Digestion B

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Digestion B

• Chapter 25

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GI tract components

• Oral cavity (buccal cavity)
• Pharynx
• Esophagus
• Stomach
• Small large intestine (colon/rectum)

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Accessory organs

• Teeth
• Tongue
• Salivary glands
• Liver
• Gall bladder
• Pancreas

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Digestive system
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Buccal cavity

• Roof
• Hard palate
• Maxillary palatine bones
• Soft palate
• Fleshy posterior extension
• Separates oral nasal cavity
• Floor
• Tongue
• Skeletal muscle
• Posterior
• Palatoglossal arches- muscles
• Palatine tonsils
• Palatopharyngeal arches- muscles
• Uvula- extenion of soft palate
• Fauces- entrance into pharynx

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Buccal Cavity
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Hard Palate
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Soft Palate
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Separates Cavities
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Arches
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Oral Cavity Accessory Structures

• Teeth
• Salivary glands
• Salivary ducts
• Tongue
• Papillae
• Taste buds
• frenulum

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Teeth

• Mechanical breakdown of food
• Mechanical digestion in buccal cavity
• Physical reduction of food size
• Churning in buccal cavity

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Teeth
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Salivary glands

• Chemical digestion
• Occurs in buccal cavity
• Secrete saliva
• 1-1.5 L/ day
• Lubrication
• 3 primary glands
• Parotid
• Inf to Zygomatic arch, posterior to masseter
• Submandibular
• Inf to mandible
• Sublingual
• Inf to tongue
• Salivary ducts
• Deliver salivary secretions to oral cavity

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Salivary Glands
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Salivary Glands
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Sublingual gland
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Tongue

• Manipulates food provides sensory analysis
• Mechanical digestion of food in oral cavity
• Structure
• Skeletal muscle
• Covered with modified mucus membrane

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Tongue
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Papillae

• Cone-like projections of thickened epithelium
• 3 types
• Filiform papillae (thread)
• Numerous, thin across 2/3 of tongue surface
• Fungiform papillae (mushroom)
• Medium size, across surface of tongue
• Primary Taste structures
• Circumvallate papillae (around)
• Large size, posterior of tongue
• Primary taste structures

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Papillae
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Papillae
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Taste buds

• Sensory nerve cells lining surface of papillae
• Sensitive to 6 taste modalities
• Sweet
• Sour
• Bitter
• Salty
• Umami
• Water

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Taste receptor
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Taste receptors
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Frenulum

• Tissue anchoring tongue to floor of mouth

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Frenulum
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Pharynx

• Common space where nasal oral cavity meet
• Passageway for both air ingested substances
• 3 divisions
• Nasopharynx
• Superior aspect of pharynx
• Oropharynx
• Medial aspect of pharynx
• Between soft palate hyoid
• Laryngopharynx
• Inferior aspect of pharynx
• Between hyoid esophagus

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Laryngopharynx
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Swallowing

• Deglutition aka swallowing
• Passage of partially digested food (bolus) from
  buccal cavity into esophagus
• 3 stages
• Buccal Phase
• Pharyngeal phase
• Esophageal phase

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Buccal phase

• Contraction of buccal muscles
• Tongue moves food to the back of the oral cavity

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Buccal phase
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Pharyngeal phase

• Contraction of pharangeal muscles
• Raises larynx (voice box)
• Uvula soft palate block nasopharynx
• Pushes cartilage plate over opening to
  respiratory passages
• Opening glottis
• Cartilage plate epiglottis

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Swallowing
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Esophageal phase

• Contraction of esophagus muscles
• Moves food bolus thru esophagus to stomach
• Massages food down via peristalsis

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Esophageal phase
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Glottis
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Esophagus

• Comprises 1 ft of GI tract
• Carries food from pharynx to stomach
• Peristalsis
• Propells bolus (1-2 sec)
• Secretes mucus- lubricates moistens bolus

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Esophagus
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Esophagus
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Peristalsis
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Esophagus structure

• Posterior to trachea (windpipe)
• Passes through mediastinum
• Passes through diaphragm
• Muscles separating thoracic abdominal cavities
• Exits through lower esophageal sphincter
• Smooth muscle ring between stomach esophagus

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esophageal sphincter
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esophageal sphincter

• Prevents reflux of stomach (gastric) substances
• Improper closing of sphincter
• Gastroesophageal reflux disorder (GERD)
• Acid reflux- heart burn painful irritation of
  esophagus
• Inability to relax sphincter
• Achalasia

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Achalasia
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Esophageal histology

• Mucosa
• Stratified squamous epithelium
• Submucosa
• Mucous secreting glands

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Mucosa
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Submucosa
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Stomach

• J shaped
• Enlargement of tract
• Temporary Food storage
• Alexis st. martin- 1822

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Stomach Functions

• Protein digestion
• initiation
• Mechanical digestion churning
• Temporary storage
• 2-4 hours

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Stomach Structure

• Cardia
• Superior region
• Surrounds opening to esophageal sphincter
• Fundus
• Superior lateral to cardia
• Enlarged rounded region
• 1st storage region
• Body
• Large central region
• Primary storage churning site
• Pyloris
• J portion, Connects stomach to sm intestine

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Stomach
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Stomach
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Cardia
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Fundus
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Body
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Pyloric Sphincter
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Pyloric Sphincter

• Smooth muscle ring
• Regulates slow entrance of food into intestine

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Pyloric Sphincter
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Gastric ulcers
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Stomach Rugae

• Rugae- macroscopic folds in mucosa
• Segregate digestion- physical separation of
  partially digested foods
• Allows expansion during filling
• Rugae most distinct when stomach is empty

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Rugae
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Rugae
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Rugae
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Stretchy
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Histology

• All 4 tissue layers present
• Mucosa

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Mucosa

• Exocrine secretion
• Simple columnar epithelium
• secretory sheet
• Gastric pits
• Shallow depressions into lamina propria
• Contain mucus secreting cells
• Protect stomach wall from gastric enzymes acids
• Active cell division 2-3 days
• Gastric glands
• Extension of gastric pits into lamina propria

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Mucosa
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Gastric Pits
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Gastric Glands
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Gastric Glands

• Chief cells
• Secrete pepsinogen (pepsin)
• Exocrine
• Protein digesting enzyme
• Parietal cells
• Secretes hydrochloric acid (HCl)
• Exocrine
• Assists in protein digestion
• Enteroendocrine cells
• Endocrine
• Secrete 7 different hormones
• G cells secrete gastrin
• Stimulate chief parietal cell activity

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Gastric Glands

• Goblet Cells
• Enteroendocrine
• Parietal cells

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Gastric secretions

• Gastric Juice
• All glandular secretions
• 1500 ml/day
• Acid Chyme
• Bolus gastric juice

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Muscularis Externa

• 3 muscle layers
• 3 different orientations provide efficient
  churning
• Outer longitudinal
• Middle circular
• Inner oblique

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Muscularis Externa
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Small Intestine

• Site of completion absorption
• 90 nutrient absorption
• Rich blood supply for absorbing carrying
  nutrients
• 20 ft long (6M)
• Supported by mesenteries
• Double sheets of serous membrane

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Small Intestine
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Mesenteries
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Mesenteries
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Mesentary Function

• Stabilizes relative position of sm intestine
• Prevents entanglement
• Conduit for blood vessels nerves
• Secured to dorsal body wall
• Stores fat

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Small Intestine Structure

• Divided into 3 regions
• Duodenum
• Jejunum
• Ileum

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Duodenum

• 12 fingers
• Shortest segment 10 in
• Curves in a C
• Entrance regulated by pyloric sphincter
• Receives contents from stomach
• Acid chyme
• Small intestine, pancreas, liver
• Enzymes chemicals
• Neutralizes acid chyme

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duodenum
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Pyloric Sphincter
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Jejunum

• Aka empty
• 8 ft long ( 2.5 M)
• Last stages of chemical digestion
• Nutrient absorption

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Jejunum
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Ileum

• twisted
• 12 ft long (3.5 m)
• Longest segment
• Joined to large intestine (cecum)
• Ileocecal Valve sphincter
• Regulates passage into large intestine

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Ileum
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Joins To Large Intestine
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Ileocecal Valve sphincter
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Mesentaries

• Supportive sheets of serous membranes
• Double layer
• Greater omentum
• Mesentary proper
• mesocolon

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Greater omentum

• fat skin
• Anterior folds of serosa
• Form large fatty filled pouch
• Maintains relative position of sm intestine
• Insulates abdominal viscera
• Keeps stomach in place

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Greater omentum
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Mesentary Proper

• Extensive, broad mesentary between folds of the
  sm intestine
• Stabilizes prevents entanglement
• Conduit for blood vessels nerves

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Mesentary Proper
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Mesentery Proper
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Mesocolon

• Mesentary attached to the large intestine
• Stabilizes
• Conduit for blood nerves

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Mesocolon
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Large Intestine

• Terminal portion of the GI tract
• Primary functions
• Absorption of water electrolytes
• Absorption of vitamins (bacteria)
• Liberated by resident bacterial flora
• Compaction elimination of waste

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Large Intestine
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Large Intestine
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Gastric Bypass Surgery
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Gastric Bypass
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Large Intestine structure

• Large bowel
• 5 ft (1.5 M)
• 3 regions
• Cecum
• Colon
• rectum

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Cecum

• pouch-like region
• Ileocecal valve
• Regulates passage from ileum into cecum
• Stores begins compaction
• appendix
• finger-like extension filled with lymph tissue
  (3)
• Immune function
• Bacteria storage

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Ileocecal valve
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Appendix
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Colon

• Largest portion of large intestine
• 4 regions
• Ascending colon- rt side
• Cecum to Rt Colic flexure
• Transverse colon- rt to Lt
• Rt to Lt colic flexure
• Descending colon- lt side
• Lt colic to sigmoid flexure
• Sigmoid colon- S- shaped
• Sigmoid flexure to rectum

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Colon
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Colon

• Taenia coli- ribbon of the colon
• Longitudinal strips of smooth muscle
• Shorter than colon
• Results in pouch formation
• Haustra
• Expandible pouches capable of compaction during
  contraction of taenia coli

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Taenia coli haustra
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Colon fauna

• Variety of prokaryotes- bacteria
• Good bacteria produce vitamins
• stomach bug bacterial infection
• Diarrhea- colon not working
• Dehydration
• Constipation
• Slow peristalsis
• Lack of exercise or fiber

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rectum

• Terminal passage
• Last 6 in (15 cm)
• Fecal reception triggers urge to defecate
• Passage regulated by
• Internal anal sphincter
• Unconscious control
• External anal sphincter
• Conscious control

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rectum
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GI Tract Histology

• Macroscopic folds
• Stomach- rugae
• Prominent adjustable folds
• Permit stomach expansion
• Size variable according to stretch
• Small Intestine- Plicae Circularis
• Permanent folds
• Includes mucosa submucosa
• Enhance digestion absorption
• Increase surface area
• Cause chyme to spiral- Mixing

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Stomach Rugae
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Stomach Rugae
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Plicae Circularis
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Plicae Circularis
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Plicae Circularis
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Small Intestine Histology

• Addition modification
• Villi
• Microvilli
• Lamina Propria

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Villi

• Microscopic finger-like folds of mucosa
• Includes epithelium lamina propria
• Permanent Feature
• Enhance digestion absorption
• Increase surface area

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Villi
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Villi
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Villi
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Microvilli

• Microscopic finger-like folds of epithelial
  cell membrane
• Increase surface area
• From .33 m2 to 200 m2
• Enhance digestion absorption

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Microvilli
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Enhance Surface Area
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Lamina Propria

• Nutrient absorption
• Villi blood vessel network
• Carry absorbed nutrients from intestine to the
  liver
• Lacteal
• Villi lymph vessels
• Absorb transport lipids to blood circulation

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Lamina Propria
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Lacteal
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Intestinal Histological specializations

• 3 Microscopic distinct regions
• Duodenum
• Jejunum
• ileum

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Duodenum histology

• Submucosal (brunners) glands
• Duodenal ampulla

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Submucosal (brunners) glands

• Located in submucosa
• Produce copious amts of basic mucous
• Protect epithelium from acid chyme
• Alter pH 1-2 up to 7-8 (neutral)

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Submucosal (brunners) glands
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Duodenal Ampulla

• Chamber Receiving secretions from the liver
  pancreas
• Releases contents into Duodenum
• From liver
• Common bile duct
• From pancreas
• Pancreatic duct

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Duodenal Ampulla
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Jejunum

• No Submucosal glands
• Large villi, microvilli Plicae Circularis
• Increases absorption

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Jejunum Histology
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Ileum histology

• Lymphoid nodules
• Peyers Patches
• Located within submucosa
• Contain aggregation of WBCs for immunity
• Protect against resident bacteria from large
  intestine

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Peyers Patches
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Ileum histology
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aggregation of WBCs
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aggregation of WBCs
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In submucosa
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