Download Digestion - Resources

Digestion
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Forms of digestion
•Mechanical digestion: when the food is broken down by chewing, or
muscular movement in the stomach. This increases the surface area of
the food, which is in the form of complex substances such as
carbohydrates, proteins and lipids.
oWhy does the surface area need to be larger?
•Chemical digestion: when enzymes break down the complex
substances.
Main roles of the digestive
system
1. Ingestion- the taking in of nutrients
2. Digestion- the breakdown of complex organic molecules into
smaller components by mechanical and chemical means.
3. Absorption- the taking up of digested molecules into the cells
digestive tract.
4. Egestion- the removal of waste food products from the body.
NOTE: All animals have specialized organs to aid in digestion, they will just appear
different.
You are a tube inside a tube…
The tube starts
here:
And although
there are a few
twists and turns
along the way…
It comes out here:
Ingestion
Ingestion: Once food has entered the mouth, molar teeth at the back
of the mouth grind food into smaller pieces. As this is happening, the
enzyme Amylase is secreted from salivary glands situated near the
base of the tongue. The tongue also breaks apart food against
teeth.
This enzyme is present in saliva and specifically chemically breaks
down complex carbohydrates, such as starch into simpler
carbohydrates such as sucrose. The action of the teeth increase the
surface area to volume ratio of the food for greater action by the
enzyme.
How much does an average human male eat in their lifetime?
50 TONNES=7.2X
Types of teeth
There are different types of teeth for different functions:
Sharp pointed teeth
for cutting and
tearing food
Grinding and
mashing food
Crushing and
grinding food
Cutting and chopping food
Digestion
When you swallow, your tongue pushes the food
into your oesophagus, which then moves down by
contractions known as peristalsis. The epiglottis
closes of the windpipe, preventing food from
entering.
 What happens when you puke?
Retroperistalsis
 STOMACH: Chemically digests proteins. Circular
muscles called sphincters regulate the movement
of food into and out of the stomach. Mechanical
digestion occurs with the contraction of muscles
within the stomach.




Gastric juices are secreted from the cells
lining the stomach wall- mucus, water,
hydrochloric acid and protein digesting
enzymes such as pepsin and protease
which break down the long amino acid
chains in proteins into smaller ones.
Why would your puke be chunky?
Food remains here until it looks like soupchime. Further digestion along the length of
the gastronintestinal tube ensures the amino
acids are small enough to be absorbed into
the cells of the body.
SMALL INTESTINE has three main
areas1. The duodenum
2. The jejunum
3. The ileum
Secretions from the pancreas enter the
duodenum at the top of the small
intestine. These secretions,
(pancreatic juice), contain a mixture
of amylase, trypsin, lipase and
biocarbonate.(neutralizes the acidity
of the hydrochloric acid.)

Bile is produced by the liver and
stored in the gallbladder, then moves
down into the duodenum.
 Bile mechanically breaks fats down
into smaller pieces, thereby increasing
the surface area for the enzyme
lipase, which breaks the fats down to
fatty acids and glycerol. Trypsin
breaks long-chain polypeptides down
to shorter-chain peptides, which are
then broken down into individual
amino acids by erepsins.


Food then enters the jejunum and the
ileum where the digestion of all food
nutrients continues. Digestion of proteins
continues and eventually the smaller
amino acids are available for absorption
into the blood and from there to the body
cells. Carbohydrates continue to be broken
down into simple sugars such as glucose,
which can then be absorbed also.
Liver
Stomach
Gall
bladder
Duodenum
Pancreas
Absorption
Occurs length of the gut. Alcohol and
some drugs can be absorbed through
the stomach wall into the bloodstreameffects of such substances are felt very
quickly.
 Most nutrients are absorbed along the
length of the small intestine. Glucose,
amino acids, fatty acids and glycerol
move from the gut into the blood by
means of diffusion and active transport.

The structure of the small intestine is
perfect for the uptake of nutrients. The
lining is thin with a rich supply of blood
vessels.
 Special structures, villi, increase the
surface area of the gut lining and thus
facilitate efficient absorption. Each villus
is supplied with a network of capillaries
that intertwine with lymph vessels called
lacteals that transport materials. Along
with the digested nutrients, water
absorption also occurs in the small and
large intestines.

A closer look at absorption…
Food is absorbed (taken in) to the body in the small
intestine. The wall of the small intestine has small holes in
it. Only small particles can pass through it:
INSIDE THE
GUT
BODY (BLOOD)
starch
starch
G
starch
G
G
G
G
G
starch
Digestive Enzymes

There are 3 main types of digestive
enzymes:
Amylase breaks starch down into
glucose.
 Protease breaks protein down into
amino acids.
 Lipase breaks fats down into fatty
acids and glycerol

Villi
Absorption takes place through
villi.
These are small finger like
structures that stick out into the
small intestine tube.
They help to increase the
surface area of the small
intestine.
Egestion

The large intestine is the final length of the
gut. It consists of two main parts, the colon
and the rectum. It compacts undigested food
material, such as dietary fibre, and absorbs
water and some salts back into the body.

Bacteria in the colon act on the undigested
matter, producing vitamins A and K. These
vitamins are absorbed through the lining of
the large intestine.
oPeristalsis continues through the lining of the
large intestine, pushing the waste material into
the rectum. This waste material, faeces is
eliminated through the body through the anus.