16. The Endocrine Pancreas Flashcards
Which five hormones does the endocrine pancreas secrete and by what cell type?
Insulin from B cells Glucagon from a cells Somatostatin from d cells Pancreatic polypeptide from F cells Ghrelin from a fifth cell type.
What are the functions of the five hormones secreted by the endocrine pancreas?
Insulin and glucagon for regulation of metabolism of carbohydrates, proteins and fats.
Somatostatin for islet cell secretion function.
Pancreatic polypeptide for GI function.
Ghrelin for appetite.
What are the target tissues of insulin?
Liver, adipose and skeletal muscle.
What are the target tissues for glucagon?
Liver and adipose.
What is the renal threshold of plasma glucose, what happens if it is exceeded and how is it affected in pregnancy and old age?
10mmol/L, if exceeded glucosuria (glucose in the blood) spit is decreased in pregnancy and increased in the elderly.
What is the structure of insulin?
A big peptide. Two unbranched peptide chains connected by 2 disulphide bridges for security.
How is insulting synthesised and excreted?
mRNA production of preproinsulin gene transcription.
Synthesis of preproinsulin and then excision of a single peptide to form proinsulin with disulphide bonds.
Proinsulin get transported to Golgi.
Proinsulin is converted to insulting and packaged.
Insulin is stored in a granule.
Granule fuses with membrane and insulting is exocytosed.
What is the half life of insulin?
5 mins.
What is the response to increased glucose levels?
Release of insulin. Glucose is transported into B cell by facilitated diffusion thorough GLUT2. Membrane depolarisation and influx of extracellular calcium. This triggers exocytosis of insulin-containing secretory granules.
What is the structure of insulin receptor?
A dimer with two identical subunits that span the cell membrane. The subunits are made of one a chain and one B chain connected by a single disulphide bond. The alpha chain goes on the exterior of the cell membrane, with the beta chain spanning the cell membrane.
What happens to the insulin receptor when activated?
The a chains move together and fold around the insulin. The beta chains are moved together and form an active tyrosine kinase, initiating phosphorylation cascade increasing GLUT4 expression so cells take up more glucose.
Where is glucagon synthesised?
In rough ER then transported to the Golgi in packaged granules.
What is margination?
Movement of storage vesicles to cell surface.
What is exocytosis?
Fusion of vesicle membranes with the plasma membrane with the release of the vesicle contents.
What is the the structure of glucagon?
29 amino acids in one polypeptide chain. There are no disulphide bridges.
