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Chapter 6
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 Objectives
What is Nutrition?
Objective 1:
State the definition of
nutrition.
Definition of Nutrition
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 Nutrition?
1. Feeding or ingestion: food is taken into the body.
5 Processes of Nutrition What is 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 System Which parts of the body are involved 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.
The Digestive System Which parts of the body are involved in digestion?
salivary gland
stomach
pancreas
pyloric sphincter
descending colon
rectum
anus
mouth teeth
oesophagus
liver
Gall bladder
duodenum
ileum ascending colon
caecum
appendix
pharynx
The Digestive System - Mouth
• Food enters the body through the mouth.
• The mouth leads to the buccal cavity.
The Digestive System - Mouth 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 - Pharynx
• 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 - Pharynx
• 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 - Oesophagus
• Also known as the gullet. • A narrow, muscular tube. • Passes through the thorax
(chest) and the diaphragm to join the stomach.
The Digestive System - Oesophagus
• 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 wall longitudinal muscles
The Digestive System - Oesophagus
• 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 wall longitudinal muscles
The Digestive System Which parts of the body are involved in digestion?
mouth
teeth
oesophagus
salivary gland
food mass
circular muscles longitudinal muscles
The Digestive System - Oesophagus 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
The Digestive System - Oesophagus 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.
Process of nutrition??
Which parts of the body are involved in digestion?
Objective 2:
Describe the functions
of the main regions of
the alimentary canal.
The Digestive System - Stomach
• 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 Digestive System - Stomach
• 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 Digestive System - Stomach • 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?
Process of nutrition??
The Digestive System – Small Intestine
• Consists of 3 parts: – Duodenum – Jejunum – Ileum
progressively
more coiled
The Digestive System – Small Intestine
• 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.
Process of nutrition??
The Digestive System – Large Intestine
• 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
The Digestive System – Large Intestine
• Only undigested food enters the colon.
• It absorbs water and mineral salts from the food.
• No digestion occurs in the colon.
colon
The Digestive System – Large Intestine
• The rectum temporarily stores faeces.
• When it contracts, faeces is expelled through the anus.
rectum
The Digestive System – Large Intestine
• 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
appendix Process of nutrition??
The Digestive System Which parts of the body are involved in digestion?
Which parts of the body are involved in digestion?
Objective 3:
Describe the functions of the organs
associated with digestion.
The Digestive System Which parts of the body are involved in digestion?
salivary gland
stomach
pancreas
pyloric sphincter
descending colon
rectum
anus
mouth teeth
oesophagus
liver
Gall bladder
duodenum
ileum ascending colon
caecum
appendix
pharynx
The Digestive System - Liver
• 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
The Digestive System - Liver
• 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
?
The Digestive System - Liver
• 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
Process of nutrition??
The Digestive System - Pancreas
• Connected to the duodenum via the pancreatic duct
• Secretes pancreatic juice which contains digestive enzymes.
• Also secretes hormones which control blood glucose level.
Process of nutrition??
What is Digestion?
Objective 4:
State the definition of
digestion.
Definition of Digestion
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 Digestion?
Physical digestion
The 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 Digestion What is Digestion?
• 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 / mastication peristalsis
emulsification
Physical Digestion What is Digestion?
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/carto
ons/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 Proteases Lipases
What is Digestion? Chemical Digestion
Chemical Digestion What is Digestion?
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
Chemical Digestion What is Digestion?
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
Chemical Digestion What is Digestion?
In the stomach... Action of Pepsin Pepsinogen is activated to pepsin by hydrochloric acid. Pepsin then digests protein to polypeptides.
pepsinogen pepsin hydrochloric acid
proteins polypeptides pepsin
Chemical Digestion What is Digestion?
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 rennin hydrochloric acid
caseinogen casein rennin
casein polypeptides pepsin
Chemical Digestion What is Digestion?
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
pepsin
rennin
Chemical Digestion What is Digestion?
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
Chemical Digestion What is Digestion?
In the small intestine...
All 3 fluids are alkaline: – Neutralize acidic chyme – Provide suitable pH for the action of pancreatic and
intestinal enzymes
Chemical Digestion What is Digestion?
In the small intestine... Carbohydrate digestion
starch maltose
pancreatic amylase
lactose glucose + galactose
sucrose glucose + fructose
glucose maltase
lactase
sucrase
Chemical Digestion What is Digestion?
In the small intestine... Protein digestion
trypsinogen trypsin enterokinase
proteins polypeptides trypsin
polypeptides amino acids erepsin
Chemical Digestion What is Digestion?
In the small intestine... Fat digestion
fats fatty acids + glycerol lipase
Recall: What process
speeds up fat digestion
in the small intestine?
Digestive Enzymes What is Digestion?
starch maltose
pancreatic amylase
lactose glucose + galactose
sucrose glucose + fructose
glucose maltase
lactase
sucrase
Carbohydrate digestion
starch maltose
salivary amylase
mo
uth
sm
all i
nte
stin
e
Digestive Enzymes What is Digestion?
Protein digestion
smal
l in
test
ine
trypsinogen trypsin enterokinase
proteins polypeptides trypsin
polypeptides amino acids erepsin
prorennin rennin hydrochloric acid
caseinogen casein rennin
casein polypeptides pepsin
sto
mac
h
What happens to the food after digestion?
Objective 6:
Describe how digested
food is absorbed.
Absorption What happens to food after 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
Absorption What happens to food after digestion?
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 Intestine What happens to food after digestion?
Adaptations of the Small Intestine for Absorption
• The rate of absorption of digested food substances depends on 3 factors:
1. Surface area
2. The thickness of
cell membranes
3. Concentration
gradient
Absorption: Small Intestine What happens to food after digestion?
1. Surface Area
• The surface area of the small intestine is increased for absorption in 4 ways:
1. Inner walls have folds
2. 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.
Absorption: Small Intestine What happens to food after digestion?
Absorption: Small Intestine What happens to food after digestion?
Absorption: Small Intestine What happens to food after digestion?
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.
fats
sugars
amino acids
Egestion What happens to food after digestion?
• 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
What happens to the food after digestion?
Objective 7:
Describe how digested
food is assimilated.
Transport and Assimilation What happens to food after digestion?
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.
Transport and Assimilation What happens to food after digestion?
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 What happens to food after digestion?
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.
What happens to the food after digestion?
Objective 8:
State the functions of
the liver.
Functions of the Liver What happens to food after digestion?
The Liver has 7 Functions
1. Regulation of blood glucose concentration
2. Production of bile
3. Protein synthesis
4. Iron storage
5. Deamination of amino acids
6. Detoxification
7. Heat production
Functions of the Liver What happens to food after digestion?
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??
Functions of the Liver What happens to food after digestion?
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.
Functions of the Liver What happens to food after digestion?
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.
Functions of the Liver What happens to food after digestion?
1. Regulation of Blood Glucose Concentration
high blood glucose
concentration
normal blood glucose concentration
low blood glucose
concentration pancreas
secretes insulin
pancreas
secretes
glucagon
converts glucose
to glycogen converts glycogen
to glucose
Functions of the Liver What happens to food after digestion?
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)
gall
bladder
emulsification
Functions of the Liver What happens to food after digestion?
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.
Functions of the Liver What happens to food after digestion?
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
Functions of the Liver What happens to food after digestion?
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.
Functions of the Liver What happens to food after digestion?
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
Functions of the Liver What happens to food after digestion?
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 Glands
In digestion
Absorption
Assimilation
Egestion
Jejunum
Duodenum
Ileum
Liver Pancreas
Gall bladder
Bile Pancreatic
amylase Hormones
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 Glands
In 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