Lecture 30: microstructure GI

Question 1

Four layers of GI tract

Answer 1

1. mucosa (innermost lining)
epithelial lining cells
lamina propria
muscularis mucosae
2. Submucosa (supports the mucosa)
loose tissue; contains blood vessels, nerves, lymphatics
3. Muscularis propria (muscle proper)
inner circular muscle, outer longitudinal muscle
4. Serosa (thin outer lining)

Question 2

What are the functions of the two layers of muscularis propria

Answer 2

inner circular muscle –> Contracts food

outer longitudinal muscle –> propels muscle

Question 3

myenteric plexus vs. submucosal plexus

Answer 3

Nerves are clustered in two different areas of the tract, differentiated by function.
Myenteric (also called auerbach’s plexus) between two muscle proper layers. Well represented throughout the gut, muscles needed in all of alimentary canal.
Submucosal/Meissners above submucosa, mostly seen in small intestine in large intestine, more functional in absorption/digestion.

Question 4

Enteric Nervous System

Answer 4

Own nervous system of gut. Nerves arise in gut, communicate with other nerves. Can work without communication from CNS, seen paraplegic patients with spinal cord injuries.

Question 5

parasympathetic vs. sympathetic innervation of the gut

Answer 5

sympathetic go through pre-vertebral ganglion, while the parasympathetics communicate directly through one nerve system.

Question 6

Key features histo of exophagus

Answer 6

stratified squamous epithelium (non-keratinized)
muscularis propria varies –> upper 1/3 skeletal, middle 1/3 mixed, lower 1/3 smooth
No serosa here.

Question 7

Squamo-columnar junction

Answer 7

Between stomach and esophagus, the squamous epithelium abruptly transitions to the columnar epithelia of the stomach.
But only the epithelia transitions, the lamina propria and rest of mucosa stays the same.

Question 8

key structural features of the stomach

Answer 8

Epithelium:
Parietal cells –> secrete acid; intrinsic factor
chief cells –> secrete pepsinogen
G cells –> secrete hormone gastrine
Mucous cells –> protect, lubricate mucosa
Muscularis propria –> 3 layers, additional oblique layer

Question 9

Part of stomach that is reservoir

Answer 9

Fundus and body, also where acid is added

Question 10

Part of stomach that does mechanical digestion

Answer 10

Mixing and Grinding of food happens in antrum

Question 11

Three types of glands in stomach

Answer 11

Fundic –> in fundus and body of stomach
Pyloric –> antrum and pyloric
Cardiac –> proximal stomach

Question 12

What are in fundic glands

Answer 12

long branched glands with mucous, parietal, chief, and endocrine glands

Question 13

Contents of Pyloric glands

Answer 13

Mucous and endocrine glands, long branched glands

Question 14

Contents of cardiac glands

Answer 14

short branched tubular glands, mostly mucuous glands

Question 15

Gastric pits

Answer 15

The pit is leading to the gland, seen in the folds of the stomach. Lined with mucous producing cells to protect the stomach from acid produced by stomach.

Question 16

Foveolar cells

Answer 16

Located at surface line the gastric pits, mucous cells with faint, pink cytoplasm; rectangular shape

Question 17

Mucous neck cells

Answer 17

located at base of gastric pits; pale mucous vacuoles

Question 18

parietal cells

Answer 18

located lower in fundic gland; eosinophilic cytoplasm with central nucleus (“fried egg” appearance); lots of mitochondria lead to v. pink cytoplasm. PM lots of invaginations

Question 19

Chief cells

Answer 19

Located near parietal cells, pyramidal cells with more basophliic cytoplasm (lots of RER), have granules

Question 20

Endocrine cells

Answer 20

Seen with special IHC stains, eosinophilic granules

Question 21

Stem Cells

Answer 21

located in mucous neck region

Question 22

Small Intestine, key structural features

Answer 22

Highly adapted for maximal srface area
very long organ (15-18 feet)
folds of mucosa/submucosa (not muscularis propria)
mucosa has finger-like projections (villi)
epithelial cells have microvilli

Question 23

Villi vs. Crypts

Answer 23

Villi are extensions up of tissue, crypts are folds into tissue. both are present in small intestine. Usually 4:1 height ratio of villi:crypt

Question 24

Villi features

Answer 24

Finger like extensions into lumen of small intestine. Site of absorption. The lamina propria is rich in blood vessels, lymphatics, nerves.
Central core of lamina propria has lacteal (lymphatic channel), tendons of muscularis mucosae (give villi structural integrity). Things can be absorbed directly into veins or lymphatics.

Question 25

Crypt

Answer 25

Are invaginations that are continuous with villi in small intestine.
Site of secretion of fluids and electrolytes.
Paneth cells found at base –> make lots of defensive substances against dangerous substances in lumen, especially the nearby stem cells.
Stem cells found in crypt, cells born here and mature as they migrate up the crypt.

Question 26

Can villi move?

Answer 26

Yes have muscles (muscularis mucosae) which also give it structural integrity.

Question 27

what makes up the brush border

Answer 27

Microvilli membrane, found on columnar cells of the small intestine. have actin filaments inside. Have enzymes critical for digestion of certain food (lactose).

Question 28

enterocyte

Answer 28

Other word for columnar absorptive cells of small intestine.
Have microvilli.
Tall cells with basal membrane.
Junctional complexes –> attach cells
intercellular clefts –> spaces between enterocytes, at base of cells.

Question 29

Chylomicrons

Answer 29

Encapsulate fat, go into lymphatic channels.

Question 30

Panneth cells in histo

Answer 30

v. obvious pink granules

Question 31

duodenum functions

Answer 31

neutralize acidic chyme that exits the stomach through secretions of the brunners glands, which secrete alkaline mucus from submucosal cells.
Also the site of absorption of most minerals

Question 32

Jejunum function

Answer 32

absorption of most nutrients

Question 33

ileum function

Answer 33

absorption of many nutrients.
absorb B12 and bile proteins.
Peyers patches (lymphoid aggregates) seen here

Question 34

Why does colon need to be strong?

Answer 34

Bc it has to move solidified stool. Tenia coli are the longitudinal muscles seen in the colon, are now arranged in rings. instead of longitudinal to increase strength.

Question 35

Function of colon

Answer 35

Absorb water, solidify the stool

Question 36

Histo structures of colon

Answer 36

No villi, only crypts in mucosa. Mostly goblet cells. Muscularis propria has tenia colia (3 layers) of longitudinal muscle.

Question 37

Cell types of colon

Answer 37

Mostly goblet cells 
Columnar absorptive cells
rare enteroendorcine cells
rare paneth cells (even though there are lots of bacteria in the colon)
Stem Cells seen in base of crypt

Question 38

anal canal junction

Answer 38

squamo-columnar junction. Anal canal has squamous stratified

rectum has columnar

Question 39

Anal Canal functions

Answer 39

Controls continence

Question 40

Key structural feature of anal canal

Answer 40

mucosa has stratified squamous epithelium

Question 41

two parts of anal sphincter

Answer 41

external anal sphincter –> skeletal muscle, coluntary

internal anal sphincter –> smooth muscle, continuous with colonic muscle, involuntary.

Question 42

Villus vs. Crypt cells of small intestine

Answer 42

Villus cells are columnar, have microvilli/terminal web, Golgi/ER
Crypt Cells are cuboidal, no microvilli/terminal web/golgi-ER