How do digestive glands develop?
- They develop from evagination of endodermal tube near the start of the small intestine- around 6th week of embryogenesis.
- Connections are maintained as ducts that drain all three glands to the small intestines.
What are the three digestive glands?
What is the sphincter of Oddi?
- Sphincter that controls what comes out of the pancreas, liver, and gall bladder into the small intestine
- Embedded in pancreatic tissue
- Smooth muscle of muscularis is dominant
Where is the pancreas located?
Located on the posterior abdominal wall behind stomach and duodenum.
What is the function of the pancreas?
- Dual exocrine/endocrine gland
- Endocrine- ductless 'islets' secrete insulin and glucagon
- Exocrine - Acini secrete digestive enzymes and bicarbonate ions into ducts
What are the two major cell types in the endocrine islets of the pancreas?
- alpha cells- secrete glucagon which increases the blood glucose level
- beta cells- secrete insulin which decreases the blood glucose level
Name one important difference between type I and type II diabetes?
Type I diabetes occurs I is a result of a decrease in functional ß cells which results in a decrease in insulin production; In contrast, in Type II diabetes there is often a decrease in responsiveness of target cells to insulin
How do the endocrine islets appear under LM and EM?
- LM: appear as pale/chromophobic cells under H&E
- EM: small secretory vesicles
What are the two main types of cells in the exocrine islets?
- Acinar cells (zymogenic)- secrete digestive enzymes in their inactive forms (zymogens)
- Centroacinar cells- secrete bicarbonate ions to prevent the activation of zymogens until they reach the duodenum
How do zymogenic cells appear under LM and EM?
- Dark/chromophilic with H&E staining (L.M.)
- Large vesicles (E.M.)
How do centroacinar cells appear under LM and EM?
- Pale/chromophobic with H&E staining (L.M.)
- No large secetory vesicles, many tight junctions between cells (E.M.)
What stimulates the activity of exocrine cells in the pancreas?
- endocrine hormone- Cholecystokinin (CCK)
- Produced by DNES cells in the small intestines
Which chemical relaxes the sphincter of Oddi?
Name four functions of the liver.
- Bile production (exocrine gland)
- Plasma protein production (endocrine gland)
- Detoxification ie. Alcohol dehydrogenase
- Storage ie. glycogen
- All these functions are performed by hepatocytes (multiple functions in the same cell)
Which two blood vessels supply the liver?
- Hepatic Portal Vein: high in nutrients and bilirubin- drains GI tract, spleen, and enters liver
- Hepatic Artery: high in O2 from abdominal aorta and enters liver
- These two mix in venous sinusoids
What are the components of the hepatic portal triad?
- Hepatic portal vein
- hepatic artery
- hepatic bile duct- drains liver of exocrine product (bile)
How does blood leave the liver?
- Blood from branches of the hep. artery and hep. portal vein flow inward via hepatic sinusoids (expanded capillaries), mix, and enter central veins of the hepatic lobule
- The central veins drain into the inferior vena cava
Describe the important cellular features of a hepatocyte.
- Prominent euchromatin
- RER produces plasma proteins
- SER involved in detox (drugs/bile)
- Glycogen granules
What are the secretory domains of a hepatocyte?
- 1) Biliary domain (apical): empties into Bile Canaliculi, closed by hepatocyte tight juctions, drain to bile ducts
- Exocrine products include conjugated/water soluble bilirubin, bile salts, and cholesterol
- 2) Sinusoidal Domain (Basal): empties into sub-sinusoidal 'Space of Disse'
- Endocrine products include plasma proteins and lipoproteins
- Hepatocytes can have more than one apical or basal doman because of their particular orientation
What are Kupffer cells?
macrophages which patrol sinusoids and Space of Disse
What is cirrhosis?
- Chronic inflammation of the liver
- Fibrosis= increased CT/collagen and decreased hepatocytes, form nodules on the surface of the liver
- Fibrosis decreases blood flow through the sinusoids leading to portal vein hypertension- blood backs up in veins that drain the GI tract, can lead to terminal venous swelling ie. esophageal veins and hemorrhoidal veins can burst/hemorrhage
Describe the structure of the gall bladder.
- Simple columnar epl- highly absorptive to concentrate bile
- Lamina propria- highly vascular, loose CT
- Mucosa- highly folded without clearly organized villi or crypts/glands
- No seperate muscularis mucosa or muscularis externa
- Prominent muscularis of overlapping smooth muscle fibers- contractions initiate peristaltic waves in response to CCK and autonomic stimulation
- Adventitia- dense CT
What are gall stones?
Precipitation of bile (esp. salts and cholesterol) that becomes trapped in the draining cystic duct