Transcript Animal & Human Nutrition

Animal & Human Nutrition
Digestion
Contents
Heterotrophs
Digestion
Stages of Human Nutrition
Digestion in the mouth
Types of teeth
Chemical Breakdown by
Enzyme
The oesophagus & peristalsis
The Stomach
The Small Intestine
From the Pancreas
From the Liver
From the wall of the
Duodenum
The Ileum
Absorption
Liver
The Large Intestine
Fibre in the diet
A Balanced Diet
Digestive disorders (not
examinable)
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Heterotrophs
Are organisms that cannot make their own
food.
They feed on food made other organisms e.g.
cows eat grass, etc. (get other examples
from class)
Question: what do you call organisms that can
make their own food?
Answer: Autotrophs.
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Types of heterotrophs
Herbivores – eat plant material only e.g.
sheep.
Carnivores – eat other animals only e.g. seals,
wolves.
Omnivores – eat both plant and animal
material e.g. humans.
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Digestion
is the physical (chewing = mastication) and
chemical process by which large particles
and molecules of food are broken down into
simpler, soluble, absorbable, usable forms.
This is necessary as the biomolecules in the
food are too large to pass directly into the
bloodstream.
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Digestive System
Digestion takes place in the digestive system.
It is a long hollow muscular tube which runs
through the body from mouth to anus.
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The human digestive system
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Stages of Human Nutrition
(1/2)
1. Ingestion: the process of taking food into the
body at the mouth.
2. Digestion: the physical (chewing =
mastication) and chemical process by which
large particles and molecules of food are
broken down into simpler, soluble,
absorbable, usable forms. It takes place in
the mouth, stomach and small intestine.
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Stages of Human Nutrition
(2/2)
3. Absorption: the taking in, by the blood
and lymph systems, of the end products of
digestion (monosaccharides, amino acids,
fatty acids and glycerol). It takes place
through the walls of the stomach and
intestines.
4. Egestion: elimination of faeces i.e.
undigested or undigestible and unwanted
material through the anus.
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Digestion in the mouth
Occurs in two ways: -
a) Physical breakdown by teeth
b) Chemical breakdown by enzyme
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Physical Breakdown by Teeth
There are three types of teeth:
incisors,
canines and
cheek teeth – premolars and molars
Teeth break down food into smaller pieces – it
is now easier to swallow and provides a
large surface area for enzymes to work on.
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Types of teeth
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Teeth in the mouth
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Teeth in the skull
Molar tooth,
V.S. VLP
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Characteristics of human teeth
Tooth type
Function
Number in Number in
adult set
child set
Incisor
Cut & Bite
8
8
Canine
Cut & Bite
4
4
Premolar
Crush & Grind
8
8
Molar
Crush & Grind
12
0
Total: 32
Total: 20
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Milk tooth
over
developing
permanent
tooth
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Dental Formula
A method used to indicate the number of
different types of teeth found in the upper
and lower jaws of one side of the mouth, in
mammals.
e.g. man
i2, c1, p2, m3, upper jaw
2 1 2 3 lower jaw
Total = 32
Note:
i = incisor;
p = premolar;
c = canine;
m = molar.
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Chemical Breakdown by Enzyme
As food is chewed, saliva from salivary
glands is added to it.
Saliva consists of water (moistens), mucus
(lubricates) and salivary amylase (an
enzyme)
Salivary amylase acts on starch and breaks it
down to maltose – in a slightly alkaline
environment (pH = 7.5).
Food now swallowed into the oesophagus.
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The oesophagus & peristalsis
The oesophagus is lined with circular muscles,
which contract and relax rhythmically to
move substances (e.g. food) along it to the
stomach.
This is peristalsis.
Peristalsis in the stomach churns the food and
helps the mechanical digestion of food and
also mixes it with the gastric juice and
enzymes.
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Oesophagus T.S. L.P.
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Peristalsis in the small intestine
Here it produces a slower backward and
forward shunting action.
Allows for longer contact
(a) between food and enzymes – to complete
digestion and
(b) between chyle and wall of intestine – to
allow for absorption.
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Peristalsis in the large intestine
Here there is a much slower movement of the
material.
Water reabsorbed here.
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The Stomach
Food enters the stomach through the cardiac
sphincter muscle.
Sphincter muscles regulate the opening and
closing of various parts of the alimentary
canal and control the movement of substances
through it.
Food remains here for 3 to 4 hours being
churned and acted upon by enzymes.
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Gastric
lining
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Stomach wall
Contains gastric glands which produce: a. Hydrochloric acid (HCl)
– makes an acidic environment (pH = 1)
– needed for enzyme (pepsin) to work
– and kills bacteria and other m/os that
may have been swallowed with the food.
b. Mucus – protects the stomach wall from
the acid and enzymes.
c. Enzymes – pepsin convert proteins (long
chains) to polypeptides (shorter chains)
and rennin acts on protein in milk.
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The Small Intestine
The chyme from the stomach passes via the
pyloric sphincter muscle into the duodenum–
the first of two parts of the small intestine.
Called small because of its diameter not its
length (3m).
The ileum is the second part of the small
intestine
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Functions of Small Intestine
1. Complete the digestion of food
2. Absorption of the products of digestion
into the blood and lymph systems.
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Lining of Small Intestine
Not smooth – thrown into folds.
Folds covered by thousands of tiny projections
called villi.
Villi increase surface area for
- release of enzymes and
- absorption of digested food
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Small intestine wall showing villi
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Small intestine blood vessels injected
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The small intestine wall
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A villus
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The Duodenum
The food (chyme) entering here receives
juices from three regions: The pancreas,
The liver and
The wall of the duodenum itself.
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The stomach, duodenum and
pancreas
Back to Slide 34
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From the Pancreas
An organ lying under the stomach.
Secretes pancreatic juice into the duodenum
through the pancreatic duct.
Pancreatic juice contains: Water
Sodium bicarbonate (NaHCO3) – to neutralise
the acidic chyme,and
Enzymes
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Pancreatic enzymes
Pancreatic amylase – converts starch to
maltose
Pancreatic lipase – converts lipids to fatty
acids and glycerol
Pancreatic protease (trypsin) – converts
proteins to peptides.
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From the Liver
An organ lying to the right of the stomach.
Produces bile.
Bile stored in gall bladder.
Bile enters duodenum via bile duct.
See slide 30
Bile is a greenish / yellow liquid containing
bile salts.
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Functions of Bile
Emulsify fats i.e. break fat into fat droplets –
makes it easier for the enzyme lipase (from
the pancreas) to work.
Is alkaline (NaHCO3) and helps neutralise the
acidic chyme from the stomach.
Does not contain any enzymes.
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From the wall of the Duodenum
Secretes intestinal juice which contains more
enzymes and these continue the process of
digestion.
The enzymes in the duodenum and ileum work
best in a slightly alkaline environment.
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The Ileum
The wall of the ileum secretes enzymes that
complete digestion.
Most of the digested food is absorbed into the
blood and lymph.
Food remains here for about 6 hours.
Food containing cellulose (e.g. …) cannot be
broken down (digested) as we do not
produce cellulose-digesting enzymes.
Undigested material enters the large intestine.41
Summary of digestion
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Digestion of starch
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Absorption
Glucose, amino acids, vitamins, minerals
absorbed into blood and travel in the hepatic
portal vein to the liver.
Fatty acids and glycerol are absorbed through
lacteals in villi into the lymph system –
eventually return to the bloodstream in the
left sub-clavian vein and are finally
transported to the liver.
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Products of digestion
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A villus
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Absorption of digested food
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The structure of the Ileum is
suited to its function
(1/2)
1. Very long (8m) – allows digested food to
stay in contact with the ileum for a long
time.
2. Folded wall and presence of villi provide a
large surface area for absorption.
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The structure of the Ileum is
suited to its function
(2/2)
3. Cells lining the ileum are thin walled –
allows for rapid movement of materials
through them.
4. Ileum wall is well supplied with blood
vessels and lacteals to carry the absorbed
food away rapidly.
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Liver
(1/2)
Largest gland in the body.
Has a large blood supply: –
hepatic artery (what type of blood does this
carry? From where does it come?)
hepatic vein (what type of blood does this
carry? From where does it come?)
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Liver
(2/2)
hepatic portal vein – carries digested nutrients
to liver in hepatic portal vein from ileum
Nutrients are then transported from the liver
to all the cells of the body where they are
needed by the bloodstream.
The blood also transports the waste products
of cell metabolism to the kidneys.
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Functions of the liver
(1/4)
1. Production of bile
Bile is made by the liver cells, stored in the
gall bladder and used in the small intestine.
2. Breakdown of effete red blood cells
Old damaged red blood cells are destroyed
by the liver. The iron released from the
haemoglobin is kept for the making of new
red blood cells in the bone marrow.
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Functions of the liver
(2/4)
3. Detoxification of blood
Drugs and poisonous substances are made
harmless e.g. H2O2 changed to H2 and O2
Excess of toxins over a long time can
damage the liver e.g. alcohol.
4. Storage
Excess glucose is stored as gylcogen
Vitamins: A, D, K & B12 Minerals: Fe & K
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Functions of the liver
(3/4)
5. Protein metabolism
a) Excess amino acids deaminated (i.e. -NH2
group removed) and converted to urea (for
excretion via the kidneys).
b) Production of blood proteins prothrombin, fibrinogen and factor VIII
(all needed for blood clotting)
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Functions of the liver
(4/4)
6. Carbohydrate metabolism
Excess glucose converted to glycogen and
stored. If blood sugar levels fall, insulin is
produced and glycogen is converted to
glucose.
7. Lipid metabolism
Excess carbohydrate can be converted to
fat and transported to cells beneath the
skin for storage.
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The Large Intestine
Called large because of its diameter not length.
Made up of the caecum, appendix, colon and
rectum.
Undigested food passes into the caecum.
Caecum and appendix have no digestive
function in humans.
Food now enters the colon.
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The Colon
Muscular tube
– smooth mucus-secreting lining
– mucus lubricates the food and helps its
movement by peristalsis
– no villi
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Function of Colon
Absorption of water and mineral salts back
into the blood.
Prevents the body becoming dehydrated.
Waste (faeces) becomes more semi-solid.
Passes into rectum and stored.
Eventually released through anus.
This is egestion.
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Egestion
Is the elimination of faeces from the body i.e.
undigested or undigestible and unwanted
material.
It is under the control of the anal sphincter
muscle.
This is not excretion.
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Bacteria in the Colon
Some bacteria living here produce vitamin B
and vitamin K.
The body absorbs these vitamins.
This is an example of symbiosis.
The type of symbiosis is mutualism.
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Fibre in the diet
Fibre is the cellulose walls of plant cells.
Humans cannot digest it.
It passes along the alimentary canal
unchanged.
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Benefits of dietary fibre
(1/2)
• Provides bulk – gives the muscles of the gut
wall something to push against – keeps the
contents of the gut moving.
• Absorbs water – keeps faeces soft – easier
to egest – prevents constipation.
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Benefits of dietary fibre
(2/2)
• Helps prevent bowel (colon) cancer.
Caused by carcinogens produced by
bacteria in the colon. Carcinogens are then
present in faeces. Fibre increases the bulk
of the faeces and dilutes the carcinogens.
• Eating fibre makes you feel full – can
prevent you overeating – as part of a
balanced diet.
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A Balanced Diet
contains the correct proportions of each of the
following: carbohydrate, fat, protein,
minerals, vitamins, water and fibre.
To get a balanced diet eat a varied diet
containing a little of everything.
The Food Pyramid shows the recommended
servings of each food group for teenagers.
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The food pyramid
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A Balanced Diet (cont’d)
Depends on: age, sex and activity of person.
Growing children need more protein, calcium
and iron.
A manual labourer needs more carbohydrate
than a person sitting at a desk all day.
Elderly people need less carbohydrate but still
need protein, vitamins and minerals to keep
healthy.
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Digestive disorders
Not examinable
for information only
Appendicitis
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Cancer of the colon
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Haemorrhoids
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END
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