GPAT

1. Lumen

2. Mucosa

epithelium

basement membrane

tunica (lamina) propria

--glands

--areolar connective tissue

lymphatic tissue (diffuse & nodular), plasma cells, esoinophils, macrophages

muscularis mucosae

3. Submucosa

areolar CT (often fatty)

nerve plexus & ganglion cells (submucosal/Meissner's), Cajal cells

blood plexus

lymphatics

glands may be present: esophagus and duodenum

no submucosal glands in stomach!

4. Muscularis Propria

inner circular

nerve plexus & ganglion cells (myenteric/Auerbach's) Cajal cells

outer longitudinal

5. Adventitia - Loose CT or Serosa - thin layer of loose CT and mesothelium

ENS

• independent nervous system
• located in myenteric and submucosal plexuses
• control GI motility, absorption, secretion, and blood flow
• Interstitial cells of Cajal are non-neural pacemaker cells that receive, transmit and integrate neurogenic signals and muscular activity
  • Tyrosine kinase receptor (CD117) - hematopoetic cells; defects in ICC are

Esophagus

component tissues

Mucosa
- (Non-keratinized) Stratified squamous epithelium
- Muscularis mucosa
Submucosa
- Mucous esophageal glands
- Collagen and elastic fibers
- Submucosal venous plexus (drain to portal and systemic venous systems)
Muscularis – Skeletal (upper, from cricopharyneal & inf. pharyngeal constrictor muscles) and smooth m. (lower)
Adventitia (thorax) or Serosa (in abdomen)

Regions of stomach:

Cardia: junction of esophagus and stomach; very narrow region (may be absent in some people)

Fundus/body: oxyntic ("acid producing") region; fundic stomach

Pyloric antrum/pylorus: next to duodenum

Mucosa:

Surface/Foveolar region: Simple columnar epithelium

-Lines surface and pits,
-Alkaline Mucous secretion: protection

Lamina (tunica) propria:

-Cardiac (mucous), fundic (oxyntic), pyloric (mucous) glands
-Loose connective tissue

Muscularis mucosa

Submucosa: present as in the GPAT and forms core of rugae

Muscularis: 3 layers, rather than 2: including the inner oblique layer

Mucous neck cells (in neck/isthmus region): stem cells here differentiate upwards into foveolar mucous cells or downwards into parietal, chief, enteroendocrine, or pyloric mucous cells

Rugae == non-permanent longitudinal folds

gastric pits == foveolae

Fundic (gastric/oxyntic) glands vs. Pyloric glands:

Fundic: thickness of glands is greater than thickness of pits in longitudinal section

pyloric: thicken of pits and glands are about equal

surface/foveolar epithelium

Simple columnar epithelium

-Lines gastric surface and pits,
-Alkaline Mucous secretion: protection

mucous neck cells/stem cells

(in neck/isthmus region): stem cells here differentiate upwards into foveolar mucous cells or downwards into parietal, chief, enteroendocrine, or pyloric mucous cells

chief cells

Occupy lower third of gland
Typical protein producing cells
Produce: Pepsinogen and Gastric lipase
-Converted to pepsin in stomach
-Digests most proteins

-rER in basal location

apical zymogen granules

Parietal cell

•Common to upper fundic glands
•HCl production in resp. to Ach, histamine, and gastrin
•Intrinsic factor - necc. for B12 abssoption
•Numerous mitochondria - necc. for pumping H+ ions
•Intracellular canaliculi with microvilli - incorporate proton pumps
•Tubulovesicular system - store extra plasma membrnae between meals

Enteroendocrine Cells (part of the diffuse neuroendocrine system)
•Regulate water, electrolytes and enzyme secretion
•Regulate GI motility and mucosal growth
•Stimulate release of other hormones
•Near base of glands within epithelial lining
•Secretory granules face basement membrane
•Hormones vary with location: Secretin, gastrin, cholecystokinin, gastric inhibitory peptide, motilin

Major endocrine cell: ECL (enterochromaffinlike cell): produces histamine & stimulates HCl production via parietal cells; ECLs are stimulated by gastrin, made by G cells of gastric antrum

•Duodenum, jejunum, ileum
•Plicae circulares: permanent folds in mucosa and submosa
•Intestinal villi: upward projections of mucosa
•Intestinal glands: in the crypts
•Digestion and absorption
•Simple columnar epithelium

•Microvilli: forms the brush border

duodenum: (1) Brunner's glands (secrete alkaline mucous), (2) ampulla of Vater, (3) Pancreas, (4) retroperitoneal (has adventitia)

ileum: (1) Peyer's patches, (2) aggregations of MALT, M cells endocytose antigens and pass antigens along the underlying lymphocytes, (3) mesothelial (serosal) surface (since intraperitoneal)

large intestine

•Cecum •Ascending colon •Transverse colon
•Descending colon •Sigmoid colon •Rectum

no folds, parallel tubular intestinal glands, as deep as the muscularis mucosa, absorptive cells called coloncytes--columnar, and have short irregular microvilli, •Intestinal glands
•No plicae circulares
•No villi

•No panteth cells

•more goblet cells

•more individual nodules of lymphatic tissues are present than small bowel (not like Peyer's, however), limited to immediately adjacent to muscularis mucosae

Muscularis propria: outer longitudinal layer forms 3 bands (taenia coli) -> wall structure sacculates; blood and lymph penetrate from mesocolon through the muscularis to supply and drain the mucosa and submucosa

functions: produces mucus and absorbs water; storage for feces until defectation, flatus, water & short-chain fatty acids are produced as byproducts of carbohydrate-consuming bacteria that are normal fora of the colon; flatus water, and short chain FA are produced as byproducts of carb-consuming bacteria in the flora of coon

Appendix
•Resembles colon
-No taenia coli
•Intestinal glands
•Lymphatic tissue
-M cells

enterocytes

• Five day cycle (from bottom of gland to villi)
• Microvilli – Striated border
-Actin present
-Membranous enzymes
•Glycocalyx coat
•Junctional complexes

functions: (1) digestion of oligo and disaccharides at microvilli; (2) sodium transport from lumen to capillaries; (3) protein digestion, (4) fat digestion: TAG -> glycerol + FA; then TAGs are reconstituted, and then packed into chylomicrons, and excocytosed through the basal and lateral membrane (lacteals pick up the CMs)

goblet cell

• Mucous production
-Acid glycoproteins
-Protects intestinal lining
• Increase in abundance from duodenum to colon

NOT FOUND IN STOMACH

Paneth cells: red-orange secretion granules

•At base of intestinal glands
•Secretory products protect epithelium from pathogens
•Products: -Lysozyme  -Defensins

limited to the small bowel

enteroendocrine cells/cells of the diffuse neuroendocrine system

•Open type: have microvilli and contact the lumen

vs. closed type: contact basement membrane only
•Secretory product delivered to capillaries

secrete different hormones, e.g. pancreozymin/cholectstokinin, secrotnin (enterochromaffin EC cells), gastrin (G-cells), gastrin-inhibitory polypeptide, secretin (S cells), and somatostatin

stem cells

•Located near base of crypt
•Daughter cells differentiate & migrate down (Paneth cells) or up (enterocytes, goblet cells, etc.)

M cells: antigen transport

specialized enterocytes, found immediately over intramucosal lymphoid aggregates; transport antigens from gut lumen to underlying lymphoid tissues

Parietal cell

•Common to upper fundic glands
•HCl production in resp. to Ach, histamine, and gastrin
•Intrinsic factor - necc. for B12 abssoption
•Numerous mitochondria - necc. for pumping H+ ions
•Intracellular canaliculi with microvilli - incorporate proton pumps
•Tubulovesicular system - store extra plasma membrnae between meals

chief cells

Occupy lower third of gland
Typical protein producing cells
Produce: Pepsinogen and Gastric lipase
-Converted to pepsin in stomach
-Digests most proteins

-rER in basal location

apical zymogen granules

Enteroendocrine Cells (part of the diffuse neuroendocrine system)
•Regulate water, electrolytes and enzyme secretion
•Regulate GI motility and mucosal growth
•Stimulate release of other hormones
•Near base of glands within epithelial lining
•Secretory granules face basement membrane
•Hormones vary with location: Secretin, gastrin, cholecystokinin, gastric inhibitory peptide, motilin

Major endocrine cell: ECL (enterochromaffinlike cell): produces histamine & stimulates HCl production via parietal cells; ECLs are stimulated by gastrin, made by G cells of gastric antrum

Pyloric glands

•Pit depth/gland length – 1:1
•Coiled mucous glands
-Lysozyme; 

•glands produce mucous and lysozymes
•Enteroendocrine cells
-G cells (produce gastrin): directly stimulate parietal cell HCl production and indirectly by histamine release by ECLs