Home > Flashcards > Print Preview
The flashcards below were created by user
on FreezingBlue Flashcards. What would you like to do?
What are some ways in which the alimentary canal protects the body from pathogens?
- 1. Specialized epithelial cells (M-cells) for antigen sampling
- 2. Large aggregations of diffuse and nodular lymphoid tissues (Peyer's patches in ileum)
- 3. Mucus coating traps potential pathogens (eg. bacteria)
GI Tract Organization
- 1. Lumen →
- 2. Mucosa (epithelium, lamina propria, muscularis mucosa)
- 3. Submucosa (may have glands, nerves)
- 4. Muscularis Externa
- 5. will either have an Adventitia or Serosa, depending on where in GI tract you are
- lined by epithelium
- covered by the Lamina Propria: loose CT
- then covered by the Muscularis Mucosa: smooth muscle layer
- all together = MUCOSA (epithelium, loose CT, SM muscle)
- another muscular layer comprised of three components
- 1. muscularis mucosa: thin layer of smooth muscle that can assist in emptying glands
- 2. lamina propria: loose CT that contains immune cells
- 3. luminal epithelium: epithelial layer covering entire luminal surface of GI tract
- contains many of the structural and functional specializations of the different regions of the GI tract
- (eg. intestinal villi, crypts, gastric pits or glands)
- a connective tissue layer that lies between the muscularis externa and the muscularis mucosa
- contains blood vessels, nerves, parasympathetic ganglia, & lymphatics
- muscular layer deep to the serosa that consists of two layers of smooth muscle – an outer one that is longitudinal and inner one that is circular
- wave-like contractions of these opposed muscle layers (peristalsis) results in the efficient propulsion of food
- contractions are regulated by parasympathetic nerves & ganglia (myenteric plexus) that lie between the muscle layers
- outermost layer along most of the GI tract
- consists of two components: 1) simple squamous epithelium (mesothelium) that forms a slippery surface allowing intestines to slide over one another & 2) adventitia made of loose CT
- the serosa contains blood vessel, nerves & lymphatics
What is the sole conduit for blood vessels/nerves to enter AND exit the intestines, and for lymphatics to exit?
- the outermost layer connecting the GI tract to the body wall in regions where there is NO serosa, due to the absence of an epithelium
- most of the esophagus & part of the gall bladder
- In the esophagus it is a stratified squamous epithelium
- throughout the remainder of the tract it is a simple columnar epithelium (gastric epithelium)
- this epithelium is also continuous with the epithelial lining of the ducts and glands of the accessory digestive organs (the pancreas, liver & gall bladder)
Where is the Serosa layer located in the esophagus?
- the outer esophagus lining = Adventitia until it crosses the diaphragm
- in the Thorax the outer layer = Adventitia
- within the abdominal cavity it's outermost region consists of a Serosa
Where might skeletal muscle be found in the esophagus?
in the upper 1/3
Where might both skeletal & smooth muscle be found in the esophagus?
in the middle 1/3
Where is only smooth muscle found in the esophagus?
How does the muscularis mucosa run in the esophagus?
located in between muscle layers of the gut & esophageal wall of the Muscularis Externa
- nerve plexus in the submucosa that innervates the muscularis mucosa to control it’s contraction
- further down in the GI system it controls the emptying of glands
Where are regions of the GI tract where the submucosa contains glands?
1. esophagus: producing a lubricating/protective mucous
visually the only place there's a submucosal gland deep to a SSNKE = esophagus
2. duodenum (small intestine): neutralizes partially digested acidic chyme (food from the stomach)
What happens to the luminal epithelium at the esophageal-stomach junction (squamo-columnar)?
- it undergoes an abrupt change from the stratified squamous epithelium (of the esophagus) to the simple columnar epithelium (the gastric epithelium) of the stomach (and subsequently the intestines)
- when acidic contents of the stomach chronically bypass the lower esophageal sphincter (one-way valve), the esophageal SSNKE epithelial cells can undergo a transition to simple columnar epithelium
- associated with the subsequent development of esophageal adenocarcinoma (lethal)
Regions of the Stomach
- Cardiac region: short pits & glands; mucous & enteroendocrine cells
- Fundus/Body region: short pits, long glands; thick surface mucous, mucous neck (clear), parietal, chief, & enteroendocrine cells
- fundus also has SM muscle cells running through mucosa to contract it, forcing gland contents into lumen
- Pyloric region: long pits, short glands; mucous & enteroendocrine cell
Where is intrinsic factor synthesized?
- in the stomach by parietal (fried egg) cells
- made in the stomach but used in the gut for the absorption of vitamin B12
- issues with stomach lining or parietal cells can cause Vitamin B12 deficiency & eventually pernicious anemia
Where is there a third, oblique muscle layer present in the Muscularis Externa of the GI tract?
- in the stomach where food is also subjected to a grinding action
- outer (longitudinal), middle (circular) & inner (oblique)
What are the 5 types of cells in the glands of the stomach (including the pits)?
1. surface mucous: simple columnar; protective against acid made in stomach
2. mucous neck
4. parietal: make HCl & intrinsic factor
5. gastric chief: make pepsinogen --> pepsin in acid
the cardiac & pyloric glands contain ONLY the first 3 cell types
the fundic/gastric glands contain all five
What are the general turnover rates for gastric cells as a result of stem cell proliferation (derived from base of gastric glands)?
- mucous: 3-5 days
- endocrine: weeks
- chief & parietal: 90-200 days (months)
- PAS stained surface mucus & mucous neck cells
- mucus cells making thick bicarbonate mucus that serves to protect the stomach lining
- Parietal cells
- make HCl & Intrinsic Factor
- look like red (eosinophilic) fried eggs
- packed with mitochondria (red dots)
- clear areas in cell represent Intracellular Canaliculus - implies cells were active (secreting HCl)
- purple cells = chief cells
- basophilic because of abundant RER making pepsinogen
- typical protein secreting cells
- have a ton of zymogen granules that contain inactive enzymes: pepsinogen, lipase, chymosin
- when released into acid environment of gut from chief cells, the low pH (<5) causes autocatalytic activity, turning pepsinogen into pepsin
- when pepsin gets to neutral pH of duodenum, it's inactivated
- chronic inflammation of the stomach mucosa leading to loss of gastric glandular cells & their eventual replacement by intestinal & connective tissue
- ability for stomach to secrete substances is impaired (deficiency in intrinsic factor leads to vitamin B12 deficiency, pernicious anemia)
- can be caused by autoimmunity or by Helicobacter pylori infection
- will see lymphocyte infiltration
H. Pylori Infection
- bacteria convert urea to ammonia via urease
- this neutralizes acid of the stomach, & allows bacteria to penetrate into mucosal lining
- bacteria have proteins that look similar to stomach lining itself, so when the stomach makes antibodies against the bacteria, it damages self (autoimmune attack to the stomach lining)
- if chronic this can lead to Gastritis
- an cell abundant in the GI tract that requires special staining
- make numerous products including Gastrin, Somatostatin, Ghrelin, Enterochromaffin
- here they're visualized in the pyloric region (end) of the stomach (can see long pits, short glands)
a peptide hormone secreted by Eneteroendocrine (G) cells that stimulates secretion of HCl by parietal cells
- inhibits Gastrin release
- also inhibits release of CCK & Secretin, inhibiting pancreatic & gall
- bladder secretions
- the last part of the stomach overlies the pyloric sphincter, a thickened part of the Muscularis Externa that closes the stomach & only opens when digestion within the stomach is sufficient (material is liquid)
- as the sphincter opens it squirts that fluid into the duodenum (1st part of the SI)