Download Nutrition in humans

Nutrition
in Humans
Chapter 6
Learning Objectives
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?
What is Nutrition?
Objective 1:
State the definition of
nutrition.
What is 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?
5 Processes of Nutrition
1. Feeding or ingestion: food is taken into the body.
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.
Which parts of the body
are involved in digestion?
The Digestive System
• 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.
Which parts of the body
are involved in digestion?
mouth
teeth
The Digestive System
salivary gland
pharynx
oesophagus
stomach
liver
Gall bladder
pancreas
pyloric sphincter
duodenum
ileum
ascending colon
caecum
appendix
descending colon
rectum
anus
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.
Process of nutrition??
mouth
teeth
salivary gland
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.
pharynx
air
glottis
trachea
(windpipe)
larynx
(voicebox)
oesophagus
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
food
particles
epiglottis
glottis
larynx
(voice-box)
trachea
(windpipe)
oesophagus
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
longitudinal
muscles
Part of the gut wall
The Digestive System - Oesophagus
• The muscles cause
peristalsis – rhythmic, wavelike contractions of the gut
walls.
• It helps to move food along
circular
the gut while mixing the
muscles
food with digestive juices.
longitudinal
muscles
Part of the gut wall
Which parts of the body
are involved in digestion?
mouth
teeth
oesophagus
The Digestive System
salivary gland
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 dilates to allow
food to enter
circular muscles
longitudinal
muscles
food mass
wall constricts to push food forward
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 welldeveloped.
• 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
Where
else can
we find circular
• The stomach stores food for
a few muscles?
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.
Process of nutrition??
The Digestive System – Small Intestine
• Consists of 3 parts:
– Duodenum progressively
– Jejunum
more coiled
– Ileum
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
large
intestine
• The large intestine is
about 1.5 m long
– Shorter and wider than
the small intestine
• Consists of 2 parts:
– Colon
– Rectum
colon
rectum
small
intestine
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
Process of nutrition??
appendix
Which parts of the body
are involved in digestion?
The Digestive System
Which parts of the body are involved in
digestion?
Objective 3:
Describe the functions
of the organs
associated with
digestion.
Which parts of the body
are involved in digestion?
mouth
teeth
The Digestive System
salivary gland
pharynx
oesophagus
stomach
liver
Gall bladder
pancreas
pyloric sphincter
duodenum
ileum
ascending colon
caecum
appendix
descending colon
rectum
anus
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
The Digestive System - Liver
liver
• It is also the largest
Whygland in
the body. alkaline
– 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
gall
bladder
bile duct
The Digestive System - Liver
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.
Process of nutrition??
gall
bladder
bile duct
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.
What is 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.
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.
What is Digestion?
Physical 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
chewing / mastication
– Along the alimentary canal
peristalsis
– Physical digestion of fats in the small intestine
emulsification
What is Digestion?
Physical 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
Chemical Digestion
What is Digestion?
• 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:
Carbohydrases
Lipases
Proteases
• Chemical digestion occurs mainly in 3 parts of the
alimentary canal:
– Mouth, stomach, small intestine
What is Digestion?
Chemical 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
maltose is pH 7.
• The optimum pHstarch
of salivary amylase
– 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.
What is Digestion?
Chemical 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
What is Digestion?
Chemical Digestion
In the stomach... Action of Pepsin
 Pepsinogen is activated to pepsin by hydrochloric acid.
 Pepsin then digests protein to polypeptides.
pepsinogen
proteins
hydrochloric acid
pepsin
pepsin
polypeptides
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
caseinogen
casein
hydrochloric acid
rennin
pepsin
rennin
casein
polypeptides
What is Digestion?
Chemical Digestion
In the stomach... Purpose of Hydrochloric Acid
 Stops the activity of salivary amylase by denaturing it
 Activates pepsinogen and prorennin to form pepsin and
rennin
respectively
 Provides acidic medium for the action of pepsin and
rennin
 Kills harmful microorganisms in food
What is Digestion?
Chemical 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.
SMILEE!
– Pancreas secretes pancreatic juice, which contains
pancreatic amylase, pancreatic lipase, and ALT
trypsinogen.
– Gall bladder releases bile. It does not contain enzyme
What is Digestion?
Chemical Digestion
In the small intestine...
 All 3 fluids are alkaline:
– Neutralize acidic chyme
– Provide suitable pH for the action of pancreatic and
intestinal enzymes
What is Digestion?
Chemical Digestion
In the small intestine... Carbohydrate digestion
starch
pancreatic
amylase
maltose
lactose
sucrose
maltase
lactase
sucrase
glucose
glucose + galactose
glucose + fructose
What is Digestion?
Chemical Digestion
In the small intestine... Protein digestion
trypsinogen
proteins
polypeptides
enterokinase
trypsin
erepsin
trypsin
polypeptides
amino acids
Chemical Digestion
What is Digestion?
In the small intestine... Fat digestion
fats
lipase
fatty acids + glycerol
Recall: What process
speeds up fat digestion
in the small intestine?
What is Digestion?
Digestive Enzymes
small intestine
mouth
Carbohydrate digestion
starch
salivary
amylase
maltose
starch
pancreatic
amylase
maltose
maltase
glucose
lactose
lactase
glucose + galactose
sucrose
sucrase
glucose + fructose
Digestive Enzymes
What is Digestion?
Protein digestion
stomach
prorennin
caseinogen
small intestine
casein
hydrochloric acid
rennin
pepsin
rennin
casein
polypeptides
trypsinogen
proteins
polypeptides
enterokinase
trypsin
erepsin
trypsin
polypeptides
amino acids
What happens to the food after
digestion?
Objective 6:
Describe how digested
food is absorbed.
What happens to food
after digestion?
Absorption
• 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
What happens to food
after digestion?
Absorption
How does absorption take place in the small intestine?
• Glucose and amino acids:
– Absorbed by diffusion into blood capillaries of the villi.
– Absorbed by active transport when there is lower
concentration of digested food substances in the small
intestine than in the blood capillaries.
• Fatty acids and glycerol:
– Absorbed by diffusion into the epithelium
– Combine to form fat globules which enter the lacteals
• Water and mineral salts:
small intestine
– Absorbed by the
and colon
– Most of the water is absorbed by the ileum
What happens to food
after digestion?
Absorption: Small Intestine
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
What happens to food
after digestion?
Absorption: Small Intestine
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.
What happens to food
after digestion?
Absorption: Small Intestine
What happens to food
after digestion?
Absorption: Small Intestine
What happens to food
after digestion?
Absorption: Small Intestine
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 fats away from the
villus, while the blood capillaries transports sugars
and amino acids away.
• This maintains the concentration gradient needed for
the absorption of food substances.
What happens to food
after digestion?
Egestion
• 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 anus .
• This process is known as egestion or defecation.
What happens to the food after
digestion?
Objective 7:
Describe how digested
food is assimilated.
What happens to food
after digestion?
Transport and Assimilation
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.
What happens to food
after digestion?
Transport and Assimilation
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.
What happens to food
after digestion?
Transport and Assimilation
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.
What happens to food
after digestion?
Functions of the Liver
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
What happens to food
after digestion?
Functions of the Liver
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??
What happens to food
after digestion?
Functions of the Liver
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.
What happens to food
after digestion?
Functions of the Liver
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.
What happens to food
after digestion?
Functions of the Liver
1. Regulation of Blood Glucose Concentration
high blood
glucose
concentration
pancreas
secretes insulin
converts glucose
to glycogen
pancreas
secretes
glucagon
low blood
glucose
concentration
converts glycogen
to glucose
normal blood glucose concentration
What happens to food
after digestion?
Functions of the Liver
2. Production of Bile
• The liver produces bile which is stored in the gall
bladder before use.
• Bile is used in the emulsification 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)
What happens to food
after digestion?
Functions of the Liver
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.
What happens to food
after digestion?
Functions of 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.
glycogen
• Excess glucose is converted to
.
What happens to food
after digestion?
Functions of the Liver
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.
What happens to food
after digestion?
Functions of the Liver
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
What happens to food
after digestion?
Functions of the Liver
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.
Pure Biology Chapter 6
Nutrition
Alimentary Canal
consists of
consists of
Ingestion
Mouth
Organs and Glands
In digestion
Teeth
consists of
Tongue
Liver
Pharynx
Salivary
glands
Pancreas
contains
leads to
secretes
Gall bladder
Oesophagus
stores
Digestion
Pancreatic
amylase
Bile
secreted into
Hormones
consist
of
Stomach
Duodenum
Insulin
Small intestine
Absorption
Colon
Jejunum
Ileum
Hepatic
portal vein
Glucagon
walls
have
Large intestine
unite to form
Folds
Rectum
Assimilation
Anus
Simple
sugars
Villi
via
Amino
acids
Microvilli
Egestion
Fats
absorbs
via
Blood
capillaries
Lacteals
Pure Biology Chapter 6
Nutrition
Alimentary Canal
consists of
consists of
Mouth
Organs and Glands
In digestion
Teeth
consists of
Tongue
Pharynx
Salivary
glands
contains
leads to
secretes
Gall bladder
stores
Pancreatic
amylase
secreted into
consist
of
Hepatic
portal vein
Colon
Hormones
Glucagon
walls
have
unite to form
Folds
Rectum
Simple
sugars
Anus
via
Amino
acids
Microvilli
Fats
absorbs
via