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Digestive System
5.2 Investigate A&P of digestive
• Label the major organs on a diagram of the digestive
• Identify at least three organs that are located in the mouth
and aid in the initial breakdown of food
• Cite two functions of the salivary glands
• Describe how the gastric juices act on food in the stomach
• Explain how food is absorbed into the body by the villi in
the small intestine
• List at least three functions of the large intestine
• List a t least four functions of the liver
• Explain how the pancreas helps digest foods
• Describe at least five diseases of the digestive system
Digestive or GI system
• Physical and chemical breakdown of food so
that it can be taken into the bloodstream and
used by body cells and tissues.
• Alimentary canal plus accessory organs
Alimentary canal
• Long, muscular tube that begins at the mouth
and includes the mouth (oral cavity), pharynx,
esophagus, stomach, small intestine, large
intestine, and anus.
Accessory organs
Salivary glands
• Buccal cavity
• Receives food- then food is tasted, broken
down physically by the teeth, lubricated and
partially digested by saliva, and swallowed
• Special structures in the mouth that physically
break down food by chewing and grinding.
• mastication
• Muscular organ that contains special receptors
called taste buds
• Sweet, salty, sour, and bitter sensations
• Aids in chewing and swallowing
Hard palate
• Bony structure that forms the roof of the
mouth and separates the mouth from the
nasal cavity
Soft palate
• Behind the hard palate, separates the mouth
from the nasopharynx
• Uvula- cone-shaped muscular structure, hangs
from the middle of the soft palate
• Prevents food from entering the nasopharynx
during swallowing
Salivary glands
• Three pairs- parotid, sublingual, and
submandibular, produce saliva which
lubricates the mouth during speech and
chewing and moistens food so it can be
swallowed easily. Contains an enzyme called
salivary amylase which begins the chemical
breakdown of carbohydrates or starches into
• Food chewed and mixed with saliva is called a
• When swallowed the bolus enters the pharynx
(throat). Carries both food and air.
• Food-esophagus
• Air-trachea
• During swallowing epiglottis closes over larynx
to prevent bolus from entering respiratory
• Muscular tube dorsal to trachea. Carries bolus
to stomach.
• Peristalsis- rhythmic , wavelike, involuntary
movement of muscles
• Enlarged part of alimentary canal.
• Receives food
• Mucous membrane lining contains folds called
• Rugae disappear as stomach fills and expands
• Cardiac sphincter- circular muscle between
esophagus and stomach, closes after food
enters to prevent food from going back up.
Stomach cont.
• Pyloric sphincter- circular muscle between
stomach and small intestine, keeps food in
stomach until food ready to enter small
• 2-4 hours
• Food converted into a semi fluid material ,
called chyme, by gastric juices produced by
glands in stomach
Stomach cont.
• Gastric juices- HCL and enzymes
• HCL kills bacteria, facilitates iron absorption,
and activates the enzyme pepsin.
• Enzymes- lipases- starts the chemical
breakdown of fats, and pepsin- starts protein
• Infants- enzyme rennin aids in digestion of
Small Intestine
Chyme enters from stomach
Coiled section of alimentary canal
20 ft length and 1 inch diameter
Duodenum (first 9-10 inches)- bile from the
gallbladder and liver and pancreatic juice from
the pancreas enter this section through ducts
or tubes.
Small Intestine
• Jejunum- 8 ft length- middle section
• Ileum-final 12 ft connects with large intestine at
the cecum.
• Circular muscle called ileocecal valve separates
the ileum and cecum- prevents food from
returning to ileum.
• Process of digestion completed in small intestine
• Products of digestion absorbed into bloodstream
for use by cells
Small intestine- intestinal juices
• Enzymes maltase, sucrase and lactasebreakdown sugars
• Enzymes- peptidases- complete digestion of
• Enzyme Steapsin (lipase) aids in digestion of
• Bile from liver and gall bladder emulsifies
(physically breaks down) fats.
Small intestine- intestinal juices
• Pancreatic enzymes- amylase (acts on sugars),
trypsin and cymotrypsin (acts on proteins),
lipase or steapsin (acts on fats).
Small intestine
• After food digested, absorbed into
• Walls of intestine lined with fingerlike
projections called villi.
• Villi contain blood capillaries and lacteals.
• Blood capillaries absorb digested nutrients
and carry them to liver where they are stored
or released into general circulation for use by
body cells.
Small intestine
• Lacteals absorb most of digested fats and
carry them to the thoracic duct in lymphatic
system which releases them into circulatory
• When food completed passage through SI,
only wastes, indigestible materials, and excess
water remain
Large Intestine
• Final section of alimentary canal
• 5 ft long and 2 inch diameter
• Absorption of water and remaining nutrients
• Storage of indigestible materials until
• Synthesis and absorption of some b-complex
vitamins and vitamin K by bacteria present in
• Transportation of the waste products out of
the alimentary canal
Connects with ileum of small intestine
Contains a small projection called the
vermiform appendix
• Ascending colon continues up on right side of
body from cecum to lower part of liver
• Transverse colon extends across the abdomen,
below liver and stomach but above small
• Descending colon extends down the left side of
the body
• Sigmoid colon
• Connects with descending colon
• S-shaped section that joins with the rectum
• Final 6-8 inches
• Storage area for indigestibles or wastes
• Narrow canal called the anal canal which
opens at a hole called anus
• Fecal material or stool, the final waste product
of digestive process, expelled through this
• Largest gland in the body
• Accessory organ
• Under diaphragm in upper right quadrant of
Secretes bile
– Used to emulsify or physically break up fats
– Makes fats water soluble, which is necessary for
Stores sugar in the form of glycogen
glycogen is converted to glucose
Released into the bloodstream when additional
blood sugar is needed
Functions cont.
• Stores iron and certain vitamins
• Produces heparin (prevents blood clotting)
• Produces blood proteins such as fibrinogen
and prothrombin, which aid in clotting of the
• Produces cholesterol
• Detoxifies substances such as alcohol and
pesticides, destroys bacteria that have been
taken into the blood from the intestine
• Small muscular sac
• Under liver attached to it by connective tissue
• Stores and concentrates bile (which it receives
from liver)
• When bile needed in digestive tract to
emulsify fats, it contracts and pushes the bile
through the common bile duct into duodenum
• Fish-shaped organ located behind stomach
• Produces pancreatic juices
– Juices enter duodenum through pancreatic duct
– Contain enzymes to digest food
• Pancreatic amylase to break down sugars
• Trypsin and chymotrypsin to break down prteins
• Lipase to act on fats
Pancreas cont.
• Produces insulin
– Secreted into the bloodstream
– Regulates the metabolism or burning of
carbohydrates to convert glucose to energy