12. Celluar Secretions Flashcards
Define what an exocrine gland is and give an example of the location substance of secretion
They produce and secrete substances onto an epithelial surface via a duct.
For example in the gut, secreting bicarbonate and sodium
Define what an endocrine gland is and give and example of what they are usually made of and what they excrete
Endocrine glands secrete proteins and steroids directly into the blood without a duct. They are usually hormones!
Where are secreted proteins synthesised in a cell? And how are they transported?
Proteins are synthesised on ribosomes on the rough ER (via translation!)
Transported in a vehicle
What do all proteins have when they enter the secretory pathway?
They all have a signal sequence at the N-terminus (about 15-20 amino acids long - a sequence to indicate where to go)
What are proteins packaged into and give an example of the exocytosis in the pancreas, what its protecting itself from and how its triggered
Proteins are packed into SECRETORY VESICLES!
For example, digestive enzymes secreted by the acinar cells of exocrine pancreas.
The vesicles protect the digestive enzymes from the proteolytic enzymes (enzymes that break protein down)
Triggered by calcium
What’s the difference between constitutive secretion and regulated? Give an example for each
Constitutive: proteins are continuously secreted eg secretion of serous proteins by the liver hepatocytes
Regulated: proteins released only when the cell receives a signal, usually due to a rise in cytosolic calcium. Eg digestive enymes
What is exocytosis?
The release of secretory vesicles from inside the cell and the fusion of the vesicles (that contains the proteins) with the cell membrane
What is endocytosis?
The entrance of proteins from outside the cell to the inside, the vesicles binds to the cell membrane and releases its contents
How does the sidedness of membranes change when a vesicle binds to it?
The outside of the vesicle become the inner layer of the cell membrane
The inside of the vesicle becomes the outer layer of the cell membrane
What do insulin-secreting Beta-cells contain and why do they store this?
They store a semi-crystalline core of insulin (secretory proteins) inside vesicles - these can be regulated and exit the cel in large amounts when triggered
Why is endocytosis important to exocytosis?
Because in exocytosis, the vesicle membranes bind to the cell membrane, making the cell large. Endocytosis is necessary to keep the cell at a constant size.
What are the three types of exocrine secretions? Give an example for each
Mucous - viscous
Serous - watery
Mixed (seromucos) salivary glands
What are the three types of exocrine gland cells that make gastric juice in the gastric pits (stomach).
What is the role of all three exocrine gland cells?
Mucous neck cells - mucous - synthesise alkaline mucus that covers the surface
Chief cells - enzymes - synthesises and secretes the protease precursor
Parietal cells - hydrochloric acid - makes the gastric lumen acidic
What does bicarbonate do in the duodenum?
Neutralisation of stomach acid - pH buffer. Its secreted by the brunners endocrine gland in the upper duodenum
What percentage of exocrine and endocrine gland is in the pancreas? What is the smaller percentage one called?
About 98% exocrine and 2% endocrine
The endocrine gland is called the Islets of Langerhans
