Flashcards in 14 - GI Anatomy and Histology Deck (57)
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Motility
Movements of the bowel that influence the transport of luminal contents
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Ingestion
Act of taking food into the mouth
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Mastication
Chewing food and moistening it with saliva
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Deglutition
Swallowing
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Peristalsis
Oral contraction and anal relaxation, which is propulsive
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Secretion
Exocrine to lumen of gut, endocrine to blood
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Digestion
Breakdown of ingested macromolecules into absorbable smaller subunits
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Absorption
Transport of end products of digestion to blood and/or lymph
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Storage
Temporary holding of ingested contents
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Elimination
Getting rid of indigestible material
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Sphincters of the gut
Upper Esophageal
Lower Esophageal
Pyloric
Iliocecal
Internal Anal
External Anal
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Gut Wall - Luminal
Mucosa:
Epithelium
Lamina propria
Muscularis mucosa
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Gut Wall - Middle Layer
Submucosa:
Submucosal plexus
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Gut Wall - Basal
Muscularis Externa:
Inner circular muscle
Outer longitudinal muscle
Myenteric Plexus
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Gut Wall - Non-retroperitoneal parts
Adventitia:
Serosa
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Esophagus - To resist abrasion
Stratified squamous nonkeritanized epithelium
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Stomach - To digest
Simple columnar epithelium
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Basic plan of the gut wall layers (illustrated by esophagus)
Stratified squamous nonkeritanized epithelium (to resist abrasion)
Lamina propria
Muscularis mucosa (express lymph and fluid from the fluid in the lamina propria) - contains fenestrated blood vessels, the most permeable in the body.
Muscularis externa: Inner circulate & outer longitudinal
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Upper esophagus - Muscularis externa
Mostly striated
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Middle esophagus - Muscularis externa
Mix of striated and smooth
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Lower esophagus - Muscularis externa
Mostly smooth
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Regions of the stomach
Lower esophageal sphincter
Fundus
Body
Antrum
Pylorus
Duodenum
Also split into Orad and Caudad region, about halfway through the body.
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Fundic region
Rises above the entrance of the esophagus.
Contains air very often.
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Body/corpus
Large region into which food is delivered.
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Antrum
Different
Separated from duodenum by pyloric sphincter.
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Oxyntic region of the stomach
Corpus + Fundus
Makes HCl
Makes pepsinogen
Contains parietal cells
Contains chief cells
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Parietal Cells
Make HCl
Make Intrinsic Factor
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Chief Cells
Make Pepsinogen
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HCl
Acid!
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Intrinsic Factor
The one component made by stomach completely vital for health.
Need it to digest Vitamin B12. Without IF, you get pernicious anemia and demyelination of the spinal cord. B12 deficiency.
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Pepsinogen
Pepsin precursor
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Pyloric region
Antrum
Makes Gastrin
Makes mucus pepsinogen
Contains G cells
Contains Mucous cells
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Gastrin
Stimulates the production of more HCl.
Stimulates growth of gastric mucosa
Produced in pyloric region of the stomach.
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Mucus pepsinogen
Provides protection of mucosa from HCl
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G Cells
Produce gastrin if stimulated by alkaline environment or nerve activation.
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Mucous Cells
Produce mucous pepsinogen
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Cells in the stomach
Surface mucous epithelial cells
Mucous neck cells
Parietal cells
Chief cells
Endocrine cells
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Surface Mucous Cells
Superficial lining of surface and beginning of the pit area of the gland
Defend stomach against HCl
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Mucous neck cell
Stem cells to regenerate lost surface cells
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Parietal cell
Oxyntic cells
Abundant surface area when secreting
Contains intracellular canaliculi & microvilli
MANY Mitochondria
Large
Complex cristae
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Chief cell
Secretes pepsinogen
Specialized for regulation of secreted protein
Abundant RER
Huge number of zymogen granules
Big Gogli
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Endocrine cell
Scattered through the glands
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Components of a gastric gland
Pit (SurfaceMucous Cells)
Neck (Parietal cells, Mucous Neck Cells, Stem Cells, Enteroendocrine cells)
Base (Chief Cells, Parietal Cells, Enteroendocrine Cells)
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What do parietal cells store?
MEMBRANE!!
In the resting state, there are tons of small tubulovesicles.
These will become microvilli by exocytosis
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What allows a parietal cell to secrete acid?
A H+/K+ pump!!
Trades hydrogen for potassium
Funded by ATP hydrolysis
Cl- exits through channels in luminal membrane. Meets up with H+ and forms HCl in the lumen.
Bicarb is made as a byproduct of reverse-combusting water and CO2. This bicarb exits into the interstitial space in exchange for Cl-.
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Once HCl is secreted by a parietal cell, what pH changes occur where?
Lumen is acidic
Blood is alkaline
Digestion - YAYYYY
CNS - sleepyyyyyy
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What effects does stimulation of a parietal cell have?
Adds membrane and H+/K+ ATPase to the parietal cell surface.
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Pepsin
Digestive enzyme
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What is needed for the conversion of pepsinogen to pepsin?!
Low pH!!
Once some is converted, though, Pepsin can catalyse other pepsinogen, so it quickly becomes autocatalytic.
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What happens to pepsin in an alkaline environment (Like in the duodenum)?!
It is irreversibly inactivated once it hits a pH > 3.5!!
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Enteroendocrine Cells
Secrete into the lamina propria
Secretion granules are basolateral, not apical
Respond to luminal, neural or endocrine signals
Polarized basolaterally
Golgi lies between nucleus and base of cell
Few to no apical granules
Microvilli may be sensory
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GI Peptides
Involved in endocrine, paracrine and neurocrine signaling
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Cholecystokinin (CKK)
Promotes gall bladder contraction.
Promotes secretion of pancreatic enzymes
Delays gastric emptying
Induces satiety
Trophic to pancreas and gall bladder.
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Secretin
First hormone ever discovered
Promotes bicarb secretion from the pancreas, helps deal with the acid
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Glucose-dependent Insolinotropic Peptide (GIP)
Promotes insulin release
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Glucagon
Opposes insulin and promotes glycogenolysis
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