The Digestive System
Let me break it down for you
Where does the name come from?
• It comes from the Latin
Root which means to
arrange.
What is digestion?
A chemical reaction which breaks down large food particles
into tiny molecules that can be absorbed into the
bloodstream.
Why does food need to enter the blood?
• So it can get to every cell of the
body.
– Needed to provide every cell with
energy.
– C6H12O6 + 6O2 --> 6CO2 +
6H2O + energy
(from food)
The Digestive Tract
• Complex creatures have a digestive tract--a tube made up of several
organs through which food passes.
• General path:
Teeth
• 4 types of teeth
• Incisor- Cuts
• Molar- Grinds
• Canine- Tears
• Premolar- Grinds
•
Mechanical vs. Chemical Digestion
• Mechanical digestion is physically smashing
large chunks of food into smaller chunks of
food.
• Chemical digestion uses chemicals (enzymes) to
change the food into different chemicals.
(Starch into sugar, for example.)
Analogy:
– Mechanical digestion is like using a chainsaw
to make firewood.
– Chemical digestion is like burning the
firewood
About Enzymes
• Enzymes are special protein molecules produced by the body.
• They make chemical reactions in the body happen faster
(make food break down much faster than it would otherwise).
• They are not used up in these reactions - they can be used
over and over again.
Chemicals in the Digestive System Mouth:
• Amylase - enzyme in saliva that begins to break down starch
into sugar.
Stomach:
• Pepsin - enzyme in gastric juices (stomach juices) that begins
digesting protein.
• Hydrochloric acid - allows pepsin to work more quickly
– Common stomach problems:
– Heartburn - stomach acid gets up into the esophagus
– Ulcer - stomach juices begin to digest the wall of the the
stomach
- mucus normally helps protect
stomach lining
Small intestine
•
•
•
Most of our food is digested in the first 25 cm or so called the duodenum.
–
Intestinal juice
–
produced by cells in the wall of the small intestine
contains enzymes that digest carbs, fats, proteins.
–
Pancreatic juice
–
produced by the pancreas and squirted into the small
contains enzymes that digest carbs, fast, proteins
–
–
•
intestine
Bile
produced by the liver and stored in the gall bladder
until needed.
NOT an enzyme! It DOES NOT chemically change food - it mechanically breaks
up big globs of fat into smaller globs so the enzymes can work on it easier.
Absorption
• Absorption of most nutrients (carbs, fats, proteins, some vitamins and
minerals) happens in the lower portion of the small intestine called the
ileum.
• Food nutrients diffuse through the wall of the small intestine into the
bloodstream.
• Nutrients must be dissolved in water for this to take place.
– Villi - small, finger-like projections that line
the surface of the ileum.
• Give a velvety appearance - shag carpet
– Villi contain blood vessels and lymph vessels
– Blood carries sugars, amino acids, minerals,
some vitamins
• Lymph carries fatty acids and some vitamins.
• The folds of the villi greatly increase the
surface area of the small intestine, giving more
opportunities for nutrients to be absorbed.
Villi
Large Intestine
– The large intestine (colon) removes excess water from the
undigested materials and returns it to the body.
– Diarrhea - not enough water is absorbed by the large
intestine.
• Constipation - too much water is removed or not
enough fiber in the person’s diet.
• Some bacteria in the colon feed on cellulose (fiber)
and produce vitamins the body needs.
Anus
• Opening below the rectum
through which solid waste exits
the body