13.1 - Functional Histology of GI System Flashcards
1
Q
What are the specialized functions of the esophagus?
A
- 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
2
Q
Describe the specific characteristics of the layers of the esophagus from epithelium to adventitia/serosa
A
- 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
3
Q
What are the two sphincters of the esophagus
A
1) Upper Esophageal Sphincter (UES)
2) Lower Esophageal Sphincter (LES)
4
Q
Describe the UES.
A
- functions in the initiation of swallowing
- prevents the entrance of air into the esophagus
5
Q
Describe the LES
A
= 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
6
Q
Describe the 2 deviations of the esophagus from the general organization of the GI
A
1) Skeletal muscle presence in the muscularis externa of the upper esophagus
2) Lack of ICL in muscularis mucosae
7
Q
What are the major and minor functions of the stomach
A
- Major function = physical and chemical digestion of ingested food
- Minor functions = propulsion, protection against invasion, protection against self-digestion
8
Q
Describe the mechanical and chemical breakdown in the stomach
A
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
9
Q
What are the 4 anatomical regions of the stomach
A
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
10
Q
What are the 3 histological regions of the stomach
A
- 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
11
Q
What are gastric pits
A
= foveolae
= simple tubular invaginations of the stomach’s surface epithelium
- approx. 3.5 million gastric pits in human stomach
12
Q
Describe surface mucous Cells
A
- 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
13
Q
What is the visible mucus
A
= 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
14
Q
Describe the turnover of stomach surface epithelium
A
- Stem cells replace the surface epithelium every 3-5 days
- is sufficient to restore the luminal surface from normal “wear and tear”
15
Q
Describe the muscularis mucosae in the stomach
A
- 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
16
Q
Describe the submucosa of the stomach
A
- contain rugae = longitudinal submucosal folds
- allow the stomach to distend when filled
17
Q
What are rugae
A
= longitudinal submucosal folds in the stomach
- allows the stomach’s distention when filled
18
Q
Describe the muscularis externa of the stomach
A
- 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
19
Q
Describe the cardiac glands in the stomach
A
- 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
20
Q
Describe the gastric glands in the stomach
A
- 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
21
Q
Describe the pyloric glands in the stomach
A
- characterize the pyloric region where the stomach joins the duodenum
- Mucus-secreting cells predominate
- enteroendocrine cells are common
- stem cells are present
22
Q
What are the 5 cell types that can be present in stomach glands depending on the gland’s location
A
1) mucous neck cells
2) Enteroendocrine cells
3) Stem cells
4) Parietal cells
5) Chief cells
23
Q
Describe the mucous neck cells of the stomach glands
A
= 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
24
Q
Describe the enteroendocrine cells of the stomach glands. Include alternative names.
A
= 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
25
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
26
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
27
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
28
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
29
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)
30
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
31
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
32
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
33
Describe the goblet cells of the small intestine epithelium
- increase in relative frequency toward the large intestine
34
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
35
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
36
What is lysozyme
= digests the cell walls of certain bacteria
| - plays a role in regulating levels of bacteria in the small intestine
37
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
38
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
39
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
40
Describe the submucosa of the small intestine
- Brunner's glands = diagnostic feature of the duodenum
| - Peyer's patches = diagnostic feature of the ileum
41
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
42
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
43
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
44
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
45
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
46
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
47
What are taeniae coli
- the 3 pronounced longitudinal strips formed by the OLL of the muscularis externa in the large intestine
48
What are haustra coli
= the visible sacculations between the taeniae coli
49
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
50
What are fatty appendices?
= also called mental appendices
| = sacs of fat contained in the serosa of the large intestine
51
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
52
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
53
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
54
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
55
What are the transverse rectal folds?
= three flexures of the rectum
- superior, intermediate, inferior
- help to distinguish the upper rectum from the colon
