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BIOL 302 – Gastrointestinal System

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University of Waterloo
BIOL 302
Mungo Marsden

BIOL 302 – Tissues – Gastrointestinal System Digestive System  Mucosa o Epithelium o Lamina propria (loose connective tissue) o Muscularis mucosae (smooth muscle)  Submucosa o Loose/dense irregular connective tissue o Contains glands in esophagus and duodenum o Blood vessels, nerves  Muscularis externa o Inner – circular smooth muscle o Outer – longitudinal smooth muscle o Waves of contraction - peristalsis  Adventitia or Serosa o Outermost layer o Small amount of connective tissue o Adventitia – when connective tissue blends with surrounding structures (ex. Esophagus) o Serosa – when connective tissue faces a body cavity, it is lined by simple squamous epithelium (mesothelium) Esophagus  Mucosa o Epithelium - stratified squamous o Lamina propria – loose connective tissue o Muscularis mucosa – longitudinal muscle fibres o Deeply folded so allow for stretch  Submucosa o Loose connective tissue o Submucosal glands that secrete mucous  Muscularis externa o Inner circular smooth muscle o Outer longitudinal smooth muscle o Skeletal muscle for voluntary contractions, smooth muscle for involuntary movement Stomach  Stomach receives food for esophagus  Rugae: folds of mucosa and submucosa for expansion of stomach to accommodate bolus  chime  Mucosa: o Surface of stomach lined by simple columnar epithelium o Gastric pits: invaginations of surface epithelium into the lamina propria; lined by surface mucous cells; glands in lamina propria empty in bottoms of these pits o 4 zones (based on nature of glands) o Cardiac stomach:  Near opening of esophagus, contains cardiac glands, protect against acid reflux  Composed on mucous-secreting glands  Has a 1:1 ratio of pits to glands in the mucosa  No glands in the submucosa o Fundic stomach:  Majority of stomach, contains gastric/fundic glands  Glands extend to muscularis mucosae  Mucosa is mostly glands with small pits  Not many goblet cells  Glands contain parietal cells (large, round, secrete HCl)  Peptic/chief cells (smaller, darker, basal nucleus, secrete pepsinogen)  Enteroendocrine cells (clear, hershey kiss shaped, secrete hormones) o Pyloric stomach:  Contain pyloric glands  Mostly pits, deep into muscularis mucosae  Specialized gland cells are not common in these glands  Pits are very long, wide, and highly branched.  Small mucosa compared to pits *Quick comparison:  Cardiac Stomach. Pits do not appear deep because they are same depth in mucosa as glands  Fundic Stomach. Shallow pits, tall glands look like cords of cells  Pyloric Stomach. Pits take up most of mucosa, shallow glands  Look for lumen  see pits  mucosal layer (glands)  mucosa muscularis  submucosa  muscularis externa  Submucosa: o Dense irregular connective tissue  Muscularis Externa: o Inner oblique o Middle circular o Outer longitudinal  Serosa o Continuous with peritoneum Small Intestine  Largest component of digestive tract; the major site of digestion and absorption.  Consists of duodenum, jejunum, and ileum.  Mucosa: o Villi  Simple columnar epithelium: Microvilli and goblet cells; number of goblet cells increases as you travel through the small and large intestines  Lamina propria: core is extension. Blood supply, lymphatic vessels. Lacteals are found in the villi in the lamina propria, they are specialized lymphatic vessels, for lipid absorption  Muscularis mucosae: Crypts of Liberkuhn: extend downwards toward base. Paneth cells can be found here – secrete antimicrobial enzymes. o Enterocytes: tall columnar cells with microvilli and basal nucleus specialized for transport. o Goblet cells: secrete mucous  Submucosa: o Duodenum  Receives bile from gall bladder and digestive enzymes from pancreas  Brunner’s glands: neutralize acid from stomach (massive compared to pits). o Jejunum  Plicae circularis: large, numerous folds of submucosa  Leaf shaped – long villi, long and wide spaces between them o Ileum  Short, branched, finger-like villi  Lots of goblet cells  Peyer’s patches – large, dark, lymphoid patches Large Intestine  For reabsorption of water and electrolytes and elimination of undigested food and wastes.  Consists of colon,
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