Flashcards in 36 - GI System IV Deck (95):
What is colonic diverticula?
A "pouching out" of mucosa and submucosa that is found in the large intestine at a site of weakness between tinea coli
Why would we only see colonic diverticula in the large intestine and not in the rectum?
Because the rectum has a complete and continuous muscularis externae (no sites of weakness)
What areas of the large intestine are even more susceptible to colonic diverticula?
Sites where blood vessels and nerves penetrate
Is a colonic diverticula a true diverticula or a false diverticula? Why?
A false diverticula because a true diverticula would include all layers of the wall whereas a colonic diverticula only involves the mucosa and submucosa
What portion of the intestines do we commonly see polyps?
What procedure allows us to see polyps of the GI tract?
Colonoscopy procedure via a colonoscope
Are polyps usually removed when they are found or are they usually left?
Why do polyps develop in the first place?
Due to the hyperproliferation of cells
What are the two types of polyps we see?
- Tubular adenoma
- Villous adenoma
Note that sometimes we see a mix between the two types
Which type of polyp is more invasive?
Is the size of the polyp clinically relevant?
Yes - the larger the polyp, the more likely it is to be invasive
Which statement regarding lymphatic vessels in the lamina propria of the large intestine is true?
a. Is well endowed with lymphatic vessels
b. Is poorly developed
c. Is better developed in the presence of inflammatory bowel disease
a. Is well endowed with lymphatic vessels = FALSE
b. Is poorly developed = TRUE
c. Is better developed in the presence of inflammatory bowel disease = TRUE
Why is there an increased density of lymphatic vessels in inflammatory bowel disease?
This is a compensatory response to the inflammatory edema that exists
What are some tissue modifications that you will see in inflammatory bowel disease?
- The architecture of the wall will be modified
- Lamina propria will be full of dark blue inflammatory cells
- The lamina propria will contain an increase density of lymphatic vessels
What are the two major forms of inflammatory bowel disease?
- Ulcerative Colitis
- Crohn's Disease
Where is ulcerative colitis typically found?
Confined to the large intestine
Where is Crohn's disease typically found?
Anywhere along the GI tract
Which form of inflammatory bowel disease is more likely to form fissures and fistulas that invade neighboring organs?
Crohn's disease - because it is found anywhere along the GI tract
What is the difference between a fissure and a fistula?
A fissure will open into the peritoneal cavity and leak the intestinal contents into this space
A fistula will open into a neighboring organ and leak the intestinal contents into this organ
What is Hirschsprung's disease?
AKA congenital megacolon
- A condition caused by neural crest cells failing to properly migrate into the affected segment of the colon
- The result is that there will be a lack of both plexuses in that segment of the colon (myenteric and submucosal plexuses)
What does the lack of plexuses in Hirschprung's disease lead to?
The area lacking the plexuses will remain constricted, which causes the proximal area to dilate (megacolon) in order to compensate for the damming effect
What areas of the colon are involved?
The rectum is ALWAYS involved and the more proximal segments may also be involved
Case study: patient has difficult/painful swallowing for 3 years and a long history of irritable bowel syndrome - a CT scan shows a large thickening of the esophagus explaining the swallowing problems... What is this from?
A fissure that extends into the submucosa of the esophagus - the fissure as well as the endoscopy and biopsy are indicative of Crohn's disease
What is the capsule that surrounds the liver called?
What is Glisson's capsule composed of?
- Outermost layer is visceral peritoneum (mesothelium of simple squamous epithelium)
- Fibrous connective tissue
- Type III collagen reticular fibers
Is Glisson's capsule innervated? How would we know?
Yes, richly innervated - we know this because distension of the liver causes pain
What pattern will you see of the reticular fibers of Glisson's capsule?
You will see the reticular fibers penetrate into the liver parenchyma
What does an excessive amount of connective tissue in the liver indicative of?
Scar tissue formation that can cause problems
What is the classic hepatic lobule?
The pattern of liver cell architecture that is seen histologically - Hexagonal plates of hepatocytes and sinusoids
What structures are found at the corners of the hexagonal lobules?
Portal canals - each corner has 3-6 portal canals
What do portal canals contain?
- Connective tissue
- The portal triad
- Lymphatic vessels
- Autonomic nerve fibers
What is found in the "portal triad"?
1 - Hepatic artery
2 - Portal vein
3 - Bile duct
What is the periportal space?
AKA space of Mall
- the area between the hepatic lobule and the portal triad
- believed to have originated from lymphatics
What do the lymph vessels in the periportal space do?
Collect lymph and shunt it back into venous circulation
Can you see a clear delineation between each liver lobule in humans?
No - it isn't as well defined in humans, but you can see some borders and the portal canals at the corners
Note that the portal canal is sometimes called the portal space
Just note it
Is the classic liver lobule well supplied with blood?
Yes, very well supplied
There is "dual blood supply" to the liver. What are the two sources?
Portal vein (75%)
Hepatic artery proper (25%)
Describe the blood flow from the portal vein
- Blood enters the lobule via the inlet venule
- The inlet venule dumps the blood into the hepatic sinusoidal capillaries between hepatocytes
- The liver is supplied with rich nutrients from the GI tube
Describe the blood flow from the hepatic artery proper
- Blood enters the lobule via the arteriosinusoidal branch
- The arteriosinusoidal branch dumps into the hepatic sinusoidal capillaires between the hepatocytes
- This blood supply is rich in oxygen
What is the portal vein blood rich in? What is the hepatic artery proper blood rich in?
Portal vein - nutrients
Hepatic artery - oxygen
What are Kupffer cells?
Phagocytic cells of the liver that remove pathogens and worn-out RBCs from the blood
What is normally the main site of blood filtering pathogens and worn-out RBCs?
- The liver can take over if the spleen is removed
What are sinusoids of the liver?
Discontinuous endothelium with large fenestrations and discontinuous basal lamina
Why is the basal lamina absent in the sinusoids of the liver?
The basal lamina would be a barrier to rapid exchange of materials from the blood to the tissue of the liver
What is the perisinusoidal space?
AKA Space of Disse
- The space between epithelial cells and hepatocyte cytoplasm
What would you find in the perisinusoidal space?
Numerous hepatocyte microvilli which function to increase the surface area for rapid exchange
What else would you find in the perisinusoidal space (cells types)?
Hepatic stellate cells (AKA perisinusoidal cells)
What is the signature feature of hepatic stellate cells?
Large lipid droplets
What is stored in the hepatic stellate cells? Why?
Vitamin A - we don't know why (function unknown)
What is the hepatic acinus?
A diamond shaped area that extends from a central vein to a hepatic canal then back to the original central vein
The diamond shaped area is divided into zones that represent the areas that receive blood supply first
What are the three zones of the hepatic acinus?
Zone 1 (closest to blood supply)
Zone 3 (furthest from blood supply)
Describe Zone 1
AKA perilobular region
- More oxygen
- More extrahepatic hormones
- More enzymes for glucose-liberation
- More enzymes for fatty-acid lxidation
Describe Zone 3
AKA centrolobular region
- Closest to central vein
- More enzymes for glycolysis
- More enzymes for fatty-acid synthesis
- More waste products
- Most susceptible to damage (during detoxification)
Where would acetominophen toxicity cause necrosis first?
- More waste products
- Less access to filtering blood supply, detoxification
What will you see in ischemic-induced necrosis of Zone 3?
Necrosis of the tissue
Describe a hepatocyte
- Involved in numerous functions
- Large variety of organelles
- rER for protein synthesis
- sER for detox
- Mitochondria for fuel
What are two main functions of the liver that require a well developed sER?
1 - Detoxification
2 - Glycogen metabolism
What are two main functions of the liver that require a well developed rER?
1 - Protein synthesis
2 - Carbohydrate storage
What happens to colloid osmotic pressure and blood clotting with severe injury?
Albumin and clotting factors (fibrinogen and prothrombin) are made by the liver
What is the effect of less albumin during injury?
What is the effect of less clotting factors during injury
It takes longer for the blood to clot
What organ is responsible for the synthesis and secretion of bile acids?
Liver - this is another key function
How is bile produced and/or processed
Most of the bile is actually reabsorbed from the intestine and reused, but some is freshly synthesized in the sER
What organ is responsible for the conjugation and secretion of bilirubin?
Liver - this is another key function
What type of bilirubin is unconjugated?
What type of bilirubin is conjugated?
What is the difference between unconjugated and conjugated bilirubin?
Unconjugated (indirect) bilirubin is insoluble
- Released from lysed RBCs
- Before it is processed by liver
Conjugated (direct) bilirubin is soluble
- After it has been processed by liver
- The liver makes it soluble
What is the MDR-2 protein?
A protein found on membrane cells lining the bile collecting system
What is the function of an MDR-2 protein?
Transport conjugated bilirubin into the bile
What is Dubin Johnson Syndrome?
A defect in the MDR-2 protein
What is the clinical presentation of Dubin Johnson Syndrome?
- Elevated levels of conjugated (direct) bilirubin
- Fairly benign condition
What is Gilbert syndrome?
A defect in the enzyme involved in conjugation of bilirubin within the liver (UGT1A1)
What is the clinical presentation of Gilbert syndrome?
- Decreased levels of conjugated (direct) bilirubin
- Fairly benign condition
What is Crigler-Najjar syndrome/Neonatal Hyper-bilirubinemia?
There are two types
- Type I: the conjugation of bilirubin is completely absent
- Type II: the conjugation of bilirubin is decreased
What are the clinical presentations of Crigler-Najjar syndrome/Neonatal Hyper-bilirubinemia Type I and II?
Type I = fatal
Type II = can be benign
How fast will the liver begin to regenerate?
Quickly - significant regeneration can be seen in 1 week
What will you see in Alcoholic Liver disease?
- Fatty liver
- Increased collagen deposition
- Damage is REVERSIBLE
What will you see in Alcoholic Cirrhosis of the liver?
- Continued abuse leads to cirrhosis
- Cirrhosis is IRREVERSIBLE
- Liver nodules will be seen
- Liver becomes highly dysfunctional
Why do liver nodules form in alcoholic cirrhosis of the liver?
- Collections of hepatocytes
- Liver is trying to regenerate
- Connective tissue has proliferated and confines the dividing hepatocytes to nodules
What are stellate cells? How do they change during cirrhosis?
Normal stellate cells are quiescent (dormant) but injury/assult activates stellate cells
What do activated stellate cells do during cirrhosis?
- stellate cells proliferate and begin producing CT components
- the CT components become contractile and constrict blood flow
- active stellate cells are damaging to the liver
What do we call the beginning portion of the bile collecting system?
Bile flows through a system of channels. What are they called?
Canal of Hering
What lines the canal of Hering?
- Stem cells
- Cholangiocytes and hepatocytes
- Ductal cells
What two types of cells can regenerate liver cells?
- Stem cells (activation can stimulate liver cell recovery)
- Periductular null cells (sit in the periportal space)
What layers do we find in a gall bladder?
- CT layer of serosa/adventitia
What three components of the mucosa will we find in the gall bladder?
1 - Epithelium
2- Basal lamina
3 - Lamina propria
What is cholesterolosis?
Elevated cholesterol levels that lead to the formation of foam cells in the gallbladder
Do foam cells in the gallbladder cause harm?
No, this is a fairly benign, reversible condition
How do exocrine cells of the pancreas generally function?
First they synthesize enzymes, then they store them until they receive a signal
What is the role of acinar cells of the exocrine pancreas?
What is the role of ductal cells of the exocrine pancreas?
Secrete water and ions (HCO3-)
Case study: abdominal pain in epigastric region, radiation to back, nausea, vomiting, recent history of binge drinking, fever, tachycardia
- Elevated serum amylase
- Elevated lipase
- Acute pancreatitis