Histology of the GIT Flashcards

1
Q

What comprises the mucosa?

A
  • epithelium
    • simple columnar or stratified squamous
    • can include endocrine cells, hormone secreting cells
    • renewed every 5-6 days by local stem cells
  • lamina propria
    • loose CT
    • contains nerves, small blood vessels, immune cells
  • muscularis mucosae
    • thin layer of smooth muscle, facilitates mixing
    • boundary of mucosa
  • it is the most diverse layer of the gut
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2
Q

What comprises the submucosa?

A
  • dense, irregular connective tissue
    • fibroblasts, collagen
  • gives structural stability, strength, and elasticity
  • contains nerves, small ganglia, blood vessels
    • sometimes glands and immune cells
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3
Q

What comprises the muscularis externa?

A
  • two layers of smooth muscle:
    • inner circumferential
    • outer longitudinal
  • small myenteric ganglia between layers
  • responsible for gut movement
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4
Q

What comprises the serosa and adventitia?

A

serosa - ‘non-stick’ surface

  • not attached to anything
  • fluid secreting surface
  • simple squamous flattened epithelium w/ thin layer of CT underneath
  • prevents organ adhesion

adventitia

  • in some parts of the gut where the gut is connected to other organs
    • top of oesophagus and rectum
  • connective tissue, no secretive surface
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5
Q

The enteric nervous system is a component of the

A

ANS

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6
Q

Nerves of the ENS are in

A

submucosa: regulate absorptive and secretory processes

(between the 2 layers of) smooth muscle: myenteric ganglia

contain sensory neurons, motor neurons, and interneurons

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7
Q

The ENS regulates

A

absorption and secretion via the submucous ganglia

smooth muscle activity via the myenteric ganglia

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8
Q

The oesophagus epithelium is comprised of

A

non-keratinised squamous epithelium

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9
Q

What are the layers of the oesophagus?

A

non-keratinised squamous epithelium

lamina propria

submucosal glands (mucous-secreting)

two muscle types: striated (voluntary) muscle @ top, smooth (involuntary) muscle @ bottom

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10
Q

What characterises the structure of the stomach?

A

gastric glands (infoldings of epithelial cells, containing multiple cell types)

extra layer of oblique muscle (varies between regions)

pyloric sphincter

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11
Q

What are the 4 main types of cells in the gastric glands?

A
  • mucous cells - secrete mucus
  • parietal cells - secrete hydrochloric acid
  • chief cells - secrete proenzymes (pepsinogen)
  • enteroendocrine cells - secrete hormones (gastrin)
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12
Q

In the stomach, mucous cells are primarily located

A

surface, pale staining

some lower down amongst other cell types

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13
Q

In the stomach, parietal cells are located

A

scattered through gastric glands, never at the surface

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14
Q

Parietal cells secrete

A

hydrochloric acid

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15
Q

Chief cells secrete

A

pro-enzymes eg pepsinogen

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16
Q

In the stomach, chief cells are located

A

at the base of the gastric glands

17
Q

Enteroendocrine cells secrete

A

hormones (eg gastrin) into the bloodstream

18
Q

In the stomach, enteroendocrine cells are

A

scattered amongst other cells of the gastric glands

seen with special stains

19
Q

The small intestine is responsible for what percentage of absorption?

20
Q

What is the general structure of the small intestine?

A

muscularis externa

submucosal connective tissue w/blood vessels folded into plicae circulares (valves of Kerckring), covered w/villi (mucosa)

21
Q

How is the surface area of the small intestine increased?

A

folds of submucosa (plica circulares/valves of Kerckring)

covered in villi (projections of mucosa)

villi covered by enterocytes (simple columnar epithelium), each w/microvilli

22
Q

What is the structure of the villi of the small intestine?

A

absorptive zone

  • simple columnar epithelium w/multiple cell types (some goblet cells, fewer than stomach)
  • lamina propria (connective tissue) at core of villi
    • projections of muscularis mucosae for movement
    • blood vessels, lymph vessels, and immune cells

secretory zone

  • crypts of Lieberkuhn - tubular glands between villi secreting fluid and mucous into the lumen
23
Q

What cell types are found within the epithelial cells of the small intestine?

A
  • enterocytes - fluid transport, absorption
  • goblet cells - mucus secretion
  • enteroendocrine cells - hormone secretion (don’t look different)
  • paneth cells - special to SI, seen on EM w/special stain, deep in glands, secrete anti-microbial peptides (immune system)
  • stem cells - renew epithelium
24
Q

What are the distinctive features of the duodenum?

A

Brunner’s glands in submucosa

lower plica circulares, longer villi

25
What is the function of Brunner's glands?
secrete alkaline mucus from submucosa into the glands at the base of the crypts to inactivate stomach enzymes and acid that may enter the duodenum
26
What are the distinctive features of the ileum?
Peyer's patches short villi, +goblet cells
27
What are Peyer's patches?
aggregates of immune cells in submucosa of the **ileum**
28
What are the general features of the large intestine?
muscularis externa (lognitudinal) in taeniae coli, not a continuous sheath more goblet cells in the rectum immune cells
29
What comprises the mucosa of the large intestine?
no villi straight tubular glands w/lamina propria in between (non-motile) simple columnar epithelium
30
What comprises the epithelial layer of the large intestine?
* enterocytes - fluid transport, absorption * goblet cells - mucus secretion * enteroendocrine cells - hormone secretion (unknown function) * stem cells - renew epithelium (deep) **compared to small intestine:** * fewer paneth cells * higher proportion of goblet cells * some differences in enteroendocrine cell types (different hormones) * no villi
31
What is the cell type of the anal mucosa?
stratified squamous epithelium (like oesophagus)