Digestion IGCSE
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Transcript of Digestion IGCSE
DIGESTION
B M Subramanya Swamy M.Sc. B.Ed. CIE Co ordinator & Examination Officer
Kanaan Global School Jakarta
Indonesia [email protected]
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