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Digestive
System
The digestive system is
responsible for the
physical and chemical
breakdown of food so it
can be taken into the
bloodstream and used by
body cells and tissues.
The Digestive System includes:
 The Alimentary Canal:
 Long muscular tube
 Begins at the mouth and includes the
pharynx, esophagus, stomach, small
intestines, large intestines, and the
anus.
• The Accessory Organs:
• The salivary glands, tongue, teeth, liver,
gallbladder, and pancreas
Where does digestion start?
Mouth, buccal, or oral cavity
 A. Receives food as it enters the body
 B. Actions in the mouth
1. Food is tasted
2. Broken down physically by the
teeth
3. Lubricated and partially digested
by saliva
4. Swallowed
Teeth
Special structures in
the mouth
 2. Break down food
physically by chewing
and grinding the
food, a process called
mastication
Tongue
Muscular organ
2. Contains special
receptors called taste
buds that allow person to
taste sweet, salt, sour, and
bitter sensations
3. Also aids with chewing
and swallowing of food
Within the mouth:
Hard palate
1. Bony structure that forms the
roof of the mouth
2. Separates the mouth from the
nasal cavities
Soft palate
1. Located behind the hard
palate
2. Separates the mouth from
the nasopharynx
Uvula
(a) Cone-shaped
muscular structure
(b) Hangs from the
middle of the soft palate
(c) Prevents food from
entering the
nasopharynx during
swallowing
Salivary Glands
 1. Three pairs of glands
 Parotid, sublingual, and submandibular
 2. Produce a liquid called saliva
 (a) Lubricates the mouth during speech and chewing
 (b) Moistens food so it can be swallowed easily
 (c) Also contains an enzyme called salivary amylase
 aa. Substance speeding up a chemical reaction
 bb. Begins the chemical breakdown of carbohydrates
or starches into sugars that can be taken into the
body

Pharynx or Throat
A. After the food is chewed and mixed
with saliva, it is called a bolus and it
enters the pharynx or throat
B. Tube that carries both air and food
C. Carries the air to the trachea or
windpipe
D. Carries food to the esophagus
In the esophagus:
When bolus is swallowed, muscle
action causes the epiglottis to
close over the larynx
2. Prevents bolus from entering
respiratory tract
3. In this way, the bolus enters the
esophagus
Normal Swallow Animation - Thick and Easy
Dysphagia - YouTube
www.youtube.com/watch?v=1YfO11Pry6Y&fe
ature=player_detailpage
Esophagus
 Muscular tube dorsal to the trachea
 Receives bolus from the pharynx and
carries it to the stomach
 Relies on a rhythmic, wavelike
involuntary movement of its muscles,
called peristalsis, to move the food in a
forward direction
Stomach
Enlarged part of the alimentary
canal
Receives the food from the
esophagus
Mucous membrane lining contains
folds called rugae, which disappear
as the stomach fills with food and
expands
Cardiac Sphincter
Circular muscle between the
esophagus and stomach
Closes after food enters the
stomach
Prevents food from going
back up into the esophagus
Pyloric Sphincter
Circular muscle between the
stomach and small intestine
Keeps food in the stomach
until it is ready to enter the
small intestine
Food usually remains in the
stomach for about one to four
hours
Gastric Juices
•
Produced by glands in the
stomach
• Converts food into a semi
fluid material called chyme
Gastric Juices
 Juices contain hydrochloric
acid
Kills bacteria
Facilitates the absorption of
iron
Activates the enzyme pepsin
Gastric Juices
 Contain enzymes:
 Lipase, which begins the chemical
breakdown of fats
 Pepsin, which starts protein digestion
 In an infant, the enzyme rennin is
secreted
1) Aids in the digestion of milk
2) Not present in an adult
Small Intestine
Coiled section of
the alimentary
canal about 20
feet long and 1
inch in diameter
Receives food,
in form of
chyme, from
stomach
Small Intestines
There are three
sections:
Duodenum—first 9-10 inches
Jejunum—next 8 feet
Ileum—final 12 feet
Small Intestines--Duodenum
 The first 9-10 inches
Bile from the gallbladder and liver
enter this section through ducts or
tubes
Pancreatic juices from the pancreas
also enter this section through
ducts or tubes.
Small Intestines--Jejunum
Eight feet long
Forms the middle section
of the small intestine
Small Intestines--Ileum
 Final 12 feet of the small intestine
Connects with the large intestine at
the cecum
 Circular muscle called the ileocecal
valve separates the ileum and
cecum and prevents food from
returning to the ileum.
Functions of the Small Intestines:
Completes the process of
digestion
Absorbs the products of
digestion into the
bloodstream for use by
body cells
Intestinal Juices of the Small
Intestines
 Produced by the small intestine
 Contain the enzymes maltase, sucrase,
and lactase, which break down sugars into
simpler forms
 Contain enzymes known as peptidases,
which complete the digestion of proteins
 Contain the enzyme steapsin, which aids
in the digestion of fat
Bile
Liquid that enters
small intestine
from liver and
gallbladder
 2. Emulsifies or
physically breaks
down fats
Pancreatic Juice
 1.Liquid that enters small intestine
from pancreas
 2. Contains enzymes that complete the
process of digestion
 A) Pancreatic amylase or amylopsin,
which acts on sugars
 B) Trypsin and chymotrypsin, which
act on proteins
 C) Lipase or steapsin, which acts on
fats
Small Intestine--Villi
Fingerlike projections
that line wall of small
intestine
Allow food to be
absorbed or taken
into bloodstream
Contain blood
capillaries and lacteals
Small Intestine—Blood Capillaries
Blood capillaries
absorb the digested
nutrients and carry
them to the liver
where they are
stored or released
into general
circulation for use
by body cells
Small Intestines--Lacteals
Lacteals pick up most
of the digested fats
and carry them to the
thoracic duct in the
lymphatic system,
which releases them
into the circulatory
system
Small Intestines
When food has completed its
passage through the small
intestine only wastes,
indigestible materials, and
excess water remain
Large Intestines
Final section
of the
alimentary
canal
About 5 feet
long and
about 2
inches in
diameter
Large Intestines--Functions
 Absorption of water and any remaining
nutrients
 Storage of indigestible materials before
they are eliminated from the body
 Synthesis (formation) and absorption of
some B-complex vitamins and vitamin K by
bacteria present in intestine
 Transportation of the waste products out
of the alimentary canal
Large Intestines--Sections
Cecum:
First section
Connects with the ileum of the
small intestine
Contains a small projection called
the vermiform appendix
Large Intestines--Sections
Ascending colon:
continues up on
the right side of
the body from
the cecum to
the lower part of
the liver
Large Intestine--Sections
Transverse colon:
extends across
the abdomen,
below the liver
and stomach, but
above the small
intestine
Large Intestines--Sections
 Descending colon:
extends down the
left side of the
body
Large Intestines--Sections
Sigmoid colon:
Connects with
descending colon
S-shaped section
that joins with
the rectum
Large Intestines--Sections
 Rectum:
 Final 6 to 8inches
 Storage area for the
indigestibles or wastes
 Has a narrow canal called
the anal canal, which
opens at a hole called the
anus
 Fecal material or stool,
the final waste product of
the digestive process
Accessory Organs
Liver:
 Largest gland in the
body
 Accessory organ for
the digestive tract
 Located under the
diaphragm in the
upper right quadrant
of the abdomen

Functions
of
the
Liver:
• 1. Secretes bile
•
•
a. Used to emulsify or physically break up fats
b. Also makes fats water soluble, which is necessary for absorption
2. Stores sugar in the form of glycogen
a. Glycogen is converted to glucose
b. Released into the bloodstream when additional blood sugar is needed
• 3. Stores iron and certain vitamins
• 4. Produces heparin, a substance that prevents clotting of the
blood
• 5. Produces blood proteins such as fibrinogen and
prothrombin, which aid in the clotting of blood
• 6. Produces cholesterol
• 7. Detoxifies (renders less harmful) substances such as alcohol
and pesticides, and destroys bacteria that have been taken into
the blood from the intestine
Accessory Organs
 Gallbladder:
 1. Small muscular sac
 2. Located under the liver and
attached to it by connective
tissue
 3. Stores and concentrates
bile, which it receives from
the liver
 4. When the bile is needed in
the digestive tract to emulsify
fats, it contracts and pushes
the bile through the common
bile duct into the duodenum
Accessory Organs
 Pancreas:
 1. Fish-shaped organ located behind the
stomach
 2. Produces pancreatic juices
 a. Juices enter duodenum through
pancreatic duct
 b. Contain enzymes to digest food

(1) Pancreatic amylase or amylopsin to
break down sugars

(2) Trypsin and chymotrypsin to break
down proteins

(3) Lipase or steapsin to act on fats
 3. Produces insulin
 a. Secreted into the bloodstream
 b. Regulates the metabolism or burning
of carbohydrates to convert glucose
(blood sugar) to energy