Download Digestion

Digestion
Part 1: Digestion in
Humans
We need to get all this
goodness to our cells.
I’m helping to
prepare this food
to cross a
membrane.
Part 2: Digestion in
other organisms
Who needs to eat?
•Autotrophs make their own food by converting sunlight into chemical
energy. Therefore they do not need to eat food. Which type of
organisms are autotrophs, and how do they make their own food?
•Some bacteria that live at the bottom of the ocean use the gases that
rise up from deep-sea vents in order to make their own food. They are
known as chemotrophs because they make organic chemicals which
they use as food from inorganic chemicals.
•Heterotrophs cannot make their own food from either the sun or
inorganic chemicals, they must eat other living things in order to gain
the nutrients they need to survive.
•Heterotrophs eat autotrophs and other heterotrophs. The autotrophs
are always at the start of the food chain and are responsible for
bringing energy into the food chain.
Part 1
In humans, digestion can be broken down
into
4 main sections:
1.
Ingestion: this is where food is taken into our bodies through
our mouths. We call this ‘eating’.
2.
Digestion: large organic molecules are broken down either
chemically or mechanically into their smaller components.
3.
Absorbtion: these nutrients must pass across the intestine
wall, then into the surrounding tissue fluid and then into the
circulatory system or lymphatic system. They are then
circulated around the body to cells where they are utilized.
4.
Egestion: the nutrients that are not absorbed are stored
temporarily in the rectum before elimination via the anus.
The Main Parts of the Alimentary Canal
Salivary Glands
Tongue
Epiglottis
Liver
Oesophagus
Cardiac Sphincter
Stomach
Gall Bladder
Pyloric Sphincter
Pancreas
Bile Duct
Duodenum
Pancreatic Duct
Transverse Colon
Ilium
Ascending Colon
Descending Colon
Rectum
Appendix
Anus
Ingestion
Ingestion is simply ‘eating’ our food. We need to place
food at the opening of the alimentary canal (the mouth) to
start the process of digestion. Bon Appetite!
Mmnn lots of goodness
here for our cells to
use.
I am going to ingest this
cake as soon as I have
blown out the candles!
Ingestion starts here
Digestion
Mouth:
Site of both
Mechanical
and Chemical
Digestion
1. The Oral Cavity
Consists of:
1.
Teeth
2.
Jaw
3.
Tongue
4.
Saliva
Digestion
Mechanical Digestion in the Mouth
•Teeth provide a means to break food into smaller parts by either
ripping or slicing and then grinding. This not only makes the food
easier to swallow, but increases the surface area to volume ratio
of the food making chemical breakdown more efficient.
•The jaw acts like a lever to help the teeth breakdown tougher
material that has been ingested.
•The tongue can move the food around the mouth which assists
digestion. When the food is suitably masticated the tongue moves
the food – now called a ‘bolus’ - to the back of the throat for
swallowing.
Digestion
Different Teeth Have Different Jobs
•Different teeth are used for different types of mechanical breakdown
•The incisors are used to get food into the mouth, the canines to tear
food apart, and the molars to grind food down to smaller pieces.
•What are the main differences between the herbivore and carnivore jaw?
Molars
Incisors
Canines
Molars
Digestion
Chemical digestion in The Mouth
•Saliva released from the salivary glands contains the digestive
enzyme amylase. Amylase breaks down the more complex
carbohydrates (such as starch) into simple carbohydrates (such
as sugar).
Long chain carbohydrate
Amylase
Many short chain
carbohydrates
Digestion
2. Moving food to the stomach
Oesophagus moves
the bolus down into
the stomach with
muscular
contractions known
as peristalsis. Some
chemical digestion
will still be taking
place.
Epiglottis closes
over the trachea
to prevent bolus
entering the
respiratory tract
and causing
choking
Digestion
3. Digestion in the Stomach
Cardiac
sphincter
helps
prevent
reflux
Pyloric
sphincter holds
the chyme in
the stomach
before it
passes into the
small intestine.
Stomach:
Mostly Chemical
& some
Mechanical
Digestion. Food
stays in the
stomach from
1-4 hours on
average
The fluid in
the stomach
is known as
chyme
Digestion
Mechanical Digestion in the Stomach
•The stomach consists of many layers of muscle that
can churn the contents around as digestion takes place.
As you may have experienced before, the stomach can
expand to accommodate a great deal of food!
Digestion
Chemical Digestion in the Stomach
•Gastric juices in the stomach contain mucus, hydrochloric
acid (HCl), enzymes and water
•One of these enzymes is pepsin. Pepsin (a protease) first acts
on proteins here in the stomach
•The HCl can also help breakdown chemical bonds
•Amylase is still breaking down carbohydrates
Large protein chain
Amylase
Pepsin
Smaller protein chains
Digestion
4. Digestion in the Small Intestines
Duodenum:
While the chyme is
here;
•bile made in the
liver and stored in
the gall bladder is
added to the
mixture. Bile
emulsifies fats
•bicarbonates made
in the pancreas are
used to neutralize all
the acids
Ilium
Liver
Gall Bladder
Pancreas
Jejunum
Duodenum +
Jejunum + Ilium
= Small Intestine
Glycerol
Digestion
Fatty
Acids
Chemical Digestion in the Small Intestines
Pancreatic Amylase
Pepsin
Bile Salts
Pancreatic Lipase
Glucose ready for
absorption into blood
Peptidase
Amino Acids ready for
absorption into the blood
Fatty Acids & Glycerol ready for
absorption into the lymph
Digestion
Summary of Digestive Enzymes
Complex
carbohydrates
+
Disaccharides
+
Proteins
+
Polypeptides
Fats
+
+
H2O
H2O
Amylase
Disaccharides
Disaccharase
Monosaccharides
Pepsin
H2O
H2O
H2O
Polypeptides
Peptidase
Lipase
Amino Acids
Fatty acids
+
Glycerol
Note: bile and HCl help break down food but are not enzymes
Absorption
•Some absorption can take place in the stomach.
•There is also some absorption in the colon, it consists mostly of
water uptake. Up to 40mls of water a day is absorbed from the
colon.
•Most absorption takes place in the small intestines immediately
after digestion is complete. The surface of the small intestines is
folded to increase surface area and therefore allow more
absorption. The folded surface also has small projections called
villi that protrude into the lumen & further increasing the area
over which absorption can take place.
•Water, vitamins & minerals can be absorbed without digestion.
Absorption
Folds
Microvilli
Villi
Lacteal:
Blood
capillaries
a.
Longitudinal section of small intestine showing folds.
b.
Villi with an appearance like fingers. They contain blood capillaries
which carry food from the gut to the cells.
c.
Cell of the small intestine
Absorption
Micrograph of
microvili on the
inner lining of the
small intestines
Microvili
Absorption
•The Lacteal carries
the glycerol and the
fatty acids to the
lymphatic system.
•The lymph in the
lymphatic system
carries them towards
the head where they
enter the blood
stream near the
shoulder.
•The blood in the
circulatory system
carries the digested
food to all the cells in
our bodies.
Absorption
What happens to the food once it enters the cell?
How long would we last without food?
Egestion
•Faeces are stored
in the rectum until
they are expelled
by the anus.
•Faeces contain
food remains that
have not been
absorbed, water,
dead cells from the
digestive tract and
bacteria
Anus
Rectum
Part 2: Digestion in other organisms
Digestive Systems in
Mammalian Herbivores
It says here that herbivores need to take a large proportion of the
carbohydrates in their diets from the cellulose in plant cell walls. As
mammals lack the enzymes to digest cellulose they need to enter into a
symbiotic relationship with bacteria that live in their gut.
This book says that the bacteria break down the
cellulose by fermentation which makes it available
for the animals to absorb.
This one says that therefore the
digestive systems of herbivores
are modified by being enlarged in
certain portions to allow for the
fermentation to take place.
Digestive Systems in
Mammalian Herbivores
Mammalian Digestive System
No ‘fermentation sac’
Fermentation sac
Carnivore
Herbivore
Foregut Fermenter
Modified
oesophagus
Modified
stomach
Ruminant
Non-Ruminant
Hindgut Fermenter
Caecum fermenter
Colon fermenter
Wombats!
Digestive Systems in
Mammalian Herbivores
So which are foregut and which are
hindgut fermentors?
Digestive Systems in
Mammalian Herbivores
Coprophagy –
We rabbits are unusual
in that we produce two
kinds of faeces
faecal ingestion
The small dark round pellets you
see is the type we egest during
the day. But at night we egest a
soft green faeces that you don’t
usually see because we ingest it.
That’s great when we get the midnight munchies!
The night pellets are made up mostly of
bacteria that ferment the carbohydrates we eat
during the day….that’s very good for us. The
bacteria also provide us with some vitamins.
We rats are coprophiliacs too!!
Digestion in other organisms
Ameoba
Ameoba change their shape to engulf their food. They
secrete enzymes to break the food down.
Digestion in other organisms
Paramecium
Paramecium
use their cilia to
move food
towards the
food vacuole.
Digestion in other organisms
The tapeworm hangs on to the
inside of the host gut and
absorbs its digested food.
The earthworm has a long digestive
tract. It digests nutrients in the soil and
absorbs them directly into blood stream.
Digestion in other organisms
In the sponge, cells trap food when the water passes over it.
Digestion in other organisms
Digestion in Birds
Crop stores
undigested
food ready to
be used for
overnight
feeding
Intestines
Anus
Stomach
Gizzard grinds food
into smaller pieces
And that is the end of the digestive story!