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COT - Exam 2 > 13.1 - Functional Histology of GI System > Flashcards

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
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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
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3
Q

What are the two sphincters of the esophagus

A

1) Upper Esophageal Sphincter (UES)

2) Lower Esophageal Sphincter (LES)

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4
Q

Describe the UES.

A
  • functions in the initiation of swallowing

- prevents the entrance of air into the esophagus

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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
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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

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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
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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

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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

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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
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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

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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
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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
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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”

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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
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16
Q

Describe the submucosa of the stomach

A
  • contain rugae = longitudinal submucosal folds

- allow the stomach to distend when filled

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17
Q

What are rugae

A

= longitudinal submucosal folds in the stomach

- allows the stomach’s distention when filled

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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
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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
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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
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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
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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

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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
Q

Describe the stem cells of the stomach glands

A
  • 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
Q

Describe the parietal cells of the stomach glands. Include any alternative names.

A

= 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
Q

Describe the chief cells of the stomach glands. Include any alternative names

A

= 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
Q

Describe the division/organizatoin of the small intestine

A

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
Q

What is the ileocecal valve? (include location + function)

A
  • 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
Q

Describe the general histology of the small intestine

A
  • 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
Q

Describe the epithelium of the small intestine

A
  • 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
Q

Describe the absorptive cells of the small intestine epithelium

A

= 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
Q

Describe the goblet cells of the small intestine epithelium

A
  • increase in relative frequency toward the large intestine
34
Q

Describe the enteroendocrine cells of the small intestine epithelium

A

= APUD cells, Argentaffin cells

- secretes different hormones in response to material in the intestinal lumen into the underlying lamina propria

35
Q

Describe the Paneth cells of the small intestine epithelium

A

= 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
Q

What is lysozyme

A

= digests the cell walls of certain bacteria

- plays a role in regulating levels of bacteria in the small intestine

37
Q

Describe the stem cells of the small intestine epithelium

A

= 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
Q

Describe the M cells of the small intestine epithelium

A
  • 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
Q

Describe the muscularis mucosae of the small intestine

A
  • 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
Q

Describe the submucosa of the small intestine

A
  • Brunner’s glands = diagnostic feature of the duodenum

- Peyer’s patches = diagnostic feature of the ileum

41
Q

Describe the muscularis externa of the small intestine

A
  • 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
Q

Describe the serosa or adventitia of the small intestine

A
  • only a small portion of the duodenum is attached to the body wall
  • the remainder is lined with a serous layer
43
Q

Describe the general organization + function of the large intestine

A

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
Q

Describe the genial histology of the large intestine

A
  • 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
Q

Describe the Lamina propria of the large intestine

A
  • 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
Q

Describe the muscularis externa of the large intestine

A
  • the OLL forms 3 pronounced longitudinal strips = taeniae coli
  • this visible sacculations between the taeniae coli are known as = hausfrau coli
47
Q

What are taeniae coli

A
  • the 3 pronounced longitudinal strips formed by the OLL of the muscularis externa in the large intestine
48
Q

What are haustra coli

A

= the visible sacculations between the taeniae coli

49
Q

Describe the Serosa/adventitia of the large intestine

A
  • 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
Q

What are fatty appendices?

A

= also called mental appendices

= sacs of fat contained in the serosa of the large intestine

51
Q

Describe the glands of the large intestine

A
  • 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
Q

Describe the lymphatic tissue of the large intestine

A
  • 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
Q

Describe the appendix

A
  • 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
Q

Describe the rectum and anal canal

A
  • 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
Q

What are the transverse rectal folds?

A

= three flexures of the rectum

  • superior, intermediate, inferior
  • help to distinguish the upper rectum from the colon

COT - Exam 2 (28 decks)

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