2. System Overview
The digestive tract, often called the
alimentary tract or canal, is a muscular tube
that contains the organs of digestion
The tube begins with the mouth and ends at the anus
In between these two points are the pharynx,
esophagus, stomach, small intestines, and
large intestines
Accessory organs, such as teeth, salivary
glands, liver, pancreas, and gallbladder, are
necessary for processing materials into
useable substances
3.
4. System Overview
The components of the digestive system
work together to perform the following
general steps:
1. Ingestion
2. Mastication
3. Digestion
4. Secretion
5. Absorption
6. Excretion (defecation)
5. System Overview
Food first enters the mouth, an activity
called ingestion
Once food is ingested, the tongue and
teeth work together to mechanically
process the food by physically breaking it
down
The chewing process is called mastication
Digestion is the chemical process of
breaking down food into small molecules
This is necessary so nutrients can be absorbed by
the lining of the digestive tract
6. System Overview
The secretion of acids, buffers, enzymes,
and water aid in the breakdown of food
Once the food is broken down both
physically and chemically, it is ready for
absorption through the lining of the
digestive tract for use by the body
Finally, waste products and unusable
materials are prepared for excretion and
are eliminated by the body through
defecation
7. The Mouth and Oral
Cavity
Your mouth is the opening that leads to the
oral cavity, also called the buccal cavity
Your lips, or labia, act as the door to this
cavity
The hard and soft palates create the roof of
the cavity while the tongue acts as the floor
The tongues base (area of attachment) and
the uvula (dangles from the soft palate) act
as a boundary between the oral cavity and
the pharynx
The uvula aids in swallowing , it helps direct food toward
the pharynx and helps block food from coming out your
nose
8. The Mouth and Oral
Cavity
The lingual tonsils are at the back of the
cavity
They aren’t important for digestion, they help fight
infection as part of the lymphatic system
The sides of the cavity are created by
your cheeks
The mouth receives, tastes, mechanically
breaks down, and begins the process of
chemical breakdown of food, adding saliva
9.
10. Tongue
Your tongue is a muscle that provides
taste stimuli to your brain, senses
temperature and texture, manipulates
food while chewing, and aids in swallowing
As the tongue moves food around in the
oral cavity, saliva is added to moisten and
soften it, while teeth crush the food until it
reaches the right consistency
11. Tongue
The tongue pushes the food into a ball-like
mass, called a bolus, so it may be swallowed
and passed to the pharynx
The lingual frenulum, a membrane under the
tongue, keeps you from swallowing your
tongue and aids in speaking
An abnormally short frenulum prevents clear speech=
tongue-tied
The area under the tongue has many blood
vessels
This sublingual blood vessel network readily absorbs
substances and is a rapid means of administering
medication
12. Salivary Glands
There are three pairs of salivary
glands, which are controlled by the
autonomic nervous system
A large parotid salivary gland is found
slightly inferior and anterior to each ear
These are the ones that swell when you get mumps
The ducts from these glands empty into
the upper portion of the oral cavity
13. Salivary Glands
The smallest of the salivary glands, the
sublingual salivary glands are found under
the tongue
The submandibular salivary glands are
located along both sides of the inner
surface of the mandible, or lower jaw
On average, the salivary glands produce
1–1.5 liters of saliva daily
Small amounts of saliva keep the mouth
moist, but the idea or presence of food
increase production significantly
14. Salivary Glands
Although saliva is almost totally water
(99.4%), it also contains antibodies,
buffers, ions, waste products, and
enzymes
Enzymes are formed by cells
Enzymes act as organic catalysts to speed
up chemical reactions
One enzyme, salivary amylase, speeds up the
chemical activity of breaking down carbohydrates
into smaller molecules that are more easily
absorbed by the digestive tract
After eating, saliva cleans the oral
surfaces, reducing the amount of bacteria
that grows in your mouth
15.
16. Teeth
You will only have two sets of teeth in your
lifetime
The first set, are called baby teeth, or
deciduous teeth
They will eventually fall out
The 1st tooth appears around 6 months of
age
The lower central incisors appear first, with
all 20 teeth in place by age 2½
Between 6 and 12 years these teeth fall out
and are replaced by your second set of 32
permanent teeth
The exception to this are the wisdom teeth which may
not appear until an individual is as old as 21
17. Tooth Types
Incisors are located at the front of the mouth
Blade shaped, and are used to cut food
Canine teeth are for holding, tearing, or
slashing food
They are also known as eyeteeth or cuspids, and are
located next to incisors
Bicuspids, or premolars, are transitional teeth
Molars are the final type of teeth and have
flattened tops
Both bicuspids and molars are responsible for crushing
and grinding food
18.
19. Tooth Structure
Each tooth has a crown, neck, and root
The crown is the visible part of the tooth
It is covered by the hardest biologically
manufactured substance, enamel
The neck is the transitional section that
leads to the root
Internally, most teeth are made up of
dentin, a mineralized bone-like substance
The next layer is connective tissue called
pulp, located in the pulp cavity
The pulp cavity contains blood vessels and
nerves providing nutrients and sensation
The nerves and blood vessels get to the pulp cavity
via the root canal
20. Tooth Structure
The root is nestled in a bony socket and is
held in place by fibers of the periodontal
ligament
In addition, cementum covers the dentin
of the root, aiding in securing the
periodontal ligament
Cementum is a soft version of bone
Healthy gums, or gingiva, also help hold
the teeth in place
Epithelial cells form a tight seal around
the tooth to prevent bacteria from coming
into contact with the tooth’s cementum
