Lecture 3: HIstology of the Esophagus, Stomach, Small intestine and Colon Flashcards
What is the general architecture of hollow visceral organs?
From lumen to the capillaries 1. surface epitheium 2. lamina propria 3. muscularis mucosae (smooth muscle) 4. Submucosa 5. Inner circular muscle layer (smooth) 6. Outer longitudinal muscle layer (smooth) 7. Adventitia IF NO ADVENTITIA 8. Serosal layer
Where are the nerves located?
- submucosal nerve plexus (meissners)
2. Myenteric plexus (nerves in between the inner circular muscle layer and outer longitudinal muscle layer (auerbachs)
What makes up the “mucosa” of a GI tube structure?
The combination of
i. surface epithelium
ii. lamina propria
iii. muscularis mucosae
What are desmosomes?
Molecular complexes of cell adhesion proteins and linking proteins that attach the cell surface adhesion proteins to intracellular keratin cytoskeletal filaments
What are the characteristics of tight junctions?
Network of sealing protein fibers of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly
What are the key characteristics of gap junctions?
Directly connects CYTOPLASM of two cells through hydrophilic channels, which allows various MOLECULES and IONS to pass freely between cells
What is the epithelium in the esophagus?
Squamous (stratified non keratinized squamous epithelium)
No absorption and no secretion
What is the Latin word for grapes?
Acini
What can be seen in the esophagus?
Acini below the muscle layers
What is the gastric environment?
- exposure of food to acid
- No significant absorption in stomach
Secretion = needs glands
Epithelium = glandular
What type of epithelium is typical of stomach?
Glandular
What is the cardiac type mucosa of stomach?
The transition from esophagus to stomach
Z line
Metaplasia
Squamous to gastric oxyntic mucosa
What are oxyntic glands?
Glands forming or secreting acid
Parietal cells of gastric glands
What are the three glandular regions of stomach and what are their functions?
- cardia
-area of reactive changes - Corpus
-oxyntic mucosa (acid producing - Antrum
-mucous glands predominate
NO OXYNTIC glands
Gastrin producing endocrine cells
What are the gastric pits?
The pits that contain glandular cells of the stomach
Parietal and chief cells
What produces acid production? Where?
Produced in CORPUS of the stomach Parietal cells (“P” for pH)
What do parietal cells do?
Stimulated to produce acid by
i. histamine ii. gastrin
What does gastrin do?
Acts on parietal cells
Stimulates enterochromaffin like cells in the corpus
Enterochromaffin cells make histamine
Secreted by ANTRAL neuroendocrine cells into the blood stream
What do enterochromaffin-LIKE cells do?
Make histamine
Stimulated by gastrin
What happens if you see a shitload of inflammatory cells in lamina propria of stomach?
Abnormal
What happens if you lack parietal cells?
Autonomous proliferation of neuroendocrine cells in the gastric fundus
What happens if you immunologically destroy parietal cells?
Leads to hyperacidity
What are the histological features of the parietal cells?
HCl producing parietal cells are PINK
So P for pink for pH
What are the histological features of the chief cells?
Blue cells
Where do the enterochromaffin-LIKE cells reside?
In between parietal and chief cells
What do chief cells do?
Releases the following
i. pepsinogen ii. gastric lipase iii. rennin
What does pepsinogen do?
Works in conjunction with parietal cell
Gastric acid converts pepsinogen to pepsin
What is pepsin?
An enzyme that degrades food proteins into peptides
What is the histological summary of the corpus?
- rugae
- gastric pits
- pits are lined by FOVEOLAR epithelium
- beneath the pits lie large amounts of secretory cells including
i. parietal cells
ii. chief cells
iii. neuroendocrine cells
What are the histological features of the cardia?
Transition point
So you see gastric pits as well as squamous epithelium
What are the key characteristics of the gastric antrum?
- Foveolae
- Antral glands
- Acid and enzyme
Producing glands
Disappear - Mostly MUCUS
Secreting glands - also gastrin
Producing
Neuroendocrine cells
Present
How is gastrin delivered to parietal and enterochromaffin cells?
Through the blood stream
Gastrin stimulates both acid and histamine production
No direct transport from antrum to corpus
What is the muscularis propria?
Name that is put in front of the circular and longitudinal types of muscle around the visceral gut tubes
Why are there B and T cells in the small intestine?
Because body is now subjected to inflammatory material
What are the two things lining the small intestine?
- villi (epithelium outside)
2. crypts (epithelium inside)
What are the functions of the microvilli?
- absorption
- secretion
- cellular adhesion
- mechanotransduction
What increases the surface area of small intestine?
- formation of villi
- formation of crypts
- formation of microvilli
What organ secretes the DIGESTIVE enzymes?
The pancreas
i. lipase ii. carbohydrase iii. protease iv. Nuclease
What are the four types of absorption?
- passive diffusion
- lipid soluble objects diffuse most rapidly
- Facilitated passive diffusion
- used for glucose (non lipid soluble shit)
- Active transport
- ions, vitamins, sugar and amino acids
- Pinocytosis
- fluid or particles are engulfed by a cell
- cell membrane invaginates and encloses fluid or particles then fuses again
- protein absorption
Where are the lymph vessels present in the large intestine?
Present in the LAMINA PROPRIA of the small intestin
What are paneth cells?
Located in the small intestine
Provides phagocytosis and intracellular digestion of intestinal microorganisms
Mostly in the crypts
What are Brunner glands? Where are the located?
Located in the SUBMUCOSA
In the DUODENUM only
Function:
i. protection from gastric acid (secretes alkaline mucus that contains BICARBONATE)
ii. alkalization to allow digestive enzymes to work
What is the significance of bicarbonate?
Neutralizes acid of stomach in duodenum
Secreted by Brunner glands in the submucosa
What are the different cell types we need to pay attention to in the small intestine?
- Peyer’s patches
- Brunner glands (produces bicarb in duodenum)
- Paneth cells (macrophage like)
What does the appendix look like?
Mucosa with crypts (no villi)
Same general architecture of the entire GI tube
Lymphoid aggregates!
But colon can have lymphoid aggregates too
What is the function of the colon?
- Absorption
- water
- sodium
- chloride
- Secretion
- bicarbonate
- mucus
- Goblet cells secrete mucus in response to tactile stimuli from luminal contents, lubricant and binds ingested material to form feces
What do goblet cells do in the colon?
- secrete mucus in response to tactile stimuli from luminal contents
- secrete lubricant to protect epithelium
- binds ingested material to form feces
What are the histological features of the colon?
NO VILLI
All crypts
On top of a BASEMENT MEMBRANE
What happens if you have a thick basement membrane in colon?
You cant absorb water and you get diarrhea
Does the amount of lymphocytes and plasma cells in colon signal abnormality?
NO because impossible to tell what is normal
Where are the lymph vessels of colon located?
Beneath muscularis mucosae so it is harder for muscle to spread
What usually has more lymph metastases, small or large intestines?
Small intestine because lymph is in lamina propria (in between surface epithelium and muscularis mucosae
What are the architectural/histological features of the rectum?
- a bit irregular architecture
- shows lymph vessels only below muscularis mucosae
- shows paneth cells increasing from proximal to distal sites
- shows villi for active iron absorption
- shows rgular crypts reaching through muscularis propia
Are paneth cells located in the colon?
Yes
Located in ½ of colon
What type of lymphoid tissue is associated with mucosa?
Mucosa-associated lymphoid tissue (MALT)
Protects from enormous quantity of antigens
What are M cells?
Stands for microfold cells
Found in follicle associated epithelium of Peyer’s patch
They transport organisms and particles from the gut lumen to immune cells across epithelial barrier
What ig’s are made by B cells in Peyer patches?
IgA and IgM
When do you see T-cells in esophagus?
In reflux disease
NO SIGNIFICANT lymphoid tissue in esophagus
When do you get lymphoid cells in stomach?
During chronic gastritis
Lamina propria usually contains no lymphoid cells
What is the key disease in the SMALL INTESTINE that leads to accumulation of T-cells?
Celiac disease
What is the key disease in the LARGE intestine that leads to accumulation of T-cells in surface epithelium?
Lymphocytic colitis
