3. GI cellular anatomy

Question 1

name the 4 layers of the GI tube

Answer 1

1. mucosa (innermost)
2. submucosa
3. inner circular and outer longitudinal muscle layers
4. serosa (continuous with mesenteries)

Question 2

name the 3 layers of the GI mucosa and state their function

Answer 2

1. epithelium (innermost) - absorption and mucus/hormone production
2. lamina propria - contains lymph nodules and macrophages, produces IgA
3. muscularis mucosae - SM layers in diff. orientations to keep epithelium in contact with gut wall and help keep crypt contents dynamic

Question 3

which antibody type is produced by the GI mucosa

Answer 3

IgA - resistant to proteases

Question 4

where are the 2 enteric plexuses found

Answer 4

1. submucosal/Meissener’s plexus - submucosa

2. myenteric/Auerbach’s plexus - inner circular muscle layer

Question 5

what type of epithelium is found in the gut and why

Answer 5

• stratified squamous in oesophagus and distal anus - withstands abrasion
• simple columnar - absorption

Question 6

name the area of division in the anal canal and the differences on either side of the line

Answer 6

• PECTINATE LINE
• above 2/3 = simple columnar epithelium derived from endoderm of hindgut
• lower 1/3 = stratified squamous derived from proctoderm ectoderm

Question 7

name the most common cell of the GI epithelium and describe its characteristic features

Answer 7

• ENTEROCYTE
• have microvilli (forming brush border) to increase surface area for absorption and digestion via enzymes
• short lifespan (2-4 days): prevents bowel perforation and can adapt to nutrient changes

Question 8

which cells produce mucus in the GI tract - describe their shape

Answer 8

• GOBLET CELLS
• increase in no. from duodenum to colon
• narrow base and larger apical end, mucus droplet compresses nucleus to base

Question 9

describe 4 functions of mucus in GI tract

Answer 9

protects epithelia from:

1. friction (acts as lubricant)
2. chemical damage (acidic environment)
3. bacterial inflammation (forms physical barrier)
4. food source for normal intestinal flora

Question 10

which type of mucus-secreting cell is found in the stomach?

Answer 10

• GASTRIC SURFACE MUCOUS CELLS (foveolar cells)
• line most of gastric mucosa/gastric pits
• secrete mucus/HCO3 (higher pH than other mucus) that forms barrier to stomach acid

Question 11

name 4 structures that increase surface area for absorption in GI tract

Answer 11

permanent folds

1. plicae circulares
2. villi (in small intestine, not colon)
3. microvilli

temporary folds
4. rugae (for stomach expansion)

Question 12

in which areas of the GI tract are crypts of Lieberkuhn found

Answer 12

small and large intestine

Question 13

name 5 different cell types found in the crypts

Answer 13

1. enterocytes
2. goblet cells
3. enteroendocrine cells
4. stem cells
5. paneth cells

Question 14

what is the function of stem cells in the crypt

Answer 14

migrate up to renew epithelium

Question 15

what is the function of enteroendocrine cells

Answer 15

secrete hormones

Question 16

what is the funciton of paneth cells

Answer 16

secrete antibacterial proteins to protect stem cells

Question 17

which type of exocrine gland is found in the duodenum

Answer 17

tubular BRUNNER’S GLANDS - secrete HCO3- rich mucus to neutralise acidic chyme