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I.
DIGESTION is the MECHANICAL(changes size of food) and
CHEMICAL(changes chemical composition) breakdown of
food.
II. Processes of the digestive system: Mechanical and chemical
digestion, ingestion, propulsion, absorption, and defecation.
III. The digestive system is made up of the ALIMENTARY
CANAL and accessory organs.
A. The alimentary canal is an 8 meter
long tube made up of the mouth,
pharynx, esophagus, stomach, small
and large intestine, and anal canal.
B. The accessory organs are the gall
bladder, salivary glands, liver, and
pancreas.
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IV. Structure and movements of the tube.
A. 4-layered wall: Mucous membrane (or MUCOSA),
SUBMUCOSA, MUSCULAR LAYER, and SEROSA (Or
serous layer).
1. Mucosa: Composition - epithelial and some
connective and smooth tissue. It has enfolding and
may contain glands. Function - absorption,
protection and
secretion.
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2. Submucosa: Composition - loose connective tissue,
blood vessels, lymphatic vessels, and nerves.
Function - nourishes surrounding tissue and
transports absorbed materials.
3. Muscular layer: Composition Smooth muscle fibers arranged
in circular and longitudinal
groups. Function - movements
of the tube and its contents.
4. Serosa: Composition Epithelium, connective tissue.
Function - Protection and
lubrication.
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B. Two types of movements: Mixing and propelling.
1. Mixing occurs when smooth muscles in small segments of
the tube contract rhythmically.
2. Propulsion - peristalsis
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V.
Stops along the way
A.
The mouth
•Performs mechanical digestion
(chewing) and mixes food with
saliva for chemical digestion.
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•Cheeks - pads of fat that help
with chewing.
•Lips - contain sensory receptors that judge temperature
and consistency of foods.
•Tongue - covered with mucous membranes;
connected to floor of mouth by lingual
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move food toward pharynx; covered with
PAPILLAE (taste buds/provide friction);
the root of the tongue is anchored to the hyoid bone
•PALATE - roof of oral cavity; hard anterior and soft
posterior part; uvula moves upward during swallowing to
prevent food from entering the nasal cavity; PALATINE
tonsils composed of lymphatic tissue lie at the back of the
mouth on either side of the tongue;
PHARYNGEAL tonsils (also called
ADENOIDS) are behind them and
may be surgically removed.
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•Teeth - hardest body structures; kind of like bone, but
with extra proteins; adapted to handle different kinds of
food
B.
The Salivary Glands
•
Secrete saliva to moisten food and begin chemical
digestion
•
Solvent allows food tasting
•
Scattered through tongue, palate, and cheeks
•
Glands have both sereous cells (secrete digestive
enzymes) and mucous cells (mucous make food easier to
swallow)
•Parotid, submandibular, and sublingual glands
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C. Pharynx
•
Constrictor muscles allow for swallowing.
•
Swallowed food is called a bolus.
•
Swallowing begins as a voluntary action, but
becomes involuntary.
D. Esophagus
•
25 cm long collapsible muscular tube
•
Lined with mucous cells
•
The lower esophageal sphincter is located
where the esophagus joins the stomach.
It remains contracted (except
during peristalsis) to prevent
regurgitation.
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E. Stomach
•
J-shaped pouch-like organ that
holds over a liter; thick folds
(RUGGAE) of mucosal and
submucosal tissue; mixes food
with gastric juices; begins
digesting proteins; limited absorption
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•The PYLORIC SPHINCTER controls
emptying of the stomach
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•Gastric secretions - gastric glands are
lined with goblet cells, parietal cells
(release HCl), and chief cells (release digestive enzymes)
•Gastric absorption - the stomach absorbs some water, certain
salts and lipid-soluble drugs, and alcohol.
•Mixing and emptying - Food enters the stomach causing the
stomach to enlarge while the muscles hold their tone (eating too
much spikes pressure and signals pain receptors); food is mixed
with gastric juices to form a liquid called chyme; stomach
contractions push cyme (5-15 ml at a time) through the pyloric
sphincter
F. The Pancreas
•
Secretes pancreatic juice full of enzymes that digest
carbohydrates, fats, proteins, and nucleic acids.
•
The head of the pancreas is in the first portion of the small
intestine (DUODENUM)
•
The pancreatic duct connects with the duodenum.
G. The Liver
•
The largest internal organ
located inferior to the diaphragm.
•
Composed of large right lobe,
smaller left lobe, and two even
smaller lobes.
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•Functional units, called HEPATIC LOBULES, are filled with blood
vessels. BILE CANALS receive secretions from hepatic cells.
Many canals merge to form the HEPATIC DUCT.
•Liver functions - carbohydrate metabolism and maintenance of
blood sugar; oxidizing fatty acids; making lipoproteins,
phospholipids, and cholesterol; converting carbs and proteins into
fats; making urea; converting amino acids; storing vitamins,
nutrients, and blood; destroying damaged blood cells; removing
toxins from the body (alcohol, drugs, etc.); making bile
•Bile - a yellowish green liquid made of water, bile salts, bile
pigments, cholesterol, and electrolytes. Bile salts are the only
substances with digestive properties. It absorbs fat-soluble
vitamins and cholesterol and breaks down fat globules.
H. The Gallbladder
•
Pear-shaped sac located in a
depression
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in the liver.
•
Stores bile
•
Its CYSTIC DUCT joins with the joins with hepatic duct
to form the COMMON BILE DUCT.
I.
Small Intestine
•
Fills abdominal cavity - in cadavers it is 18-20 ft long,
but only 1/2 that in living people.
•Parts - DUODENUM (small attached first part), Jejunum
(unattached portion), Ileum (joins with jejunum); the Jejunum
and Ileum are covered by a serous membrane called the
MESENTARY. It