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
● Glycerol and fatty acids move into a parallel circulation
called the lymphatic circulation Absorption of molecules in the villi
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 maltose maltase
glucose
Protein pepsin
peptides peptidase
amino acids
Lipids(Triglycerides)
lipase
glycerol + fatty acidsGlucose
Enzymes and the break down of biomacromolecules