digestion igcse

DIGESTION

B M Subramanya Swamy M.Sc. B.Ed. CIE Co ordinator & Examination Officer

Kanaan Global School Jakarta

Indonesia subramanyaswamy1591978@gmail.com

DIGESTION DIGESTION

Digestion

Process by which the body breaks down food (carbohydrates, fats and proteins) into simpler substances

These substances are absorbed and used by cells in the body

Types of digestion

Types of digestion Process

Mechanical Mastication (chewing, mashing and breaking) into smaller particles In the mouth, teeth cuts and grinds food. Rolling action of tongue and secretion of saliva rolls food into bolus Bolus is swallowed and transported through pharynx to stomach by waves of rhythmic contraction called peristalsis

Chemical Changing food into smaller particles through action of enzyme Involves hydrolysis (addition of water) e.g. amylase converts carbohydrates into simple sugars

THE HUMAN DIGESTIVE SYSTEM

THE WORKING OF HUMAN DIGESTIVE SYSTEM

MOUTHFunctions : analysis material before swallowing, mechanical processing by the teeth, tongue and palatal surfaces, lubricating, limited digestion

TEETHFunctions :Grinding action (mastication) breaks down foodExpose large area for enzyme action

adult

child

TONGUEFunctions : Rolls food into bolus

SALIVARY GLANDSSecretions Functions

Saliva contains: Water

Mucus Salivary amylase

Moisten and soften food As solvent and for hydrolysis Sticks food together to form bolus Starch maltose

PHARYNXFunction : involuntary action pushes bolus into oesophagus

Nasal cavityPalate

Oral cavity

Tongue

Mandible

Pharynx

OESOPHAGUSFunctions : • Walls made up of circular and longitudinal muscles• Peristalsis transports food to the stomach

CARDIAC SPHINCTERFunction :• Controls entry of food into the stomach

The swallowing process

Peristalsis Characteristic Automatic

Length of alimentary canal made up circular and longitudinal muscle Alternate contraction and relaxation of muscle

Result Movement of food down the canal

Peristalsis

STOMACHSecretions Functions

Gastric juice

Hydrochloric acid

Water

Mucus

Pepsin

Rennin

Muscular walls churn food into chymeStored food for 2 – 6 hoursAbsorbs glucose and alcohol

Acidic medium (pH 1) for enzyme actionKills bacteria brought in with foodActivates enzymes

As solvent and for hydrolysis

Protects stomach wall from acidic gastric juiceLubricant for movement of food in the stomach

Protein polypeptides Converts protein into insoluble curds (coagulates milk) for hydrolysis of pepsin.

PHYLORIC SPHINCTERFunction : controls entry of food into duodenum

Stomach

Duodenum

FundusEsophagus

Body

Pyloric Den

Pylorus

Anatomy of the stomach

PANCREASSecretions Functions

Pancreatic juice

Amylase

Trypsin

Lipase

Water

Insulin

Hydrolysis of food in duodenum

Starch → maltose

Polypeptides → peptides

Fats → fatty acids and glycerol

As solvent for hydrolysis

Excess glucose is converted to glycerol in the liver

LIVER

Secretions Functions

Dark green bile Provides alkaline pH Bile is stored in the gall bladder Emulsifies fats, provides increased surface area for action of lipase Neutralise acidic chyme

Anatomy of the liver

Anatomy of the liver

SMALL INTESTINE

DUODENUM

Secretion Intestinal juice

Function Final stage of digestion pH 8 (alkaline)

Secretions Functions

Erepsin Lactase Sucrase Maltase Water

Peptides → amino acidsLactose → glucose and galactoseSucrose → glucose and fructoseMaltose → sucroseAs solvent and for hydrolysis

JEJUNUMFunction : absorption of food

ILEUM Function : absorption of food

The region of small intestine

The intestinal wall

The intestinal wall

The intestinal wall

LARGE INTESTINEFunction : absorption of water from undigested food

CAECUM AND APPENDIXFunction : Vestigial organs with no particular function Forms junction of small and large intestine

COLON

Secretion Function

Mucus Peristalsis compact undigested food to form faeces Lubricates faeces and protects wall from digestive juice

Large intestine

RECTUMFunction : stored faeces before defaecation

ANUSFunction : regulate emptying of rectum

What goes in must come out!

Comparison of human and herbivore digestive system

Human Herbivore

Food

Alimentary canalStomach

Caecum

Carbohydrates, fats and proteins

Short Simple

Very small

Mainly plant proteins and cellulose

Long Several chambers Contains bacteria for digestion of cellulose

Large caecum with cellulase to break down cellulose to glucose

ABSORPTION OF DIGESTED FOOD

Nutrients from digested food must be moved from intestines to the bloodstream

This process is called absorption Almost all of the digested food is absorbed in the ileum The small intestine is about 6 -7 m long Water soluble end – products of digestion enter the blood

system by diffusion Fatty acids and glycerol are absorbed by the lacteals Once inside, fatty acids recombine with glycerol to form

globules of fat They are carried by the lymphatic system to the veins

Structure of the Villi in the Small Intestine

Structure of a villus

Adaptation of the ileum to absorb digested foodFeatures Adaptation

Length Longest part of the alimentary canal

Internal surface area Internal walls are folded to increase surface area for absorption

Villi Further increase surface area for absorption

Microvilli Villus covered with epithelial cellsThe plasma membrane of each cell has minute finger – like projections (microvilli)Further increase surface area

Movement Villi move back and forth independentlyMotion faster after mealsAbsorption rate increases

Membrane Absorption across membraneEither by diffusion or active transport

capillary network Dense capillary network close to epitheliumCarry away absorbed food particles quicklyMaintain concentration gradient between ileum and blood capillaries to aid diffusion

ASSIMILATIONAssimilation uptake and use of food within the body

Fate of end products of digestionEnd – product Fate

Glucose Excess is converted to glycogen (insoluble granules) and stored in the liver Converted back to glucose when body needs energy and blood sugar level is low Further excess of glucose is stored as fats in the adipose tissue Used in cellular respiration

Fats Part of it stored as fats in adipose tissue Used in synthesis of cell membrane Utilised in respiration when glucose and glycogen is used up Fats stored under skin and around organs act as energy store and insulation

Fate of end products of digestion

End – product Fate

Amino acids Synthesis of proteins, enzymes and hormones For growth and development Excess amino acids are not stored in the body It is broken down and deaminated in the liver to form ammonia and glycogen (glycogen is stored in the liver)

Egestion In the large intestine water and vitamins (synthesised by bacteria) compact undigested food to form faeces Propelled along colon and rectum

LIVER

• Structure Large, reddish brown organ Located just beneath the diaphragm and overlaps the stomach Plays an important role in metabolism, homeostasis and excretion

• Anatomy

• Vessels associated with the liver

Vessels Function

Hepatic portal vein

Hepatic artery

Hepatic vein

Blood capillaries of villi join to form the hepatic portal vein Carries blood containing end products of digestion from ileum to liver

Carries oxygenated blood to liver

Carries blood containing waste products away from liver

• Function of the liver Function Mode of action

Metabolism of glucose Regulates the blood sugar concentration in the body Excess sugars stored as glycogen granules This occurs in the presence of insulin When plasma sugar levels fall, glucagon converts glycogen to glucose

Metabolism of amino acids Regulates amount of amino acids in the body Excess amino acids cannot be stored Converted during deamination into glucose and urea Excess glucose is stored as glycogen Urea is excreted

Function Mode of actionProduction of bile Produces bile, which is used in digestion

Storage of iron Stores iron from breakdown of haemoglobin Used in the synthesis of new haemoglobin

Excretion of the bile pigment

Haemoglobin is broken down into bile pigments biliverdin and bilirubin Both pigments are excreted into duodenum as bile pigments

Synthesis of plasma proteins

Synthesises plasma protein (fibrinogen, serum globulin and serum) from amino acids They are responsible for the clotting of blood

Storage of vitamins Stores vitamin A and D

Reservoir for blood Blood spaces and network of blood capillaries hold a large volume of blood

Function Mode of actionSource of heat energy Metabolically active, producing a large

amount of heat energy to replace that lost by the body Heat distributed to all parts of the body

Detoxification Toxins produced bacteria in large intestines are absorbed and converted to harmless substances in the liver Liver removes about 95% of alcohol from blood Alcohol oxidised in the liver to energy May also be converted to fats The other 5% lost as sweat, urine and during breathing

DENTITIONSTRUCTUREMechanical digestion is carried on in the mouth by the actionof the teeth and the tongue.

adult

child

Vertical section of molar

EnamelDentine

Gum

Pulp cavity containing nerves and blood vessels

Jaw boneCementum

Crown

Root

Tooth structure and function

Tooth structure Components Function

Enamel Non – living layer of hard calcium salts

Protects dentineForms a hard biting surface

Dentine Softer bone – like layer Acts as a shock absorber

Pulp cavity Contains tooth cells, nerves and blood capillaries

Tooth cells divide to form dentineSupply food and oxygen to cells

Cement Thin layer of bone – like material

Covers dentine of rootHolds root in socket

Root opening Pathway for blood capillaries and nerves

For blood supply, growth and replacement of toothNerves carry messages to and from brain

Tooth structure Components Function

Jaw bone with socket Bone made of calcium phosphate

Tooth fits into socket of jaw bone

Incisor Single rootSharp cutting edge

Biting of pieces of food

Canine Single rootSharp and pointed

Tearing, seizing food

Premolar and molar Wide and flat surfaceHas cusps (points) or ridges

Crushing and grinding food

Different types of dental formulaOmnivore Carnivore Herbivore

Dental formula

i : 2 c : 1 pm : 2 m :3 i : 3 c :1 pm : 4 m: 2 i : 0 c : 0 pm: 3 m: 3

2 1 2 3 3 1 4 3 3 1 3 3

Mode of nutrition

Plant and animal Animal Plant

Incisor Chisel shaped Sharp and pointed Upper incisor absent Small lower incisor, bites against upper horny pad

Canine About the same size as incisors

Long, pointed, curved Upper canines absent Lower canines have sharp edges, bites against upper horny pad

Diastema X X

Omnivore Carnivore Herbivore

Premolar / molar Surface has small cusps

Surface has sharp, pointed edges

Surface flattened with small cusps

Carnassial teeth X X

Feeding action Upper and lower jaw meet Grind food with lateral movements (side to side) of lower jaw

Upper and lower jaw move up and down Scissor – like action Tight jaw attachment

Upper and lower jaw meet Grind food with lateral movements (side to side) of lower jaw Loose jaw attachment

Example Adult human Dog Goat

Tooth Decay Dental plaque is the result of bacteria acting on food or sugar

stuck on teeth Tartar is the hard deposit on the teeth caused by bacterial

plaque, calcium phosphate and calcium carbonate It leads to gum disease resulting in gum irritation and swollen

gum As the bacteria in plaque grow, it produces acid in the layer of

plaque This acid destroys the enamel and later, the dentine layer of

the teeth When the decay (cavity) spreads to the pulp cavity, the entire

tooth is affected The result is painful and swollen gum

Prevention of gum diseasePrevention Action

Taking food rich in calcium, phosphorous and vitamin D

Form strong teeth

Drinking water or using toothpaste with added fluoride

Hardens tooth surfaceMakes them less susceptible to acids

Brushing teeth regularly Remove food particles in teeth

Flossing teeth Remove food lodged between teeth

Reducing sugar in the diet Reduce bacterial affect

Regular dental check up Monitor health of teeth