Digestion I Lab 42 Alimentary Canal

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Digestion ILab 42 Alimentary Canal

• THE BEAST

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Functions of digestive system

• Ingestion of food
• Physical and chemical breakdown of food
• Food storage
• Water absorption
• Vitamin synthesis
• Food absorption
• Elimination of indigestible material

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Alimentary Canal

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small Intestine
• Large Intestine
• Rectum
• Anus

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Mouth

• Digestion Begins
• Food placed into oral cavity
• Teeth grind food to increase surface area
• Salivary glands (accessory organs) add salivary
  amylase, begin carbohydrate digestion
• Tongue forms ball bolus
• Food swallowed into esophagus

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Gums (gingivae)
Nonkeratinized stratified squamous epithelium
Hard Palate
Soft Palate
Palatine Tonsils
Uvula
Tongue (genioglossus muscle)
Lingual Frenulum
Salivary Duct Orifices
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Apical foramen
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Esophagus

• Bolus enters oropharynx
• Swallowing causes epiglottis to cover glottis
  prevents food from entering trachea
• Esophagus food travels via peristalsis
• Transition from skeletal and smooth muscle to
  smooth muscle

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Gastrointestinal Tract Layers

• 4 layers are present
• Serosa (adventitia or visceral peritoneum)
• Connective tissue
• Muscularis externa
• Two or three layers of smooth muscle
• Submucosa
• Connective tissue
• Vascular
• Mucosa
• Mucous membrane (stratified squamous epithelium)
• Lamina propria (connective tissue)
• Muscularis mucosae (smooth muscle)

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Alimentary Canal

• Tube within a tube
• Inside the abdominal cavity (coelom)
• Parietal peritoneum lines the outer trunk wall
• Dorsal mesentery is continuous and connects P.
  peritoneum with . . .
• Visceral peritoneum (serosa)
• Lines the alimentary canal and connects with . .
  .
• Ventral mesentery
• Both mesenteries contain arteries, veins, nerves,
  and lymphatics

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Stomach

• Bolus arrives from esophagus and mixes with
  pepsin and HCL to form chyme
• acids denature proteins and pepsin reduces
  proteins to shorter fragments

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Stomach

• Anatomical Features
• Regions
• Cardia
• Esophogeal sphincter
• Fundus
• Body
• Pyloric region
• Antrum
• Pyloric canal
• Pyloric sphincter
• Greater curvature
• Lesser curvature
• 4 layers present (serosa, muscularis externa,
  submucosa, mucosa)

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Fundic region
Cardiac region
antrum
Pyloric canal
body
Pyloric region
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Stomach Histology

• Depressions in stomach called gastric pits
• Contain gastric glands which contain . . .
• Chief cells
• Secrete pepsinogen (inactive form of pepsin)
• Parietal cells
• Secrete HCL
• Inner lining (mucosa), simple columnar epithelium
• Secretes mucus
• Protect stomach lining from HCL and pepsin

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Small Intestine

• Chyme (digested food) is squirted, in little
  bits, into Small Intestine through pyloric
  sphincter
• Most absorption takes place in Small Intestine
• 3 sections of Small Intestine
• Duodenum
• Jejunum
• Ileum

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Parts of the Small Intestine

• All sections
• -Purpose is absorption
• -All 4 layers - mucosa, submucosa, muscularis,
  and serosa
• -Villi - ciliated columnar epithelial cells, and
  goblet cells
• -Increase surface area for absorption
• -Blood vessels to transport sugars and amino
  acids
• -Lacteals - transport fatty acids to lymphatic
  system, to venous system

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Intestinal Villi
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Parts of the Small Intestines

• Duodenum
• C-shaped, 10in long, receives fluid from the
• Pancreas
• digestive enzymes and bicarbonate
• Gallbladder
• bile which emulsifies lipids
• Has duodenal (Brunners) glands in submucosa
  which produce alkaline secretion
• -Where secretions from pancreas gallbladder
  enter

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• Jejunum
• 6.5 ft long
• submucosa has no glands, just connective tissue

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• Ileum
• 10 ft long
• Connects with large intestine at the ileocecal
  valve
• Aggregated lymph nodules (Peyers patches) in
  submucosa
• Protect body from bacteria in small intestine

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(take in fats)
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Large Intestine

• At Ileocecal valve, chyme passes from Small
  Intestine to Large Intestine
• Large Intestines major function
• H2O absorption
• some vitamin and solute absorption
• feces formation
• There are no villi in mucosal layer (simple
  columnar epithelium w/ goblet cells)

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Large Intestine

• Longitudinal layer of muscularis externa is not
  continuous but in 3 bands teniae coli
• Contraction of teniae coli form haustra
  (singular, haustrum) or pouches
• Epiploic appendages fat lobules on outer wall
  of Large Intestine
• 4 layers
• Mucosa simple columnar epithelium with lots of
  goblet cells

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Parts to know - L. Intestine

• Cecum
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Rectum w/ hemorrhoidal veins

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Anal Canal

• Involuntary control of internal sphincter
• Voluntary control of external sphincter
• Defication is a mass peristalsis event

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Rectal Valve
Anal Canal
Int. Anal Sphincter
Anus
Ext. Anal Sphincter
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