Esophagus, Stomach, Small and Large intestine Flashcards
What are the components of the general plan of the GI tract (from esophagus → large intestine)?
Mucosa:
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Submucosa → Loose or Dense CT
Muscularis:
- Internal (circular)
- External (longitudinal)
*Stomach has a 3rd layer
Serosa (or Aventitia) → Loose or Dense CT depending where
What is the general plan specifically in the esophagus like?
Mucosa:
- Epithelium → Non keratinize squamous stratified epithelium
- Lamina Propria → Loose CT
- Muscularis Mucosae
Submucosa → Loose or Dense CT
- Contains esophageal glands that secrete mucous to lubricate the dry food
Muscularis:
- Internal (circular)
- External (longitudinal)
Adventitia Mucosa:
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Submucosa → Loose or Dense CT
Muscularis:
- Internal (circular)
- External (longitudinal)
*Stomach has a 3rd layer
Adventitia → Loose or dense CT depending
What are the main actions of the stomach in food digestion?
Add an acidic fluid to the ingested food to transform it into viscous mass called “chyme”
pH ~ 2.0
- Stomach also secretes intrinsic factor essential to absorb vitamin B12
- Produces hormones which will act later in the GI tract such as gastrin
What are the different areas of the stomach?
What allow to differentiate them?
Cardia → 1:1 (Pit : Gland length)
Fundus
Body → 1:3 (Pit : Gland length → much longer glands)
Pylorus → 2:1 (Pit : Gland length → longer pit)
What are the portions of the stomach epithelium?
Which cells are found where?
Pit → Surface mucous cells
Neck of the Gland → Mucous Neck cells + Parietal cells
Base of the Gland → Zymogenic cells + Parietal cells
*1 continuous layer of epithelial cells resting on a basement membrane
What are the characteristics of surface mucous cells?
*Stomach
Carbohydrate-rich glycoproteins described as the visible mucus because of its cloudy appearance → forms a thick viscous gel-like coat that adheres to the epithelial surface
Its high concentration of bicarbonate → local buffer to neutralize the acid so it doesn’t eat up the cells
- Mucous granules → stained dark in EM bc electron dense structures
- Centrally located nucleus
- Many mitochondrias
What are the characteristics of mucous neck cells?
- Have a triangular/neck appearance
- The mucous they secrete is more soluble as it allows other substances to pass through the lumen of the gland (secretory granules)
What are the characteristics of Zymogenic cells?
*Stomach
Secrete Zymogenic Granule → help with breakdown of food later in the GI tract, but released in the lumen of the stomach
What is common to all epithelial cells lining the stomach?
- Rest on a Basement membrane
- Have microvili on their apical surface
- They are connected by tight junctions
What are the characteristics of Argentaffin cells?
*Stomach
Also called enter-endocrine cells
Release argentaffin granules → Gastrin, Serotonin, Histamine, VIP, Glucagon, Somastotatin → hormones are released through the BASEMENT MEMBRANE
*Called this way because the proteins stain well in silver-stains
What are the characteristics of parietal cells?
*Also called Oxyntic cells
- Secrete intrinsic factor → for absoprtion of Vitamin D12
- Have canaliculi with microvilli in them → more suface area
- BIG centrally located nucleus (looks like a fried egg)
- Secrete HCl → acidify the stomach
*Have Carbonic Anhydrase: CO2 + H2O → H+ + HCO3-
With Cl- → HCl
What disease/condition is caused by malfunction of the parietal cells?
- Atrophic Gastritis
- Pernicious Anemia
What is the main role of the small intestine in digestion?
- Macromolecules are terminally digested in the SI → action of Pancreatic Enzymes
- Terminal digestion occurs on the mucosa wall
- Amino acids, monosaccharides, fatty acids, monoglycerides are absorbed along the vast absorptive surface of the SI
What allows histological differentiation of the Duodenum, Jejunum and Ileum?
At the level of the submucosa (Dense CT):
Duodenum:
- Thick submucosa filled with Brunner’s glands → secrete alkaline fluid in bicarbonate (pH~9.0)
- Secretions mix with and neutralizes the acidic stomach contents to allow pancreatic enzymes to be active in their optimal neutral pH
Jejunum:
- Submucosa forms Plicae Circulares which are “eruptions” that push the mucosa up into peaks → allows to further increase surface area for better absorption of nutrients (in addition to crypts and villi)
- Increase surface area ~3x
- Extend around 1/2 - 2/3 of the circumference of the small intestine
Ileum:
- Thin boring submucosa
In the small intestin, is it an Adventitia or a Serosa?
Serosa