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Describe the comparison of small intestine and large intestine histologically

Histological features are similar to the small intestine


What are the differences in the large intestine in the mucosa?

- No folds (plicae circulares) except for the rectum and anal canal)
- Absence of villi ***
- Intestinal glands are more numerous and longer ***
- Intestinal glands contain fewer Paneth cells
- Columnar cells have short, irregular microvilli: this presents an ill-defined striated (brush) border
- Goblet cells are more numerous ***


What are the differences in the large intestine in the muscularis externa?


- Outer longitudinal layer of smooth muscle does not completely surround the large intestine
- Instead, three longitudinal bands of smooth muscle are found: these are the teniae coli****


Describe the vermiform appendix

- Lymphatic nodules are found in the lamina propria and submucosa
- Contains fewer and shorter intestinal glands
- Lacks teniae coli

Similar to the large intestine in that there are no villi


Describe appendicitis

- Appendix is very narrow, so a "ficalith" can form (a plug of fecal material) where mucus will still form but will have no where to go
- The result is an increase in pressure
- The increase in pressure decreases blood flow leading to ischemia, necrosis and inflammation/infection
- "Ficalith" is not always found in appendicitis, so other mechanisms are likely but unknown


Describe Crohn's disease

- Inflammatory bowel disease
- A disease of the colon
- Impacts several layers of the wall of the intestine
- A lot of lymphatic tissue will be present
- Due to the inflammation, fissures can form which reach down to the muscularis layer and also breech the intestine and impact other organs such as the urinary bladder


Describe the rectum folds

- Longitudinal folds (temporary) - Folds of submucosa and mucosa)
- Plicae transversales recti (transverse rectal folds; aka folds or valves of Houston)

Include folds of...
- circular muscle of muscularis externa (some folds also have longitudinal muscle)
- submucosa
- mucosa


What is absent in the rectum that was present in the small intestine?

Teniae coli


Describe the anal canal

- Anal columns (columns of Morgagni) - longitudinal folds of submucosa and mucosa
- Muscularis mucosae is absent distal to the sinuses - no submucosa inferior


What does the lamina propria of the anal canal contain?

- Lamina propria contains a large plexus of veins
- This is where hemorrhoids form


Describe the internal anal sphincter

- Formed by the inner circular smooth muscle layer of the muscularis externa
- Does become thickened


Describe the external anal sphincter

Formed from skeletal muscle


What are diverticula?

- Outpocketings of the colonic wall are diverticula.
- A "true diverticulum" involves all wall layers; whereas, a pseudo-diverticulum only involves the mucosa and submucosa
- Can be genetic or acquired


What causes diverticula?

- Due to the weakness in the muscularis externa (tinea coli)
- Does not happen in the rectum due to complete muscular wall
- Also, blood vessels and lymph vessels contribute to weakening in the wall


Describe Hirschsprung's disease

- Congenital megacolon
- There is a constricted area (no enteric nerve plexuses form here)
- Always involves rectum and always involves more proximal segments
- Proximal to the constricted area, we see a distended colon ("megacolon")


Describe the pancreas

Both an exocrine and endocrine gland


Describe to exocrine portion of the pancreas

- Compound acinar gland
- Acinar cells


Describe the endocrine portion of the pancreas

- Pancreatic islets or islets of Langerhans


What is the pancreas covered by?

Covered by thin connective tissue capsule


Describe the thin connective tissue capsule

- Septa extend into the gland and divide it into lobules
- Secretory acini are tightly packed together in the lobules


Describe acinar cells of the pancreas

- Form acinus
- Triangular appearance
- Contain centroacinar cells
- Form intercalated ducts (leaves the acinus)
- Intralobular and interlobular ducts lead to the main and accessory ducts


Describe the pancreatic duct cells

Pancreatic duct cells
- Secrete the inorganic component of pancreatic juice
- Water, ions of which HCO3- is important to neutralize the acidic chyme


Describe acute pancreatitis

- Acute pancreatitis can be caused by insult (alcohol, gall stone, virus, ischemia, metabolic injury, trauma
- If the insult is chronic (alcoholism), the acute pancreatitis can become chronic


Describe the histology of the liver

Covered by thin, yet strong connective tissue capsule (Glisson's capsule)

Internal organization
- Classic liver lobule, Hepatic acinus (of Rappaport), and Portal lobule


Describe the components of the classic liver lobule

- Lobules are not demarcated by interlobular septa in human liver tissue - hard to differentiate
- Lobules are polygonal in shape
- Portal spaces are found at some of the corners of the lobule (3-6/lobule)
- Portal triads are found in the portal spaces
- Central vein is in center of lobule
- Trabeculae (cords) of hepatocytes
- Sinusoids
- Space of Disse


What is the space of Disse?


- Subendothelial space between the endothelial cells of the sinusoids and the hepatocytes
- Microvilli of hepatocytes extend into this space
- Reticular fibers
- Perisinusoidal cells (Ito cells) which accumulate vitamin A in LIPID DROPLETS ****and secrete growth factors

The SIGNATURE FEATURE of the perisinusoidal cells (Ito cells) are the LIPID DROPLETS ***


What are the component of the hepatic acinus?

- Zones: 1, 2, and 3
- Response of cells in the three zones to nutrients, drugs, and toxic chemicals

There are two adjacent liver lobules and a hepatic portal tract between the two

Zone 1 of each of the lobules are closest to blood supply, zone 2 is next and zone 3 is the furthest from the blood supply in each lobules - The implication of this is that if there is low oxygen, zone 1 is going to get oxygenated, but the further out you get, the more ischemia you will see.

Also, when drugs are broken down, the metabolic breakdown occurs mostly in zone 3, so if blood flow is decreased there is less potential to take away the drug, so it has the ability to damage zone 3.


Describe the blood to zone 1

- Increased oxygen
- Decreased carbon dioxide
- Decreased metabolic waste products
- Increased nutrients


Describe the blood to zone 3

- Decreased oxygen
- Increased carbon dioxide
- Increased metabolic waste products
- Decreased nutrients
- Main site of drug and alcohol detoxification

MORE susceptible to damage
- Decreased nutrients, particularly during states of malnutrition
- Hypoxic damage


Describe a hepatocyte

- Polyhedral in shape
- Microvilli develop on the lateral domains of the cell extending into the space of Disse
- Abundant mitochondria, SER and RER
- Well developed golgi and many lysosomes
- Contains Lipid droplets and glycogen granules