Flashcards in 35 - GI System III Deck (116):
What four mechanisms does the stomach use to protect the mucosa from the harsh acidic environment?
1 - Presence of permanent layer of mucous
2 - Continuous secretion of mucous by epithelial cells
3 - Cell renewal by stem cells
4 - Alkaline tide
What is the alkaline tide?
- After a meal, parietal cells secrete HCl (acidic)
- Parietal cells then release bicarbonate into the blood stream
- Blood stream is more alkaline
- Alkaline blood is delivered to superficial epithelial cells
- Epithelial cells secrete bicarb into mucous layers
- Neutralization occurs
What happens when the protective mechanisms are breached?
Damage to the mucosa of the gastric lining
What happens when this damage penetrates into the submucosa?
What is the difference between an ulcer and erosion?
Erosion occurs if the damage is confined to the mucosal layer and it has not penetrated into the submucosa
What is the junction between the stomach and the duodenum called?
What is located at the gastroduodenal junction?
What is the pyloric sphincter?
A thickening in the muscularis externa
- Primarily the circular layer thickens
- The longitudinal layer somewhat thickens
- There is no oblique layer here
What is the primary function of the small intestine?
Increase the surface area for enzymatic degradation of nutrients as well as their absorption
What is the main structural modification that exists in the small intestine to increase functionality?
- Permanent folds of mucosa and submucosa
- Slow the movement of chyme
- Increase time for enzymatic degradation and absorption
What other structural modifications help to increase the function of the small intestine?
Villi and microvilli
Are plicae circulares permanent or do they come and go with increased chyme?
How much do plicae circulares increase the surface area of the small intestine?
Where are villi found?
Along the plicae circulares
What are villi?
Folds of the mucosa
- Superficial portion is columnar cells with goblet cells interspersed
- Core is lamina propria
How much do villi increase the surface area of the small intestine?
What are microvilli?
Extensions of the villi
- Found along apical domain of columnar cells
- Form the brush or striated border of the small intestine
How much do microvilli increase the surface area of the small intestine?
What is the overall increase in the surface area of the small intestine from plicae cirulares, villi and microvilli?
3 x 10 x 20 = 600 fold
What happens to the small intestine in a state of inflammation?
Villi can be damaged
What will a sensitivity to gluten result in?
Gluten enteropathy (celiac sprue disease)
What are the four histologic features of gluten enteropathy (celiac sprue)?
1 - Enterocytes (columnar cells) are disorganized
2 - Villus atrophy (no longer see villi)
3 - Crypt hyperplasia (intestinal gland proliferation)
4 - Inflammation of lamina propria
What is an esophageal stricture?
A narrowing of the lumen of the esophagus that results in difficulty swallowing solid foods (but not liquids)
What causes an esophageal stricture?
Regurgitation of stomach acid
What is Zollinger-Ellison syndrome?
- A gastrinoma is present (tumor of gastrin-producin cells)
- Causes proliferation of gastrin producing cells and therefore more gastrin
- Gastrin stimulates secretion of HCl
What is the gastrinoma triangle or Passaro's triangle?
A triangle in the abdomen where 90% of gastrinomas occur
Where is the gastrinoma triangle or Passaro's triangle?
- Junction of cystic and common hepatic ducts
- Junction of parts 2 and 3 of the duodenum
- Junction of pancreatic head and neck
In the small intestine, what type of lymphocytes maintain surveillance of the gut?
Why is the gut always under a "controlled state of inflammation"?
Because there is constant immunologic challenges in the gut (lots of bacteria, microbes, etc.)
What happens when the gut is in a uncontrolled state of inflammation?
Inflammatory bowel disease
Where do lymphatic channels exist in the small intestine?
In the core of the villi (within the mucosal layer)
What are the channels of the lymphatic system called?
What is absorbed through the lacteals?
Where does to fat go after it is absorbed by the lacteals?
Into the larger lymphatic structures
How does the lymph move?
Contraction of smooth muscles in the lamina propria - they compress the lacteal and move the lymph from the lacteal into the lymphatic duct and then into the submucosa
What other immune system cells are found in the small intestine? What layer?
Plasma cells (secrete IgA) are found in the lamina propria
What are crypts of Lieberkuhn?
The points where the epithelium invaginates up into the lamina propria to form the intestinal glands
Where are stem cells of the intestinal glands located?
Deep in the gland at the base
Recall that in gastric glands of the stomach they were further up in the isthmus of the gland
What are Paneth cells?
A specialized cell population that is found at the bottom of the intestinal gland that secrete acidophilic granules
What do the granules of Paneth cells contain?
Lysozymes which are bacteriolytic
What are enteroendocrine cells?
Hormone secreting glands that secrete their product into the connective tissue of the lamina propria, NOT the lumen of the small intestine
Why are the hormones of the enteroendocrine cells secreted into the lamina propria?
So they can be picked up by the microcirculation and enter the greater circulation of the body
What type of epithelium will you find in the duodenum?
Simple columnar epithelium
What will you find in the submucosa of the duodenum?
What specific type of glands are a hallmark feature of the duodenum?
What do Brunner's glands secrete?
Alkaline mucus and human epidermal growth factor
What portion of the duodenum has more abundant Brunner's glands?
The proximal duodenum
Do Brunner's glands exist in the jejunum?
No - they are a signature feature of the duodenum
What does human epidermal growth factor stimulate?
It also inhibits acid secretion form the parietal cells
What other prominent cell type will you find in the duodenum?
Why is the duodenum named the duodenum?
It means "12" and is named because it is the length of 12 fingers
What is histologically remarkable about the jejunum relative to the other segments of the small intestine?
Nothing - no hallmark features, nothing remarkable
What type of epithelium will you find in the jejunum?
Simple columnar epithelium of goblet cells
What is different about the ileum?
It is flat - no plicae circulares
What is a prominent feature of the ileum?
The presence of lymphatic nodules in the submucosa called Peyer's patches
What is the function of M cells in the small intestine?
M cells are lymphocytes that are involved in immune surveillance
How do M cells function?
They pick up antigenic material, process it internally and transport it then deliver the antigen to lymphocytes
What antibodies do M cells deliver to?
How are IgA formed?
- B lymphocytes
- Plasma cells
- Release IgA
- IgA taken up by epithelium of gut tube
- IgA secreted into lumen to bind to antigen
Does the outer longitudinal layer of smooth muscle completely surround the large intestine?
No - Instead, three longitudinal bands of smooth muscle are found
What do we call the three longitudinal bands of smooth muscle found running along the large intestine?
Does the presence of segmented smooth muscle (teniae coli) make the wall of the large intestine stronger or weaker?
Is there teniae coli found in the rectum?
Why is it clinically important that there is no teniae coli in the rectum?
Surgeons use this as a landmark
The large intestine appears segmented. What are the segments called?
Plicae semilunares are found in the large intestine. What are these?
What type of epithelial cells are found in the epithelium of the large intestine
Simple columnar epithelium
Does the large intestine have villi?
Is the brush border of the large intestine well developed or poorly developed?
Poorly developed - there are a few microvilli present, but not many
How abundant are goblet cells in the large intestine?
How dense are the crypts in the large intestine?
Crypts are invaginations of epithelium into the lamina propria
How abundant are lymphatic vessels in the large intestine?
Depends on the layer
- Very poorly developed in lamina propria
- Much better developed in the submucosa
Which direction do lymphatic vessels spread out in the large intestine?
Radially (not longitudinally)
Is the radial orientation of the lymphatic vessels in the large intestine favorable or unfavorable from a clinical standpoint?
Favorable - it is easier to go in surgically when they are not longitudinally oriented
Are glands found abundantly in the large intestine?
Yes - you will see an increased intestinal gland density
How does the mucosa of the appendix appear?
Similar to the large intestine - no villi
In the appendix, which layer will be rich in lymphatic tissue?
What layers does the muscularis externa have in the appendix?
An inner circular layer and an outer longitudinal layer
What other part of the GI tract does the muscularis externa of the appendix resemble?
What happens in appendicitis?
- Ulcers in mucosal layer
- Hard mass of feces blocks the appendix
- Luminal pressure within the appendix increases
What accounts for the increased luminal pressure in appendicitis?
- Fecal material plugs the lumen of the appendix (remember it is just a tubular sac)
- Secretions from the appendix have no where to go
- Build up and cause pressure
- Compresses blood vessels in the appendix
- Tissue pressure exceeds blood pressure
- Blood vessels collapse
- Ischemia occurs
- Eventually necrosis occurs
- Appendicitis results
What is an alternative way to get appendicitis?
How do you know the difference between the two ways to get appendicitis?
If it is acquired by the alternative way, feces will not be blocking the appendix when they take it out
What layers of the muscularis externa exist in the rectum?
Complete circular layer and longitudinal layer
What are the three folds of the rectum called?
Transverse rectal folds or the "valves of Houston"
What are they called?
1 - Distal/inferior fold
2 - Middle fold
3 - Proximal/superior fold
What is the function of the three transverse rectal folds?
Support and suspend the fecal mass that is held in the rectum until defecation occurs
Can you identify these folds endoscopically?
What three wall layers exist in the transverse rectal folds?
Remember, AKA Valve of Houston
- Muscularis externa
What defines the anal canal?
It is the part that extends to the perianal skin and includes the skin around the anus
What is the landmark that divides the rectum from the anal canal?
Pectinate (dentate) line
What is the pectinate line of the anal canal?
The line that separates two different types of gut tube lining
What are the two types of gut tube lining that the pectinate line separates?
Above - gut tube lining derived from the hind gut (typical mucosa)
Below - gut tube lining derived from proectodeum
What type of innervation occurs above and below the pectinate line
Above - autonomic and NO pain sensation
Below - somatic
What lymphnodes exist below the pectinate line?
Why is this clinically relevant that the inguinal nodes lie below the pectinate line?
Because if a patient has cancer below the pectinate line, the cancer will drain into the inguinal nodes
What are the layers of the anal canal before the pectinate line (proximal)?
- Muscularis mucosae
What type of epithelium is found in the anal canal before the pectinate line (proximal)?
Simple columnar epithelium with large population of goblet cells
What are the anal columns?
Ridges of the anal canal that project up into the lumen of the anus
What are the three anal columns that are highly distended known as?
What are the three anal cushions?
- Left lateral
- Right anterior
- Right posterior
Why are the anal cushions names as they are?
Named for the anatomical position the anal cushions are in when the patient is supine
What is the clinical relevance of the three anal cushions?
This is where hemorrhoids develop
When the bottom of the anal columns come together, what do we call the base region?
The wall at the base of these structures is known as the anal valves
What are the depressions at the distal ends of the anal columns called?
What accumulates in the anal sinuses?
What happens when glands in the anal sinuses become infected?
After the pectinate line (distal end), the epithelium begins to transition. What form(s) does it transition into?
- Simple columnar (around pectinate line)
- Stratified squamous non-keratinized
- Stratified squamous keratinized
When does the epithelium transition from simple columnar to stratified squamous non-keratinized?
At the intersphincteric groove (AKA white line of Hilton) which is a ring-like depression just below the pectinate line
What does the intersphincteric groove represent?
The border between the internal anal sphincter and external anal sphincter
What is an anorectal abscess?
- First, an anal sinus becomes plugged by gland secretions or fecal matter
- This leads to infection and inflammation
- Can spread to surrounding tissues
- Pockets of pus (abscesses) accumulate
How are anorectal abscesses named?
Based on their located
Where is the most common site of an anorectal abscess?
What is a fistula in ano?
An anorectal abscess that develops into a tube which can then penetrate from the anal canal onto the skin of the perineum
How are fistulas in ano named?
Based on their location