Human digestive
system
The Digestive System
Purpose of the Digestive system:
• Breaks down food into substances that cells can absorb
and use.
How is food digested?
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Breaking down of food into smaller piece
The mixing of food
Movement through the digestive tract
Chemical breakdown of the large molecules of food
into smaller molecules
Nutrition
Process by which organisms obtain and utilize their food.
There are two parts to Nutrition:
1. Ingestion- process of taking food into the
digestive system so that it may be
hydrolized or digested.
2. Digestion- the breakdown of food (either
chemically or mechanically) in order to
utilize nutrients
Types of Nutrients
• Micronutrients- vitamins, minerals, & water
• Macronutrients- proteins, lipids, carbohydrates,
etc…
Mouth
• Mechanical digestion - teeth
• Chemical digestion – saliva
• Chewing mixes the food with
saliva, from salivary glands
around the mouth and face,
to make it moist and easy to
swallow = BOLUS
• Enzymes in the saliva begin
digestion of carbohydrates.
• Epiglottis – flap of cartilage
that blocks trachea when
swallowing
Esophagus
• Muscular tube
• It moves food by waves
of muscle contraction
called peristalsis.
• Physically moving the
food along to the
stomach.
• Mechanical Digestion
Stomach
• The stomach lining
produces strong
digestive juices (HCl,
pepsin)– chemical
digestion
• These create chemical
reactions in the
stomach, breaking
down and dissolving its
nutrients = CHYME
• Digests proteins and
fats in the stomach
• Peristalsis = mechanical
digestion
Small Intestine
• Enzymes continue the
chemical reactions on
the food – chemical
digestion
• The nutrients are
broken down small
enough to pass through
the lining of the small
intestine, and into the
blood (diffusion).
• Digests proteins, fats,
and carbohydrates.
• Peristalsis = mechanical
digestion
Absorption by Small Intestines
• Absorption through villi & microvilli
– finger-like projections
– increase surface area for absorption
VILLI
Pancreas
• Accessory organ
• Food does not go
through the pancreas
• Produces chemicals to
help break down
macromolecules =
chemical digestion
• Also produces insulin =
helps control blood
sugar levels
Liver
• Produces bile to help
digest fat – Mechanical
Digestion, fats are
broken into smaller “fat
globules”
• Bile is stored in the Gall
Bladder and released
into the small intestine
Large intestines
(colon)
• Function
– re-absorb water
– (NO DIGESTION)
• use ~9 liters of water every
day in digestive juices
• > 90% of water reabsorbed
– not enough water absorbed
» diarrhea
– too much water absorbed
» constipation
Large Intestine
• Solid materials pass
through the large intestine.
• These are undigestible
solids (fibers).
• Water is absorbed.
• Vitamins K and B are
reabsorbed with the water.
• Rectum- solid wastes exit
the body.
You’ve got company!
• Living in the large intestine is a community
of helpful bacteria
– Escherichia coli (E. coli)
• produce vitamins
– vitamin K; B vitamins
• generate gases
– by-product of bacterial metabolism
– methane, hydrogen sulfide