Small Intestine Histology

Question 1

4 Main Layers of S.I

Answer 1

MUCOSA
Inner most layer
Contains epithelium, lamina propria + muscularis mucosae

SUBMUCOSA
Connective tissue layer
Contains blood vessels, lymphatics + submucosal plexus

MUSCULARIS EXTERNA
2 smooth muscle layers
Outer longitudinal layer + inner circular layer
Mesenteric plexus between both layers

ADVENTITIA
Outermost layer
Comprised of loosely arranged fibroblasts + collagen
Majority = covered by mesothelium (called ‘serosa’)

Question 2

Modifications to aid absorption

Answer 2

Mucosa + submucosa form large fold (plicae)
Arranged in circular fashion in lumen (plicae circulares)
Contain microvilli to INCREASE SURFACE AREA and INCREASE ABSORPTION

Question 3

Types of cells in Epithelium

Answer 3

Enterocytes 
Goblet Cells 
Paneth Cells 
Peyer's Patch
Crypts of Leiberkhuns

Question 4

Enterocytes?

Answer 4

Tall columnar cells (absorptive function)

Contain Brush Border Enzymes on surface (digestive function)

Question 5

Goblet cells?

Answer 5

Exocrine glad secreting mucin

Question 6

Crypts of Leiberkhuns?

Answer 6

Glands found in epithelial lining
Contain numerous cells:
Stem cells = replenish cells lost due to absorption
Enteroendocrine cells = synthesise + secrete hormones

Question 7

Paneth Cells

Answer 7

Protect from pathogens

Secrete protective agents (defensins + lysosomes)

Question 8

Peyer’s Patches

Answer 8

ONLY FOUND IN ILEUM 
Contain Mucosal-Associated Lymphatic Tissue (MALT)
Have white blood cells + lymphocytes 
Produce antibodies 
Protect SI from infection

Question 9

Enteroendocrine cells? (+ where found)

Answer 9

Located in CRYPTS OF LIEBERKUHN 
Secrete hormones in response to various stimuli 
4 main classes of enteroendocrine cells:
I Cells
S Cells
K Cells
Enterochromaffin Cells

Question 10

I cells

Answer 10

Secrete Cholecystokinin (CCK)
Stimulated by presence of fat in SI
CCK = stimulates contraction of gallbladder (pushing bile into cystic duct) +
Stimulates release of pancreatic enzymes

Question 11

S cells

Answer 11

Secrete secretin (in response to low pH of chyme)
Induces HCO3- secretion from pancreas
Inhibits gastric emptying

Question 12

K cells

Answer 12

Secrete gastric-inhibitory peptide (GIP) - ((has a misleading name))
In response to chyme entering SI
Stimulates insulin release
Ready to put newly digested cars into storage

Question 13

Enterochromaffin cells

Answer 13

Mechanically stimulated by presence of chyme in SI
Release serotonin (acts on enteric nervous system)
Activates Cystic Fibrosis Transmembrane Regulators (CFTR) - ion channels

Question 14

Lysozymes? Where?

Answer 14

Destroy peptidoglycan bonds in bacteria membrane (the influx of water ruptures the bacteria)
PANETH CELLS

Question 15

Defensins? Where?

Answer 15

Protein that produces ion channels in pathogen cell membranes to increase permeability
PANETH CELLS

Question 16

TNF-alpha? Where?

Answer 16

Produces inflammation in response to pathogens

PANETH CELLS