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GI Exam 1 > Histology of the SI and LI > Flashcards

Histology of the SI and LI Flashcards

1
Q

What 3 parts is the SI made up of?

A

1. Duodenum

2. Jejunum

3. Ileum

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2
Q

What is the purpose of the SI?

A

The SI is the main site of digestion of food and absorption.

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3
Q

What is a hallmark of the SI, which is more visible in the jejunum than the ileum?

A

The jejunum (and less so the ileum) of the SI has plicae circulares.

  • Plicae circulares are transverse folds of the entire mucosa with a submucosal core with intestinal villi, which prevent the jejunum from flatting out as food passes through.
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4
Q

What part of the SI are the plica circulares located?

A
  • Duodenum- absent
  • Jejunum- visible
  • Ileum- less prominent
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5
Q

The jejunum (and less so the ileum), have plicae circulares, transverse folds with a submucosal core. What covers the plicae circulares?

A

Intestinal villus

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6
Q

What are intestinal villus?

A
  • Intestinal villus are folds of mucosa made up of a core of loose CT with lacteal that project into the lumen and are located on the plicae circulares. They are lined with enterocytes and goblet cells.
  • They increase the absorptive SA.
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7
Q

What are the roles of the enterocytes and goblet cells located in the intestinal villus?

A
  • Enterocytes→ simple columnar cells that make enzymes for digestion and absorption
  • Goblet cells→ makes a coat a mucous to protect from abrasion and bacteria
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8
Q

Enterocytes and goblet cells are located in the intestinal villus of the plicae circulares.

Which of the two has microvillus?

A

Enterocytes.

Goblet cells do not have microvillus.

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9
Q

Describe enterocyte microvillus.

A
  • Enterocytes have microvillus, which create a striated border.
    • The microvillus are covered in a glcocalyx coat, which help take up nutrients.
    • An actin microfilament core connects to other proteins and myosin 1 via a terminal web, allowing microvillus to contract.
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10
Q

Describe the layers of the SI.

A
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11
Q

What innervates the SI and LI?

A
  • Motility is controlled by the ANS
  • Enteric (intrinsic) NS is made up of the submucosal plexus of Meissner and the myenteric plexus of Auerbach. Enteric NS consists of
      1. Sympathetic fibers
      1. Parasympathetic ganglia
      1. Preganglionic and postganglionic parasympathetics (vagus and pelvic nerves).
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12
Q

Extrensics (ANS) of the SI and LI regulate what?

A

1. Preganglionic parasympathetics (Vagus and pelvic nerves)

2. Postganglionic sympathetics

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13
Q

Describe intestinal glands.

What are they lined by?

Location?

What cells make them up?

A

Between the intestinal villus are crypts. Located within these crypts are intestinal glands (also called Crypts of Lieberkuhn). They are lined by s_imple columnar epithelium_. They are continuous with the intestinal villus and open into the lumen. They have 4 different types of cells:

    1. Enteroendocrine cells
    1. Paneth cells
    1. Intestinal stem cells
    1. M (microfold) cells
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14
Q

Intestinal glands are also called what?

A

crypts of Lieberkuhn

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15
Q

Enteroendocrine cells

Where are they found?

Role?

A
  • Location: Intestinal glands.
  • Role: release peptide hormones that
    1. control motility
    2. regulate the secretion of enzymes, HCl and bile and other things to help with digestion
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16
Q

What peptide hormones do enteroendocrine cells secrete that help with digestion?

A
  1. Gastrin
  2. GIP
  3. CCK
  4. Motilin
  5. Secretin
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17
Q

Paneth cells (mainly only located in SI)

Shape?

Location?

Role (2)?

A
  • Pyramid shaped and located at the base of the intestinal gland.
  • Role:
  1. Fx in innate immunity by secreting antimicrobial substances
  2. Maintain bacterial flora by getting rid of bacteria and phagocytosis
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18
Q

Paneth cells

Are there alot of panath cells in the colon?

A

No. Normally there are not alot but they increase in pathologic condition.

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19
Q

Intestinal Stem Cells (ISCs)

Location?

role?

A

Located: located at the base of the crypt, near Paneth cells.

Role:

    1. Repopulates the epithelial lining
    1. Can move out of the crypt and become [goblet, enterocytes, enteroendocrine cells].
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20
Q

M (Microfold Cells)

A

M (microfold) cells have microfolds and a glycocalyx that cover Peyer’s patches. They have deep pockets that store DCs, macrophages and T and B cells in them.

The apical surface of the M-cells has receptors that can take up antigens–> transfer them to immune cells. Thus, they are antigen-transporting cells.

21
Q

When differentiating the pyloris (thick wall d/t sphincter) of the stomach and the duodenum of the SI at the gastroduodenal junction, what layer is important to look at?

A

the submucosal layer

22
Q

What is different about the submucosal layer of the of the duodenum compared to the pyloris? *hallmark*

A

Submucosa of the duodenum has BRUNNER’S GLANDS, DEEP to muscularis mucosae.

23
Q

Does the pyloris have glands?

A

Yes. It has pyloric glands at the base of each pit.

24
Q

The submucosa of the duodenum has Brunner’s glands.

What do they do?

A

produce alkaline secretion that neutralizes the chyme.

25
Q

What does the duodenum collect?

A

bile and pancreatic secretions via the hepatopancreatic ampulla

26
Q

What part of the SI has the longest finger-like villi , with no submucosal glands or peyer’s patches?

A

Jejunum

27
Q

What part of the SI has [shorter finger-like villi & PEYER’s patches]?

A

Ileum

28
Q

Food is propelled from the [ileum –> cecum via ileoceccal valve].

Here we can see an abrupt transition from villi of SI to?

A

Villi of SI → glandular epithelium of LI

29
Q

What is the main job of the large intestine?

A

_absorb water *, sodium, vitamins, minerals_

30
Q

What are the 2 hallmarks of LI?

A
  • 1. LI mucosa has opening of intestinal glands (crypts of Lieberkuhn), BUT NO INTESTINAL VILLUS
  • 2. Goblet cells
31
Q

Describe the layers of the LI

A
32
Q

The mucosa of the LI ha simple columnar epithelium and a lamina propria and muscularis mucosae are present. What is extensive here and may penetrate the submucosa?

A

GALT

33
Q

The LI submucosa is typical along with the inner layer of muscularis externa. What is different about the outer longitudinal layer?

A

it is organized into taeniae coli which form the haustra to help propel food

34
Q

Veriform appendix–> a diverticulum of the cecum with layers similar to those of LI.

What are characteristic of the mucosa, submucosa, muscularis and serosa here?

A
  • Mucosa –> simple columnar epithelium and goblet cells
  • Sub–> ADIPOCYTES and dense ireg CT
  • Muscularis–> has undeveloped outer longitudinal layer
  • Covered in serosa
35
Q

What disease is due to mutations in the RET gene, causing failure of neural crest cells (NCC) to migrate and make the plexuses (enteric NS) of the bowel?

A

Hirschprung’s Disease, aganglionosis in the distal colon

(85% are short segment confined to rectosigmoid, 10% long-segment from rectosigmoid to splenic flexure, 5% affects entire colon)

36
Q

Hirschprung’s disease occurs 1:5000 neonates. Presents with constipation, poor feeding and abdominal distention. How does one treat this?

A

Remove affected colon segment and reattach ends

37
Q
  • IBD includes both ulcerative colitis and chron’s disease.
  • Characterized by diarrhea, pain and relapses.

What regions do Chron’s and ulcerative colitis affect?

A
  • Chrons- any region
  • Ulcerative colitis- mucosa of the LI
38
Q

Chrons is observed in the LI and terminal ileum. Inflammatory cells produce cytokines that damage the mucosa.

Neutrophils attack the into the crypts of lieberkuhn and destroy them.

A
39
Q

What are the divisions of the rectum?

A
  1. Rectum proper (upper part)
  2. Anal canal (lower part), made up of 3 zones:
  • Colorectal zone
  • Anal transitional zone
  • Squamous zone
40
Q

The rectum proper (upper part) has typical mucosa: [intestinal glands] & [transverse folds].

The anal canal (lower part) has what three things?

A
  • Anal columns with mucosal folds
  • Anal sinuses: depressions between columns
  • Anal glands: extend into submucosa/muscularis externa
41
Q

What other special glands does the rectum have?

A

Circumanal glands, which are large apocrine glands that surround the anal orifice.

42
Q

What is the main job of anal sinuses?

A

to keep poop inside :)

43
Q

The ENS stops at the pectinate line

What then controls the external anal sphincter?

A

skeletal muscle

44
Q

Anal canal has three zones: colorectal zones, ATZ, and the squamous zones.

How do the cells types change in the zones?

A
  • Colorectal zone: simple columnar epithelium, similar to the rectum
  • ATZ: simple columnar epithelium–> stratified squamous epithelium
  • Squamous zone: nonkeratinized stratified squamous epithelium continous with perineal skin
45
Q

The ATZ is where simple columnar epithelium –>

A

Stratified squamous epithelium of perianal skin (middle 1/3 of anal canal)

46
Q

At the anus, what layer forms the internal anal sphincter?

A

Thickening of the inner circular layer

47
Q

At the recto-anal junction, what two types of cells can be seen?

A
  1. nonkeratinized stratified squamous epithelium
  2. simple columnar with intestinal glands
48
Q

Differentiate the three parts of the SI/

A
  1. Duodenum- Brunners glands in the submucosa, leaf-like villus and intestinal glands
  2. Jejunum- No submucosal glands, large finger-like villus and intestinal glands
  3. Ileum- Peyers patches, shorter villus, and intestinal glands

GI Exam 1 (13 decks)

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