Histology - Gastrointestinal Tract

*attached to stomach & large intestine
*7 meters long
*duodenum (smallest, 20 cm); jejunum (3m); ileum (longest, 4m)

fuctions:
1 - movement of food to large intestine
2 - digestion of food by enzymes secreted from intesinal wall & supporting glands
3 - absorption of nutrients and fats to blood and lymph
4 - hormonal secretion

1 - mucosa (epithelial layer / lamina propria / muscularis externa)
2 - submucosa
3 - muscularis externa
4 - serosa

1 - epithelium
2 - lamina propria
3 - muscularis mucosae

Epithelial layer - fast renewal
i. acts as a selective barrier lining the outside environment; lymphocytes present
ii. secretion - digestive enzymes, hormones, mucus, antibiotics
iii. absorption - nutrients, water, electrolytes - into blood and lymph

*along canal different cells adapt to specific functions

Lamina propria = CT layer
*loose connective tissue
*reticular fibers
*rich in cells - esp. immune system cells
*blood and lymph cessels
*lacteal in small intestine
*immune system protection* via GALT & Peyer's patches in the ileum

GALT = Gut Associated Lymphatic Tissue
*numerous lymphocytes, plasma cells, macrophages and eosinophils

*2 layers of smooth muscle
*inner layer + longitudinal layer
*boundary between mucosa + submucosa
*"fibers" into the villi

@ ileum in lamina propria and submucosa
aggregartes of lymph nodes
important part of GALT
visible ovals, devoid of villi
instead of absorptive cells - M (microfold) cells over epithelium

Dense irreugular connective tissue
w/blood vessels
lymph vessels
secreting (submucosal) glands in the duodenum
nerve ganglia - Meissner's/submucosal plexus

*two muscle layers (three in stomach) organized circularly - like a corkscrew - and also longitudinally.
*produces PERISTALSIS
*smooth muscle is innervated by enteric nervous system
*Auerbach's / myenteric plexus (ganglia between layers of muscularis externa)

Ganglia between layers of muscularis externa

Autonomic nervous system
*sympathetic system
*parasympathetic system
*enteric system

Nerve ganglia in submucosal layer

*allows for maximal absorption
*spiral circular structure
* located @ mucosa + submucosa
*2/3 of the tube is folded allowing 3x larger surface area
*most prominent in duodenum + ileum

*finger-like protrusions, folds of the mucosa
*simple columnar epithelium
*apical side to lumen / basal side to basement membrane and lamina propria