BIOL 1080 Chapter Notes - Chapter The Digestive System: Gastric Acid, Gastric Glands, Salivary Gland

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26 Aug 2017
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Week 8 Lecture 15 Readings: 3b(ii)
The Digestive System:
pg. 239
Digestive system: consists of the gastrointestinal tract, into which various accessory glands release
their secretions
Gastrointestinal (GI) tract: a long, hollow tube, in the digestive system, into which various accessory
glands release their secretions
Structure
Description/ Functions
Mechanical Digestion
Chemical Digestion
Mouth
Receives food; contains teeth
and tongue; tongue
manipulates food and
monitors quality
Teeth tear and crush
food into smaller
pieces
Digestion of
carbohydrates begins
Pharynx
Area that both food and air
pass through; role in
swallowing
None
None
Esophagus
Muscular tube that
transports food from mouth
to stomach
None
None
Stomach
J-shaped muscular sac for
food storage; secretes gastric
juice (pepsin and HCl)
Churning of stomach
mixes food with
gastric juice, creating
liquid chyme
Protein digestion
begins
Small Intestine
Long, muscular tube where
digestion is completed and
most nutrients and water are
absorbed
Segmental
contractions mix food
with intestinal
enzymes, pancreatic
enzymes, and bile
Carbohydrate,
protein, and fat
digestion completed
Large Intestine
Final tubular region of GI
tract; absorbs water and
ions; houses bacteria; forms
and expels feces
None
Some digestion is
carried out by
bacteria
Anus
Terminal outlet of digestive
tract; expels feces
None
None
Four basic layers of the GI tract:
1) Mucosa: the innermost layer of the GI tract; mucous membrane that lines the GI tract and
secretes mucus that lubricates and protects the GI tract
2) Submucosa: connective tissue containing blood vessels, lymph vessels, and nerves
3) Muscularis: responsible for movement of materials through the GI tract and for mixing ingested
materials with digestive secretions; a double layer of smooth muscle one circular and one
longitudinal
4) Serosa: a thin layer of epithelial tissue supported by connective tissue, wraps around the GI tract;
secretes lubricating fluid to the outside of the GI tract to reduce friction with contacting surfaces
of the intestine and other abdominal organs
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Accessory Structures:
o Salivary glands: three pairs of glands that secrete saliva; saliva moistens food; enzyme (amylase)
in saliva begins starch digestion
o Liver: large organ in abdominal cavity; secretes bile, which emulsifies fats; plays role in
processing and storing certain nutrients
o Gallbladder: small sac; stores bile; releases bile into small intestine
o Pancreas: gland located behind stomach; secretes enzymes that digest all major nutrients;
secretes buffers that neutralize HCl from stomach; releases secretions into small intestine
Specialized Compartments for Food Processing: pg. 241
Mouth: pg. 241
functions: begins mechanical and chemical digestion; monitors food quality; and moistens and
manipulates food so that it can be swallowed
incisors slice food as we bite
canines tear food
premolars and molars grind, pulverise, and crush food
Plaque: an invisible film of bacteria, mucus, and food particles which promotes tooth decay because
it holds the acid against the enamel
Gingivitis: swollen gums that are an early stage of gum disease occurs when plaque formed along
the lining of the teeth and gums causes the gums to become inflamed and swollen
Periodontitis: inflammation of the teeth auses teeth to eoe loose as the tooth’s oy soket
and the tissues that hole the tooth in place are eroded
3 pairs of salivary glands
o sublingual (below the tongue)
o submandibular (below the jaw)
o parotid (in front of the ears)
Salivary amylase: enzyme contained within saliva that begins to chemically digest starches into
shorter chains of sugar
tongue = skeletal muscle
Pharynx: pg. 243
Pharynx: shared by the respiratory and digestive systems
Esophagus: the tube that connects the pharynx to the stomach
swallowing consists of a voluntary component (tongue moves food to back of throat) followed by an
involuntary one (involuntary swallowing reflex stimulated by the presence of food in the wall of the
pharynx)
Epiglottis: covers the opening to the airways of the respiratory system prevents food from
entering the airways
Esophagus: pg. 244
Peristalsis: rhythmic waves of muscle contraction occurs in the esophagus, stomach, and small
intestine produced by two layers of muscle in the muscularis
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