GI histology: Herron Flashcards
Describe the mucosa and glands of the esophagus.
SS nonkeratinized epithelium.
Thin lamina propria with cardiac (mucus) glands (esophageal glands proper) at upper and lower ends.
In the esophagus, the GALT is found in which layer? Mucosa Submucosa Muscularis externa Adventitia/Serosa
Mucosa
Auerbach’s plexus is found where in the esophagus?
Btwn the inner circular and outer longitudinal layers of the muscularis externa
Describe the relative proportions of smooth muscle and skeletal muscle down the length of the esophagus. I.e.- upper 1/3, middle 1/3, lower 1/3.
Upper 1/3- all skeletal
Middle 1/3- mixed skeletal/SM
Lower 1/3- all SM
Enables voluntary control of upper 2/3 and involuntary control of lower 1/3
Which layer of the muscularis externa is responsible for the sphincters in the GI tract?
inner circular
Name the 4 regions of the stomach from where the esophagus ends to where the duodenum begins.
Cardia, fundus, body, pylorus
The large longitudinal gastric folds of the stomach are called:
Rugae
Describe the wall of the stomach.
Simple columnar epithelium
LP filled with CT, gastric glands, and lymphatic cells
Typical muscularis mucosa
Submucosa- forms core of rugae
Muscularis externa has 3 layers: inner oblique, middle circular, outer longitudinal
Outer serosa, not adventitia
Describe the different types of cells composing the simple columnar epithelium of the stomach and the gastic pits.
::Mostly mucus secreting cells. Mucus protects mucosa from stomach acid.
::Parietal (pink, acidophiles) cells in pits secrete HCl
::Chief cells (dark, basophiles) of pits secrete pepsinogen (found at ends of glands)
::Enteroendocrine cells secrete a variety of gastric hormones into LP
Describe cell renewal of the stomach.
Cell division restricted to the isthmus of gastric pits where stem cells are located. Think of the gastric pit/gland as a branching structure (upside-down Y). The isthmus is the area before the branch.
What is the difference between rugae and mammillated folds?
Rugae are folds of the submucosa. Mammillated folds are folds of the LP.
Describe the 3 modifications made by the intestinal wall to increase surface area.
1) plicae circularis (aka valves of Kerchring)- permanent mucosal folds (submucosal core) (x3 SA). MC in jejunum.
2) Villi- finger-like projections of mucosa (x10 SA)
3) Microvilli- on surface of epith. cells. Forms striated (brush) border. (x100 SA)
Celiac disease damages which surface area modification (plicae, villi, microvilli)?
Destroys villi.
Describe the varying cell types of the intestines.
::Enterocytes- primary absorptive cell, also secrete water/electrolytes
::Goblet cells- secrete mucus
::Paneth cells- Found in base of crypts of Lieberkuhn. Acidophilic granules. Role in regulating bacteria in glands. Secrete lysozyme to digest bact. cell walls. Phagocytize bact. and protozoa.
::M cells- antigen presenting cells that overly lymphatic nodules.
::Enteroendocrine cells- secrete peptide hormones.
::Intermediate (stem) cells- pluripotent cells that can become any epithelial cell needed.
How can you distinguish the 3 parts of the small intestine from one another on histological section?
Duodenum
Jejunum
Ileum
Submucosal Brunner’s glands in duodenum.
Nothing special about jejunum.
Abundance of Peyer’s patches (lymph nodules) in ileum
How do we absorb fat in the intestines?
Lymphatic capillaries called Lacteals run up length of villi. Fat circulates in lymph and is then dumped into venous circulation.
Describe how the villi move to provide intestinal motility?
Fibers of the muscularis mucosa extend up into the villi and contract to provide motility to the villi.
Whereas the function of the small intestine is continued digestion and absorption of nutrients, what is the function of the large intestine?
Absorption of water and electrolytes and elimination of solid wastes
Does the large intestine have permanent mucosal folds like the stomach and small intestine?
Nope.
What is the difference between the mucosa and epithelial cells of the large intestine and small intestine?
No villi, so no lacteals. (slow metastasis of colon cancer)
Large intestine- more goblet cells as you move distally, no Paneth cells.
Large intestine has outer longitudinal musclularis externa that forms teniae coli, responsible for forming non-permanent haustra (folds of large intestine).
What three structures form the portal triad?
Hepatic bile duct
Portal vein
Hepatic artery
A portal canal contains a portal triad and….
Lymphatic vessels, nerves, and connective tissue
Outline the flow of blood to and from the liver.
Portal vein and hepatic artery—> combined venous/arterial blood in sinusoids—> central vein (@ center of lobule)—> Sublobular vein—> Hepatic vein—> IVC
Functions and regenerative capacity of hepatocytes:
Make proteins
Involved in storage (glycogen), metabolism, waste removal.
Can regenerate
What are Ito cells?
Ito (stellate) cells are distributed among the hepatocytes and store Vit. A.
What are Kupffer cells?
Macrophages found in hepatic sinusoids capable of removing bacteria and damaged RBCs from circulation.
Whut is the space of Disse?
The perisinusoidal space between the fenestrated sinusoid capillaries and the hepatocytes. This is where the microvilli on the basal surface of hepatocytes come into contact with the mixed venous/arterial blood from the sinusoids.
Describe the passage of bile from hepatocytes to the hepatic bile duct.
bile canaliculi—> canal of Hering—> interlobular bile ducts—> R or L hepatic duct—> Hep. bile duct.
Bile flows in the opposite direction to flowing blood. Blood flows to center of lobule, bile flows to perimeter of lobule where it joins canals of Hering.
Describe the contents of bile.
Hint: good and bad
The Good:
Phospholipids (lecithin)
Bile salts (for emulsifying lipids)
Electrolytes
The Bad: (taken from gut for disposal)
Bile pigments, the end product of hemoglobin degradation from bilirubin.
Describe the functions of the gallbladder.
Concentrate/store bile
Discharge bile into cystic duct—> common bile duct, when secretion stimulated by hormones* of small intestine
*Cholecystokinin stimulates gallbladder release of bile. Secretin stimulates liver secretion of bile.
Describe the exocrine and endocrine functions of the pancreas and where these respective cells are found.
::Exocrine: secretes enzymes (proteolytic, amylolytic, lipases, nucleolytic) and bicarbonate into ducts. Located in acinar pancreas. You can see zymogen granules in serous acini.
::Endocrine: secreted hormones (insulin, glucagon, somatostatin) into blood. Located in islets of langerhans.
Describe the journey of exocrine secretions from the centroacinar cells to the main pancreatic duct and the cell types lining each duct type.
Secretions released by centroacinar cells—> intercalated duct (Sqau. cells)—> intralobular duct (cub./low columnar cells)—> interlobular duct (low columnar, lots of CT)—> main pancreatic duct
