Histology of Lower GI Tract - Cole Flashcards
What does peristalsis do?
Mixes food with gastric secretions including HCl, pepsinogen, gastric lipase and intrinsic factor to create chyme
Structure and function of the small intestine
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
What are the four degrees of folding in the small intestine?
- Plicae circulares
- Intestinal villi
- Intestinal glands (Crypts of Liberkuhn)
- Microvilli on apical surface of enterocytes (brush border)
Where are the plicae circulares distinct?
The jejunum
Disappear in the mid-ileum
The villi extend into what area and form what things?
Extend into mucosa to form the crypts
Ends at muscularis mucosae
-length depends on distention
What is the muscularis externa responsible for?
Segmentation - mix chyme, ANS
Peristalsis - movement, coordinated with relaxation below
What is the boundary between the mucosa and submucosa?
Muscularis mucosa
What is the main distribution site of blood and lymphatic flow?
The intestinal submucosa
Lacteals job
Convey chyle that is packaged in chylomicrons
Defining characteristics of duodenum
Brunner’s glands (mucus) in submucosa
Relatively few goblet cells
Leaf-like villi
Defining characteristics of jejunum
Plicae circulares
Irregular villi
More goblet cells
NO Brunner’s glands and Peyer’s patches
Defining characteristics of ileum
Many lymphoid nodules (Peyer’s patches) in LP and submucosa
Finger-like villi
Most goblet cells
What part of small intestine has Peyer’s patches?
Ileum
- finger-like villi
- most goblet cells
Crypts are lined by 4 types of cells types
Enterocytes - absorptive cells
Goblet cells
Paneth cells
Enteroendocrine cells
Defining characteristics of Goblet cells
Columnar mucus-secreting
Secretory product - 80% carbs, 20% protein
Forms a protective gel coat to shield from abrasion and bacteria
Gastrin
Stimulates gastric motility, HCl and insulin
Secretin
Stimulates pancreatic bicarbonate secretion and enhances insulin secretion
CCK
Acts on pyloric sphincter to slow emptying, stimulates release of bile and pancreatic enzymes
Paneth cells
Secrete antimicrobial proteins
Kill bacteria directly
What protects the small intestine?
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
Defining characteristics of IBD
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
What is the major function of enterocytes in the large intestine?
Transport of ions and water
-have short apical microvilli
What is the mucosa of the large intestine lined by?
Simple columnar epithelium formed by enterocytes and abundant goblet cells
What is not found past the ileocecal valve in the large intestine?
Plicae circulares and intestinal villi
What is the big difference between small and large intestine?
Large has no Paneth cells
Defining characteristics of large intestine?
Taeniae coli - fused bundles of the outer smooth muscle layer
Haustra
Saccular structures on large intestine domed by contraction of taeniae coli and inner circular smooth muscle layer
Appendix
Large accumulations of lymphoid tissue in LP and submucosa
Often fatty tissue in submucosa
Innervation of rectum
Above pectinate line - endoderm, like viscera
Below - ectoderm, like skin
*why external hemorrhoids hurt like hell
Colorectal tumors
Polyp - common > 60
Can be familial adenomatous polyposis
