14 - GI Anatomy and Histology Flashcards
Motility
Movements of the bowel that influence the transport of luminal contents
Ingestion
Act of taking food into the mouth
Mastication
Chewing food and moistening it with saliva
Deglutition
Swallowing
Peristalsis
Oral contraction and anal relaxation, which is propulsive
Secretion
Exocrine to lumen of gut, endocrine to blood
Digestion
Breakdown of ingested macromolecules into absorbable smaller subunits
Absorption
Transport of end products of digestion to blood and/or lymph
Storage
Temporary holding of ingested contents
Elimination
Getting rid of indigestible material
Sphincters of the gut
Upper Esophageal Lower Esophageal Pyloric Iliocecal Internal Anal External Anal
Gut Wall - Luminal
Mucosa:
Epithelium
Lamina propria
Muscularis mucosa
Gut Wall - Middle Layer
Submucosa:
Submucosal plexus
Gut Wall - Basal
Muscularis Externa:
Inner circular muscle
Outer longitudinal muscle
Myenteric Plexus
Gut Wall - Non-retroperitoneal parts
Adventitia:
Serosa
Esophagus - To resist abrasion
Stratified squamous nonkeritanized epithelium
Stomach - To digest
Simple columnar epithelium
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
Upper esophagus - Muscularis externa
Mostly striated
Middle esophagus - Muscularis externa
Mix of striated and smooth
Lower esophagus - Muscularis externa
Mostly smooth
Regions of the stomach
Lower esophageal sphincter Fundus Body Antrum Pylorus Duodenum
Also split into Orad and Caudad region, about halfway through the body.
Fundic region
Rises above the entrance of the esophagus.
Contains air very often.
Body/corpus
Large region into which food is delivered.
Antrum
Different
Separated from duodenum by pyloric sphincter.
Oxyntic region of the stomach
Corpus + Fundus Makes HCl Makes pepsinogen Contains parietal cells Contains chief cells
Parietal Cells
Make HCl
Make Intrinsic Factor
Chief Cells
Make Pepsinogen
HCl
Acid!
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.
Pepsinogen
Pepsin precursor
Pyloric region
Antrum Makes Gastrin Makes mucus pepsinogen Contains G cells Contains Mucous cells
Gastrin
Stimulates the production of more HCl.
Stimulates growth of gastric mucosa
Produced in pyloric region of the stomach.
Mucus pepsinogen
Provides protection of mucosa from HCl
G Cells
Produce gastrin if stimulated by alkaline environment or nerve activation.
Mucous Cells
Produce mucous pepsinogen
Cells in the stomach
Surface mucous epithelial cells Mucous neck cells Parietal cells Chief cells Endocrine cells
Surface Mucous Cells
Superficial lining of surface and beginning of the pit area of the gland
Defend stomach against HCl
Mucous neck cell
Stem cells to regenerate lost surface cells
Parietal cell
Oxyntic cells Abundant surface area when secreting Contains intracellular canaliculi & microvilli MANY Mitochondria Large Complex cristae
Chief cell
Secretes pepsinogen Specialized for regulation of secreted protein Abundant RER Huge number of zymogen granules Big Gogli
Endocrine cell
Scattered through the glands
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)
What do parietal cells store?
MEMBRANE!!
In the resting state, there are tons of small tubulovesicles.
These will become microvilli by exocytosis
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-.
Once HCl is secreted by a parietal cell, what pH changes occur where?
Lumen is acidic
Blood is alkaline
Digestion - YAYYYY
CNS - sleepyyyyyy
What effects does stimulation of a parietal cell have?
Adds membrane and H+/K+ ATPase to the parietal cell surface.
Pepsin
Digestive enzyme
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.
What happens to pepsin in an alkaline environment (Like in the duodenum)?!
It is irreversibly inactivated once it hits a pH > 3.5!!
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
GI Peptides
Involved in endocrine, paracrine and neurocrine signaling
Cholecystokinin (CKK)
Promotes gall bladder contraction. Promotes secretion of pancreatic enzymes Delays gastric emptying Induces satiety Trophic to pancreas and gall bladder.
Secretin
First hormone ever discovered
Promotes bicarb secretion from the pancreas, helps deal with the acid
Glucose-dependent Insolinotropic Peptide (GIP)
Promotes insulin release
Glucagon
Opposes insulin and promotes glycogenolysis
3 Secretogogues stimulating parietal cell acid secretion
Direct pathway - ACh from nerves, Gastrin, Histamine
Indirect pathway - Nerves act on enteroendocrine cell, affecting histamine.
Gastrin? I don’t know…
