Transcript DIGESTION AND ABSORPTION

DIGESTION AND ABSORPTION
by ASLI ALP
Digestive System
A complex system of organs that converts food into energy. The human
digestive system is a coiled, muscular tube (6-9 metres long) extended from
the mouth to the anus.
Several specialized compartments occur along this length; mouth,
pharynx, oesophagus, stomach, small intestine, large intestine and anus.
Accessory digestive organs are connect to the main system by a series of
ducts; salivary glands, parts of the pancreas, liver and gall bladder.
Each part of the digestive system has a specific function (breaking
down food and absorbing its nutrients).
THE MOUTH

Mechanical breakdown begins in the mouth
by chewing and actions of the tongue, the
tongue move food around and the saliva
produced coats and lubricates the food for
easier chewing and swallowing.

Saliva contains an enzyme called “amylase”
helps
to
chemically
break
down
carbohydrates in the meal. Teeth helps to
chemically break down food into smaller
pieces by tearing and shredding it.

Mixing food with saliva (water, amylase and
mucus) parts digest food so it can be
swallowed easily. The food is then pushed
into the oesophagus. The amylase
hydrolyses starch into maltose.
THE OESOPHAGUS

The oesophagus is a tube in the chest that
connects the mouth and throat to the
stomach.

Muscles in the wall of the oesophagus work
in a coordinated manner to push food and
liquids down into the stomach. This
muscular movement is called “peristalsis”

Peristalsis involves a series of muscular
contractions and relaxations which propel
food forward until it reaches a ring-like valve
called the “sphincter”, at the junction of the
oesophagus and the stomach.

Mucus is secreted from grandular tissue in
the walls, to lubricate food`s passage
downwards.
THE STOMACH

The stomach is located at the bottom of the chest,
just below the oesophagus.

The stomach`s first job is to accept and store food
which is enters in. It can hold up to 4 litres of food
and liquid.

There are glands in the lining of the stomach
produce stomach acid (or gastric acid) another
digestive juice.

Muscles in the wall of the stomach helps to move
the food and acid around, making sure that they mix
throughly. The entrance and exist of the stomach
are controlled by “sphincter muscles”.

Gastric juice is the material that breaks down the
food. Gastric juice contain HCl and some enzymes,
including pepsin, rennin, traces of lipase. Pepsin is
an endopeptidase, it hydrolyses peptide bonds in
the middle of polypeptide ,molecules, breaking them
into smaller polypeptide chains.
THE SMALL INTESTINE
 The small intestine also known as
the “small bowel”.
 It is the longest portion of the
digestive tract, it is more than 6
metres long and is located within
the middle of the abdomen.
 It
has
two
sections,
duodenum and ileum.
the
 Much of the small intestine is
coiled and suspended in a thin
layer of fat, which give the
intestine a lot flexibility and
mobility.
THE DUEDONUM
The Duodenum is located at the junction of the stomach and the small
intestine.
The duodenum is the first part of the small intestine. It is C-shaped and
about 25 cm long.
 This is the place where the ultimate destruction of food digestion reaches
its completion and where the acidity of chyme is nullified

Bile is a complex fluid containing water, electrolytes and a battery of organic molecules including
bile acids

The gall bladder stores and concentrates bile during the fasting state, then it enters the duodenum
through the bile duct. Bile duct breaks down fat particles into fatty acids and glycerol to neutralize
stomach acid

Pancreatic juice is produced by pancreas and pours into the small intestine through a tube, a duct.
The pancreatic juice contains enzymes trypsin amylase and lipase. Trypsin breaks down the partly
digested proteins, amylase changes into starch into simple sugars

Exopeptidases hydrolyse peptide bonds found at the end of polypeptide chains, giving free amino
acids

Intestinal juice is produced by the walls of the small intestine. It contains more digestive enzymes,
more lipase, maltose, exopeptidases and dipeptidases
THE ILEUM
The inner linings of ileum contain very small finger-like bumps
called “villi”. The presence of these tiny bumps on the inside of the
small intestine means that the surface area is much larger than if the
lining were just a flat surface. Absorption is through diffusion,
facilitated diffusion and active transport.
THE PANCREAS
 The pancreas is an oblongshaped organ in the posteriors
part of the abdominal cavity,
behind the stomach
 The pancreas secretes
approximately 2 litres of digestive
juices into the duodenum per day
 It release pancreatic juice into the
duodenum via the pancreatic duct.
 Pancreatic juice contains amylase,
tyrpsin, the endopeptidase
chymotrypsin, and lipase
THE LARGE INTESTINE
o
The large intestine is the part of the digestive system where waste
products from the food you eat are collected and processed into the faeces.
o
The large intestine is about 1.5 m long and consists of the caecum,
appendix, colon and rectum
The large intestine performs the following functions;
 reabsorbs water and maintains the fluid balance of the body
 absorbs certain vitamins
 processes undigested material
 Stores waste before it is eliminated

The colon has a folded wall to
provide a large surface area for
absorption. The faeces are stored
in the rectum and then pass
through sphincter muscles, at the
anus during defecation
Enzymes and Digestive Juices have different functions;
site of production
site of action
function
Amylase
Salivary gland
Mouth
Starch to glucose
Pepsin
Stomach
Stomach
Protein to polypeptides
Amylse
Pancreas
Duodenum
Starch to maltose
Bile salts
Liver (stored in the gall
bladder)
Duodenum
Emulsify fats and
neutralise the acidity of
chyme
Lipase
Pancreas
Duodenum
Fats to fatty acids and
glycerol
Maltase
Duodenal glands
Duodenum
Maltose to glucose
Trypsin
Pancreas
Duodenum
Protein to polypeptides
Chymotrypsin
Pancreas
Duodenum
Protein to polypeptides
Endopeptidases
Stomach, pancreas
Stomach, duodenum
Long polypeptides to
shorter ones
Exopeptidases
Pancreas, duodenal
glands
Duodenum
Short polypeptides to
amino acids
Dipeptidases
Duodenal glands
duodenum
Double acids to single
ones
REFERENCES
 A-2 Level Biology. AQA A Revision Guide. Coordination Group
Publications Ltd. 2005
 www.gesa.org.au/digestive-system/oesophagus.cfm