GI Tract 1

Question 1

What are the 4 principal layers of GI lining from inside to outside?

Answer 1

Mucosa
Submucosa
Muscularis externa
Serosa

Question 2

Describe the mucosa and it’s functions

Answer 2

3 subdivisions:

1. Lining epithelium
2. Lamina propria: loose CT with blood and lymphatic vessels, wandering plasma cells/eosinophils
3. Muscularis mucosae: thin layer of smooth muscle, produces movement that creates ridges/valleys for absorption and secretion
   - 3 funtions: protection, absorption, secretion

Question 3

Describe the submucosa and it’s function

Answer 3

• Consists of dense irregular CT with blood vessels, lymphatic vessels and Meissner’s nerve plexus (periphery)
• Has glands in the esophagus and duodenum

Question 4

Describe the muscularis externa and it’s function

Answer 4

• 2 thick layers of smooth muscle: inner circular layer and outer longitudinal layer
• Auerbach’s plexus in between layers
• Contraction mixes and propels intestinal contents

Question 5

Describe the serosa or adventitia and it’s function

Answer 5

• Serosa when simple squamous epithelium (mesothelium) is present
• Adventitia when fixed directly to the abdominal or pelvic wall
• Contains CT, blood/lymph vessels, nerves

Question 6

Describe the tongue

Answer 6

• Inside made of skeletal muscle (criss crossing bundles)
• Mucosal/serous glands and adipose tissue between muscle bundles
• Dorsal surface has epithelium with lingual papillae

Question 7

Describe the 4 types of papillae found on the tongue

Answer 7

• Filiform: lack taste buds, only type with stratified squamous keratinized epithelium
  Stratified squamous epithelium with taste buds:
  - Fungiform: taste buds on dorsal surface
  - Foliate: taste buds on lateral surface
  - Circumvallate: taste buds on lateral surface

Question 8

Describe the organization of the esophagus

Answer 8

• Mucosa: stratified squamous nonkeratinizing epithelium, lamina propria, muscularis mucosae, esophageal cardiac glands (secrete neutral mucus, found at both ends of esophagus but more are near stomach end)
• Submucosa: CT and esophageal glands proper –> secrete viscous, slightly acidic mucus that facilitates food transport/protects epithelium
• Muscularis externa: upper 3rd - skeletal muscle, middle 3rd mixed skeletal/smooth muscle, lower 3rd - smooth muscle
• Has adventitia about diaphragm and a serosa below

Question 9

Describe the upper esophageal sphincter

Answer 9

• Circular skeletal muscle

- Under voluntary and reflexive control

Question 10

Describe the lower esophageal sphincter

Answer 10

• Physiological sphincter, thickened circular smooth muscle - not defined well anatomically

Question 11

What are the functions of the stomach?

Answer 11

1. Acts as a mixed endocrine and exocrine organ
2. Continues digestion of carbs (started in oral cavity)
3. Adds acidic liquid to digester foods
4. Forms chyme
5. Pepsin initiates protein digestion
6. Gastric lipases help digest TG

Question 12

Mucosa of the stomach

Answer 12

• Lining epithelium: simple columnar epithelium, surface mucous cells (secreting sheet)
• Gastric pits: permanent invaginations into lamina propria, serve as ducts for mucosal glands
• Mucosal glands: branched tubular glands, 3 types: cardiac, gastric/fundic, pyloric), each has an isthmus, neck and base
• Lamina propria: well-vascularized and cellular
• Muscularis mucosae: 2 layers, sends strands up between glands

Question 13

Cardiac glands

Answer 13

• In the stomach (gastric gland)
• Short pits
• Short coiled glands
• Produce mucus
• A few HCl and lysozyme producing cells present

Question 14

Gastric/fundic glands

Answer 14

• In the stomach (gastric gland)
• Medium pits
• Long straight glands
• 4 cell types: mucous neck cells, parietal (oxyntic) cells, chief cells, and enteroendocrine cells

Question 15

Pyloric glands

Answer 15

• In the stomach (gastric gland)
• Long pits
• Short slightly coiled glands
• Most mucous cells, few parietal

Question 16

4 regions of the stomach

Answer 16

Cardia, fundus, body, pylorus

Question 17

Submucosa and muscularis externa of stomach

Answer 17

• Submucosa has no permanent folds seen in small intestine
• Muscularis externa has extra inner layer of oblique smooth muscle
• There is a serosa

Question 18

Surface mucous cells

Answer 18

• In the stomach
• Secretes bicard-rich mucus that protects stomach surface from acid
• Insoluble, cloudy, visible mucus

Question 19

Mucous neck cells

Answer 19

• In the stomach
• Between parietal cells in the neck of gastric glands
• Secrete soluble mucus, more mobile

Question 20

Parietal (oxyntic) cells

Answer 20

• In the stomach
• Secrete HCl and intrinsic factor (required for B12 absorption in ileum)
• FOund in middle and upper part of gastric gland
• Can be binucleate, have an intracellular canaliculus for HCl secretion

Question 21

Chief cells

Answer 21

• In the stomach
• synthesize pepsinogens and gastric lipases
• Serous cells, columnar shape
• Found in basal half of gastric glands

Question 22

Enteroendocrine cells

Answer 22

• In stomach
• Produce gastrin, somatostatin, and ghrelin, which act in paracrine and endocrine signaling
• Occur singly near base of gastric glands

Question 23

Stem cells in the stomach

Answer 23

• Found in isthmus and neck of mucosal glands
• Move upward to replace surface mucous cells (turn over every week)
• Move downward to replace glandular cells (turn over every 1-2 months)