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Copyright © 2011 Pearson Education, Inc.
Digestive System
• Two groups of organs
1. Alimentary canal (gastrointestinal or GI tract)
• Digests and absorbs food
• Mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Copyright © 2011 Pearson Education, Inc.
Digestive System
2. Accessory digestive organs
• Teeth, tongue, gallbladder
• Digestive glands
• Salivary glands
• Liver
• pancreas
Copyright © 2011 Pearson Education, Inc. Figure 22.1
Mouth (oral cavity)Tongue
Esophagus
LiverGallbladder
Anus
DuodenumJejunumIleum
Small intestine
Parotid glandSublingual glandSubmandibulargland
Salivaryglands
PharynxStomachPancreas(Spleen)
Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal
Largeintestine
Copyright © 2011 Pearson Education, Inc.
Digestive Processes
• Six essential activities
1. Ingestion
2. Propulsion
3. Mechanical digestion
4. Chemical digestion
5. Absorption
6. Defecation
Copyright © 2011 Pearson Education, Inc. Figure 22.2
FoodIngestion
PropulsionEsophagus
Stomach
PharynxMechanicaldigestion
Chemicaldigestion
• Chewing (mouth)• Churning (stomach)• Segmentation (small intestine)
Smallintestine Largeintestine
Defecation Anus
Feces
Bloodvessel
Lymphvessel
Absorption
• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)
Mainly H2O
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Blood Supply: Splanchnic Circulation
• Arteries
• Hepatic, splenic, and left gastric
• Inferior and superior mesenteric
• Hepatic portal veins
• Drains nutrient-rich blood from digestive organs
• Delivers it to the liver
Copyright © 2011 Pearson Education, Inc.
TISSUES OF THE ALIMENTARY CANAL
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Histology of the Alimentary Canal
• Four basic layers (tunics)
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
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MucosaInner layer of lumen
Three sublayers:
1. Epithelium – simple columnar and goblet cells
• Secrete mucus and enzymes
2. Lamina propria – areolar basement membrane
3. Muscularis mucosae– thin layer of smooth muscle
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Simple Columnar with Microvilli
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Submucosa, Muscularis Externa and SerosaSubmucosa
• Connective tissue
• Blood and lymphatic vessels
Muscularis externa
• Responsible for segmentation and peristalsis
• Smooth muscle
Serosa
• Fibrous covering (visceral peritoneum)
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ORAL CAVITY
Mouth, teeth, salivary glands and tongue
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Mouth• Oral (buccal) cavity
• Bounded by lips, cheeks, palate, and tongue
• Lined with stratified squamous epithelium
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Oral Cavity
• Lips form anterior border
• Cheeks form lateral border
• Palate forms superior border
• Hard palate: maxillae and palatine bones
• Ridges help create friction
• Soft palate: closes the nasopharynx for swallowing
• Uvula projects down from free edge
Copyright © 2011 Pearson Education, Inc.
Tongue
Oral cavity muscle• Assists in chewing
• forming bolus
• swallowing, speech, and taste
Contains taste buds
Frenulum attaches tongue to the floor of oral cavity
Copyright © 2011 Pearson Education, Inc.
Salivary Glands
Extrinsic salivary glands
•Secrete saliva, contains digestive enzymes
1.Parotid gland – buccal area• Duct opens near 2nd molar
2.Submandibular – medial mandible• Duct opens under tongue
3.Sublingual – anterior to submandibular, under tongue
Copyright © 2011 Pearson Education, Inc. Figure 22.9
Teeth
Ducts ofsublingualgland
Sublingualgland
Submandibularduct
Posterior bellyof digastric muscle
Parotid ductMasseter muscleBody ofmandible (cut)
Parotidgland
Tongue
Submandibulargland
(a)
Frenulumof tongue
Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle Mucous
cells (b)
Serous cellsforming demilunes
Copyright © 2011 Pearson Education, Inc.
Teeth• 32 permanent teeth
• Covered by enamel – hardest substance in body
• Periodontal ligament• Forms fibrous joint called a gomphosis
• Incisors - chisel shaped for cutting
• Canine - fanglike
• Premolars (bicuspids) and molars • Have broad crowns for grinding or crushing
Copyright © 2011 Pearson Education, Inc.
Tooth Structure
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Pharynx and Esophagus
Muscular tubes allow passage of water and food
Esophagus uses peristalsis to move food
• Travels through diaphragm
• Esophageal sphincter
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STOMACH AND INTESTINES
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Stomach Regions
• Cardiac region• Connects to esophagus
• Fundus• Dome region below
diaphragm
• Body• midregion
• Pyloric region: • antrum, pyloric canal,
and pylorus
• Connects to duodenum via pyloric sphincter
• Greater curvature
• Lesser curvature
Copyright © 2011 Pearson Education, Inc. Figure 22.14a
CardiaEsophagus
Pyloric sphincter(valve) at pylorus
Pyloriccanal
Pyloricantrum
Body
Lumen
Fundus
Lessercurvature
Greatercurvature
(a)
Duodenum
Copyright © 2011 Pearson Education, Inc.
Stomach: Layers• Four tunics
• Three muscular layers and outer tunic (serosa)
• Muscularis externa
1.longitudinal
2.circular
3.oblique
• Covered by omentums
• Greater & lesser
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Stomach: Tissues • Mucosa
• Simple columnar epithelium with mucus covering
• Contain gastric pits• Produce gastric acid = HCl
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Digestive Processes so Far…
• Physical digestion (chewing)• Teeth and tongue
• Creates bolus• Enzymatic digestion • Enzymes in saliva
• Gastric acid
• Delivers chyme to the small intestine• Creamy food mass
Copyright © 2011 Pearson Education, Inc.
Small Intestine• Major organ of absorption
• Pyloric sphincter to ileocecal valve (2-4 m long)
• Subdivisions
1. Duodenum : beginning portion
• connects to stomach via pyloric sphincter
2. Jejunum : intermediate portion(~8ft)
3. Ileum : end portion (~12ft)
• Connects to large intestine via ileocecal valve
Copyright © 2011 Pearson Education, Inc.
Small Intestine
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Duodenum• Ducts for gallbladder and pancreases empty into
the hepatopancreatic ampulla• Bile duct
• Main pancreatic duct
• Enter at the duodenal papilla• Are controlled by the hepatopancreatic
sphincter
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Absorption of Small Intestine
• Modification help increase surface area (absorption):
1. Circular folds (plicae circulares)
2. Villi
3. Microvilli
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Villi and MicrovilliVilli
• fingerlike extensions of mucosa
• Simple columnar absorptive cells
• With microvilli – increase surface area
• Goblet cells – produce mucus
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Large Intestine• Compacts fecal mater (food waist) and
propels it out
• Regions
1. appendix
2. cecum
3. colon
4. rectum
5. anus
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Colon• Regions of colon
• Ascending colon
• Right (hepatic) flexure
• Transverse colon
• Left (splenic) flexure
• Descending colon
• Sigmoid colon (S – shaped)
• Contains pocketlike sacks haustrum
Copyright © 2011 Pearson Education, Inc.
Large Intestine
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Rectum and Anus• Rectum• Inferior holding chamber
• Anal canal• Last segment of the large intestine
• Sphincters• Internal anal sphincter —smooth muscle
• involuntary
• External anal sphincter —skeletal muscle
• voluntary
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Functions of the Large Intestine
• Major function: propulsion of feces toward the anus
• Reclaims : vitamins, water, and electrolytes
• Colon is not essential for life
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Motility of the Large Intestine
• Haustral contractions• Slow segmenting movements
• Haustra sequentially contract in response to distension
• Gastrocolic reflex• Initiated by presence of food in the stomach
• Three slow powerful peristaltic waves per day in the colon (mass movements)
Copyright © 2011 Pearson Education, Inc.
Defecation
• Mass movement of feces into rectum
• Distension initiates defecation reflex
• Parasympathetic signals• Stimulate contraction of the sigmoid colon and
rectum
• Relax internal anal sphincter
• Conscious control relaxation of external anal sphincter
Copyright © 2011 Pearson Education, Inc. Figure 22.29b
(b)
Rectal valveRectum
Anal canal
Levator animuscle
AnusAnal sinuses
Anal columns
Internal analsphincter
External analsphincter
Hemorrhoidalveins
Pectinate line