13.1 - Functional Histology of GI System Flashcards
What are the specialized functions of the esophagus?
- main specialization = propulsion
–> the entire esophagus is normally contracted so the bolus of food moves along with a wave of relaxation followed by contraction - secondary specialization is for protection from:
A) invasion from microorganisms
B) simple mechanical damage
C) Chemical damage
Describe the specific characteristics of the layers of the esophagus from epithelium to adventitia/serosa
- Epithelium: SSNK
- Lamina Propria: Highly Vascularized
- Muscularis Mucosae - movement is independent of the peristaltic movement of the wall of the GI tract + this layer aids in the FXN of swallowing
- Submucosa = loose CT
- Muscularis Externa:
A) Upper:skeletal muscle
B) mid: mix of skeletal and smooth muscle
C) lower: smooth muscle - Adventitia/Serosa: serosa lines a small portion of the esophagus that is in the peritoneal cavity
What are the two sphincters of the esophagus
1) Upper Esophageal Sphincter (UES)
2) Lower Esophageal Sphincter (LES)
Describe the UES.
- functions in the initiation of swallowing
- prevents the entrance of air into the esophagus
Describe the LES
= gastroesophageal sphincter
- prevents reflux of gastric contents
- doesn’t have pronounced morphologic thickening of ICL into a sphincter –> has somewhat thickened circular muscle surrounding esophagus at lower sections
- maintained in tonic contractile state (except is relaxed when swallowing)
- controlled by the enteric nervous system
- its FXN is aided by diaphragm
Describe the 2 deviations of the esophagus from the general organization of the GI
1) Skeletal muscle presence in the muscularis externa of the upper esophagus
2) Lack of ICL in muscularis mucosae
What are the major and minor functions of the stomach
- Major function = physical and chemical digestion of ingested food
- Minor functions = propulsion, protection against invasion, protection against self-digestion
Describe the mechanical and chemical breakdown in the stomach
Mechanical breakdown
- churning + dilution in large volume of stomach juices with ph of ~2.0 (aids in breakdown)
Chemical Breakdown
- limited to proteins
- Pepsin = breaks down proteins into polypeptides
What are the 4 anatomical regions of the stomach
1) Cardia - surrounds esophageal orifice
2) Fundus - above and to the left of cardia
3) Body - below level of cardia
4) Pyloric = funnel-shaped, leads to narrow sphincter between the stomach and small intestine
What are the 3 histological regions of the stomach
- they are based on the types of glands occurring the in mucosa
1) Cardia - near LES
2) Fundus - forming majority of the organ
3) pyloric - near the pyloric sphincter and junction with duodenum
What are gastric pits
= foveolae
= simple tubular invaginations of the stomach’s surface epithelium
- approx. 3.5 million gastric pits in human stomach
Describe surface mucous Cells
- produce blanket of thick mucus in the stomach
- lubricates and protects the stomach
- the mucus layer they secrete = visible mucus
- the interface with the visible mucus is ~ neutral pH due to the trapped bicarbonate ions in it
What is the visible mucus
= the thick mucus layer secreted by surface mucus cells
- is gel-like layer
- adheres to lining of the stomach
- protects it from auto digestion
- traps bicarbonate ions in the mucus layer to maintain relatively neutral pH at surface interface of epithelial cells
Describe the turnover of stomach surface epithelium
- Stem cells replace the surface epithelium every 3-5 days
- is sufficient to restore the luminal surface from normal “wear and tear”
Describe the muscularis mucosae in the stomach
- some smooth muscle fibers from the muscularis mucosae extend into the inter glandular lamina propria
- these smooth muscle cells are thought to facitilitate the outflow of gastric gland secretions
Describe the submucosa of the stomach
- contain rugae = longitudinal submucosal folds
- allow the stomach to distend when filled
What are rugae
= longitudinal submucosal folds in the stomach
- allows the stomach’s distention when filled
Describe the muscularis externa of the stomach
- 3 layers = unique feature solely to the stomach
- arrangement of layers mixes chyme during the digestive process
- forces the partially digested contents into the small intestine
Describe the cardiac glands in the stomach
- occur at the proximal end of the stomach (in the cardiac region)
- composed mostly of mucin-secreting cells
- few stem cells
- maybe few parietal cells
- enteroendocrine cells
Describe the gastric glands in the stomach
- characterize the body (corpus) and the fundus of the stomach
- also called “fundic” glands
- are the most numerous glands
- are the working glands of the stomach
- -> produce the acid that creates a pH=2.0
- also produce gastric intrinsic factor (required for B12 absorption), pepsin
- contain five cell types:
1) Mucous Neck cells
2) Enteroendocrine (argentaffin; enterochromaffin,APUD) cells
3) Stem cells
4) Parietal (oxyntic) cells
5) Chief (peptic;zymogenic) cells
Describe the pyloric glands in the stomach
- characterize the pyloric region where the stomach joins the duodenum
- Mucus-secreting cells predominate
- enteroendocrine cells are common
- stem cells are present
What are the 5 cell types that can be present in stomach glands depending on the gland’s location
1) mucous neck cells
2) Enteroendocrine cells
3) Stem cells
4) Parietal cells
5) Chief cells
Describe the mucous neck cells of the stomach glands
= mucus-producing cells found in the neck of all 3 glands
- mucus is distinct form the mucus of the surface epithelium
- cells are concentrated in the neck region of the glands
- form a slightly foamy narrow apical region of the gland
Describe the enteroendocrine cells of the stomach glands. Include alternative names.
= Argentaffin cells, Enterochromaffin cells, APUD cells
- secrete a variety of hormones (glucagon, serotonin, gastrin, SST) into blood vessels of the lamina propria in all 3 glands
- generally one cell type secretes only 1 hormone
- the # and kinds of these cells vary in different segments of the stomach
- hormone is contained in numerous spherical granules concentrated in basal portion of the cell
Describe the stem cells of the stomach glands
- found in all 3 glands
- confined to isthmus of the gland
- extend up into the base of the pits
- they are the source of new surface mucous cells + the other types of cells of the glands
Describe the parietal cells of the stomach glands. Include any alternative names.
= oxyntic cells
- occur throughout the gastric gland
- are most numerous in upper + middle portions of the neck
- have unusual morphology - facilitates their production of HCL:
a) abundant mitochondria,
b) intracellular canaliculus (formed by extensive invagination of the apical cell surface
c) intracellular tubulovesicular system - FXN: secrete the HCl of the gastric juice + release bicarbonate into lamina propria
- produce GIF = essential for vitamin B12 absorption in the sm. intestine
- parietal cell stimulation - primarily activated by hormone gastrin
Describe the chief cells of the stomach glands. Include any alternative names
= Peptic cells, zymogenic cells
- occur only in the gastric glands
- produce pepsinogen
- numerous zymogen granules contain the pepsinogen
- chief cells appear basophilic in H&E due to abundant rER
Describe the division/organizatoin of the small intestine
1) Duodenum
- first, shortest, widest part of small intestine
- beings at the pylorus of the stomach
- ends at the duodenojejunal junction
2) Jejunum
- approximately 2.5meters long
- gradually changes in histological characteristics to become the ileum
3) Ileum
- ends at the ileocecal junction
- ileocecal valve is located at this junction –> prevents reflux of the contents of the colon back into the ileum
What is the ileocecal valve? (include location + function)
- located at the ileocecal junction
- prevents reflux of the contents of the colon back into the ileum
- is an anatomical sphincter (thickening of the ICL of the mucularis externa)
- is a physiological sphincter (increase in the resting tone of the muscle)
Describe the general histology of the small intestine
- principle functions are both digestion of food + absorption of digestion products
- propulsion continues to be a necessity
- but protection becomes increasingly important (because absorption specializations makes exogenous organism invasion easier)
- absorptive surface is increased by permanent specializations of the mucosa + submucosa
a) plica circulares
b) intestinal villi
c) microvilli - also secretes water + electrolytes = primarily a function of the intestinal glands –> maintain the appropriate liquid state of the intestinal chyme
Describe the epithelium of the small intestine
- simple columnar
- contains two predominant cell types
1) absorptive cells (enterocytes)
2) goblet cells - contains several less frequent cell types
1) enteroendocrine cells (APUD or Argentaffin)
2) Paneth cells
3) Stem cells
4) M cells
Describe the absorptive cells of the small intestine epithelium
= enterocytes
= specialized for transport of substances from lumen to underlying circulatory system
- cells have striated border of microvilli
- coated with thick glycocalyx (or membrane-bound glycoproteins)
- are also secretory cells –> produce enzymes needed for terminal digestion, water, electrolytes
Describe the goblet cells of the small intestine epithelium
- increase in relative frequency toward the large intestine
Describe the enteroendocrine cells of the small intestine epithelium
= APUD cells, Argentaffin cells
- secretes different hormones in response to material in the intestinal lumen into the underlying lamina propria
Describe the Paneth cells of the small intestine epithelium
= intesnely acidophilic apical secretory granules that contain antibacterial enzyme lysozyme + other glycoproteins + zinc
- lysozyme - functions in digesting cell walls of certain bacteria –> paneth cells play a role in regulating levels of bacteria in the small intestine
What is lysozyme
= digests the cell walls of certain bacteria
- plays a role in regulating levels of bacteria in the small intestine
Describe the stem cells of the small intestine epithelium
= pluripotential cells
- situated near the base of the crypts
- are the source of new epithelial cells
- re-populate the surface epithelium every 3-5 days
- re-populate Paneth and enteroendocrine cells that turn over every 3-5 weeks
Describe the M cells of the small intestine epithelium
- names for micro folds on their luminal aspect
= antigen transporting cells - located in epithelium that overlies the GALT
- take up microorganisms from the lumen + discharge their contents in the underlying lymphoid tissue
Describe the muscularis mucosae of the small intestine
- fascicles of the ICL fibers extend up into the core of the intestinal villus
- -> serve to move it around within the lumen - aiding absorption
Describe the submucosa of the small intestine
- Brunner’s glands = diagnostic feature of the duodenum
- Peyer’s patches = diagnostic feature of the ileum
Describe the muscularis externa of the small intestine
- two types of muscle contraction take place in the small intestine
1) contractions of the ICL - circulate the chyme locally
- mixing it with the digestive juices + moving it toward the mucosa for absorption
2) Peristalsis - involves the coordinate action of both OLL and ICL muscle layers
- moves the contents through the intestinal tract
Describe the serosa or adventitia of the small intestine
- only a small portion of the duodenum is attached to the body wall
- the remainder is lined with a serous layer
Describe the general organization + function of the large intestine
A) large intestine includes
- cecum
- vermiform appendix
- colon (Ascending, transverse, descending, sigmoid)
- rectum
- anal canal
B) Basic functions
- re-absorption of water and salts from feces
- propulsion of feces out of the body through the rectum and anus
- protection from abrasion by the solidifying feces
Describe the genial histology of the large intestine
- colon accounts for the majority of the length of the large intestine
- chyme is propelled from ileum through the ileocecal valve (is both a physiological and anatomical sphincter)
- material arriving from ileum enters the expanded pouch –> cecum
- histologically the cecum and colon are indistinguishable
Describe the Lamina propria of the large intestine
- thick layer of collagen and protelgycans participate in the regulation of water and electrolyte transfer –> from the epithelium to the blood vessels
- lymphatic vessels are absent in the lamina propria
- -> results in slower rate of metastasis of certain colon cancers
Describe the muscularis externa of the large intestine
- the OLL forms 3 pronounced longitudinal strips = taeniae coli
- this visible sacculations between the taeniae coli are known as = hausfrau coli
What are taeniae coli
- the 3 pronounced longitudinal strips formed by the OLL of the muscularis externa in the large intestine
What are haustra coli
= the visible sacculations between the taeniae coli
Describe the Serosa/adventitia of the large intestine
- different surfaces of the large intestine may be covered with a serosa or adventitia as it adheres to the wall of the abdomen
- serosa contains numerous sacs of fat called = fatty appendices or omental appendices
What are fatty appendices?
= also called mental appendices
= sacs of fat contained in the serosa of the large intestine
Describe the glands of the large intestine
- goblet cells of the crypts predominate in the crypts
- in the distal aspect of the large intestine the epithelium may consists almost entirely of goblet cells
Describe the lymphatic tissue of the large intestine
- there is diffuse lymphatic tissue
- there is organized nodules that function like the lymphatic tissue of the small intestine
- no lymphatic vessels in lamina propria
Describe the appendix
- tube-like blind out pouching of the large intestine
- found at the junction with the small intestine
- wall is occupied almost entitle with both diffuse lymphatic tissue and nodules
- Apendicitis = acute inflammation of the appendix
- -> in early stages - ulceration of the mucosa with overlying exudate causes vague central abdominal pain
- -> in later stages - inflammation spreads throughout all layers of the wall resulting in peritonitis and may lead to perforation of the appendix
Describe the rectum and anal canal
- rectum = dilated distal portion of the alimentary canal - an expandable organ that allows for temporary storage of feces
- mucosa of rectum = similar to distal colon - however crypts are deeper with many goblet cells
- taeniae coli are not present at the rectum
- has the transverse rectal folds = three flexures of the rectum (superior, intermediate, inferior) –> help to distinguish the upper rectum from the colon
- anal canal = most distal portion of the alimentary canal - avg. length = 4cm. - extends to the anus
- crypts of anal canal are short
What are the transverse rectal folds?
= three flexures of the rectum
- superior, intermediate, inferior
- help to distinguish the upper rectum from the colon
