GI II

Question 1

small intestine

Answer 1

• 3 segments
• duodenum- 25 cm
• jejunum- 2.5 m
• ileum 3.5 m
• move chyme, absorb nutrients, immunodefense

Question 2

lumenal SA

Answer 2

• increased 400-600x by three structures
• plica circularis
• villi
• microvilli

Question 3

plica circularis

Answer 3

-permanent transverse circular folds of mucosa and submucosa that increase SA 2-3 times

Question 4

villi

Answer 4

• finger like projections of surface epithelium and lamina propria that increases SA 10x
• 0.5-1.5 mm tall

Question 5

microvilli

Answer 5

• projections of apical plasma membrane that icease SA 20 times
• 1 micron tall

Question 6

crypts of lieberkuhn

Answer 6

• intestinal glands that are simple tubular glands

- extend from the surface epithelium down to the muscularis mucosae

Question 7

6 major cell types

Answer 7

• absorptive cell
• goblet cell
• enteroendocrine cell
• paneth cell
• stem cell
• M cell (microfold

Question 8

absorptive cells

Answer 8

1. tall columnar cells with a striated border
2. each microvillus is 1 micron tall and 0.1 micron in diameter
3. disaccharides and peptidases are secreted by the absorptive cells and bind to microvilli where they produce mono saccharides and amino acids for absorption
4. lipids are absorbed and re-esterified to triglyverides, converted into chylomicrons, and released from lateral surfaces into the lamina propria where they are absorbed by the central lacteals

Question 9

goblet cells

Answer 9

1. unicellular glands that produce acid glycoproteins of the mucin type that lubricate and protect the small intestine
2. less abundant in the duodenum and increase in number as one approaches the ileum
   - most goblet cells in villi in ileum, but overall in large intestine

Question 10

enteroendocrine cells

Answer 10

1. unicellular glands that synthesize hormones and vasoactive peptides
2. in the small intestine most occur in the basal portion of the crypts

Question 11

paneth cells

Answer 11

1. exocrine cells found in small groups at the base of the crypts
2. the apical cytoplasm is filled with large, eosinophilic granules of lysozyme that has antibacterial activity which controls intestinal flora
   - also contain phospholipase A2, and defensins
   - crohn’s disease may be a specific disorder of paneth cells
   - replaced every 30 days

Question 12

stem cells

Answer 12

1. located near the base of the crypts

2. move upwards, repopulating the crypts and villi in 2-6 days

Question 13

M (microfold) cells

Answer 13

1. only found in the ileum
2. specialized epithelial cells that cover Peyer’s patches
3. The basement membrane beneath M cells is discontinuous

Question 14

GALT

Answer 14

• prominent in the lamina propria of the small intestine
  1. about 25% of the mucosa is gut associated lymphoid tissue
  2. peyers patches in the ileum are groups of 20-40 lymphatic nodules covered by M cells
• antigens from the lumen are taken up by the M cells and delivered to lymphocytes and other cells in peyer’s patches
  3. IgA synthesized here
  4. SC (secretory component)- 75kDa glycoprotein synthesized by absorptive cells and inserted into basal PM
• dimers of IgA bind, enter by endocytosis, and exit the apical PM with SC bound, forming secretory IgA that binds antigens, toxins, and microorganisms
• host defense

Question 15

regional differences

Answer 15

• duodenum has brunner’s glands in the submucosa and squat villi
• jejunum has most developed plicae circularis, more goblet cells, and more slender villi
• ileum has longest villi, most goblet cells, and Peyer’s patches

Question 16

Brunner’s glands

Answer 16

-secrete an alkaline mucous that helps protect against stomach acid and provide and optimum pH for pancreatic enzyme action

Question 17

gross divisions of large intestine

Answer 17

• colon
• cecum-don’t need to know histologically
• appendix
• rectum
• anal canal
• functions are to:
• absorb water, salts, minerals, vitamins
• mucous secretion
• storage and elimination of fecal material

Question 18

colon and cecum

Answer 18

• plicae semilinares-temporary folds of mucosa and submucosa
• no villi, only crypts
• outer longitudinal smooth muscle thickened into three bands-taenia coli
• transverse and sigmoid colon have serosa
• ascending and descending colon have an adventitia
• leaflets look like daisies

Question 19

vermiform appendix

Answer 19

1. epithelium resembles the colon, fewer and shorter crypts
2. lamina propria has many lymphoid cells and lymph nodules that often interrupt the muscularis mucosae
   - submucosa is frequently edematous
3. muscularis externa has two complete thin laters and no taenia
4. there is a serosa

Question 20

rectum

Answer 20

1. divided into upper and anal canal

2. upper rectum resembles the colon, but has less lymphoid tissue and no taenia coli

Question 21

anal canal

Answer 21

• 2.5-4 cm long and simple columnar epithelium of rectum changes to stratified cuboidal then stratified squamous nonkeritinized
• then crypts and muscularis mucosae disappear
• then epi to stratified squamous keritinized in ano-cutaneous area
• apocrine sweat glands called circumanal glands can be found in this area
• inner layer of circular smooth muscle thickens to form internal anal sphincter
• outer longitudinal layer of muscularis externa is replaced by skeletal muscle that forms the external anal sphincter