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The Digestive System
Tuesday, January 12th, 2010
What makes up our Body Systems?
• Specialized cells come together to form tissues
Muscle Tissue
Connective Tissue
Nervous Tissue
Epithelial Tissue
What makes up our Body Systems?
Cells
Tissues
Organs
Ex. stomach,
heart, skin
Organ
Systems
Ex. Respiratory, Circulatory, Immune, Nervous Systems
The Digestive System
What role does the
Digestive System play in
our bodies?
- Converts the food we eat into
energy our bodies can use
- Involves the breakdown of
food, absorption of nutrients
into our bloodstream, and
elimination of unused
materials
Nutrients
• Any substance consumed by an animal that is
needed for survival, growth, development,
tissue repair, or reproduction
• Used to make ATP, act as building blocks, or as
cofactors (chemical compounds attached to
proteins)
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Nutrients
Regardless of what an animal eats, an adequate
diet must satisfy three nutritional needs
– Fuel for all cellular work
– The organic raw materials for biosynthesis
– Essential nutrients, substances such as vitamins that
the animal cannot make for itself
Think About It
• What are the categories of organic nutrients
we require and why do we require each?
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Animals require…
• 5 categories of organic nutrients:
– Carbohydrates (quick energy & cell receptors)
– Proteins (enzymes, cell structure, membrane
support, muscles, skin, hair, nails)
– Lipids (stored energy, cell membrane, protectant)
– Nucleic Acids (DNA, RNA)
– Vitamins (health & strength, act as coenzymes)
• Inorganic nutrients:
– Minerals ex. Ca2+, K+, Fe3+ (health & strength, act
as cofactors)
Note:
• Water is not a nutrient, but is necessary for:
– maintaining cell functions
– transporting nutrients & wastes
– chemical reactions (breakdown of CHO, fats, proteins)
– cooling body through sweat
– lubrication (joints, mouth)
• Body requires 3 – 5 litres of water each day
Food Groups & Recommended Servings
1.
2.
3.
4.
**
Grain Products
Vegetables & Fruits
Milk Products
Meat & Alternatives
Oils & Fats
(6-7 servings)
(7-8 servings)
(3-4 servings)
(2-3 servings)
(2-3 Tbsp)
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What is one Food Guide Serving?
Canada’s Food Guide:
http://www.hc-sc.gc.ca/fn-an/food-guidealiment/index-eng.php
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Think About It
• List the digestive organs and accessory organs
of the digestive system.
Organs in the
Digestive
System
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Tongue
Salivary
glands
Salivary
glands
Cardiac
orifice
Parotid gland
Sublingual gland
Oral cavity
Pharynx
Mouth
Submandibular gland
Esophagus
Esophagus
Pyloric
sphincter
Liver
Stomach
Gallbladder
Stomach
Ascending
portion of
large intestine
Gallbladder
Liver
Pancreas
Pancreas
IIeum
of small
intestine
Small intestine
Large intestine
Duodenum of
small intestine
Small
intestines
Large
intestines
Rectum
Anus
Rectum
Appendix
Cecum
Anus
A schematic diagram of
the human digestive system
Sooo…
• How do the nutrients get into our blood to be
distributed throughout the body?
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• Food is mechanically and chemically broken
down into these molecules during digestion,
after which they can be taken up by body cells
through the separate process of absorption.
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Think About It
• What does physical digestion mean?
• What does chemical digestion mean?
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Principles of digestion and absorption
• Digestion requires enzymes capable of
hydrolyzing bonds
• Products of digestion must be absorbed
across plasma membranes
• Minerals, vitamins and monomers do not
require digestion
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Mechanical
Breakdown in the
Mouth
• Chewing involves
teeth & the skeletal
muscles of jaws, lip,
cheeks and tongue
and is controlled by
cranial nerves.
What are the functions of chewing?
 The functions of chewing are to
1) reduce the size of food in order to be
swallowed & to increase the surface area for
enzymes to act
2) move the food around mouth to stimulate
taste and touch receptors and promote
secretions of saliva
Chemical Breakdown in the Mouth
• Why is the production of saliva important for
health?
Saliva
• You produce 1-2L of saliva per day secreted at
rate of 4 ml/minute
• Saliva contains water, mucus, salivary amylase,
and bicarbonate ions
HCO3Salivary amylase
The Role of Saliva
• The functions of saliva are to:
1) moisten/soften and lubricate the food
2) neutralize acid produced by bacteria using
HCO3- ions in saliva (helps prevent tooth
decay)
3) convert starch to maltose with salivary
amylase enzyme (*enzymes are specific*)
The Role of Saliva
• How is the release of saliva controlled?
• When food is sensed (smell,
touch, thought):
Messages are sent to the
salivary center in the medulla
and nerve impulses are sent
back to the salivary glands
causing the release of saliva
The process of swallowing and
peristalsis
• Once chewed, food is called
a bolus
• Swallowing occurs when bolus
exits mouth into esophagus
(through pharynx)
• Swallowing begins as a
voluntary action
• Action continues by
involuntary peristalsis of esophagus
** NO absorption has occurred up to this point
** Carbohydrate digestion BEGAN in mouth
Pharynx
• The oral & nasal cavities connect to both trachea &
esophagus via the pharynx
• How is food prevented
from going down your
air passages?
• Why is it impossible to
breathe and swallow at
the same time?
Swallowing
1. SOFT PALATE MOVES BACK to cover openings
to nose (nasopharyngeal openings)
2. TRACHEA (WINDPIPE) MOVES UP under a flap
of tissue called the epiglottis, blocking its
opening
3. The GLOTTIS (opening to the LARYNX /
“voicebox”) is closed when the trachea
moves up
 feel you Adam’s Apple (part of larynx)
when you swallow
4. Food then has one route to go  down the
ESOPHAGUS.
• Why is it not a good idea to talk & eat at the
same time?
• Epiglottis does not fully cover trachea & food
goes down the “wrong way”
 can be coughed back up
• Soft palate doesn’t fully cover opening to
nasal cavity and food gets into nasal cavity
Esophagus
• Muscular tube ~25cm long
extending from pharynx to
stomach
• Made of several types of
tissue:
Inner surface lined with
mucus membranes. This
layer is attached by
connective tissue to a layer
of smooth muscle
containing both circular
and longitudinal muscle.
Esophagus
 Food moves down esophagus through
PERISTALSIS (rhythmical muscle contractions)
 takes about 9sec for food to move from
pharnyx to stomach
 Pressure differences caused by waves of
muscle contractions allow contents to move in
one direction towards stomach
 Normal pressure usually prevents stomach
contents from entering esophagus, but when
does creates heartburn (stomach acid
irritation)
• Can we swallow upside down?
• Yes – because the muscles around the
esophagus are strong enough to push food up
to your stomach
(However, it is not recommended you try this!)
Digestion Overview
• http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208&
alaid=ala_996421&showSelfStudyTree=true