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Alimentary tract
The four main roles of digestive system
.
Organs in the digestive system
Starting at the top - INGESTION
● Physical digestion takes place in the mouth
● Salivary glands release saliva
• water & mucous
• the enzyme amylase
● Amylase breaks down starch to maltose
going down - DIGESTION & SECRETION
● The oesophagus is a muscular tube
where food is pushed down to the
stomach
● Peristalsis=muscular contractions
propelling the food along the tract.
● The internal surface of the oesphagus
has mucous layer to assist food
movement.
● Further chemical digestion of starch
into the stomach -digestion continues
● Circular muscles regulate movement of
food in and out of the stomach
● (eg pyloric sphincter)
● Muscular contractions of the stomach
churn and mix the food and enzymes etc
● Gastric juices containing pepsin and
protease in the stomach wall are released
● Protease breaks down proteins into amino
acids
into the small intestine - digestion goes on
● The pancreas secretes pancreatic juice via the
pancreatic duct which enters the duodenum at
the top of the small intestine
● Pancreatic juice contains lipase and amylase
which act on lipids and carbohydrates respectively.
● Bile is produced by the liver but is stored in the
gall bladder
● Bile mechanically (physically) breaks down fats into
smaller globules to increase surface area
● Lipase then chemically breaks down
fat into glycerol and fatty acids
at last - ABSORPTION
●
The products of digestion are small enough to be
absorbed through the walls of the small intestine
transported to cells.
●
Villi are structures which increase the surface area for more
efficient uptake
●
Within the villi are capillaries - where glucose and amino
acids are absorbed.
●
The capillaries are interconnected with the lymphatic system
- water absorption also takes place here
●
Glucose and amino acids move from the small intestines
into the blood circulation by diffusion and active transport
●
Absorption of molecules in the villi
Glycerol and fatty acids move into a parallel circulation
called the lymphatic circulation
and now for - egestion
•The small intestine connects with the large
intestine which consists of two main parts:
1. the colon
2. rectum
• Function of the large intestine is to compact
undigested food and absorb water and
salts back into the body
• Faeces are eliminated from the body through
the anus
Overview of Digestion Nat Geog
BIOMACROMOLECULES
Carbohydrates
amylase
Protein
pepsin
maltose
maltase
peptides
Enzymes and the break down of
biomacromolecules
Lipids
(Triglycerides)
lipase
peptidase
glucose
Glucose
amino acids
glycerol + fatty acids