November 29, 2012
You are a tube inside a tube…
Digestive Tract
Gastrointestinal tract
(GI tract)
Four Stages of Food Processing Alimentary Canal
1. Ingestion - the taking in or eating of food.
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Muscular tube that passes through the body - mouth to the anus
The tube is open at both ends
6.5 - 9 m in length
Digestive Tract: Oral cavity (mouth)
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Anus
Accessory Organs: Salivary glands
Pancreas
Liver
Gall bladder
2. Digestion - the breakdown of food by mechanical &
chemical processes into molecules small
enough for cells of the body to absorb.
There are 2 types of Digestion:
1) Mechanical/Physical Digestion
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the physical breakdown of food into smaller pieces.
it involves - chewing, chopping, and grinding of food
smaller food pieces = increases its surface area .
done by teeth, beak or other similar structures, and by
rugae and contractions/churning motions in the stomach.
November 29, 2012
2) Chemical Digestion
· the chemical breakdown of nutrient/macromolecules into
smaller molecules by enzyme action (hydrolysis).
Carbohydrases
Carbhydrates
(polysaccharides &
dissacharides)
Proteins
Fats/Lipids
(triglycerides)
Proteases
Lipases
monosaccharides
(simple sugars)
3. Absorption - the transport of the products of digestion
from the digestive system into the circulatory
system.
the simple molecules(eg. glucose & amino acids) are
transported in the blood to body cells where they are
joined to make larger molecules or broken down to
provide energy
amino acids
glycerol + 3 fatty acids
4. Elimination - the removal of undigested solid waste matter
from the body through the anus.
Nucleases
Nucleic Acids
nucleotides
Enzyme Activity
Enzymes - protein molecules that increase the speed of
chemical reactions
· 2 main factors can affect enzyme action/function:
1. Temperature - as temperature
increases, enzyme activity increase.
- if temperature becomes too hot,
an enzyme will unfold from its 3-D
shape ( Denaturation ), thus
resulting in a loss of function.
2. pH - changes in pH can also
cause enzymes to denature
- different enzymes function best
at different pH levels - optimal pH.
Oral Cavity (The Mouth)
The primary functions of the oral cavity (mouth) is to ...
· to break up food particles - mechanical digestion
· to lubricate food particles - saliva
· begin digestion of complex carbohydrates (starches &
glycogen) - chemical digestion
The mouth is also used for tasting food (using the tongue)
to help determine if it should be ingested or not.
November 29, 2012
Mechanical digestion in the oral cavity ( mouth) involves:
· Teeth - to break up food into physically
smaller food particles (Mastication )
· Tongue - position/move food around mouth
· Salivary Glands - secrete saliva to lubricate food & introduce
salivary amylase (enzyme)
Your teeth look different from one another
because they are designed to do different things.
Incisors - the sharpest teeth, built to cut food
and shaped to shovel the food inward.
Canines - meant for grasping and tearing food and thus, they
have very long roots.
Premolars - meant for crushing food and thus, have a more flat
chewing surface.
Molars - much bigger than the Premolars and have bigger,
flatter chewing surfaces because their job is to chew
and grind the food into smaller pieces.
Chemical digestion in the oral cavity (mouth) involves:
· Salivary Amylase - an enzyme that chemically breaks down
the polysaccharides (carbohydrates).
BOLUS - the mass (ball) of food that has be chewed
at the point of swallowing.
November 29, 2012
Esophagus
The esophagus is a muscular tube
that transports food from the mouth
to the stomach. Its inner surface is
lined with mucus.
4 layers of the
Esophagus & the
GI tract
Food is prevented from travelling
down the trachea (windpipe) by the
epiglottis.
The movement of food down the esophagus (and intestines)
involves the process of Peristalsis.
Peristalsis - a distinctive pattern of involuntary smooth muscle
contractions that propels the bolus distally through
the esophagus and intestines.
Between swallows, the esophagus usually does not contract.
There is a sphincter muscle separating the esophagus from
the stomach (called the lower esophageal sphincter ) which
normally stays tightly closed to prevent acid in the stomach
from washing up into the esophagus.
However, when we swallow, this sphincter muscle opens up
(relaxes) so that the food we swallow can enter the stomach.
The most common problem associated with the esophagus is
Heartburn (Acid Reflux), which occurs when stomach acid
backs up into the esophagus repeatedly and irritates the lining
of the esophagus.
This happens when the lower esophageal sphincter does not
work/contract close properly.
GERD - Gastroesophageal Reflux Dieses
antacids (temporarily neutralize
stomach acids)
OR
medications can reduce that
amount of acid production in the
stomach
· both will help relieve some of the
symptoms of gastroesophageal
reflux.