Histo - GI 1

Question 1

What are the 4 Layers of the GI System?

Answer 1

1. Mucosa (mucus membrane)
   
   • epithelium
   • lamina propria (loose CT)
   • muscularis mucosa
2. Submucosa
   
   • dense irregular CT
3. Muscularis externa
   
   • 2 layers
     
     • inner circular
     • outer longitudinal
4. Adventitia or Serosa
   
   • Serosa = loose CT lined w/ mesothelium
     
     • continuous w/ peritoneum
   • Adventitia = loose CT that merges w/ other tissues
     
     • no mesothelium

Question 2

What are the 2 Nerve Plexi of the Enteric Nervous System?

Answer 2

1. Meissner’s Plexus
   
   1. Submucosal plexus
   2. Autonomic
   3. Controls secretion in mucosa & submucosa
2. Auerbach’s Plexus
   
   1. Mysenteric plexus
   2. Btw muscle layers in muscularis externa
   3. Autonomic
   4. Controls peristaltic action of muscularis externa

Question 3

What is Mucosa Associated Lymphoid Tissue (MALT)?

Answer 3

Basics:

• Diffuse lymphatic tissue
• Lymphoid nodules
• Peyer’s patches
• Appendix

Function:

• Lamina propria = immune action
  
  • lymphocytes
  • plasma cells
  • macrophages
• Plasma cells make IgA
  
  • IgA = resistant to breakdown by digestive enzymes

Question 4

What is role of the Oral Cavity?

Answer 4

Basics:

• SSK, SSNK, or parakeratinized epithelium
• Salivary glands

Function:

• Digestion begins here

Question 5

What is this?

Answer 5

Esophagus

Basics:

• SSNK epithelium
• Well-dev muscularis mucosa
• Adventitia –> Serosa after esophagus pierces diaphragm & enters peritoneal cavity

Muscle Type:

• Skeletal muscle = upper 1/3
• Mixed muscle = middle 1/3
• Smooth muscle = lower 1/3

Glands:

1. Esophageal-cardiac glands (mucosal glands)
   
   • in MUCOSA
     
     • found close to junction w/ cardiac stomach
   • secrete mucous
   • protects from acid reflux
2. Esophageal glands (submucosal glands)
   
   • in SUBMUCOSA
   • secrete mucous
   • present ALL ALONG esophagus

Question 6

What is this?

Answer 6

Esophagus (middle 1/3 - mixed muscle)

Question 7

What is this?

Answer 7

Oropharynx

• Elastic limiting layer REPLACES muscularis mucosa

Question 8

What is this?

Answer 8

Esophageal‐cardiac junction

Basics:

• Abrupt change from SSNK –> Simple Columnar epithelium

Function:

• ALL mucous secreting cells

Question 9

What are the 4 major structures & functions of the stomach?

Answer 9

Structures:

1. Simple columnar epithelium
   
   • forms PITS & GLANDS
   • invaginations from surface
2. Muscularis externa = may have add’l layer
   
   • innermost oblique
3. Serosa
4. Stem Cells = ISTHMUS region

Functions:

1. Continues digesting carbs
   
   • starts w/ saliva
2. Starts digestion of triglycerides
   
   • secretes lipase
3. Starts digestion of proteins
   
   • secretes pepsin
4. Makes chyme

Question 10

What are the 4 parts of the stomach?

Answer 10

4 Parts of Stomach

1. Cardiac
   
   • Jxn w/ esophagus
2. Pylorus
   
   • Jxn w/ duodenum
3. Fundus
4. Body

Note:

• Fundus & body are histologically identical!

Question 11

What is this?

Answer 11

Rugae in Stomach

What?

• Folds the contain mucosa & submucosa
• Flatten when stomach is full

Where?

• All along the stomach

Why?

• Gives add’l surface area

Question 12

What are the 7 Cell Types in Stomach Epithelium?

Answer 12

1. Mucous surface cells
   
   • ​secrete alkaline fluid - mucin
2. Mucous neck cells
   
   • secrete acidic fluid - mucin
3. Mucous gland cells
   
   • cardiac & pyloric regions
4. Parietal cells
   
   • ​​secretes IF & HCl
5. Chief cells
   
   • ​secretes pepsinogen & gastric lipase
6. Enteroendocrine (APUD) cells
   
   • secrete gastrin into blood
   • present in epitheliu
7. Stem Cells in ISTHMUS
   
   • make all of these cell types

Question 13

What is the Cell Type Distribution in the Stomach Mucosa?

Answer 13

Cardiac & Pyloric Stomach

• Mucous surface cells
• Mucous neck cells
• Mucous gland cells
• Stem cells in ISTHMUS
• APUD cells

Fundic & Body Stomach

• Mucous surface cells
• Mucous neck cells
• Parietal cells
• Chief cells
• Stem cells in ISTHMUS
• APUD cells

Note:

• ALL are simple columnar epithelium

Question 14

What is this?

Answer 14

Cardiac Stomach

• Short pits
• Short, coiled glands

Question 15

What is this?

Answer 15

Fundic Stomach

• Short pits
• Long, straight glands

Question 16

What is this?

Answer 16

Gastric Glands

3 Regions:

1. Gastric Pit
   
   • Mucous surface cells (SM)
   • Mucous neck cells (NM)
2. Isthmus/Neck
   
   • Mucous neck cells (NM)
   • Parietal cells (P)
   • Stem cells
3. Gastric gland
   
   • Chief cells (C)
   • Parietal cells (P)
   • G cells

Question 17

What is this?

Answer 17

Fundic Stomach

1. Parietal cells
   
   • Transport H+ & Cl- into lumen
     
     • pH 1-2
   • Secrete gastric IF
     
     • binds vit B12
   • Large, eosinophilic
     
     • open canaliculi
2. Chief cells
   
   • Secrete gastric lipase
   • Secrete pepsinogen
     
     • convers to pepsin in acid
   • Basophilic

Question 18

What is this?

Answer 18

Parietal Cell - Ultrastructure

• Deep invagination of PM
  
  • forms intracellular canaliculi - all connected to surface
• Protrudiing microvilli
  
  • into canaliculi

Question 19

What is this?

Answer 19

APUD cells

• Secrete basally
  
  • granules secreted into bloodstream
• Unicellular endocrine glands
• Amine precursor uptake & decarboxylation cells
  
  • or diffuse neuroendocrine cells
  • or enteroendocrine cells
  • or enterochromatin cells
  • or argentaffin cells

Question 20

What is this?

Answer 20

Gastric Gland - Ultrastructure

• All cells secrete into the lumen EXCEPT APUD cells
  
  • APUD secretes into bloodstream

Question 21

What is this?

Answer 21

Pyloric Stomach

Basics:

• Long pits
• Short, coiled glands

Function:

• Middle layer of muscularis externa thickens to form the PYLORIC SPHINCTER