Pure Biology Chp 6 Nutrition in Humans

Chapter 6

Nutrition in

Humans

Nutrition in

Humans

Questions to answer!1. What is nutrition?

2. Which parts of the body are involved in digestion?

3. What is digestion?

4. What happens to the food after digestion?

Learning Learning ObjectivesObjectives

What is Nutrition?

Objective 1:

State the definition of nutrition.

Definition of Definition of NutritionNutrition

Nutrition is the process of taking in food and converting it into living matter.

Animals feed by taking in complex organic matter –

HOLOZOIC NUTRITION

What is What is Nutrition?Nutrition?

1. Feeding or ingestion: food is taken into the body.

5 Processes of 5 Processes of NutritionNutrition

What is What is Nutrition?Nutrition?

2. Digestion: large food molecules are broken down into smaller soluble molecules that can be absorbed into the body cells.

3. Absorption: digested food substances are absorbed into body cells.

4. Assimilation: some of the absorbed food substances are converted into new protoplasm or used to provide energy.

5. Egestion: undigested food is being passed out of the body via the anus.

Which parts of the body are involved in digestion?

Objective 2:

Describe the functions of the main regions of the alimentary canal.

The Digestive The Digestive SystemSystem

Which parts of the Which parts of the body are involved body are involved

in digestion?in digestion?

• Consists of the alimentary canal and the glands and organs associated with it.

• The alimentary canal is like a tube that extends from the mouth to the anus.

• Most of its length is coiled in the abdominal cavity.




salivary gland

stomach

pancreaspyloric sphincter

descending colon

rectumanus

mouthteeth

oesophagus

liver

Gall bladder

duodenum

ileumascending

coloncaecumappendix

pharynx

The Digestive System - The Digestive System - MouthMouth

• Food enters the body through the mouth.

• The mouth leads to the buccal cavity.

The Digestive System - The Digestive System - MouthMouth

What do you find in the mouth?:• Teeth: chewing action

(mastication) breaks down large pieces of food into smaller pieces. This increases surface area to volume ratio of the food for enzyme action.

• Salivary glands: secrete saliva into the mouth via ducts.

• Tongue: helps to mix food with saliva. Taste buds help one to identify and select suitable foods.

salivary gland

mouth

teeth

Process of nutrition??

The Digestive System - The Digestive System - PharynxPharynx

• Connects the buccal cavity to the oesophagus and larynx (voice box).

• Leads to the trachea.• Both food and air must

pass through the pharynx then they enter the body.

• Air will pass to the trachea, while food will go into the oesophagus.

trachea (windpipe)

glottis

pharynx

oesophagus

larynx (voice-box)

air

trachea (windpipe)

glottis

pharynx

oesophagus

larynx (voice-box)

air

The Digestive System - The Digestive System - PharynxPharynx

• The epiglottis is above the larynx, and it prevents food from going the wrong way.

• During swallowing, the larynx moves up and the epiglottis moves downwards so that the epiglottis covers the larynx.

• If food or water enters the trachea, it induces coughing to force the food/water particles out and prevent choking.

pharynx

trachea (windpipe)

oesophagusglottis

epiglottis

food particles

larynx (voice-box)

pharynx

trachea (windpipe)

oesophagusglottis

epiglottis

food particles

larynx (voice-box)

The Digestive System - The Digestive System - OesophagusOesophagus

• Also known as the gullet.• A narrow, muscular tube.• Passes through the thorax

(chest) and the diaphragm to join the stomach.


• Made up of 2 layers of muscles, present from the oesophagus to the rectum:– Longitudinal muscles

(outer layer)– Circular muscles (inner

layer)• These muscles are

antagonistic muscles – when one contracts, the other relaxes

circular muscles

Part of the gut walllongitudinal muscles


• The muscles cause peristalsis – rhythmic, wave-like contractions of the gut walls.

• It helps to move food along the gut while mixing the food with digestive juices.

circular muscles

Part of the gut walllongitudinal muscles




mouthteeth

oesophagus

salivary gland

food mass

circular muscleslongitudinalmuscles


PERISTALSIS• When circular muscles contract, longitudinal muscles relax.

The gut wall constricts (becomes narrower and longer). Food is squeezed or pushed forward.

• When longitudinal muscles contract, circular muscles relax. The gut wall dilates (becomes wider and shorter). This widens the lumen for food to enter.

wall constricts to push food forward

wall dilates to allow food to enter


PERISTALSIS• When circular muscles contract, longitudinal muscles relax.

The gut wall constricts (becomes narrower and longer). Food is squeezed or pushed forward.

• When longitudinal muscles contract, circular muscles relax. The gut wall dilates (becomes wider and shorter). This widens the lumen for food to enter.



Objective 2:

Describe the functions of the main regions of the alimentary canal.

The Digestive System - The Digestive System - StomachStomach

• The stomach is a distensible (muscular) bag.

• The muscles of the stomach wall are thick and well-developed.

• When fully stretched, it sends signals to the brain to indicate that it is full.


• The stomach wall has many pits which lead to gastric glands.

• They secrete gastric juices into the stomach.What is

one enzyme found in gastric juice? pits


• The stomach stores food for a few hours. It digests food to become chyme.

• Food stays in the stomach because of the pyloric sphincter – a ring of circular muscle located between the stomach and duodenum.– Contracts: stomach exit closes– Relaxes: stomach exit opens,

food leaves the stomach.

Where else can we find

circular muscles?


The Digestive System – Small The Digestive System – Small IntestineIntestine

• Consists of 3 parts:– Duodenum– Jejunum– Ileum

progressively more coiled

The Digestive System – Small The Digestive System – Small IntestineIntestine

• Wall of small intestine has 2 functions:– Contains glands which

secrete intestinal juice. It contains digestive enzymes.

– Wall is adapted to absorb digested food products and water.


The Digestive System – Large The Digestive System – Large IntestineIntestine

• The large intestine is about 1.5 m long– Shorter and wider than

the small intestine• Consists of 2 parts:

– Colon– Rectum

large intestine

small intestine

rectum

colon


• Only undigested food enters the colon.

• It absorbs water and mineral salts from the food.

• No digestion occurs in the colon.

colon


• The rectum temporarily stores faeces.

• When it contracts, faeces is expelled through the anus.

rectum


• Between the small and large intestines lie the caecum and appendix.

• The caecum has no function in humans.

• The appendix contains bacteria that are useful to the body.

caecum

appendixProcess of nutrition??





Objective 3:

Describe the functions of the organs associated with

digestion.




salivary gland

stomach

pancreaspyloric sphincter

descending colon

rectumanus

mouthteeth

oesophagus

liver

Gall bladder

duodenum

ileumascending

coloncaecumappendix

pharynx

The Digestive System - The Digestive System - LiverLiver

• The largest internal organ in the body

• There are 3 important blood vessels attached to the liver:– Hepatic vein– Hepatic artery– Hepatic portal vein

liver

gall bladder

bile duct


• It is also the largest gland in the body.– Secretes bile into the

duodenum• Properties of bile:

– Alkaline– Greenish-yellow– Contains bile salts and bile

pigments– Produced in the liver, stored

in the gall bladder

Why alkaline

?


• Functions of bile:– Neutralize acid in chyme– Activate intestinal enzymes– Speed up fat digestion– Gives faeces its colour

• When the gall bladder contracts, bile is secreted into the duodenum via the bile duct.

liver

gall bladder

bile duct


The Digestive System - The Digestive System - PancreasPancreas

• Connected to the duodenum via the pancreatic duct

• Secretes pancreatic juice which contains digestive enzymes.

• Also secretes hormones which control blood glucose level.


What is Digestion?

Objective 4:

State the definition of digestion.

Definition of Definition of DigestionDigestion

Digestion is the process by which the body breaks down

carbohydrates, fats and proteins into simpler substances that cells

can absorb and use.

What is What is Digestion?Digestion?

Physical digestionThe mechanical break up

of food into small particles.

Chemical digestion The breaking down of

large molecules in food into small, soluble

molecules which can be absorbed.

Chemical digestion involves hydrolysis catalyzed by digestive enzymes.

What is Digestion?

Objective 5:

Describe the process of digestion in the

alimentary canal and the functions of digestive enzymes.

Physical Physical DigestionDigestion


• Physical digestion breaks down food into smaller particles.• Purpose: to increase surface area to volume ratio of the

food to aid enzyme action.• Food substances are not chemically changed during

physical digestion.• Where does physical digestion occur?

– In the mouth– Along the alimentary canal– Physical digestion of fats in the small intestine

chewing / masticationperistalsis

emulsification

Physical Physical DigestionDigestion


EMULSIFICATION• Fats do not dissolve in water – they

tend to clump together. • This reduces the surface area for

enzymes to work, slowing down fat digestion.

• Bile molecules place themselves in between the fat and water – half the molecule is hydrophilic, half is hydrophobic.

• This prevents the fat from clumping together.

• Surface area of fat molecules is increased, speeding up enzyme action.

Picture taken from http://www.colorado.edu/eeb/web_resources/cartoons/bile.html

• Breaking down of large molecules in food (starch, protein, fats) into small soluble molecules which can be absorbed.

• Hydrolytic reactions – catalysed by ENZYMES

• Three groups of enzymes:

• Chemical digestion occurs mainly in 3 parts of the alimentary canal:– Mouth, stomach, small intestine

Carbohydrases ProteasesLipases


Chemical Chemical DigestionDigestion



In the mouth...• Food in the mouth stimulates the salivary glands to

secrete saliva.• Saliva is mixed with food. Mucin in saliva softens the

food.• Salivary amylase is found in saliva:

– Digests to • The optimum pH of salivary amylase is pH 7.

– The pH of saliva is neutral. • The tongue rolls the food into small, slippery, round

masses called boli (singular: bolus).• The boli are swallowed and passed down into the

oesophagus.

starch maltose



In the stomach... The presence of food in the stomach stimulates the

gastric glands to secrete gastric juice into the stomach. Gastric juice contains 3 substances:

– Hydrochloric acid– Pepsinogen– Prorennin



In the stomach... Action of Pepsin Pepsinogen is activated to pepsin by hydrochloric acid. Pepsin then digests protein to polypeptides.

pepsinogen pepsinhydrochloric acid

proteins polypeptidespepsin



In the stomach... Action of Rennin Prorennin is activated to rennin by hydrochloric acid. Rennin curdles milk proteins by converting soluble

protein caseinogen into insoluble casein.– Soluble caseinogen would pass through the stomach as

easily as water and not be digested.– Insoluble casein can remain in the stomach to be digested.

prorennin renninhydrochloric acid

caseinogen caseinrennin

casein polypeptidespepsin



In the stomach... Purpose of Hydrochloric Acid

Stops the activity of salivary amylase by it

Activates pepsinogen and prorennin to form and respectively

Provides acidic medium for the action of pepsin and rennin

Kills harmful microorganisms in food

denaturing

pepsinrennin



In the small intestine... When chyme enters the small intestine, it stimulates 3

glands:– Intestinal glands secrete intestinal juice, which

contains enzymes sucrase, maltase, intestinal lipase, lactase, enterokinase, and erepsin.

– Pancreas secretes pancreatic juice, which contains pancreatic amylase, pancreatic lipase, and trypsinogen.

– Gall bladder releases bile. It does not contain enzyme

SMILEE!

ALT



In the small intestine...

All 3 fluids are alkaline:– Neutralize acidic chyme– Provide suitable pH for the action of pancreatic and

intestinal enzymes



In the small intestine... Carbohydrate digestion

starch maltose

pancreatic amylase

lactose glucose + galactose

sucrose glucose + fructose

glucosemaltase

lactase

sucrase



In the small intestine... Protein digestion

trypsinogen trypsinenterokinase

proteins polypeptidestrypsin

polypeptides amino acidserepsin



In the small intestine... Fat digestion

fats fatty acids + glycerollipase

Recall: What process

speeds up fat digestion in

the small intestine?

Digestive Digestive EnzymesEnzymes


starch maltose

pancreatic amylase

lactose glucose + galactose

sucrose glucose + fructose

glucosemaltase

lactase

sucrase

Carbohydrate digestion

starch maltose

salivary amylase

mou

thsm

all i

ntes

tine

Digestive Digestive EnzymesEnzymes


Protein digestion

smal

l int

estin

e

trypsinogen trypsinenterokinase

proteins polypeptidestrypsin

polypeptides amino acidserepsin

prorennin renninhydrochloric acid

caseinogen caseinrennin

casein polypeptidespepsinstom

ach

What happens to the food after digestion?

Objective 6:

Describe how digested food is absorbed.

AbsorptionAbsorptionWhat happens to What happens to

food after food after digestion?digestion?

• Where does absorption occur?

In the small intestine and large intestine

• What nutrients are being absorbed?

Simple sugars

Amino acids

Fatty acids and glycerols

Water and mineral salts

AbsorptionAbsorptionWhat happens to What happens to


How does absorption take place in the small intestine?• Glucose and amino acids:

– Absorbed by into blood capillaries of the villi.– Absorbed by when there is lower

concentration of digested food substances in the small intestine than in the blood capillaries.

• Fatty acids and glycerol:– Absorbed by into the epithelium– Combine to form fat globules which enter the lacteals

• Water and mineral salts:– Absorbed by the and – Most of the water is absorbed by the ileum

diffusion

active transport

diffusion

small intestine colon

Absorption: Small Absorption: Small IntestineIntestine

What happens to What happens to food after food after digestion?digestion?

Adaptations of the Small Intestine for Absorption• The rate of absorption of digested food substances

depends on 3 factors:1. Surface area2. The thickness of

cell membranes3. Concentration

gradient



1. Surface Area• The surface area of the small intestine is increased for

absorption in 4 ways:1. Inner walls have folds2. The surface of the folds are lined with numerous

villi (singular: villus), which are minute finger-like projections.

3. The epithelial cells of the villi have numerous microvilli.

4. The small intestine is long, providing large surface area and ample time for absorption.







2. Thickness of Cell Membranes• The villi have very thin membranes: the epithelium is

only one-cell thick.

3. Concentration Gradient• In each villus is a lacteal (lymphatic capillary)

surrounded by blood capillaries.• The lacteal continually transports away from the villus,

while the blood capillaries transports and away.

• This maintains the concentration gradient needed for the absorption of food substances.

fatssugars

amino acids

EgestionEgestionWhat happens to What happens to


• Some food substances cannot be digested and remain unabsorbed in the large intestine.

• These are stored temporarily in the rectum.• When the rectum is full, they are discharged as faeces

through the .• This process is known as egestion or defecation.

anus


Objective 7:

Describe how digested food is assimilated.

Transport and Transport and AssimilationAssimilation


Transport of Simple Sugars• After absorption, the blood in the villi is rich in sugars.• Blood capillaries unite to form the hepatic portal vein.• The hepatic portal vein transports sugars to the liver.



Assimilation of Simple Sugars• In the liver, most sugars are converted to glycogen and

stored.• Glucose leaves the liver and is distributed around the

body by the bloodstream.– Used during respiration to provide energy for cells.

• Excess glucose is returned to the liver– Hormone insulin (produced by Islets of Langerhan in the

pancreas) stimulates the liver to convert glucose to glycogen for storage.

– When more glucose is required, the liver will convert glycogen back to glucose.



Transport and Assimilation of Amino Acids• Amino acids pass through the liver before they are

transported to the rest of the body.• How are amino acids used?

– Converted to protoplasm by cells, used for growth and repair of body parts

– Used to form enzymes and hormones• Excess amino acids are deaminated.


Objective 8:

State the functions of the liver.

Functions of the Functions of the LiverLiver


The Liver has 7 Functions1. Regulation of blood glucose concentration2. Production of bile3. Protein synthesis4. Iron storage5. Deamination of amino acids6. Detoxification7. Heat production



1. Regulation of Blood Glucose Concentration• Blood normally contains about 70-90 mg of glucose per

100 cm3 of blood.• After a meal:

– Amount of glucose in the blood rises– Stimulates Islets of Langerhans in the pancreas to

secrete insulin into the bloodstream– Insulin is transported to the liver.– Insulin stimulates liver to convert excess glucose to

glycogen for storage.– Blood leaving the liver contains a constant amount of

glucose. What about adrenaline??



1. Regulation of Blood Glucose Concentration• When body cells need glucose:

– Glucose level in the blood drops.– Islets of Langerhan are stimulated to secrete hormone

glucagon.– Glucagon stimulates liver to convert stored glycogen to

glucose.– Glucose enters the blood; blood glucose level returns to

normal.



1. Regulation of Blood Glucose Concentration• If we have not eaten for a long time:

– Glucose level in the blood drops below average.– Blood that is low in glucose reaches the hypothalamus

in the brain.– Brain sends signals to the stomach.– This causes strong contractions and we feel hunger

pangs.– After eating, the blood glucose level rises. The

hypothalamus signals to the stomach to stop contracting.



1. Regulation of Blood Glucose Concentration

high blood glucose

concentration

normal blood glucose concentration

low blood glucose

concentrationpancreas

secretes insulin

pancreas secretes glucagon

converts glucose to glycogen

converts glycogen to glucose



2. Production of Bile• The liver produces bile which is stored in the

before use.• Bile is used in the of fats.

3. Protein Synthesis• Blood plasma contains amino acids from the diet.• The liver synthesizes these amino acids to form

proteins, e.g.:– Albumins, globulins, fibrinogen (for blood clotting)

gallbladder

emulsification



4. Iron Storage• Red blood cells contain a iron, which is involved in the

transportation of oxygen around the body.• These cells become worn out after some time.• They are destroyed in the spleen, a gland near the

liver.• Haemoglobin from red blood cells is brought to the

liver.• Haemoglobin is broken down, forming iron and bile.• Iron is stored in the liver.



5. Deamination of Amino Acids• Excess amino acids are transported to the liver.• The amino groups are removed and converted to urea.• Urea leaves the body in urine.• The remains of the amino acid are converted into

glucose.• Excess glucose is converted to .glycogen



6. Detoxification• This is the process of converting harmful substances

into harmless ones.• Breaks down alcohol to acetaldehyde by the action of

alcohol dehydrogenase• Acetaldehyde can be broken down to compounds

which can be used in respiration.• Excessive alcohol consumption stimulates acid

secretion in the stomach, increasing the risk of gastric ulcers.



6. Detoxification• Prolonged alcohol use can lead to cirrhosis of the liver.

– Liver cells are being destroyed and replaced with fibrous tissue

– Cells are less able to function– Can lead to liver failure and death



7. Heat Production• There are many chemical reactions taking place in the

liver.• Heat is produced from these reactions.• The heat is distributed by the blood to other parts

other body.• Helps to maintain body temperature.

Alimentary Canal

Pure Biology Chapter 6

Mouth

Pharynx

Oesophagus

Stomach

Small intestine

Large intestine

Anus

Colon

Rectum

Nutrition

Digestion

Ingestion

Organs and GlandsIn digestion

Absorption

Assimilation

Egestion

Jejunum

Duodenum

Ileum

Liver Pancreas

Gall bladder

BilePancreatic

amylaseHormones

Insulin

Glucagon

Folds

Villi

Microvilli

Blood capillaries

Lacteals

Simple sugars

Amino acids

Fats

Hepatic portal vein

consists of consists of

secreted into

leads to

contains

stores

unite to form

absorbs

via

via

consists of

secretes

consist of

walls have

Tongue

Teeth

Salivary glands

Alimentary Canal

Pure Biology Chapter 6

Mouth

Pharynx

Anus

Colon

Rectum

Nutrition

Organs and GlandsIn digestion

Gall bladder

Pancreatic amylase

Hormones

Glucagon

Folds

Microvilli

Simple sugars

Amino acids

Fats

Hepatic portal vein

consists of consists of

secreted into

leads to

contains

stores

unite to form

absorbs

via

via

consists of

secretes

consist of

walls have

Tongue

Teeth

Salivary glands

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Pure Biology Chp 6 Nutrition in Humans