Download 35 Digestion in Intestine

Digestion in Intestines
Small Intestine
Small intestines are roughly
6 metres long.
 Enzymes and bile are
added.
 Villi increase the surface
area to help absorbtion.
 Nutrients from the food
pass into the bloodstream
through the small intestine
walls.

Small intestine
Chyme passes out of the stomach through the pyloric sphincter
into the small intestine.
The small intestine is a tube about 6 metres long.
The small intestine is divided into three sections, the
duodenum, jejunum and the ileum.
The first section of the small intestine is the duodenum.
Duodenum
The duodenum receives about 12 grams of chyme each time the pyloric
sphincter opens.
The duodenum is about 25 centimetres long and in the shape of a horse
shoe.
In the duodenum, chyme is diluted with bile salts (from the gall bladder)
and pancreatic juices (from the pancreas).
Liver

Directly affects
digestion by producing
bile
– Bile is an enzyme that
helps dissolve fat

Processes nutrients in
the blood, filters out
toxins and waste.
 Is often called the
body’s energy factory
Gall Bladder
Stores bile from the
liver
 Delivers bile when
food is digested
 Fatty diets can cause
gallstones

Bile
Bile is produced in the liver and stored in the gall bladder. This contains bile
salts which emulsify fat.
Fat is normally insoluble in water. The bile salts are released into the
duodenum making it easier to break down fat.
The bile allows the fats to mix in with the watery digestive juices, and allows
the enzyme lipase to digest the fats efficiently.
Fat can take from 3 to 5 hours to be broken down and absorbed.
Pancreas
Produces compounds
to digest fats and
proteins
 Neutralizes acids that
enter small intestine
 Regulates blood sugar
by producing insulin

Pancreatic juices
The pancreas provides alkaline pancreatic juices.
These juices contain sodium bicarbonate to neutralise the
hydrochloric acid mixed into the chyme from the stomach.
Pancreatic juices also contain digestive enzymes such as:
●Trypsin and chymotrypsin – break down protein to
peptides and amino acids.;
●Pancreatic amylase – breaks down starch and glycogen
to maltose;
●Lipase – breaks down fat to fatty acids and glycerol.
Pancreas
Digestion of fats
Absorption of food lipids
Digestion of proteins
Large Intestine
About 1.5 metres long
 Accepts what small
intestines don’t
absorb.
 Absorbs water and
minerals from the
waste matter.
 Absorption means
taking into the body
via the blood stream.

Large intestine
Table Showing Proteolytic Enzymes
Sourc
e
Enzyme
Acti
vate
d by
Substrate
Functions and/or Products
Stom
ach
Pepsins
(pepsinogens)
Pancr
eas
Trypsin
(trypsinogen)
Enter Proteins and
opepti Polypeptides
dase
Cleaves peptide bonds on carboxyl side of
basic amino acids (argenine or Lysine)
Chymotrypsin
(chymotrypsinogen)
Tryps
in
Proteins and
Polypeptides
Cleaves peptide bonds on carboxyl side of
aromatic amino acids
Elastase
(proelastase)
Tryps
in
Elastin and
other Proteins
Cleaves peptide bonds on carboxyl side of
aliphatic amino acids
Carboxypeptidase A
(procarboxypeptida
se A)
Tryps
in
Proteins and
Polypeptides
Cleaves peptide bonds on carboxyl terminal
amino acids with aliphatic or aromatic side
chains
Carboxypeptidase B
(procarboxypeptida
se B)
Tryps
in
Proteins and
Polypeptides
Cleaves peptide bonds on carboxyl terminal
amino acids with basic side chains
HCl
Proteins and
Polypeptides
Cleaves interior peptide bonds of aromatic
amino acids
Small
Intestine
mucosa
Enteropeptidase
...
Trypsinogen
Trypsin
Aminopeptidases
...
Polypeptides
Cleaves amino terminal
amino acid from peptide
Carboxypeptidases
...
Polypeptides
Cleaves carboxyl terminal
amino acid from peptide
Endopeptidases
...
Polypeptides
Cleaves mid portions of
peptide
Dipeptidases
...
Dipeptides
----> two amino acids
Rectum and Anus

Rectum
– About 15cm long
– Stores waste before egestion.

Anus
– Muscular ring that controls egestion.
Write the name of each colored
organ:
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Green:
Red:
Pink:
Brown:
Purple:
Green:
Yellow:
Peristalsis
Peristalsis is the action of waves of muscular contractions
which moves food along the digestive system.
Dietary fibre aids peristalsis because it increases the bulk of
the bolus or chyme being moved along.
Wall of the small intestine
The inner surface of the small intestine is folded into fingerlike structures called villi, which greatly increase the surface
area available for absorption.
The villi have a surface area of about 30m2, this is
equivalent to the size of a tennis court!
Digestion in the wall of the
small intestine
Protease breaks down peptides to amino acids.
 Maltase breaks down maltose to glucose.
 Sucrase breaks down sucrose to glucose and fructose.
 Lactase breaks down lactose to glucose and galactose.
 Lipase breaks down fats to fatty acids and glycerol.

Substances absorbed in the
small intestine
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Water;
Alcohol;
Sugars;
Minerals;
Water soluble vitamins;
Peptides and amino acids;
Fatty acids, glycerol and fat soluble vitamins.
Absorption
The villi in the small intestine have a high blood supply.
There are two types of absorption which occur here.
Passive – through the process of osmosis the nutrients pass
through the wall of the small intestine and into the blood
supply.
Active – a carrier transports the nutrient through the wall of
the small intestine into the blood supply. This type of
absorption requires energy.
Once in the blood the nutrients are transported to the liver
via the hepatic portal vein. The liver filters, converts the
nutrients into substances that can be used by the body’s
cells for energy and growth.
Absorption
Most fatty acids and glycerol pass into the lymphatic
system, and then the bloodstream.
Once in the blood, nutrients are carried to all the cells of the
body. Some are oxidised to produce energy and other are
used to repair the cell or to build new cells.
Once the nutrients have been absorbed, the remaining
chyme passes into the large intestine or the colon.
Colon
The colon is a tube just over one meter long, which is
inhabited by bacteria.
The main function of the colon is to absorb water into the
bloodstream.
Bacteria in the colon ferment dietary fibre (NSP) and
produce fatty acids and gas.
Other bacteria produce vitamin K, which is also absorbed.
The products of bacterial digestion, along with water and
any remaining minerals are absorbed leaving a residue
behind.
Colon
The watery residue moves along the colon, and the faeces
are formed and stored in the rectum before being excreted
through the anus.
Young children gradually learn to control this action.
It may take 12-24 hours for the faeces to pass through the
colon. This time can be reduced if the diet is high in fibre.
Gut Bacteria
The gut contains bacteria
Stomach 101 – 103 cfu/ml
• 400 – 500 different
species
• includes potentially
pathogenic (e.g.
Clostridia) &
potentially beneficial
(e.g. Bifidobacteria &
Lactobacilli) bacteria.
•These are measured
in colony forming units
per millilitres (cfu/ml).
Duodenum & jejunum 102 –
105 cfu/ml
Colon 1010 – 1012 cfu/ml
Summary of the phases of digestion
Ingestion - this is the physical intake of foodstuffs into the
gastrointestinal tract.
Digestion - a series of physical and chemical processes
which begin in the mouth, but take place mainly in the
stomach and small intestine.
Absorption - the passage of the digested food substances
across the gastro-intestinal lining, or mucosa, into the blood
and lymph.
Elimination - the excretion, or elimination, of those food
substances that cannot be digested (such as cellulose) or
without any nutritional value in the faeces.
Turning food into energy
•Respiration is the conversion of glucose into energy
•Glucose is “burnt” with oxygen
•It takes place in the Mitochondria
C6H12O6 + 6O2
6CO2 + 6H2O +
ENERGY
ENERGY
Circulatory System
What is it for ?
We need 2 pumps because 1 would not have enough energy to push
blood through the lungs and then around the body.
Describe the digestion of …
Fish and chips
Hamburger
Review of the learning objectives
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To recognise the organs involved in digestion;
To understand the major functions of each body part in
the digestive process;
To understand the four major phases of digestion;
To understand the functions of different enzymes.