Esophagus And Stomach Histology

Question 1

What are the 4 layers of the GI tract?

Answer 1

From external -> internal

1) mucosa
2) Submucosa
3) muscularis externa
4) Serosa

Question 2

Details about the mucosa layer

Answer 2

Has three sub-layers (most inner -> most outer)
1) ectoderm derived epithelial tissue

2) lamina propria: loose CT and scattered smooth muscle with blood vessels/lymph vessels and small secretory glands
3) muscularis mucosae: thin layer of smooth muscle that provides localized tone and movement of the mucosa

Question 3

Details about the Submucosa

Answer 3

Is a layer of dense irregular CT with larger blood and lymph vessels

• possess the submucosal “Meissener” plexus*
• intrinsic nerve fibers and cell bodies with extrinsic nerve fibers
• functions = provides motor control over muscularis mucosae, regulates secretory cells and glands of mucosa and relays sensory feedback to myenteric “Auerbach” plexus

Question 4

What layer of the GI tract is the Gut-associated lymphoid tissue (GALT) located?

Answer 4

Submucosa layer

Question 5

Details of the Muscularis externa layer

Answer 5

Is a thick layer of both skeletal and smooth muscles arranged in two sub layers that provides the muscular contractions of peristalsis and segmentation that moves and churns chyme

Possess 3 sub layers:
1) internal sublayer: muscle cells/fibers that are circumferential

2) Myenteric “Auerbach” plexus
- is a collection of intrinsic and extrinsic neurons and nerve fibers
- has 3 functions: provides motor control to muscularis externa, regulates secretory cells and glands of mucosa, and receives input from CNS and ENS to modulate activity

3) external sublayer: muscle cells/fibers that are longitudinal

Question 6

Details about the serosa layer

Serosa membrane/adventitia

Answer 6

Serous membrane that lines the entire GI tract except for the esophagus

Has two layers:
1) loose CT: contains blood/lymph vessels and nerves just external to the muscularis externa

2) mesothelium: mesoderm-derived layer of simple squamous epithelium adhering to underlying CT

Question 7

Difference between adventitia and peritoneum

Answer 7

Both are subsets of the serosa membrane layer in the GI tract

Adventitia = organs not suspended within the body cavity. Does not have a mesothelium layer and instead only has a thick loose CT layer

Peritoneum = lining of the peritoneal cavity and is continuous with the mesenteries that secures the visceral organs to the body wall.

Question 8

What is fusion fascia?

Answer 8

Any region where two AP posing peritoneal serosa or mesenteries are in close contact and fuse together
- they lose serous properties in that region but apples more anchoring ANS support

fusion fascia of Toldt = ascending and descending mesocolon fusion fascia. One of the most clinically importaint ones

Question 9

Details about the enteric nervous system (ENS)

Answer 9

Intrinsic plexus of neurons that reside within the walls of the digestive tract that monitor and respond to local stimuli and modulate regional glandular/muscular activity

Acts independently for the most part, but also takes input from the AND (both parasympathetic and sympathetic)

Question 10

Circular vs longitudinal fibers with actions

Answer 10

Circular = peristalsis and movement of the bolus

Longitudinal fibers = churn and produce chyme/mix the bolus

Question 11

Difference between anatomical and physiological sphincters

Answer 11

Anatomical = is still present at death

• will still be constricted and/or will be obvious it is was there
• example = pyloric sphincter

Physiological = is not still present at death

• will not be constricted and/or will not be obvious it is there
• example LES And UES

Question 12

How does the muscles in the esophagus change as it travels towards the stomach?

Answer 12

Near the mouth/pharynx = all skeletal muscle

Near the stomach = all smooth muscle

transitions from skeletal -> smooth muscle as it moves down

Question 13

GERD

Answer 13

Weakening of the LES which leads to chronic reflux esophagitis (heart burn)

• leads to corrosion of the mucosal lining of the distal esophagus
• *is highly associated with asthma

Chronically, will lead to metaplasia of the esophageal mucosa and progress into Barrett esophagus -> then dysplasia
- can also lead to adenocarcinomas of the esophagus

can be caused due to direct muscle issue or a nervous issue

Question 14

Barretts esophagus

Answer 14

Due to chronic GERD

Replaces stratified squamous epithelial tissue (esophagus tissue) with simple columnar tissues (gastric tissues)

Question 15

How does the muscularis mucosa layer change in the stomach from the esophagus

Answer 15

Stomach = 3 layers of muscles

• oblique
• circular
• longitudinal

Esophagus = 2 layers of muscles

• circular
• longitudinal

Question 16

What determines the absence or presence of the gastric rugae?

Answer 16

The direct degree of gastric distention (how full is the stomach?)

Also the indirect elasticity and compliance of the Submucosa.
- NOT muscularis externa

Question 17

What cells are seen in each region of a standard gastric gland

Answer 17

1) Gastric pit (most superficial)
- contains surface mucous cells
- secretes alkaline fluid with mucin to protect the stomach from gastric acid

2) neck
- contains mucous neck cells
- secretes acidic fluids with mucin to better digest food

3) neck (continue)
- contains parietal cells
- secrete intrinsic factors and hydrochloride acid to better digest food and destroy pathogens

4) fundus
- contains G-cells (enteroendocrine cells) which secrete gastrin into the blood
- also contains chief cells which secrete pepsinogen and gastric lipase to help metabolize proteins and lipids

Question 18

Pepsinogen vs pepsin

Answer 18

Pepsinogen = inactive form

• found in fundus of the gastric glands
• has no effect

Pepsin = active form

• found in lumen and gastric pit of the gastric glands
• cleaves proteins once activated by acids

Question 19

How to differentiate pyloric glands from cardiac glands?

Answer 19

You have to know the region of the stomach they originated from
- they look very similar histologically

Question 20

What epithelial cells are never seen in pyloric or cardiac stomach glands?

Answer 20

Parietal and chief cells

Question 21

What is the direct action steps of a parietal cell?

Answer 21

1) water is hydrolyzed into hydrogen ions (H+) and hydroxide ions (OH-)
2) H+ is pumped into the lumen of the gastric gland via H+/K+ pumps
3) OH- bonds with CO2 -> bicarbonate (HCO3-)
4) bicarbonate is transferred out of the cell and at the same time Cl- is transferee into the lumen oft he gastric gland via secondary active transport
5) H+ combines with Cl- -> HCL

Question 22

What is the functional role of intrinsic factor?

Answer 22

Is secreted via parietal cells and functions to Facilities absorption of vitamin B12 within the small intestines

if it doesnt work or insufficient amounts are produced = pernicious anemia

Question 23

What are the products of chief cells?

Answer 23

Pepsinogen and gastric lipase

Question 24

Gastric ulcers

Answer 24

Painful erosive lesions of the mucosa which can extend into deeper layers.
- if left untreated that can perforate the wall fo the organ

Common causes:

• overproduction of HCL or pepsin
• lowered production of mucus or bicarbonate
• prolonged exposure to NSAIDs
• bacterial infections (especially helicobacter pylori)

Question 25

Carcinoids

Answer 25

Tumors that arise from enteroendocrine cells
- over produces serotonin which causes mass increase in gut motility and mucosal vasoconstriction and necrotic tissue damage to the stomach

Question 26

Leiomyomas

Answer 26

Benign tumors of smooth muscle cells that are the msot common tumors in the stomach and small intestine
- 50% of >50 years old population has muscularis leiomyomas