MA - Poole - Gastrointestinal Tract II - 2/17

Question 1

What structural modifications found in the small intestine facilitate the absorptive process?

Answer 1

Microvilli - increase surface area by 20x
Villi - finger like projections but bigger than microvilli - increase SA 10x
Plicae circularis - aka valves of Kerckring - permanent transverse circular folds of mucosa/submucosa, increase SA about 3x

Question 2

How is the mucosa of the duodenum protected from gastric acid?

Answer 2

Brunner’s glands in the submucosa of the duodenum. Glands are mostly mucous and secrete alkaline mucous that protects against the effects of stomach acid AND provide optimum pH for pncreatic enzymatic action.

Question 3

Where are Brunner’s gland found?

Answer 3

Duodenum, submucosa

Question 4

Describe an M cell.

Answer 4

M, for microfold, cells are found ONLY in the ILEUM. They are specialized epithelial cells that cover PEYER’S PATCHES (groups of lymph nodes). They have a discontinuous basement membrane. They are considered as part of the immunologic protecting cells of the intestine.

Question 5

List the landmarks that distinguish the duodenum from the ileum.

Answer 5

The ileum has (1) the longest villi, and (2) the highest number of goblet cells. Peyer’s patches are only found in the ileum. The ileum is much longer than the duodenum, 3.5m and 25cm, respectively.

The duodenum has Brunner’s glands. Its villi are short and squared off (like cactus leaves). The duodenum is closest to the stomach, whereas the ileum is furthest.

Question 6

What morphological features distinguish the colon from the rectum?

Answer 6

The muscularis externa is unique to the colon. The upper rectum resembles the colon, but has less lymphoid tissue and no taenia coli.

The anal canal has no crypts and no muscularis mucosa.

Question 7

What morphological features distinguish the colon from the appendix?

Answer 7

The epithelium of the appendix resembles the colon, but has fewer crypts, and they are shorter. The lamina propria of the appendix has many lymphoid cells and lymph nodules.

Question 8

Where are the stem cells located in the stomach and small intestine?

Answer 8

In the small intestine, stem cells are found at the base of the crypts and villi. The move upward to repopulate the villi every 3-6 days. They can also replace Panneth cells which turn over every 30 days.

Stem cells in the stomach are found in the isthmus and neck of the mucosal glands and move upward to replace surface mucous cells that turn over every week. They can also move down to replace glandular cells that turn over every 1-2 months.

Question 9

Give the cell type (and location of cell) that produces each of these substances:
HCl
Mucus
Pepsinogen
Lysozyme
Secretory component
IgA
Intrinsic factor
Gastrin

Answer 9

HCl AND intrinsic factor - Parietal aka oxyntic cells - found in middle to upper pat of gastric glands

Mucous - Mucous neck cells - found in small groups or alone between parietal cells in the neck of gastric glands - their mucous in soluble
Mucous - Surface mucous cells - found at surface of gastric glands - their mucous is insoluble
(Mucous - Goblet cells - some in duodenum and increase to end of small intestine - produce acid glycoproteins (mucin) which becomes mucous)

Pepsinogen - Chief cells - found in basal half of gastric glands - also secrete lipases

Lysozyme - Paneth cells - found in small groups at the base of crypts

Secretory component - Absorptive cells - small intestine

IgA - Plasma cells - found in Peyer’s patches (GALT)

Gastrin - Enteroendocrine cells - stomach, at base of gastric glands - they also produce somatostatin and ghrelin (paracrine and endocrine).

Question 10

What cell type of the small intestine is mutated and may participate in autoimunne autophagy of Chron’s disease?

Answer 10

Paneth cells

Question 11

What are the three functions of the small intestine?

Answer 11

1. Absorption
2. Movement of chyme
3. Immunodefense

Question 12

What are the 6 major cell types of the small intestine?

Answer 12

1. Absorptive cells aka enterocytes
2. Goblet cells
3. Enteroendocrine cells
4. Paneth cells
5. Stem cells
6. M (microfold) cells

Question 13

What is GALT, where is it found and what are its components?

Answer 13

GALT = gut-associated lymphoid tissue
Prominent in the lamina propria of the small intestine, represents 25% of the mucosa of the small intestine.
Made of Peyer’s patches, IgA, secretory component

Question 14

What are the five parts of the large intestine?

Answer 14

Colon
Cecum
Appendix
Rectum
Anal Canal

Question 15

What are the 3 main functions of the large intestine?

Answer 15

1. Absorption of the water, salts, minerals and vitamins
2. Mucous secretion
3. Storage elimination of fecal material

Question 16

What are taenia coli?

Answer 16

Three bands of outer longitudinal muscle of the muscularis externa of the colon. Each layer is separated by a thin layer of longitudinal smooth muscle.

Question 17

What is the adventitia or serosa situation in the large intestine?

Answer 17

Transverse colon, sigmoid colon and appendix have a serosa. Ascending and descending colon and cecum have an adventitia.

Question 18

What are circumanal glands?

Answer 18

Apocrine sweat glands in the ano-cutanous area. BUTT SWEATS

Question 19

What cell type of the small intestine has a striated border?

Answer 19

Absorptive cells

Question 20

What are the crypts of Lieberkuhn?

Answer 20

Simple tubular glands that extend from the surface of the epithelium for the muscularis mucosae.