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 + mucous cardiac esophageal glands
- Muscularis Mucosae
Submucosa → Loose or Dense CT
- Contains esophageal glands proper that secrete mucous to lubricate the dry food
Muscularis:
- Internal (circular)
- External (longitudinal)
Adventitia before the diaphragm
Serosa after the diaphragm
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?
*Gastric region
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
Zymogenic granules contain pepsinogen and lipase
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
*parietal cells secrete HCl and Intrinsic factors
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 (mucous) → 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
How is the epithelium of the mucosa of the small intestin classified?
Simple columnar epithelium with brush border and goblet cells
Which different cells are found in the villi of the SI?
- Columnar cells with brush border (Absorptive cells/Enterocytes)
- Goblet cells → secrete mucous for lubrication (not protection, thinner mucous than surface mucous cell which allows protection)
- M cells (Microfold cells) → aggregate into Peyer’s patches/Gut Associated Lymphatic Tissue and secrete Ab
*Form a simple columnar epithelium
Which cells are found in the crypts of the SI?
- Columnar cell with brush border (Absorptive cells/Enterocytes)
- Goblet cells
- Enterendocrine cells → secrete under the BM
- Paneth cells (Lysozymes) → control microbiome by regulating the killing of bacteria
- Stem cells → division and rapid turover
*Form a simple columnar epithelium
What is the turnover rate of the SI epithelium?
3-10 days → very active stem cells at the base of the crypts
What is secreted by enteroendocrine cells in the crypts of the SI?
Cholecystokinin (CCK) → promotes contraction of gall bladder and pancreatic secretions into the duodenum
*not the same cells as argentaffin cells in the stomach
How are the different digested nutrients absorbed into enterocytes?
Amino Acids + Monosaccharides (hydrophilic) → go through plasma membrane → through BM → blood vessels (passive)
Monoglycerides, Fatty Acids, Cholesterol, Phospholipids (hydrophobic) →Endocytosed → brough to the smooth ER (SER)
- Apoproteins are synthesized in the rough ER
In the Golgi, Chylomicrons are formed for transport of lipids to the liver for further digestion
What are different parts/features of enterocytes in the SI?
- Microvilli at their apical surface
- Connected to neighbouring cells by 3 types of connections (apical → basal)
- Tight junctions
- Zonula Adherens (form belt around, at level of the terminal web)
- Desmosomes
What protein are found at the level of the microvilli in SI enterocytes?
- Actin forms rod-like bundles
- At the top of actin rods (tip of the microvilli) → Dense matrix (villin = actin binding protein)
- Actin filaments interact with Myosin at the level of the terminal web → contraction allows movement of the microvilli
- At the top, on the outside, different enzymes are responsible to digestion, absorption and IgG absorption (passive immunity from mother to its baby when drinking breast milk)
Which enzymes are found at the surface of the microvilli of SI enterocytes?
- Glycoproteins
- Disaccharidases
- Dipeptidases
- Alkaline Phosphatase
- Enterokinase (duodenum): Cleaves trypsinogen → trypsin (active)
How to M cells act in the case of need?
*Unique intestinal epithelial cells
1. basal lamina becomes discontinuous to allow passage of lymphocytes
2. M cells allows uptake of lymphocytes from circulation to release them in the GI tract → make Ab
3. - And inversly, take antigens from GI and transport them to BM to be presente to immune cells
What are the different sections of the large intestine (colon)
- Vermiform appendinx
- Cecum (entry for SI contents)
- Ascending, Transverse, Descending colon
- Sigmoid colon
- Rectum
What is the general plan of the colon? (different layers)
Mucosa → ONLY crypts (no villi):
- Simple columnar epithelium
- Lamina Propria
- Muscular mucosa (1 circular layer)
Submucosa
Tunica muscularis:
- Inner circular
- Outer longitudinal → TENIAE COLI
Serosa
What is the Teniae coli?
It is the outer longitudinal smooth mucle layer of the tunica muscularis in the large intestin/colon
Smooth muscles form bundle ~3 length-wise → allows to generate more force to push the leftover contents down to the rectum
What different cells are found in the epithelium of the colon/large intestine?
- Goblet cells (LOTS of them)
- Absorptive cells
- Entero-endocrine cells
- Stem cells
What are Crypts of Lieberkühn?
The name of the crypts of the small intestine
What are valves of Kerkring?
Another word for Plicae Circulares (jejunum of the SI)
What are the differences between cilia and brush border?
Cilia:
- longer
- motility
- Microtubules (axoneme)
- Movement/Sensory function
Brush border:
- shorter
- non-motile
- Actin filaments
- Absortive/Secretion function
