GI Histology

Question 1

4 layers of GI tract

Answer 1

1. mucosa:
   epithelial layer; loose well vascularized CT called Lamina Propria (w/ lymphocytes, plasma cells, and mac); underlying SM called muscularis mucosae
2. submucosa:
   denser CT, larger bv, nerve plexuses, glands, lymphatic nodules. lymphoid cells
3. muscularis externa
   inner circular and outer longitudinal SM and nerve plex
   *peristalsis
4. serosa/adventitia: serosa: squamous epi cells separated from muscular layers by thin CT
   adventitia: esophagus above diaphragm where outer squamous layer is absent

Question 2

What is esophagus lined with?

Answer 2

non-cornified squamous epithelium
upper portion: skeletal muscle (vol)
midway: mix of skel/SM
lower 1/3: SM

mucous glands in mucosa and submucosa

Question 3

3 zones of stomach

Answer 3

cardia: mucus secreting glands around entry of esoph
fundus: body of stomach: secretes acid, peptic digestive prod/mucus.
Pyloris: secretes mucus, many endocrine cells that secrete gastrin

*outer muscularis externa has 3rd oblique layer of SM (lumenally to circular)

Question 4

Rugae or plicae mucosae

Answer 4

longitudinal folds, disappear upon distension

Question 5

Histologic folds of stomach

Answer 5

epithelial folds with spaces called “gastric pits”

Gastric glands at bottom of pits and into mucosa

Question 6

Stem cells of stomach, surface mucous cells, chief cells, glycocalyx

Answer 6

stem cells: upper neck region
surface mucous cells: w/ large vesicles full of stomach mucins and bicarb are discharged and act as protective layer (shelter epithelial cells from acid and abrasion from chyme)
Glycocalyx: Directly covering the short microvilli of
these surface cells is a more structured layer of cell surface glycoproteins, the glycocalyx

chief cells: protein secretors with apical granules and basal RER
—secrete pepsinogen (conv to pepsin in acid’s presence)

Question 7

Parietal cells

Answer 7

acid producing cells 
pump H+ ions using H/K -ATPase
-steep gradient so high energy cost
-lots of mitochondria.
-microvilli

-also secrete IF for B12 absorption

Question 8

What stimulates parietal cells to secrete acid?

Answer 8

gastrin and histamine

Question 9

Zollinger Ellison syndrom

Answer 9

excessive secretion of gastrin results in overproduction of HCl by parietal cells–> duodenal ulcers

Question 10

Enteroendocrine cells

Answer 10

in family: APUD cells
G cells: secrete gastrin, located in pylorus
A cells: secrete glucagon
EC cells: secrete serotonin
Dcells: somatostatin secreting

Question 11

VIP

Answer 11

vasoactive instestinal peptide

• increase peristaltic action of small and large int
• stimulates elim of water and ions by GI tract

Question 12

Small intestine: large surface area

Answer 12

plicae circulares: project into lumen, covered in villi. Microvilli on surface of enterocytes (epithelial cells). Glycocalyx over microvilli surface into which glycoproteins of plasma membrane extend

Goblet mucous cells are scattered between absorptive/digestive cells. Least abundant in duodenum

Question 13

Crypts of Lieberkuhn

Answer 13

intestingal gland (simple, tubular)
penetrate from base of villi deeper into mucosa.

Question 14

Paneth cells

Answer 14

contain large eosinophilic granules, containing antibacterial peptides called defensins + lysozyme and phospholipase

Question 15

Brunner’s glands

Answer 15

found only in the duodenum and release their contents into the crypts.

• secrete bicarb to neutralize acid arriving thru pyloric sphincter
• also secrete mucins

Question 16

M cells (specialized epi cells)

Answer 16

function as antigen-uptake cells,
and phagocytose luminal contents and present antigens to
underlying lymphocytes and macrophages

Question 17

Type of immunoglobulins secreted in gut?

Answer 17

IgA

Question 18

Duodenum, jejunum, ileum and brunner’s glands, goblet cells, lymphatic tissue, plicae circulares, villi

Answer 18

Duodenum
Brunners: present
goblet cells, lymphatic tiss, plicae circulares: +
number of villi: most numerous

Jejunum:
Brunner's: absent
goblet cells, lymphatic tiss: ++
plicae circulares: best developed
number of villi: decrease distally

ileum:
brunner's: absent 
goblet cells: +++
lymphatic tissue: ++++
Plicae: +
microvilli: less abundant

Question 19

Exocrine pancreas

Answer 19

secretes digestive enzymes
gland organized into acini (acinar cells)
apical portion full of secretory granules (zymogen granules)

trypsin, chymotrypsin, elastase,
carboxypeptidase, and triacylglycerol lipase (trpsinogen into trypsin by enterokinase, then trypsin activates all the others)

amylase and ribonuclease are secreted by panc in active form

Question 20

Centroacinar cells

Answer 20

found in the acini

beginning of duct systme

Question 21

duct cells

Answer 21

secrete water and bicarb (help Brunner’s glands neutralize acid)

secretion under control of secretin and CCK

Question 22

What does LI lack that SI has?

Answer 22

lacks plicae and villi

LI:
numerous straight tubular glands or crypts
-epithelial layer has two cell types, abundant mucous producing
cells and absorptive cells
-main func: recovery of water and salt

bands: called taeniae

internal anal sphincter: thickened circular layer
external anal sphincter: circular striated muscle

Question 23

Salivary glands

Answer 23

submandibular (paired)– mixed
sublingual– mucous
paired parotid glands– serous (watery w/ enz amylase, RNAse, DNAse; also trans IgA)