Lecture 10 Flashcards
What are the salivary & pancreatic digestive functions?
Need to extract nutrients from the external environment: provides energy and building blocks that support life
Problem: how to digest food in a useful and manageable way
Lipids
Starches
Proteins
Other viruses
What are the properties of salivary exocrine glands?
Classified as compound exocrine glands
Salivary glands- lubricates ingested food, initiates starch digestion, and prevents dehydration of the oral mucosa
Also secretes products with some degree of anti microbial functions
Slide 5
What are the basic properties of pancreatic exocrine glands?
Classified as compound exocrine glands
Exocrine pancreas- produces a pancreatic juice that neutralizes chyme as it enters the duodenum and is rich in a variety of zymogens that play an important role in completing the digestion of ingested carbs, protein, and fats
Slide 6
What are the 2 major cell types in salivary glands and pancreas?
Acinar cells- polarized epithelial cells specialized for the production and export of protein, easy to identify under an electron microscope, due to abundance of electron dense secretory granules stored near apical surface of cell
Duct cells- polarized epithelial cells specialized for the export of electrolytes, has much less developed ER and Golgi network compared to the acinar cells
Slide 7
What are the salivary digestive functions?
Humans produce 1.5L saliva/day
Serous type acinar cells in parotid gland secrete amylase, which initiates digestion of starch
Mucous type acinar cells in sublingual gland secrete mucin and proline rich proteins
Sub mandibular glands secrete both
Slide 9
What controls salivary secretion?
Parasympathetic nervous system via ACh plays most important role
No hormones in this process
Cranial nerves control these secretions
Slide 9
What is the role of duct cells in pancreatic digestion?
Pancreatic ducts secrete bicarbonate and isotonic fluid to neutralize the pH in the duodenum and provide hydration to the mucous layer
In total about 75% of total pancreatic secretions (pancreatic juice) come from the ducts
Slide 12
What is the cellular mechanism of duct secretions?
Bicarbonate is secreted to duct all lumen via a bicarbonate-chloride exchanger
Stimulation of cAMP production via secretin enhances chloride conductance to the lumen (chloride recycling)
Secretion also stims the Na-bicarbonate co transporter
ACh increases intracellular calcium levels
PKA and PKC modulate the activity of CTFR
Slide 13
What is the role of acinar cells in pancreatic digestion?
They secrete zymogens and other digestive enzymes to complete digestion
Amount of secretion can reach 100 grams of protein per day
Types of products include zymogens and active enzymes, collectively these enzymes can completely digest almost all absorbable nutrients
Slide 15
What are the mechanisms protecting against auto digestion?
Premature activation of digestive enzymes would lead to pancreatitis
3 things prevent this:
Enterokinase in the duodenum is required step for converting trypsinogen to trypsin
Zymogens are condensed & packaged in granules, and protected from cytosolic proteins
Inhibitors of digestive enzymes are co packaged in the secretory granules
Slide 15
What are the 2 secretion pathways of the acinar cells?
Constitutive pathway- active even during the inter digestive stage
Regulated pathway- upon nutrient ingestion, multiple factors stimulate the regulated pathway to increase secretion rates 5-10 fold
This causes the release of 10-20% of proteins stored in secretory granules
Slide 17
What is the cellular mechanism of pancreatic acinar secretions?
Cytosolic calcium oscillations play a predominate role in coordinating exocytosis of zymogen granules
If calcium spikes are too high following CCK exposure, desensitization can follow along with inhibition of protein secretion
Serves as fail safe mechanism
Secretin, VIP, and CCK can also elevate cAMP levels in acinar cells, which can potentiate the secretion of digestive enzymes from acinar cells
Slide 18
What is the systemic mechanism of pancreatic secretion?
During cephalic and gastric phase, ACh and gastrin are thought to play a major role in stimulating acinar cell secretion
In the intestinal phase, lipids stimulate the release of CCK, which stimulates the release of CCK, which stims vagal afferents and release ACh to act on acinar cells
Liquid meals trigger submaximal responses, solid foods trigger prolonged and maximal responses
More calories = greater response
Slide 19
