LEARNING OUTCOMES…LEARNING OUTCOMES… To state the substances required by cells to carry To state the substances required by cells to carry

out metabolic processes;out metabolic processes; To list the complex substances that need to be To list the complex substances that need to be

digested;digested; To explain the necessity for digestion of complex To explain the necessity for digestion of complex

substances;substances; To draw and label the human digestive system;To draw and label the human digestive system; To state and describe the functions of the To state and describe the functions of the

digestive juices and substances that aid the digestive juices and substances that aid the process of digestion.process of digestion.

FOOD DIGESTIONFOOD DIGESTION Food such as carbohydrates, Food such as carbohydrates,

proteins & lipids consist of proteins & lipids consist of large & large & complex organic compounds.complex organic compounds.

Need to be broken downNeed to be broken down into into simple substance that can be simple substance that can be absorbed by the cells in the bodyabsorbed by the cells in the body

The The process of breaking down process of breaking down large & complex substanceslarge & complex substances is is called called digestiondigestion

HUMANHUMANDIGESTIVE DIGESTIVE

SYSTEMSYSTEM

HUMAN DIGESTIVE HUMAN DIGESTIVE SYSTEMSYSTEM

Consist of theConsist of the alimentary canal & alimentary canal & digestive glandsdigestive glands

Alimentary canalAlimentary canal : oral cavity, : oral cavity, oesophagus, stomach, small intestine oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large (duodenum, jejunum, ileum), large intestine (ascending colon, transverse intestine (ascending colon, transverse colon, descending colon, rectum)colon, descending colon, rectum)

Digestive glandsDigestive glands : organs/tissues which : organs/tissues which secrete digestive juices that aid in the secrete digestive juices that aid in the process of digestionprocess of digestion

Digestive juicesDigestive juices : saliva, gastric juice, : saliva, gastric juice, bile, pancreatic juice & intestinal juicebile, pancreatic juice & intestinal juice

HUMAN DIGESTIVE HUMAN DIGESTIVE SYSTEMSYSTEM

DIGESTIVE DIGESTIVE JUICEJUICE

FUNCTIONSFUNCTIONS

SALIVASALIVA Soften foodSoften food Digests cooked starchDigests cooked starch

GASTRIC GASTRIC JUICEJUICE

Kills microorganismsKills microorganisms Contains enzymes which Contains enzymes which digest proteinsdigest proteins Provide an acidic medium Provide an acidic medium needed by the enzymesneeded by the enzymes

BILEBILE

Emulsifies lipids, breaking Emulsifies lipids, breaking them into tiny droplets them into tiny droplets suspended in watersuspended in water Increase the surface area Increase the surface area for the action of enzymesfor the action of enzymes

DIGESTIVE DIGESTIVE JUICEJUICE

FUNCTIONSFUNCTIONS

PANCREATIC PANCREATIC JUICEJUICE

Contain enzymes Contain enzymes which digest cooked which digest cooked starch, proteins & starch, proteins & lipidslipids

INTESTINAL INTESTINAL JUICEJUICE

Contains enzymes Contains enzymes which complete the which complete the digestion of proteins digestion of proteins & dissaccharides& dissaccharides

The Digestion of Carbohydrates, The Digestion of Carbohydrates, Proteins & Lipids in HumansProteins & Lipids in Humans

In the oral cavity & oesophagusIn the oral cavity & oesophagus Food chewed by the teeth Food chewed by the teeth small small

pieces : increases the surface area of pieces : increases the surface area of food for digestive enzymes to work on food for digestive enzymes to work on laterlater

3 pairs of 3 pairs of salivary glandssalivary glands secrete secrete salivasaliva into the oral cavity ( into the oral cavity (parotid parotid glands, sublingual glands, glands, sublingual glands, submaxillary glandssubmaxillary glands))

Saliva softens food (easier to swallow)Saliva softens food (easier to swallow)

Saliva contain enzyme Saliva contain enzyme ((ptyalin/salivary amylaseptyalin/salivary amylase) – able ) – able to hydrolyse cooked starch into to hydrolyse cooked starch into maltosemaltose

The tongue moves the food in the The tongue moves the food in the oral cavity while it is being oral cavity while it is being chewed, rolling it into a round chewed, rolling it into a round mass called mass called bolusbolus..

The tongue is then raised to The tongue is then raised to swallow the food into the swallow the food into the oesophagus.oesophagus.

Food is moved down the oesophagus by Food is moved down the oesophagus by peristalsisperistalsis (rhythmic contraction & (rhythmic contraction & relaxation of the alimentary tube)relaxation of the alimentary tube)

The cardiac sphincter (a ring of muscles The cardiac sphincter (a ring of muscles which guard the opening of the stomach) which guard the opening of the stomach) relaxes, food enters the stomachrelaxes, food enters the stomach

In the In the StomachStomach

The stomach wall The stomach wall contains contains gastric glandsgastric glands secrete secrete gastric juicegastric juice (contain (contain HCl acid, rennin HCl acid, rennin & pepsin& pepsin))

HCl acid (pH 1),kills HCl acid (pH 1),kills m/organisms which may m/organisms which may be present in food, be present in food, provides a suitable provides a suitable medium for action of medium for action of rennin & pepsin (active rennin & pepsin (active in acidic condition)in acidic condition)

Rennin coagulates milk by converting Rennin coagulates milk by converting caseinogen (soluble milk protein) into caseinogen (soluble milk protein) into casein (insoluble milk protein)casein (insoluble milk protein)

Pepsin hydrolyses proteins into peptones Pepsin hydrolyses proteins into peptones (fragments of protein molecule, one or (fragments of protein molecule, one or more coiled polypeptides) & more coiled polypeptides) & polypeptides.polypeptides.

ProteinProtein + + water water peptones peptones + + polypeptidespolypeptides

The stomach contracts & relaxes The stomach contracts & relaxes rhythmically (peristalsis), helps to rhythmically (peristalsis), helps to break up food physically, helps to mix break up food physically, helps to mix food with enzymesfood with enzymes

pepsin

Food digested in the stomach for Food digested in the stomach for about 4 hours.about 4 hours.

Partially digested food leaves the Partially digested food leaves the stomach, it is semi-fluidstomach, it is semi-fluid (chyme)(chyme)

Chymes enters the duodenum Chymes enters the duodenum when the pyloric sphincter of when the pyloric sphincter of stomach relaxesstomach relaxes

IN THE DUODENUMIN THE DUODENUM Duodenum Duodenum receive bilereceive bile

from the gall bladder & from the gall bladder & pancreatic juice from the pancreatic juice from the pancreaspancreas

Bile : synthesised in the Bile : synthesised in the liver liver stored in the gall stored in the gall bladder channeled through bladder channeled through the bile duct into the the bile duct into the duodenum when neededduodenum when needed

Bile contains Bile contains bile saltbile salt - not - not contain any enzymescontain any enzymes

Function in Function in emulsifying emulsifying lipids,lipids, breaking lipids into breaking lipids into tiny droplets which are tiny droplets which are suspended in water – to suspended in water – to increase the surface area increase the surface area that can be acted by that can be acted by enzymesenzymes

Reducing the surface tensionReducing the surface tension of of water so that lipids no longer float water so that lipids no longer float on top of water.on top of water.

Pancreatic juicePancreatic juice is synthesised by is synthesised by pancreas & channeled to the pancreas & channeled to the duodenum via pancreatic duct.duodenum via pancreatic duct.

Pancreatic juice : Pancreatic juice : amylase, trypsin, amylase, trypsin, lipaselipase

IN THE DUODENUMIN THE DUODENUM Pancreatic juice is Pancreatic juice is alkalinealkaline. Amylase, trypsin . Amylase, trypsin

& lipase are only active in an alkaline medium& lipase are only active in an alkaline medium

Cooked starch + water Cooked starch + water maltose maltose

Peptones & + water Peptones & + water peptides + peptides + polypeptidespolypeptides

Fats (or oils) + water Fats (or oils) + water fatty acids + fatty acids + glycerolglycerol

amylase

lipase

trypsin

In the small intestineIn the small intestine Throughout the wall Throughout the wall of the small of the small intestine there are intestine there are intestinal glandsintestinal glands (produce intestinal (produce intestinal juice - alkaline) juice - alkaline)

Contains Contains erepsin, erepsin, maltase, sucrase & maltase, sucrase & lactaselactase

Peptides Peptides ++ water water amino acids amino acids

Erepsin/ peptidas

e

In the small intestineIn the small intestine Maltose + water Maltose + water

glucoseglucose

Sucrose + water Sucrose + water glucose + fructose glucose + fructose

Lactose + water Lactose + water glucose + galactoseglucose + galactose

maltase

sucrase

lactase

LOCATIONLOCATION DIGESTIVE DIGESTIVE JUICEJUICE

DIGESTIVE DIGESTIVE GLANDGLAND

ENZYMESENZYMES BIOCHEMICAL REACTIONBIOCHEMICAL REACTION

Oral cavityOral cavity SalivaSaliva Salivary Salivary glandgland

Salivary Salivary amylase/ amylase/ ptyalinptyalin

Cooked starch + water Cooked starch + water maltose maltose

StomachStomach

Gastric juiceGastric juice Gastric glandGastric gland RenninRennin Caseinogens + water Caseinogens + water casein casein

PepsinPepsin Protein + water Protein + water peptones + peptones + polypeptidespolypeptides

HCl acidHCl acid Kill pathogens in foodKill pathogens in foodPrepared acidic medium for enzyme reactionPrepared acidic medium for enzyme reaction

LiverLiver Bile saltBile salt liverliver -- Emulsifies fatsEmulsifies fats

PancreasPancreas Pancreas Pancreas juicejuice

PancreasPancreas

AmylaseAmylase Cooked starch + water Cooked starch + water maltose maltose

TrypsinTrypsin Peptones & polypeptides + water Peptones & polypeptides + water peptides peptides

LipaseLipase Fats + water Fats + water fatty acid + glycerol fatty acid + glycerol

Small Small intestineintestine

Intestinal juiceIntestinal juice Intestinal Intestinal glandsglands

MaltaseMaltase Maltose + water Maltose + water glucose glucose

LactaseLactase Lactose+ water Lactose+ water glucose+ galactose glucose+ galactose

SucraseSucrase Sucrose+ water Sucrose+ water Glucose + fructose Glucose + fructose

Erepsin/ Erepsin/ peptidasepeptidase

Peptides + water Peptides + water amino acid amino acid

LipaseLipase Fats + water Fats + water fatty acids + glycerol fatty acids + glycerol

Digestive System in Ruminants Digestive System in Ruminants & Rodents& Rodents

Ruminants & rodentsRuminants & rodents == herbivores herbivores that that only feed on plantsonly feed on plants which which contain cellulosecontain cellulose

Cellulose can only Cellulose can only digested by digested by the enzyme cellulasethe enzyme cellulase to glucose to glucose

A herbivore has a digestive A herbivore has a digestive system that is system that is adapted to adapted to

digest cellulosedigest cellulose

Digestive System in Ruminants Digestive System in Ruminants & Rodents& Rodents

Certain parts of the alimentary Certain parts of the alimentary canal contain bacteria & protozoa canal contain bacteria & protozoa which secrete the which secrete the enzyme cellulaseenzyme cellulase to digest the cellulose.to digest the cellulose.

In ruminants (In ruminants (cows, sheep, goats & cows, sheep, goats & deerdeer), the digestion of cellulose ), the digestion of cellulose occurs in a complicated occurs in a complicated stomach stomach while in rodents, the digestion of while in rodents, the digestion of cellulose occurs in the large cellulose occurs in the large caecumcaecum

The digestion of cellulose in The digestion of cellulose in the the special stomachspecial stomach of the of the ruminant is as follow :ruminant is as follow :

The stomach of ruminants have The stomach of ruminants have four chambersfour chambers : : rumen, reticulum, rumen, reticulum, omasum & abomasumomasum & abomasum

When they eats, it When they eats, it does not chew does not chew grassgrass, but swallows it , but swallows it immediately & immediately & stores itstores it until its until its appetite is satisfied. Then the appetite is satisfied. Then the food is food is returned to the mouthreturned to the mouth & & the cow chews the cudthe cow chews the cud

DIGESTIVE SYSTEM OF DIGESTIVE SYSTEM OF RUMINANTSRUMINANTS

–When the food is When the food is first swallowedfirst swallowed, , it passes down the oesophagus into it passes down the oesophagus into the first chamber called the first chamber called rumenrumen. In . In the rumen, the rumen, bacteria & protozoabacteria & protozoa secrete the enzyme secrete the enzyme cellulase to cellulase to hydrolysehydrolyse the cellulose into the cellulose into glucose.glucose.

–The food then The food then passes into the passes into the second chambersecond chamber called the called the reticulum.reticulum.

–The bacteria & protozoa in the The bacteria & protozoa in the reticulum continue to hydrolyse reticulum continue to hydrolyse the cellulose.the cellulose.

When the ruminant is ready to When the ruminant is ready to chew the cud, the chew the cud, the food is food is returned to the mouthreturned to the mouth to be to be chewed again. Movement of the chewed again. Movement of the food from the reticulum to the food from the reticulum to the mouth is by mouth is by antiperistalsisantiperistalsis of of the oesophagusthe oesophagus

After the food has been chewed, it After the food has been chewed, it is again is again swallowedswallowed but this time, it but this time, it passes into the passes into the 33rdrd chamber chamber called called the the omasumomasum..

The inner surface of the The inner surface of the omasumomasum has has folds to act as sievesfolds to act as sieves. . GlucoseGlucose, the , the product of cellulose digestion, is product of cellulose digestion, is absorbedabsorbed & as the food passes into & as the food passes into the last chamber called, the the last chamber called, the abomasumabomasum, it is strained. , it is strained.

This is to This is to prevent any big prevent any big particlesparticles from entering the from entering the omasumomasum & & damaging it.damaging it.

The The abomasumabomasum is the true stomach and is the is the true stomach and is the only chamber which secretes gastric juice only chamber which secretes gastric juice for digestion of other food substance.for digestion of other food substance.

The Digestion of Cellulose in RodentsThe Digestion of Cellulose in Rodents

Rodents refer to a group of mammals that Rodents refer to a group of mammals that comprise rabbits, rats, mice, hamsters, comprise rabbits, rats, mice, hamsters, squirrels & porcupines.squirrels & porcupines.

Rodents have a long & large caecum for the Rodents have a long & large caecum for the digestion of cellulosedigestion of cellulose

In the caecum of rodents, the bacteria & In the caecum of rodents, the bacteria & protozoa secrete the enzyme cellulase for protozoa secrete the enzyme cellulase for the digestion of cellulosethe digestion of cellulose

COMPARISON COMPARISON BETWEEN BETWEEN HUMAN, HUMAN,

RUMINANTS & RUMINANTS & RODENTSRODENTS IN IN PROCESS OF PROCESS OF CELLULOSE CELLULOSE DIGESTIONDIGESTION

PROBLEMS RELATED TO FOOD PROBLEMS RELATED TO FOOD DIGESTIONDIGESTION

Incomplete digestion of foodIncomplete digestion of food Can cause abdominal pain, nausea & Can cause abdominal pain, nausea & vomiting.vomiting.

Several causes for incomplete digestion of Several causes for incomplete digestion of food :food :– Insufficient chewing of food before being Insufficient chewing of food before being swallowedswallowed

– Eating too much, causing the stomach to be Eating too much, causing the stomach to be distendeddistended

– Eating too much of fatty (oily) & spicy foodEating too much of fatty (oily) & spicy food– Insufficient dietary fibresInsufficient dietary fibres– Excessive consumption of alcoholExcessive consumption of alcohol– Under secretion of certain digestive enzymesUnder secretion of certain digestive enzymes– Insufficient bile saltsInsufficient bile salts

Bile stones preventing the flow of Bile stones preventing the flow of bilebile

Bile stones sometimes form in the Bile stones sometimes form in the gall bladder. They are solids gall bladder. They are solids consisting of a mixture of bile consisting of a mixture of bile pigments, cholesterol & calcium saltspigments, cholesterol & calcium salts

Bile stones may lodge in the bile Bile stones may lodge in the bile duct & prevent the flow of bile to duct & prevent the flow of bile to the duodenum. As a result, fats in the duodenum. As a result, fats in the food cannot be emulsified into the food cannot be emulsified into tiny droplets. This reduce the tiny droplets. This reduce the surface area for the action of the surface area for the action of the enzyme lipase. The digestion of fats enzyme lipase. The digestion of fats is hindered.is hindered.

Reduced production of specific Reduced production of specific digestive enzymesdigestive enzymes

Problems related to food Problems related to food digestion may be caused by too digestion may be caused by too little of a specific digestive little of a specific digestive enzyme being producedenzyme being produced

For example, if an organ such as For example, if an organ such as the pancreas is damaged, then the the pancreas is damaged, then the enzymes amylase & trypsin are enzymes amylase & trypsin are greatly reduced. As a result, greatly reduced. As a result, certain subtances in the food certain subtances in the food cannot be digested & the body cannot be digested & the body cannot obtain enough nutrients.cannot obtain enough nutrients.

REMOVAL OF GALLSTONEREMOVAL OF GALLSTONE

EXERCISE 6.4EXERCISE 6.41.1.List the complex List the complex substances that need to be substances that need to be digested.digested.

2.2.Explain the necessary for Explain the necessary for digestion of complex digestion of complex substances.substances.

3.3.Explain the digestion of Explain the digestion of carbohydrates, proteins carbohydrates, proteins and lipids.and lipids.