Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
21 Cards in this Set
- Front
- Back
|
Excess pancreatic production of somatostatin causes hyperglycemia. TRUE/FALSE
|
TRUE.
|
|
|
Where are the pancreatic islets located?
|
They are scattered throughout the pancreas, though they are more plentiful in the tail. They make up 2% of the volume of the gland. The exocrine portion comprises app. 80%.
|
|
|
How are islet cells differentiated/
|
They are divided by their staining properties. There are 4 types: A,B, D and F.
|
|
|
What do the D cells secrete?
|
Somatostatin.
F cells secrete pancreatic polypeptide. |
|
|
Of the islet cells which are the most common?
|
The B cells, are the most common and account for 60-75% of the cells.
|
|
|
What are B cell granules?
|
They are packets of insulin in the cell cytoplasm. The shape of the packets vary from specie to specie. In humans, some are round whereas others are rectangle shaped.
|
|
|
What can be said of insulin molecules?
|
It forms polymers and also complexes with zinc.
|
|
|
The A granules, which contain glucagon are relatively uniform from species to species. TRUE/FALSE
|
TRUE.
|
|
|
What is the structure of insulin?
|
It is a polypeptide containing two chains of amino acids linked by disulfide bridges. Minor differences occur in amino acid composition of the molecule from species to species. because of these differences, insulin can be antigenic, though its biological activity is maintained.
|
|
|
Almost all humans who have received commercial beef insulin for more than 2 months have antibodies against beef insulin. TRUE/FALSE
|
TRUE.
|
|
|
Pork insulin is different than human by one amino acid. TRUE/FALSE
|
TRUE.
|
|
|
What is the biosynthesis of insulin?
|
It is synthesized in the rough endoplasmic reticulum of the B cells, and then transported to the Golgi apparatus where it is packaged into granules.
|
|
|
How are these granules secreted?
|
These granules move to the plasma membrane and their contents are expelled by exocytosis. The insulin then crosses the basal lamina of the B cell and a neigboring capillary and the fenestrated endothelium of the capillary to reach the bloodstream.
|
|
|
Is insulin synthesized as a part of a larger molecule/
|
Yes. It is a part of a preprohormone. The gene for insulin is on chromosome 11.
|
|
|
What is the structure of preproinsulin?
|
It has a 23 amino acid signal peptide removed as it enters the ER. The remainder of the molecule is then folded and the disulfide bonds are formed to make proinsulin.
|
|
|
What is C peptide?
|
The peptide segment connecting the A and B chains, the connecting peptide facilitates the folding and then is detached in the granules before secretion.
|
|
|
What is involved in processing the proinsulin?
|
Two proteases are involved. C peptide has no other physiologic activity. Normally 90-97% of the product released from the B cells is insulin along with equimolar amounts of C peptide.
|
|
|
Can C peptide be measured/
|
Yes. by radioimmunoassay, and its level provides an index of B cell function in patients receiving exogenous insulin.
|
|
|
What are insulin like growth factors(IGF)?
|
Plasma contains a number of substances with insulin like activity in addition to insulin. The activity that is not suppressed by antiinsulin antibodies has been called "nonsuppressible insulin like activity(NSILA). Most if not all of this activity persists after pancreatectomy and is due to the insulin like growth factors IGF-1 and IGF-11.
|
|
|
What are these IGFs?
|
They are polypeptides. Small amounts are free in the plasma, but large amounts are bound to proteins(high molecular weight fraction) IGF factors are weak though compared to the activity of insulin.
|
|
|
How is insulin metabolized?
|
The half life of insulin is app 5 min. Insulin binds to insulin receptors and some is internalized. It is destroyed by proteases in the endosomes formed by the endocytotic process.
|
