Unit VI- GI tract I

Question 1

4 principal layers of the digestive tract

Answer 1

1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa or adventitia

Question 2

Mucosa

Answer 2

• the mucosa has three subdivisions: lining epithelium, lamina propria, and muscularis muscosae
• the three principal functions are protection, absorption, and secretion
• the epithelium changes abruptly at junctions or sphincters between the major organs
• the lamina propria is a loose connective tissue resembling the stroma of lymphoid organs that contains blood and lymphatic vessels as well as the lymphatic tissue and wandering connective tissue cells such as plasma cells and eosinophils
• the muscularis mucosae is a thin layer of smooth muscle that produces movement of the mucosa creating ridges and valleys that facilitate absorption and secretion

Question 3

Submucosa

Answer 3

• it consists of dense irregular connective tissue containing blood vessels, lymphatic vessels and a nerve plexus
• in the duodenum and esophagus, it has glands
• the submucosal (Meissner’s) plexus is found at its periphery

Question 4

Muscularis externa

Answer 4

• composed of two relatively thick layers of smooth muscle in most of the GI tract: the inner circular layer and the outer longitudinal layer
• the myenteric (Auerbach’s) plexus is located between these two muscle layers
• contraction mixes and propels intestinal contents

Question 5

Serosa or Adventitia

Answer 5

• it is a serosa when a simple squamous epithelium (the mesothelium) is present or an adventitia when the part of the digestive tract is fixed directly to the abdominal or pelvic wall
• it contains connective tissue, blood and lymphatic vessels and nerves

Question 6

Tongue

Answer 6

• the inside of the tongue is made of skeletal muscle arranged in bundles that run in three planes
• mucosal and serous glands as well as adipose tissue can be found between the muscle bundles
• the dorsal surface of the tongue has an epithelium with elevations called the lingual papillae

Question 7

Papillae

Answer 7

• there are four types of papillae: filiform, fungiform, foliate, and circumvallate
• filiform papillae lack taste buds and are the only type that have a stratified squamous keratinized epithelium
• the other three types have stratified squamous epithelium with taste buds on their dorsal (fungiform) or lateral (foliate and circumvallate) surfaces
• taste buds are onion shaped sensory structures containing 50-100 cells

Question 8

Organization of esophagus

Answer 8

• mucosa consists of the stratified squamous nonkeratinizing epithelum, lamina propria, muscularis mucosae and the esophageal cardiac glands. The esophageal cardiac glands secrete a neutral mucus and are found at both ends of the 10 inch long esophagus, but are more prominent near the stomach
• submucosa is made of CT and the esophageal glands proper. These esophageal glands proper secrete a viscous, slightly acidic mucus as well that facilitates food transport and protects the epithelium
• the muscularis externa varies along the length of the esophagus. The upper third contains skeletal muscle. The middle third has both skeletal and smooth muscle
• the esophagus has an adventitia above the diaphragm and a serosa below

Question 9

Spinchters of esophagus

Answer 9

• the upper esophageal sphincter (UES) is made of circular skeletal muscle fibers under voluntary and reflexive control
• the lower esophageal sphincter (LES) is a physiological sphincter of thickened circular smooth muscle fibers that is not well defined anatomically

Question 10

Functions of the stomach

Answer 10

• acts as a mixed exocrine and endocrine organ
• it continues the digestion of carbohydrates started in the oral cavity
• adds an acidic liquid to ingested food
• forms chyme with enzyme and muscular activity
• pepsin initiates protein digestion
• gastric lipase helps digest triglycerides

Question 11

Gross level of the stomach

Answer 11

• cardia, fundus, body, pylorus
• rugae are temporary longitudinal folds of the mucosa and submucosa that disappear when the stomach is full
• the fundus and body are histologically identical so only three histological regions are recognized: cardia, fundus/body, and pylorus

Question 12

Mucosa of stomach

Answer 12

-comped of lining epithelium, gastric pits, mucosal glands, laminal propria, and muscularis mucosae

Question 13

Lining epithelium

Answer 13

-composed of simple columnar, surface mucous cells (the secreting sheet)

Question 14

Gastric pits

Answer 14

-permanent invaginations into the lamina propria that serve as ducts for the mucosal glands

Question 15

Mucosal glands

Answer 15

• branched, tubular glands that occur in three varieties (cardiac, gastric, or fundic, and pyloric)
• each gland has an isthmus, neck and base
• one to four open into the base of each pit

Question 16

Cardiac glands

Answer 16

• have short pits and short coiled glands
• most of these glands produce mucus
• a few lysozyme and HCl producing cells are present

Question 17

Gastric or fundric glands

Answer 17

• have medium pits and long straight glands
• there are four major cell types in these glands: mucous neck cells, parietal (oxyntic) cells, chief cells, and enteroendocrine cells

Question 18

Pyloric glands

Answer 18

• have very long pits and short slightly coiled glands
• the glands have mostly mucous cells with a few parietal cells
• a moderate number of histologically indistinguishable enteroendocrine cells are also present

Question 19

Lamina propria of stomach

Answer 19

-well vascularized and cellular

Question 20

Muscularis mucosa of stomach

Answer 20

-has two layers and sends strands up between glands

Question 21

Submusa of stomach

Answer 21

-no permanent folds that will be found in the small intestine

Question 22

Muscularis externa of stomach

Answer 22

• has an extra inner layer of oblique smooth muscle in addition to the usual circular and longitinal layer
• there is a serosa

Question 23

Surface mucous cells of stomach

Answer 23

• secrete a bicarbonate rich alkaline mucus that protects the stomach’s surface from the acidic gastric fluid
• it is an insoluble, cloudy, or visible mucus

Question 24

Mucous neck cells

Answer 24

• occur in small groups or singly between parietal cells in the neck of gastric glands
• they secrete a soluble mucus

Question 25

Parietal (oxyntic) cells

Answer 25

• secrete HCl and intrinsic factor
• they are large eosinophilic cells that are found in the middle and upper part of the gastric gland
• they can be binucleate and they have an intracellular canaliculus for HCl secretion
• intrinsic factor is a glycoprotein required for vitamen B12 absorption in the ileum

Question 26

Chief cells

Answer 26

• synthesize pepsinogens and gastric lipases

- they are typical serous cells of columnar shape and found in the basal half of gastric glands

Question 27

Enteroendocrine cells

Answer 27

• produce gastrin, somatostatin, and ghrelin in the stomach

- they occur singly near the base of the gastric glands and their products act in both paracrine and endocrine signaling

Question 28

Stem cells of stomach

Answer 28

• found in the isthmus and neck of mucosal glands and move upward to replace surface mucous cells that turn over every week
• they also move downward to replace glandular cells that turn over more slowly (every 1-2 months)