Histology of Lower GI Tract - Cole

Question 1

What does peristalsis do?

Answer 1

Mixes food with gastric secretions including HCl, pepsinogen, gastric lipase and intrinsic factor to create chyme

Question 2

Structure and function of the small intestine

Answer 2

Chemical digestion
Neutralize acidic chyme from stomach
Use segmentation to mix
Absorb good shit
Secrete mucus
Secrete CCK, VIP and secretin
Longest part of GI

Question 3

What are the four degrees of folding in the small intestine?

Answer 3

1. Plicae circulares
2. Intestinal villi
3. Intestinal glands (Crypts of Liberkuhn)
4. Microvilli on apical surface of enterocytes (brush border)

Question 4

Where are the plicae circulares distinct?

Answer 4

The jejunum

Disappear in the mid-ileum

Question 5

The villi extend into what area and form what things?

Answer 5

Extend into mucosa to form the crypts
Ends at muscularis mucosae
-length depends on distention

Question 6

What is the muscularis externa responsible for?

Answer 6

Segmentation - mix chyme, ANS

Peristalsis - movement, coordinated with relaxation below

Question 7

What is the boundary between the mucosa and submucosa?

Answer 7

Muscularis mucosa

Question 8

What is the main distribution site of blood and lymphatic flow?

Answer 8

The intestinal submucosa

Question 9

Lacteals job

Answer 9

Convey chyle that is packaged in chylomicrons

Question 10

Defining characteristics of duodenum

Answer 10

Brunner’s glands (mucus) in submucosa
Relatively few goblet cells
Leaf-like villi

Question 11

Defining characteristics of jejunum

Answer 11

Plicae circulares
Irregular villi
More goblet cells
NO Brunner’s glands and Peyer’s patches

Question 12

Defining characteristics of ileum

Answer 12

Many lymphoid nodules (Peyer’s patches) in LP and submucosa
Finger-like villi
Most goblet cells

Question 13

What part of small intestine has Peyer’s patches?

Answer 13

Ileum

• finger-like villi
• most goblet cells

Question 14

Crypts are lined by 4 types of cells types

Answer 14

Enterocytes - absorptive cells
Goblet cells
Paneth cells
Enteroendocrine cells

Question 15

Defining characteristics of Goblet cells

Answer 15

Columnar mucus-secreting
Secretory product - 80% carbs, 20% protein
Forms a protective gel coat to shield from abrasion and bacteria

Question 16

Gastrin

Answer 16

Stimulates gastric motility, HCl and insulin

Question 17

Secretin

Answer 17

Stimulates pancreatic bicarbonate secretion and enhances insulin secretion

Question 18

CCK

Answer 18

Acts on pyloric sphincter to slow emptying, stimulates release of bile and pancreatic enzymes

Question 19

Paneth cells

Answer 19

Secrete antimicrobial proteins

Kill bacteria directly

Question 20

What protects the small intestine?

Answer 20

Gel blanket from goblet cells
Tight junction barrier
Peyer’s patches
IgA - neutralizes antigens
Paneth cells that secrete microbial pathogens
Acidity of the gastric juice kills microorganisms
Propulsive movement prevents colonization

Question 21

Defining characteristics of IBD

Answer 21

Defect in the protective stem - terminal ileum
Initial alteration is neutrophils into the crypts
Inflammatory process infiltrates the submucosa and muscularis
Major complications - occlusion by fibrosis and formation of fistulas
Segments affected are separated by normal stretches

Question 22

What is the major function of enterocytes in the large intestine?

Answer 22

Transport of ions and water

-have short apical microvilli

Question 23

What is the mucosa of the large intestine lined by?

Answer 23

Simple columnar epithelium formed by enterocytes and abundant goblet cells

Question 24

What is not found past the ileocecal valve in the large intestine?

Answer 24

Plicae circulares and intestinal villi

Question 25

What is the big difference between small and large intestine?

Answer 25

Large has no Paneth cells

Question 26

Defining characteristics of large intestine?

Answer 26

Taeniae coli - fused bundles of the outer smooth muscle layer

Question 27

Haustra

Answer 27

Saccular structures on large intestine domed by contraction of taeniae coli and inner circular smooth muscle layer

Question 28

Appendix

Answer 28

Large accumulations of lymphoid tissue in LP and submucosa

Often fatty tissue in submucosa

Question 29

Innervation of rectum

Answer 29

Above pectinate line - endoderm, like viscera
Below - ectoderm, like skin
*why external hemorrhoids hurt like hell

Question 30

Colorectal tumors

Answer 30

Polyp - common > 60

Can be familial adenomatous polyposis