digestion takes place here.Digestion of starch and proteins is completed here.Digestion of starch and proteins is completed here.Digestion of fats takes place only in the small intestine. Digestion of fats takes place only in the small intestine. Absorption of digested foodAbsorption of digested foodThe small, digested food molecules are absorbed into the The small, digested food molecules are absorbed into the bloodstream through the walls of the small intestine.bloodstream through the walls of the small intestine.The villi of the small intestine increase the surface area for faster The villi of the small intestine increase the surface area for faster absorption of small, digested food moleculesabsorption of small, digested food molecules..