Download Histology/Pathology – Lecture 2: Histology of the GI Tract 8/3/12

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Histology/Pathology – Lecture 2: Histology of the GI Tract
Alimentary Canal
o Mouth  esophagus  stomach  duodenum  jejunum  ileum  cecum 
large intestine  anus
General Structure of Digestive Tract
o Lumen w/ a 4-layered wall
 Mucosa
 Epithelial lining underlying the lamina propria
 Muscularis mucosae
o Thin layer of smooth muscle that separates mucosa from
 Submucosa
 Submucosal gland (only found in esophagus and duodenum)
 Denser CT w/ blood and lymph vessels
 Meissner submucosal plexus of autonomic nerves
 Muscularis
 Inner circular layer of smooth muscle
 Outer longitudinal layer of muscle
 Myenteric nerve plexus in b/t layers; also CT w/ blood vessels
 Serosa (Adventitia)
 Loose CT, blood vessels, lymphatics, fat, etc.
 Covers vast majority of GI tract
 Simple squamous covering epithelium (mesothelium)
Components of the Wall of GI Tract
o Meissner submucosal plexus
 Found in the submucosa
 Coordinates peristalsis
o Auerbach’s myenteric plexus
 Coordinates peristalsis
 Found b/t the circular and longitudinal muscle layers
Main Fxns of the Epithelial Lining
o Provide selectively permeable barrier b/t contents of tract and body tissues
o Facilitate transport and digestion of food
o Promote absorption of products of digestion
o Produce hormones that affect GI system
o Produce mucus for lubrication and protection
Anatomy and Physiology of Esophagus
o Adult esophagus: 25 cm long
o Fixed superiorly at cricopharyngeus muscle = upper esophageal sphincter
o Exits thorax through hiatus of diaphragm
o Lower esophageal sphincter is not a true sphincter; rather a functional one
 Tonic muscular contraction at lower end of esophagus creates a flutter-like
wave motion
o Anatomic Relationships
 Begins at back of pharynx
 Posterior to trachea and arch of the aorta
Histology of Esophagus
o See Lab for slides and explanations**
Normal Esophageal Mucosa
o Stratified squamous epithelium
 Tough – can handle coarse foods
 Pearly white color
 Can see a sharp line of demarcation on transition to columnar
o The gastroesophageal (GE) junction
o 4 parts
 Cardia
 Mucous cells
o Protect the stomach against acid
 Fundus
 Parietal cells
o Hydrochloric acid & intrinsic factor
 Chief cells
o Pepsin
 Much thicker glandular mucosa than in cardia
 Body
 Antrum
 Mucous cells
 G cells (endocrine cells)
o Gastrin (driver of HCl production)
o Anatomy
 Rugae
 Folds that increase the surface area; flatten out upon distention
 Most prominent in the proximal stomach
 Gland structure in body of stomach
 See slides for images from various parts of the stomach
o Gastroduodenal Junction
 Marked by the pyloris – area that gets tighter/thicker
 Duodenum contains Brunner glands
Small Bowel
o Has several segments w/ plica circularis
o Mucosa
 Many villi covered by epithelial cells of 3 types:
 Columnar absorptive cells
 Mucin-secreting cells (goblet cells)
 Few endocrine cells
 Villi terminate in the lamina propria as glandular lumina called crypts of
 Each villi contains a small lymph channel – lacteals
 Paneth cells – secrete IgA; found in the jejunum
o The foldings of the small intestine – increase the surface area for absorption
 Plica circularis
o Peyer’s Patches
 Part of the MALT system found in the ileum
o Found at the base of the cecum, near the connection w/ the ileum
o Contains
 Serosa, mesentery, follicle, lamina propria
o Storage organ
o 9 L of water pass through/day
o Contains many crypts of Lieberkuhn
o Mainly a flat surface
o Contains many goblet cells
  lubrication for peristalsis and defecation
o Layers
 Circular layer of muscles
 Longitudinal layer of muscles
o Also has lymphatic nodules
Recto-anal Junction
o Line of Hilton (aka pectinate line)
 Jxn b/t rectum and anus
 Rectum has columnar mucosa
 Anus has stratified squamous mucosa