Endocrine Pancreas Flashcards
The endocrine cells of the pancreas secrete 3 separate hormones
Beta cells secrete ____
Alpha cells secrete ____
Delta cells secrete ______
Insulin (and C peptide)
Glucagon
Somatostatin
The beta, alpha, and delta cells of the pancreas are organized into clusters called ____
Islets (of langerhans)
Which cells of the pancreas are neuronal in appearance and send dendrite like processes to beta cells?
Delta cells
Most ____ cells of the pancreas are centrally located, while most _____ are peripherally located
Beta; alpha
How do individual islets in the endocrine pancreas communicate with each other?
Via gap junctions - rapid cell-cell communication
Describe blood supply to the endocrine pancreas - which cells receive blood first?
Venous blood first flows to center for insulin; venous blood from beta cells carries insulin to alpha and delta cells
[flows through periphery, insulin rich blood inhibits glucagon release from alpha cells]
What is the major stimulating factor for insulin secretion?
Glucose
Insulin is a _____ hormone made up of 2 chains linked by _____ bridges
Peptide; disulfide
_______ = signal peptide with A and B chains with connecting C peptide - NO disulfide bonds
Preproinsulin
[preproinsulin —> proinsulin —> Insulin + C peptide]
______= no signal peptide because C peptide still attached to insulin; packaged into secretory granules, proteases can cleave it
Proinsulin
Once synthesized, insulin and cleaved C peptide are packaged together in ______
Secretory vesicles
What compound can be used as a marker of endogenous insulin secretion?
C peptide
Steps for insulin release:
- Glucose enters cell via ______
- Glucose is phosphorylated by a ________
- G6P is oxidized, promoting ___ generation
- ATP closes the inward rectifying ____ channel
- Plasma membrane is depolarized
- Activation of voltage gated ___ channels leading to its entry into the cell
- Mobilization of insulin is initiated
GLUT2 Glucokinase ATP K Ca
Rises in ATP have what effect on K channels in beta cells?
Rises in ATP close the K channels
The sulfonurea receptor associated with ATP-dependent K channels increase insulin secretion. what effect does this have on membrane depolarization?
Causes membrane depolarization to occur more easily d/t increased Ca entry - so this can be targeted and used for tx of T2DM
C peptide secretion is used as a tool to measure function of beta cells and endogenous insulin secretion. C peptide is typically secreted in the ____
Urine
Describe the biphasic release of insulin and how this is affected in diabetics
When plasma glucose increases:
Phase 1 = initial spike in insulin secretion
Phase 2 = gradual sustained rise in insulin secretion
In diabetes — phase 1 is the first phase lost
Besides blood glucose levels, what are some other modulators of insulin secretion?
Activating:
GI peptides
Glucagon
ACh
Inhibitory:
Somatostatin