GI Overview, Esophagus, and Stomach Flashcards
Principal layers in GI tract
. Mucosa
. Submucosa
. Muscularis externa
. Adventitia/serosa
Mucosa
. Formed by epithelial lining, underlying lamina propria and musculari mucosae
Epithelial lining functions
. Formation of selective permeable barrier btw contents of GI tract and tissues in body
. Facilitation is transport/digestion of food
. Promotion of digestion and absorption of food
. Production of hormones
. Protection of epithelial lining by mucous production
Lamina propria
. Loose CT w/ blood and lymph vessels
. Lymphoid tissue in diffuse and modular form
Gut-assoc.-lymphoid-tissue
. GALT
. Provides immunological barrier protecting against invasion of microbial pathogens
Muscularis mucosae
. Smooth muscle
. Inner circular and outer longitudinal
. Permits movement of mucosa independent of other movements in GI tract
Submucosa
. Dense CT
. Blood and lymph vessels, glands, and lymphoid tissue
. Contains scatter parasympathetic ganglia (submucosal/Meissner’s nerve plexus) as part of enteric system
Muscularis externa
. layers of smooth muscle (inner, outer, stomach has added oblique)
. Parasympathetic nerve cells form ganglia of myenteric (Auerbach’s) nerve plexus located btw inner and outer layers of smooth muscle
. Interstitial cells of Cajal (ICC) form network located btw neurons of myenteric plexus that serves as gastroenteric pacemaker system
. ICCs essential in maintenance of motility of GI tract
Adventitia/serosa of GI tract
. Outer layer of loose CT
. Adventitia if organ is surrounded by CT and there is no clear outer demarcation
. Where gut lies w/in abdominal cavity the outer CT layer is covered by mesothelium and outer CT layer is called serosa
Esophagus
Long (25 cm), straight. Muscular tube that transmits food from oropharynx to the stomach
Esophagus mucosa
. SSNK epithelium (can be keratinized if abrasion)
. Lamina propria: loose CT, contains esophageal cardiac glands in proximal and distal ends of esophagus
. Muscularis mucosae: longitudinally arranged smooth muscle, not present in upper portion of esophagus
Esophagus submucosa
. Dense irregular CT w/ collagen and elastic fibers
. Esophageal proper glands (compound tubuloalveolar mucus glands) scattered throughout length of esophagus
Esophagus muscularis externa
. Upper 1/3 contains only skeletal muscle continuous w/ skeletal muscles of pharynx
. Middles 1/3: smooth muscles internal to skeletal muscle
. Distal 1/3: only smooth muscle
. Auerbach myenteric plexus btw outer and inner muscle layers along whole esophagus
Lower esophageal sphincter
. Specialized zone of circular smooth muscle surrounding esophagus and it’s transit through diaphragm and short course in abdomen
Esophagus adventitia
Loose CT
GERD
. Incompetent barrier at gastroesophageal junction
. Inflammation of esophagus and damage to epithelial lining lead to erosion of esophageal mucosa
. Can lead to metaplasia if untreated (SSNK to simple columnar)
Stomach
. Mixed endocrine-exocrine organ stores and digests food and secretes hormones
. Food acidified and transformed into chyme
. Protein digestion is initiated w/ enzyme pepsin
. Triglyceride digestion initiated by lipase
. Regions: cardia, fundus and body, and the pylorus
. Mucosa and. Submucosa of empty stomach lie in longitudinally directed folds called rugae (disappear when stomach distendeD)
Cardia stomach
. 1.5-3 cm wide transition zone btw esophagus an stomach
. Glands primarily produce mucus
Stomach fundus and body
. Histologically identical
. Gastric glands release acidic gastric juice
Pylorus
. Funnel-shaped region that opens into small intestine
. Glands primarily produce mucus
Stomach epithelium
. Simple columnar surface mucous cells
. Secrete alkaline mucus forming protective coat on the epithelial surface
. Mucus protects surface of stomach from acids and enzymes produced by the stomach
. Adds in lubrication
. Turnover rate for surface epithelium is high
. Epithelium invaginates at regular intervals into lamina propria forming gastric pits
Gastric pits
. Lead into tubular glands that project into the lamina propria
. 1-7 glands open into the bottom of each gastric pit
stomach Lamina propria
. Loose CT, contains lymph tissue and blood vessel
. Gastric glands here
Stomach muscularis mucosae
. Inner circular and outer longitudinal smooth muscle layers
Cardiac glands
. Shortest and least numerous
Gastric glands
. In stomach, largest and most numerous in body and fundus
T/F Pyloric glands resemble cardiac glands
T
Isthmus of the gland
. Upper portion of gland at junction of gastric pit and gland
Neck of the gland
. Below isthmus
Base of the gland in stomach
. Lower portion of gland
Undifferentiated stem cells in stomach
. Inside isthmus and neck regions
. Low columnar w/ nasally located oval nucleus
. Highly proliferation and are source of new surface mucous cels and all other cells of gland
Mucous neck cells
. Shorter than surface mucous cells
. Round nucleus and apical secretory granules
. Include progenitor and immature surface mucous cells
. Mucus produced is more soluble than mucous from surface mucous cells
Parietal (oxyntic) cells
. Numerous in neck and upper segment of glands
. Large spherical cells w/ extremely eosinophilic cytoplasm and centrally located nucleus
. Produce hydrochloric acid absorption of B12
.
Chief (peptic/zymogenic) cells
. Found in lower third of glands
. Cytoplasm is strongly basophilic granular
. Nucleus basally located
. Produce pepsinogen and lipase
Pepsinogen converted to ____ upon release into acid
Pepsin
Enteroendocrine cells in stomach
. Base of glands
. Contain granules in basal area of cytoplasm w/ serotonin, gastrin, and somatostatin
. Part of neuroendocrine system
Stomach submucosa
. Dense CT
. Blood and lymph vessels, lymphoid cells including mast cells and macrophages
Stomach Muscularis externa
. Smooth muscle layers oriented in 3 directions
. Inner oblique, middle circular (enlarges to form pyloric sphincter), and outer longitudinal layer
. Strong contractions of muscle wall create churning action that mechanically breaks down ingested matter
Stomach serosa
. Loose CT covered by mesothelium
Cardiac region morphological appearance
. Simple or branched tubular glands . Coiled w/ large lumens . Depth of pit to depth of the gland ratio (1:2-1:3) . Most cells produce mucus and lysozyme . Some parietal cells may be present
Body/fundus morphological differences
. Mucosa has glands that produce acid-pepsin gastric juices and some mucus
. 3 7-branched gastric glands open into each pit
. Pits shallow in comparison to depth of gastric glands
. Pit: gland ratio is 1:4
Pyloric morphological appearance
. Glands simple or branched tubular, often coiled
. Secrete mucus, lysozyme, and gastrin
. Pit:gland ratio is 1:1
. Longer pits than cardia
H pylori
Present in chronic duodenal ulcers and gastric ulcers
