Lecture 8 - Endo/Repro Exam 1: Endocrine System (Other Pancreatic Hormones)

pancreas

The ________ is both an exocrine and endocrine organ

insulin

glucagon

somatostatin

pancreatic polypeptide

What are the four hormones the pancreas secretes into the bloodstream?

islet of Langerhans

function endocrine cells are clustered together in spherical ______ of which the pancreas contains approximately one million.

Beta cells

Alpha cells

Delta cells

What are the three major cell types in the islets?

beta cells

_______ occupy the central portion of the islet and produce insulin

alpha cells

What cells produce glucagon?

delta cells

What cells secrete somatostatin?

alpha and delta

What two cells surround beta cells in an islet?

glucagon

Secreted by alpha cells when insulin levels fall—during fasting between meals

hypoglycemia (blood sugar <1mg/ml)

Most potent stimulus for secretion

hypoglycemia

decreasing insulin

amino acids

sympathetic stimulation

Stimuli for secretion of glucagon

somatostatin and fatty acids

Glucagon is inhibited by ______ and ______.

liver

Glucagon primarily acts on the _____ to increase and maintain blood glucose during times of fasting. - an antagonist

proglucagon

Glucagon is a peptide hormone synthesized as ________ and then processed into the 29-residue glucagon in the alpha cells.

false

T/F: synthesis of glucagon is inhibited by insulin and somatostatin acting in an endocrine fashion

Glucose enters the alpha cells through a glucose (Glut1) transporter and undergoes glycolysis to produce ATP

First step in the secretion of glucagon

The ATP level in the alpha cell reflects the plasma glucose level

Second step in the secretion of glucagon

Hypoglycemia reduces ATP and causes the closing of ATP-sensitive K+ channels depolarizing the membrane

Third step in the secretion of glucagon

The opening of Ca++ channels and the influx of Ca++, triggers exocytosis of the hormone from storage vesicles

Last step in the secretion of glucagon

Kidneys

Heart

Adrenal Glands

GI Tract

Pancreas

Where is glucagon found in lesser amounts outside of the liver?

true

T/F: Glucagon main signaling involves G-protein activation which activates adenylyl cyclase to produce cAMP and protein kinase C, which activate downstream enzymes

receptor-mediated endocytosis

proteolysis by cellular enzymes

Glucagon signaling is inactivated by:

4-7 minutes

Glucagon’s half-life

increasing glycogenolysis, inhibiting glycogenesis and glycolysis

stimulating de novo glucose synthesis (gluconeogenesis)

during long fasts, allows glycolysis to deplete stored glycogen and gluconeogenesis take over

Glucagon increases hepatic glucose production and release to the bloodstream by:

glycogenolysis (glycogen breakdown to release glucose from the liver)

gluconeogenesis (liver converting amino acids or fats to glucose then bloodstream)

sparing of glucose for CNS

What are the main metabolic effects of glucagon?

14; 28

Somatostatin is a cyclic peptide with two isoforms, one with _____ amino acid residues and one with _____.

G-protein coupled receptors

Somatostatin acts on target cells by binding to ____________ to regulate parts of the endocrine system.

inhibiting release of both insulin and glucagon (paracrine)

Somatostatin acts in the islets of the pancreas by:

inhibiting release of growth hormone, thyroid stimulating hormone (TSH), and corticotropin from the anterior pituitary

Somatostatin acts in the hypothalamus by:

inhibiting gastrin secretion from the stomach

Somatostatin acts in the GI tract by:

inhibiting secretion of T3, T4, and calcitonin

Somatostatin acts in thyroid by:

inhibiting aldosterone secretion

Somatostatin acts in the adrenal gland by:

1-3 minutes

Half life of somatostatin:

anti-neoplastic effects on tumors and against acromegaly

What is somatostatin’s clinical use?

Pancreatic polypeptide (PP)/PP cells of islets of langerhans of pancreas

Endogenous peptide hormone secreted by F cells

inhibition of gastric emptying as well as biliary secretion

The primary role of PP is to modulate digestion of food by __________.