Histology of Small & Large Intestines

Question 1

________, _______, and _____ comprise the small intestine and are the principal sites fro digestion of food and absorption of digestion products

Answer 1

duodenum, jejunum, and ileum comprise the small intestine and are the principal sites fro digestion of food and absorption of digestion products

Question 2

• transverse folds within the SI that have a submucosal core
• cannot lay flat if distended
• visible in jejunum, less so in ileum

Answer 2

plicae circulares

Question 3

• mucosal folds that project into lumen and cover surface of SI
• covered w/ simple columnar epithelium of enterocytes and goblet cells
• core of loose CT w/ microvasculature and a lacteal

Answer 3

intestinal villi

Question 4

What is the function of villi and microvilli within the SI?

Answer 4

• enterocytes prod enzymes for digestion/absorption
• goblet cells provide mucus coating to shield from abrasion and bacterial invasion
• villi are covered w/ microvilli to increase absorptive surface area

Question 5

Describe the characteristics of the mucosa, submucosa, muscularis, and serosa within the small intestines:

Answer 5

• mucosa: simple columnar epithelium w/ tubular intestinal glands, lamina propria and muscularis mucosae
• submucosa: dense irregular CT; neurovasculature, lymphatics, and glands may be present
• muscularis: inner circular and outer longitudinal layers
• serosa: loose CT covered by visceral peritoneum

Question 6

Describe the innervation of the intestines:

Answer 6

• motility controlled by ANS
• enteric (intrinsic) NS consists of submucosal plexus of Meissner and myenteric plexus of Auerbach:
• sympathetic visceral sensory fibers
• parasympathetic (terminal) ganglia
• pregang and postgang parasympathetics
• regulated by ‘extrinsics’ > pregang parasympathetics (vagus and pelvic nerves) and postgang sympathetics

Question 7

What is the structure, location, and cell types a/w intestinal glands?

Answer 7

• structure: simple tubular glands lined by simple columnar epithelium
• location: continuous w/ simple columnar that covers intestinal villi; open onto the luminal surface of the intestine at the base of the villi
• cell types:
  1. Paneth cells
  2. M (microfold) cells
  3. intestinal stem cells
  4. enteroendocrine cells

Question 8

• pyramidal-shaped cells at the base of intestinal glands
• large, eosinophilic secretory granules in their apical cytoplasm
• functions in innate immunity by secreting antimicrobial substances (lysozyme, α-defensins)
• regulate nml bacterial flora via antibacterial action and phagocytosis

Answer 8

Paneth cells

Question 9

• cells that reside in a niche at crypt base, near Paneth cells
• repopulate epithelial lining
• daughter cells move out of the crypts > differentiate into goblet cells, enterocytes, and enteroendocrine cells

Answer 9

intestinal stem cells (ISCs)

Question 10

• epithelial cells specialized for transepithelial transport of particles and microorganism (antigen-transporting cells)
• located in the ileal mucosa, overlying Peyer patches
• pocket formed by deeply invaginated membrane and containing lymphocytes and macrophages

Answer 10

M (microfold) cells

Question 11

What is the specialized function of M cells?

Answer 11

• M cells’ apical surface expresses receptors that bind specific macromolecules and gram-negative bacteria (e.g. E. coli)
• they internalize these particles/microorganisms and transfer them to immune cells
• function as highly specialized antigen-transporting cells

Question 12

• scattered epithelial cells in the gastric mucosa, named w/ the initial letter of their main hormone prod
• these hormones are of major importance for digestive function
• most of these cells are APUD cells, process amines: amine precursor uptake and decarboxylation activity
• all cells are generally considered to be a part of the diffuse neuroendocrine system (DNES)

Answer 12

enteroendocrine cells

Question 13

What is the function, types, and hormonal effects of the enteroendocrine cells?

Answer 13

• function: release prod that exert paracrine or endocrine effects
• types:
• “closed” types: cellular apex is covered by neighboring epithelial cells, not exposed to GI lumen
• “open” type: apical end of cell contacts the lumen and has chemoreceptors that sample luminal contents
• hormonal effects:
• regulation of peristalsis and motility
• secretion of digestive enzymes, water, and electrolytes
• sense of being satiated after eating

Question 14

Duodenum

• mucosa:
• submucosa:

Answer 14

Duodenum

• mucosa: simple columnar epithelia w/ scattered goblet cells
• submucosa: duodenal glands (tubuloacinar mucous glands that prod alkaline secretion), neutralizes acidic chyme

Question 15

Jejunum

• mucosa:
• submucosa:

Answer 15

Jejunum

• mucosa:

simple columnar epithelia w/ scattered goblet cells;

long finger-like villi, villus core contains well-developed lacteal;

tubular intestinal glands;

lymphoid nodules/follicles in lamina propria

• submucosa: no submucosal glands

Question 16

Ileum

• mucosa:
• submucosa:

Answer 16

Ileum

• mucosa:

simple columnar epithelia w/ scattered goblet cells

villi typically shorter than jejunum

Peyer’s patches: lymphoid nodules (MALT)

• submucosa: no submucosal glands

Question 17

Identify where in the body this sample was obtained and identify the labeled structures:

Answer 17

duodenum

V, villi;

C, crypts,

B/DG, duodenal glands;

M,mucosa;

MM, muscularis mucosae;

SM, submucosa;

CM, circular layer;

LM, longitudinal layer;

D, excretory ducts of Brunner’s glands

Question 18

Identify where in the body the following sample was obtained:

Answer 18

jejunum

Question 19

Identify where in the body the following sample was obtained:

Answer 19

ileum

Question 20

Describe the histological structure of the gastroduodenal junction (pyloris and duodenum):

Answer 20

• pyloris: thick wall due to presence of pyloric sphincter muscle; pyloric glands at the base of each gastric pit
• duodenum: abundant duodenal glands in submucosa, DEEP to the muscularis mucosae; secretory mucosa w/ villi

Question 21

What is the function and histological structure of the LI?

Answer 21

• function: absorbs water, sodium, vitamins, minerals; uptake of sedatives, anesthetics, and steroids
• structure: openings of tubular intestinal glands are hallmark of mucosa; contains goblet cells but NO intestinal villi

Question 22

Describe the mucosal layers of the LI:

Answer 22

• mucosa:
• glandular, simple columnar epithelium: colonocytes, goblet cells, stem cells, and enteroendocrine cells
• lamine propria and muscularis mucosae are present; GALT is extensive and may penetrate submucosa
• submucosa: dense irregular CT, vascularized
• muscularis: inner layer is typical; outer longitudinal layer organized into taeniae coli, will form haustra of LI
• serosa: covers intraperitoneal portions of colon

Question 23

Identify the part of the GI in this image:

Answer 23

colon

• glands consisting of simple columnar epithelium w/ numerous goblet cells
• MM: muscularis mucosae

Question 24

Identify the part of the GI in this image:

Answer 24

colon

Question 25

Identify the part of the GI in this image:

Answer 25

colon

Question 26

Identify the part of the GI in this image:

Answer 26

colon

Question 27

- aganglionosis in the distal colon - **incidence**: 1:5000 neonates - **etiology**: mutations of the *RET* gene (required for migration/differentiation of NCC), failure of NCC development in both plexuses of a bowel segment - **types**: **short-segment disease** (85% of cases, confined to rectosigmoid colon); **long-segment disease** (10%, extends past rectosigmoid region \> splenic flexure); **total colonic aganglionosis** (5%, affects entire colon) - **presentation**: constipation, poor feeding, progressive abd distention - **dx**: delayed BM \<48 hours after birth, rectal biopsy, barium enema - **tx**: surgical removal of the affected colon segement, pull through of ganglionic colon segments

Answer 27

Hirschprung's disease

Question 28

Describe the histological structure and associated structures of the rectum:

Answer 28

- **rectum proper (upper part)**: typical mucosa w/ tubular intestinal glands, transverse rectal folds - **anal canal** **(lower part)**: * **anal columns**: mucosal folds * **anal sinuses**: depressions between columns * **anal glands**: extend into the submucosa and muscularis externa **circumanal glands**: large apocrine glands surrounding the anal orifice

Question 29

What are the anal zones?

Answer 29

- **colorectal zone**: simple columnar epithelium identical to the rectum (upper 1/3) - **anal transitional zone (ATZ)**: simple columnar epithelium \> stratified squamous epithelium of perianal skin (middle 1/3) - **squamous zone**: stratified squamous epithelium c/w perineal skin (lower 1/3) (at the anus, inner circular layer thickens to form internal anal sphincter)

Question 30

Identify the area of the GI system this sample was obtained and the label structures:

Answer 30

Question 31

Identify the area of the GI system this sample was obtained and the label structures:

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Question 32

Identify the area of the GI system this sample was obtained and the label structures:

Answer 32

Question 33

Identify the area of the GI system this sample was obtained and the label structures:

Answer 33

Question 34

Identify the area of the GI system this sample was obtained and the label structures:

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Question 35

Identify the area of the GI system this sample was obtained and the label structures:

Answer 35

Question 36

Identify the area of the GI system this sample was obtained and the label structures:

Answer 36

Question 37

Identify the area of the GI system this sample was obtained and the label structures:

Answer 37

Question 38

Identify the area of the GI system this sample was obtained and the label structures:

Answer 38

Question 39

Identify the area of the GI system this sample was obtained and the label structures:

Answer 39

Question 40

Answer 40

Question 41

Identify the area of the GI system this sample was obtained and the label structures:

Answer 41