The Gastrointestinal System
By Jennifer Turley and Joan Thompson
© 2016 Cengage
Presentation Overview
• The Process
• The Organs
• Enzymes &
Hormones
• After digestion:
– absorption
– transportation
– utilization
– excretion
What is Digestion?
• The breaking down of food
• Big food parts into smaller ones
(mechanical)
– Involves muscles and nerves
• Big nutrients into smaller ones
(chemical)
– Involves acid, enzymes, and hormones
What is an Enzyme?
• Protein that catalyze metabolic reactions,
and are necessary for most biochemical
reactions to occur.
• Digestive enzymes specifically break down
food substances.
• Examples include: amylase for
carbohydrate, protease for protein, and
lipase for Lipids/Fat.
What is a Hormone?
• Chemicals produced by
cells (typically in an
endocrine gland), and are
secreted, then affect the
behavior of cells at distal
sites in the body.
• Examples of hormones in
digestion include:
cholecystokinin and
secretin.
The journey begins in the mouth
with:
• Mechanical digestion: chewing
(mastication)
• Chemical digestion: saliva (lubrication)
and amylase (breaks down digestible
carbohydrate)
Food becomes
bolus
The Esophagus
• Peristalsis begins.
• Peristalsis is: a muscular wave action that
occurs throughout the intestinal tract. It is
controlled by the central nervous system
and facilitates excretion by propelling
food stuff through the body.
The Stomach
• Is a muscular organ & storage reservoir.
• Mechanically digests food by mixing &
churning.
• Chemically digests food with acid and
some enzymes (pepsin).
• Here, the bolus becomes chyme.
The
Small
Intestine
• Duodenum
• Jejunum
• Ileum
Signaling the accessory
organs
• Why?
– For assistance in digesting the food
stuff.
• How?
– By hormones.
– The cells of the intestinal wall
produce the hormones
cholecystokinin and secretin which
enter the blood stream and signal the
accessory organs.
The Accessory
Organs
• The Liver
– Makes bile
• The Gallbladder
– Stores bile
• The Pancreas
– Makes enzymes for the
chemical digestion of
carbohydrates, proteins,
and fats
– Makes sodium bicarbonate
to neutralize stomach acid
The Function of Bile
Emulsifier
Mechanisms of Absorption
• Passive (Simple) Diffusion (Transport):
Nutrients like water & lipid byproducts pass freely
across membranes via a concentration gradient.
• Facilitated Diffusion (Transport): Nutrients
like water soluble vitamins diffuse across
membranes using a specific/selective transport
proteins.
• Active Transport: Nutrients like glucose &
amino acids move across membranes against a
concentration gradient using a specific/selective
transport protein & energy/ATP.
Absorption
Sites of Absorption
•
•
•
•
Duodenum: many nutrients
Jejunum: many nutrients
Ileum: only selected nutrients
Colon (large Intestine): water
Transportation of Nutrients
• Blood vessels: water
soluble nutrients
• Lymphatic vessels:
fat soluble nutrients
Cellular Storage
• Short term
• Intermediate
• Long term
Metabolic Usage
• Catabolic reactions: Breaking down
(things get smaller). Involve hydrolysis
reactions. Are degrading or destructive in
nature.
• Anabolic reactions: Building up (things
get bigger). Involve condensation reactions.
Are synthesizing or constructive in nature.
• Homeostasis: The balance of catabolic
and anabolic reactions in a person so a
relatively stable internal environment or
equilibrium is achieved.
Metabolic Examples
• What action does the enzyme lipase have
on triglycerides: Anabolic, catabolic or neither?
• What action does bile have on triglycerides:
Anabolic, catabolic or neither?
• What action does the hormone secretin
have on the liver: Anabolic, catabolic or neither?
Excretion
• The Kidney: water &
water soluble waste.
• The Skin: water & water
soluble waste.
• The Lung: carbon dioxide
& water.
• The Colon (Large
Intestine): Water is
removed & waste (bacteria,
fiber, sloughed cells, &
undigested food) is
compacted.
Some
Summary Points
• Chemical & mechanical digestion.
• Enzymes vs hormones.
• The gastrointestinal tract, organs, and
accessory organs.
• Nutrient absorption & transportation.
• Assimilation of nutrients, storage, & metabolic
usage.
• Excretion of waste.
References for this presentation are the same as
those for this topic found in module 3 of the
textbook