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SMP - GI > SDL 1 - Histology of the Esophagus, Stomach, and Intestines > Flashcards

SDL 1 - Histology of the Esophagus, Stomach, and Intestines Flashcards

1
Q

Do the esophagus, stomach, and intestines have the same general histological plan?

A

YUP

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2
Q

7 parts of the general histological plan of the esophagus, stomach, and intestines?

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Adventitia and/or serosa
  5. Nerves
  6. Glands
  7. Modifications of mucosa lining
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3
Q

3 parts of mucosa? Describe each.

A
  1. Lining epithelium: protective (esophagus), secretory (stomach), and/or absorptive (small intestine) in function
  2. Lamina propria: layer of connective tissue
  3. Muscularis mucosa: muscle layer
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4
Q

Describe the submucosa.

A

Region of connective tissue under the muscularis mucosa

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5
Q

Describe the muscularis externa.

A

Thick layer of muscle outside submucosa with longitudinal and circular muscle layers responsible for peristaltic movements

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6
Q

Describe the adventitia and the serosa. Which is more common?

A
  • Adventitia: connective tissue that is continuous with connective tissue of the surrounding organs
  • ***Serosa: a thin slippery membrane surrounding the GIT consisting of a single layer of squamous or cuboidal cells called the mesothelium under which there is a variable amount of connective tissue. This allows organs in the abdominal cavity to slide over one another without damaging each other = visceral peritoneum
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7
Q

What part of the GIT do mesenteries connect to?

A

Serosa

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8
Q

Describe the nerves of the GIT.

A
  1. Meissner’s plexus = submucosal plexus in submucosa
  2. Auerbach’s plexus = myenteric plexus between circular and longitudinal muscle layers of the muscularis externa
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9
Q

Where are glands found in the GIT?

A

Submucosa or lamina propria

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10
Q

What are modifications of the lining mucosa?

A

The lining epithelium may have modifications to increase the luminal surface area:

  • Large folds that involve both the lining mucosa and submucosa (e.g., plicae, rugae)
  • Smaller projections extending into the lumen (e.g., intestinal villi).
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11
Q

Lining of esophagus? Purpose? Special characteristic?

A

Protective, non-keratinized stratified squamous epithelium that protects the esophagus from abrasive damage.

Surface cells are characterized by numerous microplicae with a layer of mucus held in the grooves between the microplicae that may protect the cells from mechanical damage

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12
Q

Is the esophagus surrounded mostly by adventitia or serosa?

A

Adventitia

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13
Q

Why is the muscularis externa of the esophagus unique? What to note?

A

In the upper third of the esophagus, the muscularis externa is composed of skeletal muscle rather than smooth muscle. However, this skeletal muscle is not under voluntary control, but is innervated by parasympathetic fibers from the vagus nerve

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14
Q

In what portion of esophagus do you find both smooth and skeletal muscle?

A

Middle third

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15
Q

Glands in the esophagus? Describe each. Purpose of both?

A
  1. Submucosal Glands: found in the submucosa throughout the length of the esophagus
  2. Cardiac Glands: located in the lamina propria of the lining mucosa at two different sites: at the junction of the esophagus and the stomach (these glands are similar to glands found in the cardiac portion of the stomach, hence, the name) and between the cricoid cartilage and the fifth tracheal ring

Both lubricate the esophagus by secreting a protective mucin

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16
Q

Modification of the lining of the stomach? Describe.

A

Rugae = large folds involving both the lining mucosa and the submucosa

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17
Q

What are gastric pits? What are they continuous with?

A

Thousands of little tiny pits in lining of stomach through which gastric secretions are dumped into the lumen, that are continuous with glands in the lamina propria

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18
Q

Where are the gastric glands? 3 types? Overall?

A

Glands stop at the muscularis mucosa layer (do not go into submucosa)

  • Cardiac glands in cardiac region
  • Gastric glands = fundic glands: in fundus and body
  • Pyloric glands in pyloric region

Overall: simple branched tubular glands

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19
Q

How many gastric glands empty into each gastric pit?

A

3-7

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20
Q

Describe the gastric surface mucus cells: shape? location? contents? purpose? special characteristic?

A

They line the surface of the stomach and are columnar and extend into the gastric pits

They have mucin granules in their apical cytoplasm that is released to provide a protective coat to the surface of the stomach

They are replaced every 3-4 days by the division of cells deep in the pits

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21
Q

3 parts of gastric glands?

A
  1. Mouth/isthmus: opening
  2. Neck: constricted region
  3. Base: rest of the gland
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22
Q

Major cell type in gastric glands?

A

Chief cells

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23
Q

Describe chief cells: shape? Location in gastric glands? What are they filled with? What do they secrete?

A
  • Truncated pyramidal shaped chief cells => mainly in the base of the gland
  • Filled with RER (so characterized by basophilia in basal cytoplasm) and Golgi + leached out granules in their apical cytoplasm
  • Zymogenic cells: actively secrete the proteolytic enzyme pepsinogen that is exocytosed into the lumen of the gland
24
Q

Describe parietal cells: Shape? What is it filled with? Special characteristics?

A

Roundish cells

Flled with mitochondria and tubular vesicular elements (similar to SER) => very eosinophilic (i.e., stains pink with H & E stain)

Deep invaginations termed canaliculi, which are lined with microvilli, through which parietal cells secrete HCl

25
Q

Describe mucus neck cells: where are they found? Role? What to note?

A

Confined to the neck region of the gastric gland, are frequently squeezed between parietal cells, and secrete an acetic mucin (as compared with the neutral mucin of the lining mucus cells).

This third type of cell found in the gastric gland is sometimes difficult to find on histological slides.

26
Q

Where do enteroendocrine cells of the stomach secrete their hormones?

A

Blood vessels in lamina propria

27
Q

Why are enteroendocrine cells of the GIT referred to as argentaffin cells?

A

Because they have a unique affinity for silver salts

28
Q

What regions of the stomach are parietal cells and chief cells rarely found in?

A

Cardiac and pyloric regions

29
Q

What are cardiac and pyloric glands lined with? What is different about each?

A

The glands of these two regions are lined by cells which are similar to the mucus neck cell and enteroendocrine cells

Differences:

  • In the cardiac glands, the associated gastric pits are usually shallow and the glands are relatively straight.
  • The pyloric glands are associated with very deep gastric pits (about 1/2 into the depth of the lining mucosa) and the glands themselves are very coiled.
30
Q

Why is the muscularis externa of the stomach unique?

A

In addition to the inner circular layer and the outer longitudinal layer there is an inner oblique layer of muscle (from out to in: longitudinal, circular, oblique). This additional layer makes the muscularis externa very thick and facilitates the churning action of the stomach.

Also, at the juncture with the small intestines, the middle circular layer of the muscularis externa is thickened to form a pyloric sphincter.

31
Q

Is the stomach surrounded by adventitia or serosa?

A

Serosa

32
Q

How does the small intestine increase the surface area available for absorption?

A
  1. Plicae circularis: large folds involving both the lining mucosa and the submucosa that run in a circular pattern around the lumen of the small intestine (begin towards the end of the duodenum and are most prominent in the jejunum; they disappear about half way through the ileum)
  2. Intestinal villi: little folds or projections involving only the lining mucosa
33
Q

What are the crypts of Lieberkuhn of the small intestine? What cells are they lined with?

A

Tubular glands that appear as invaginations into the lamina propria between intestinal villi in small intestine and are also found in the large intestine

Lined with:

  • Goblet cells
  • Intestinal absorptive cells
  • Enteroendocrine cells (along lateral borders)
  • Paneth cells (at bottom of the glands)
34
Q

What is found in the center of each intestinal villi? How do they appear after a meal? Purpose?

A

Lymphatic vessel called the central lacteal

After a fatty meal, fat accumulates in the lacteals (referring to milk) that, as a result, appear milky white

+ muscle to move them up and down to facilitate the movement of fat from the central lacteal into the lymphatics

35
Q

2 types of cells that make up the lining epithelium of the surface of the intestinal villi? Describe each. Rate of turnover of both?

A
  1. I_ntestinal absorptive cell:_ tall and columnar, with a dense microvillus brush border containing a glycocalyx (sugar rich coat)
  2. Goblet cell: filled with mucin granules and secretes a protective mucous coat over the surface of the lining epithelium.

The rate of turnover of these cells is every 2-3 days.

36
Q

What are Paneth cells of the intestinal glands?

A

Prominent population of zymogenic cells, containing large refractile eosinophilic granules in their apical cytoplasm that stand out as a histological feature

37
Q

How do the intestinal villi change throughout the small intestine?

A
  • Duodenum: more prominent, broad and leaf shaped
  • Jejunum and ileum: more slender and less numerous
38
Q

How do the goblet cells and absorptive cells change throughout the small intestine?

A

Increase in the relative number of goblet cells to the intestinal absorptive cells as one passes through the length of the small intestine.

39
Q

What are Brunner’s glands? Exact location? What are they a identifying feature of?

A

Prominent population of branched mucus glands, located in the submucosa that secrete an alkali mucin that neutralizes the acidic chyme from the stomach. Identifying feature of the duodenum

40
Q

What is the identifying histological feature of the ileum?

A

Prominent population of lymphatic nodules called the Peyer’s patches

41
Q

In what 6 ways is the large intestine different from the small intestine histologically?

A
  1. There are no villi in the large intestine
  2. The intestinal glands (crypts of Lieberkuhn) are deeper in the large intestine (i.e., .5 to .75 mm versus 0.3 to 0.5 in small intestine)
  3. There is a significant increase in the number of goblet cells relative to the number of intestinal absorptive cells.
  4. There are few, if any, Paneth cells or enteroendocrine cells in the large intestine
  5. Throughout the large intestine (except in the appendix), there is a modified muscularis externa: the outer layer is broken into three discrete bands termed the teniae coli
  6. It has sacculations called haustra
42
Q

Are the small and large intestines surrounded by adventitia or serosa?

A

Serosa

43
Q

Modification of the lining of the lower portion of the anal canal?

A

Anal/rectal columns involving both the lining mucosa and the submucosa

44
Q

What is the lower portion of the anal canal lined with? What is it continuous with?

A

Lined by a non-keratinzed stratified squamous epithelium which is continuous with the keratinized squamous epithelium of the skin

45
Q

What is a clinical correlate of the transition between one epithelium to the other at the gastroesophageal junction?

A

In some people, this transition (between the non-keratinized stratified squamous epithelium of the esophagus to the simple columnar epithelium that lines the stomach) does not occur at the physiological junction but is in the lower 1/3rd of the esophagus which may predispose patients to esophageal ulceration and increased risk of adenocarcinoma (a malignant tumor formed from glandular structures in epithelial tissue.)

46
Q

What is reabsorption limited to in the stomach?

A
  • Water
  • Salts
  • Ethanol
  • Certain drugs
47
Q

Lining epithelium of the stomach?

A

Simple columnar epithelium

48
Q

How to differentiate mucous neck cells and surface mucous cells?

A

The mucous neck cells are more triangular in shape, contain more irregularly shaped granules that are more acidic in nature then the granules in the surface mucous cells.

49
Q

Where are gastric enteroendocrine cells located?

A

Situated on the periphery of the gastric glands

50
Q

What makes parietal cells appear very esonophilic when H&E stained?

A

Mitochondria, microvilli, and tubular vesicular elements in the cytoplasm

51
Q

What are the absorptive cells of the small intestine sometimes called?

A

Enterocytes

52
Q

Role of brush border of absorptive cells of the small intestine?

A

Increases the area available for absorption and serves as a storage site for many enzymes including lactase, sucrase, maltase, amino peptidase and many others

53
Q

Other name for brush border of the small intestine?

A

Striated border

54
Q

How does a Peyer’s patch look like when viewed from the luminal aspect?

A

When viewed from the luminal aspect, a Peyer’s patch often appears as a dome-shaped area devoid of intestinal villi.

54
Q

What does the appendix contain?

A

Debris lumen and lymphatic material in its lamina propria

54
Q

Difference in lining of rectum compared to rest of large intestine?

A
  • The upper part of the rectum is similar to the colon, although the intestinal glands are deeper and the number of goblet cells increases. The last part of the rectum, the anal canal, exhibits macroscopic longitudinal folds termed the “rectal columns”.
  • About 2 centimeters before the anal opening, there is an abrupt transition from simple columnar lining epithelium with intestinal glands to a non-keratinized stratified squamous epithelium as seen at the arrow on this slide.
55
Q

Resorption of which ion will be most altered by destruction of the striated ducts of salivary glands?

A

Na+

SMP - GI (21 decks)

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