Upper GI Tract Str and Fxn

Question 1

Overall the structure of the GI tract is conserved – what are the 4 tunics?

Answer 1

1. Mucosa
2. Submucosa
3. Muscularis externa
4. Adventitia/Serosa

Question 2

What are three distinct layers of the mucosa?

Answer 2

1. Epithelium
2. Lamina propria
3. Muscularis mucosae

Question 3

What type of epithelium is present in the esophagus and anal canal versus the stomach, small and large intestine?

Answer 3

Stratified squamous non-keratinizing epithelium lines the esophagus and anal canal and serves to protect against abrasion

Simple columnar epithelium lines the stomach, small intestine, and large intestine and functions to secrete, absorb and protect

Question 4

What is the function of the submucosa?

Answer 4

Layer of loose collagenous and adipose supporting tissue
Contains blood vessels and lymphatics
Innervated by submucosal (Meissner’s) plexus

Question 5

What is the function of the muscular external?

Answer 5

It mixes luminal contents and propels contents along GI tract

Question 6

What does the muscularis externa consist of?

Answer 6

Inner circular layer and outer longitudinal layer of smooth muscle (also skeletal muscle in the anal sphincter and esophagus)

Innervated by the myenteric (Auerbach’s) plexus between the muscle layers

Question 7

What functions to protect and is the outermost covering of the GI tract?

Answer 7

The adventitia/serosa

Question 8

What is the differences between adventitia and serosa?

Answer 8

Adventitia is loose connective tissue layer OUTSIDE the peritoneal cavity

Serosa is simple squamous epithelium WITHIN the peritoneal cavity

Question 9

What is parasympathetic vs sympathetic function of the enteric nervous system?

Answer 9

Parasympathetic stimulates secretion and peristalsis

Sympathetic represses peristalsis and activates activity of sphincters

Question 10

Which cells secreted hormones?

Answer 10

Enteroendocrine cells

Question 11

What are the different types of mucosa throughout the GI tract?

Answer 11

1. Protective: stratified squamous epithelium mainly found in the upper GI and anus
2. Secretory: found in the stomach, contains an abundance of tubular glands
3. Absorptive: mucosa is folded into villi to maximize surface area; throughout the small intestine
4. Absorptive/protective: lines the large intestine; produces mucin to help fecal movement and absorb water

Question 12

What are the 2 clusters of mucosal glands in the esophagus called that help to propel food by secreting mucus?

Answer 12

Esophageal cardiac glands – these are located in the mucosa layer

Question 13

What are the two physiological sphyincters?

Answer 13

Pharyngoesophageal sphincter – prevents reflux from esophagus into the pharynx

Gastroesophageal sphincter prevents reflux from the stomach into the esophagus

Question 14

What are the 4 anatomical regions of the stomach?

Answer 14

Cardia–small area at gastroesophageal junction
Fundus–secretes acid and enzymes
Body –secretes acid and enzymes
Pyloris–regulates release of chyme into duodenum (pyloric sphincter), secretes gastrin

Question 15

Which cells secrete histamine in response to the vagus nerve to increase acid secretion?

Answer 15

Enterochromaffin-type cells

Question 16

What are the three regions of a gastric gland?

Answer 16

Isthmus, neck and base

Question 17

What are the 6 different types of cell types that can make up gastric glands?

Answer 17

1. Surface mucous/lining cells (gastric pit)
2. Parietal cells (isthmus, neck and base)
3. Neck mucous cells (neck and base)
4. Chief cells (base)
5. Enteroendocrine cells (base)
6. Stem cells (neck)

Question 18

How does the mucous in surface lining cells differ from mucous neck cells?

Answer 18

Mucous in surface lining cells is thick and dense while the mucous secreted by mucous neck cells is soluble

Surface lining cell mucous adheres to the mucosa and protects against acid digestion while the soluble mucous lubricates the stomach contents to aid in digestion

Question 19

What are enteroendocrine cells?

Answer 19

They secrete hormone-like substances into the lamina propria to influence the activity of nearby (paracrine) or distant (endocrine) cells.

Hormones secreted: Gastrin, serotonin, enteroglucagon, somatostatin, histamine

Question 20

How are parietal cells identified?

Answer 20

Cytoplasm stains heavily with eosin

Question 21

What do parietal cells have a lot of?

Answer 21

Mitochondria that provide the energy for HCl secretion

Question 22

Where are chief cells located and what do they do?

Answer 22

Columnar cells at the bottom of gastric glands
Secretory granules contain proenzymes–pepsinogen, rennin, gastric lipase
Granule release controlled by hormonal and neural action (binding of secretin and vagus nerve stimulation)

Question 23

Where are stem cells most commonly found?

Answer 23

In the neck of the gastric gland

Question 24

How often are gastric mucosa cells regenerated?

Answer 24

Every 3 days

Question 25

Which two parts of the stomach are histologically indistinguishable?

Answer 25

Fundus and body – straight tubular glands

Question 26

What are the three phases of a stomach’s response to a meal?

Answer 26

Cephalic phase: brain anticipates (30% total gastric acid)

Gastric phase: food enters stomach, increase in G cell activity (60% total gastric acid)

Intestinal phase: chyme released into duodenum, enterogastric reflex, CCK and secretin suppress gastric activity (10% total gastric acid)

Question 27

Where are “wandering cells” located in the stomach? Give some examples.

Answer 27

Submucosa

Lymphocytes, eosinophils, mast cells, and plasma cells. Also adipose tissue.

Question 28

How many gastric glands open up into each gastric pit?

Answer 28

1 - 7

Question 29

What does the mucosa in the pyloris and cardiac regions of the stomach look like?

Answer 29

Pyloris: glands are branched and mucous neck cells predominate

Cardiac: shallower gastric pits and glands are highly coiled, abundance of enteroendocrine cells