Download ALIMENTARY CANAL 1. What happen to the food that we

ALIMENTARY CANAL
1. What happen to the food that we eat?
 Mouth : food is cut up and ground by teeth into
smaller pieces for easy swallowing and fast
digestion. The tongue mixes the food with the saliva,
and rolls it into balls called bolus.
Functions of saliva:
‐ Amylase in saliva converts starch to maltose
‐ Mucus in saliva makes swallowing the food bolus
easier
The tongue then pushes the food bolus toward the
back of the throat and into the opening of the
oesophagus.
 Oesophagus : food bolus travels through the
oesophagus to the stomach by peristalsis (muscles of
the alimentary canal contract and relax alternately,
pushing food forward/downwards).
 Stomach : strong muscular walls acting like a mixer,
churning and mashing together the balls of food with
the gastric juice to form a mixture called chyme.
Gastric juice contains the enzyme pepsin and rennin,
and hydrochloric acid.
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Initial digestion of proteins to peptides takes place
by enzyme pepsin. Hydrochloric acid produced in the
stomach helps to kill bacteria and maintains optimum
environment for pepsin to work. Rennin
curdles/coagulates milk.
 Small intestine : consists of 2 parts, duodenum and
ileum.
‐ Duodenum : the first part of the small intestine
where most digestion takes place, with the help
from pancreas, liver and gallbladder.
The pancreas produces and releases pancreatic
juice into the duodenum. Pancreatic juice contains
the enzymes:
lipase: Fats --> Fatty acids and glycerol
amylase : Starch --> Maltose
trypsin (protease) : Proteins and peptides -->
Amino acids
Pancreatic juice also contains sodium hydrogen
carbonate to neutralise the acidic chyme.
Liver produced bile which is then stored in the gall
bladder. Bile is taken to the duodenum by the bile
duct.
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Bile emulsifies fat (breakdown big fat/lipid drops
into smaller droplets for easy/fast digestion by
lipase) and neutralises the acidic chyme.
‐ Ileum : the longest part of the small intestine.
Ileum produces intestinal juice which contains
carbohydrases, proteases and lipases. This is
where the final digestion takes place.
Below is the end products of digestion in the
alimentary canal:
SUBSTRATE
END PRODUCTS
Carbohydrates
Glucose, fructose, galactose
Proteins
Amino acids
Fats
Fatty acids and glycerol
2. What happen to the digested food?
ABSORPTION of digested food takes place in the
ileum, by diffusion or active transport.
The ileum is adapted to absorb digested food by the
following ways:
• Its long length which gives plenty of time for
digestion to be completed.
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• The folding of its internal surface greatly
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increases the surface area for absorption.
Tiny finger-like projections called villi on the
internal surface/epithelium further increases
the surface area for absorption
Epithelium is thin allowing rapid movement of
molecules by diffusion/active transport.
Each villus has lacteal to absorb fats.
Each villus has blood capillaries to transport
digested food to the liver and other parts of
the body.
3. What happen to the food that cannot be digested
and cannot be absorbed?
They are pass into the large intestine (Colon).
In the colon:
‐ ABSORPTION of water, mineral salts and vitamins
takes place.
‐ The undigested food / waste (faeces) is stored in
the rectum and passed out through the anus
(EGESTION)
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4. What happen to the digested food after absorption
in the ileum?
They are carried by blood through hepatic portal
vein to the liver and then, they are circulated to
other parts of the body.
i) Glucose
• used to produce energy during respiration
ii) Amino acids
• used to build new cells, repair damaged cells.
• to make enzymes and hormones.
iii) Fats
• stored in the adipose tissue.
• make cell membranes.
• stored as a future source of energy. Every
gram of fat contains 38kJ of energy.
In the liver:
‐ Level of glucose is maintained through the action
of the hormone insulin. Insulin converts excess
glucose to glycogen so that not too much glucose is
present in the blood.
‐ Excess amino acids is broken down or
DEAMINATED to urea, which is then taken to the
kidneys to be excreted in urine.
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Other roles /functions of liver :
Breakdown of small amounts of alcohol
Storage of glycogen
Storage of iron
Production of bile
Production of plasma proteins e.g. fibrinogen
(blood clotting)
‐ Breakdown of hormones
‐ Storage of vitamins A and D
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