Chapter 14: The Digestive System
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Transcript of Chapter 14: The Digestive System
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Chapter 14: The Digestive System
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Functions• Ingestion—taking in food• Digestion—breaking food down
both physically and chemically• Absorption—movement of
nutrients into the bloodstream• Defecation—rids the body of
indigestible waste
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OrgansTwo main groups:• Alimentary canal (gastrointestinal
or GI tract)– continuous coiled hollow tube–Mouth, pharynx, esophagus,
stomach, small intestine, large intestine, anus
• Accessory digestive organs– Teeth, salivary glands, pancreas,
liver, gallbladder
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Mouth
Anatomy:• Lips (labia)• Cheeks• Hard palate• Soft palate• Uvula– Helps with speech
and preventing food/liquid from entering nasal cavity when swallowing
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• Vestibule– space between lips
externally and teeth and gums internally
• Oral cavity proper– area contained by the
teeth• Tongue– attached at hyoid
bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
• Tonsils– Palatine & Lingual
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Function:• Mastication (= chewing) of food• Digestion by saliva• Swallowing by the tongue• Sense of taste– Gustatory receptors
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Pharynx• Only oropharynx and
laryngopharynx are part of digestive system
• Passageway for air and food
• 2 muscle layers alternate contractions to push food down to esophagus (=peristalsis)– Longitudinal inner layer– Circular outer layer
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Figure 14.2a
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Esophagus• ~10 inches long– Runs from pharynx to stomach through
the diaphragm• Passageway for food only• moves food through slow rhythmic
squeezing (= peristalsis)
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Layers of Alimentary Canal Past the Esophagus
4 layers from inside to outside:• Mucosa – Mostly moist epithelial tissue
• Submucosa– Connective tissue with blood vessels, nerve
endings, and lymph vessels• Muscularis externa– Muscle tissue made of inner circular layer and
outer longitudinal layer• Serosa– Fluid producing cells make up visceral
peritoneum layer that runs into parietal peritoneum (= lining of abdominopelvic cavity)
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Figure 14.3
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Nervous System’s Role• Alimentary canal controlled by
autonomic nervous system• 2 networks:–Myenteric nerve plexus: between circular
and longitudinal muscles– Submucosal nerve plexus: in submucosa
layer• Function is to regulate mobility and
secretory activity
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Stomach• Located on the left side
of the abdominal cavity• Food enters at the
cardioesophageal sphincter (sphincter = valve)
• Food empties into the small intestine at the pyloric sphincter
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Regions:• Cardiac region -
near the heart• Fundus –
rounded part next to the cardiac region
• Body - middle• Pylorus -
funnel-shaped end
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• Rugae = internal folds of the mucosa
• External regions– Lesser
curvature—concave medial surface
– Greater curvature—convex lateral surface
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Layers of peritoneum attached to the stomach
• Lesser omentum- attaches the liver to the lesser curvature
• Greater omentum- attaches the greater curvature to the posterior body wall– Sticky wall that
collects fat to insulate, cushion, and protect abdominal organs
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Physiology• Temporary storage tank for food• Site of food breakdown– The enzyme pepsinogen and
hydrochloric acid break down proteins– Gastrin is hormone that stimulates HCl
secrection– Alkaline mucus lines the inside of the
stomach to protect it from HCl• Delivers chyme (processed food) to
the small intestine
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Structure of the Stomach Mucosa
Figure 14.4c
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Small Intestine• Muscular tube extending from the
pyloric sphincter to the ileocecal valve
• Suspended from the posterior abdominal wall by the mesentery
• The body’s major digestive organ• Function: nutrient absorption into the
blood
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Divisions:• Duodenum– Attached to the
stomach– Curves around the
head of the pancreas
• Jejunum–Middle
• Ileum– From jejunum to
large intestine
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Chemical digestion begins in the small intestine• Enzymes are produced by
– Intestinal cells– Pancreas
• Pancreatic ducts carry enzymes to the small intestine
• Bile, made by the liver, enters through bile duct
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3 structural modifications that increase surface area (fom largest to smallest):
• Circular folds (plicae circulares)• Villi – fingerlike projections on circular
folds• Microvilli – smaller fingerlike projections on
villi that absorb; make the brush border
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Figure 14.7a
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Large Intestine• Larger in diameter, but shorter in
length, than the small intestine• Frames the internal abdomen• Function: absorbs water & processes
waste material
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Parts:• Cecum- saclike first part of the large
intestine• Appendix– Vestigial structure – Accumulation of lymphatic tissue that hangs
from the cecum• Colon– Ascending—travels up right side of abdomen– Transverse—travels horizontally– Descending—travels down the left side– Sigmoid—enters the pelvis
• Rectum and anal canal– External anal sphincter (skeletal muscle) and
internal involuntary sphincter (smooth muscle)
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Large Intestine
Figure 14.8
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• No villi present• Goblet cells produce alkaline mucus
which lubricates the passage of feces• Muscularis externa layer is reduced
to three bands of muscle called teniae coli– Causes the wall to pucker into pocket
like sacs called haustra
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Teeth• Function is to
masticate (chew) food
• Humans have two sets of teeth:– 20 deciduous
(baby) teeth by age 2
– 32 permanent teeth by age 12
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Classification of teeth:
• Incisors—cutting• Canines—tearing
or piercing• Premolars—
grinding• Molars—grinding
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Salivary Glands• Three pairs of salivary glands empty
secretions into the mouth– Parotid glands– Submandibular glands – Sublingual glands
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Saliva• 98% water, 2% electrolytes, mucus,
and enzymes• Dissolves chemicals so they can be
tasted• Helps to form a food bolus• Your body produces 1-2 liters per day
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Pancreas • Located deep to stomach• Produces enzymes that
break down carbohydrates
• Enzymes secreted into the duodenum
• Alkaline fluid mixed with enzymes neutralizes acidic chyme coming from stomach
• Produces hormones that regulate blood sugar:– Insulin (takes sugar from
blood to tissues)– Glucagon (takes sugar
from tissues to blood)
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Figure 14.6
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Pancreas
Figure 14.1
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Liver• Largest gland in the body• Located on the right side of the
body under the diaphragm• 4 lobes• Connected to the gallbladder via
the common hepatic duct• Functions:
– makes bile to break down fat– makes cholesterol to transport fats– makes proteins for blood plasma – detoxifies blood from drugs and
alcohol– Stores glycogen, vitamins, and
minerals
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Liver
Figure 14.1
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Bile• Yellowish-green fluid produced in the liver• Made of:– Pigments, mostly bilirubin
• Made when the liver breaks down old RBCs• Causes yellow coloring of jaundice when there is
liver disease– Salts– Cholesterol– Phospholipids– Electrolytes
• Function: breaks large fat globules into smaller ones
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Gallbladder• Sac found in hollow space of liver• When no digestion is occurring, bile
backs up the cystic duct for storage in the gallbladder
• When digestion of fatty food is occurring, bile is released into the duodenum from the gallbladder
• Gallstones are crystallized cholesterol which can cause blockages
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Figure 14.1