1 - Insulin and Glucagon Flashcards
The pancrease aids in glucose control by secreting which two hormones:
glucagon
insulin
What are the two major types of tissues in the pancreas?
- Acini - secrete digestive juices into the duodenum
- Islets of langerhans - secrete insulin and glucagon directly into the blood
Describe the three major types of islet cells:
- Alpha - 25%, secrete glucagon
- Beta - 60%, secrete insulin and amylin
- Delta - 10%, secrete somatostatin
In the pancreas, cell-to-cell communication leads to control of secretion.
Insulin inhibits ______
Amylin inhibits _______
Somatostatin inhibits ________
glucagon secretion
insulin secretion
insulin and glucagon secretion
Insulin effects the metabolism of ______
protein, fat, AND carbohydrate metabolism
Human insulin is composed of two amino acid chains connected by _______
disulfide linkages
When the two AAs are split apart, insulinf’s functional activity is lost
In a patient who is taking insulin to control their glucose, how can you tell how much insulin their pancreas is producing?
Checking C peptide levels by radioimmunoassay
What is the halflife of endogenous insulin?
6 minutes
cleared within 15 minutes
What happens when insulin binds with its receptor on a cell?
within seconds the membrane increases the uptake of glucose (EXCEPT IN NEURONS)
the cell membrane becomes more permeable to amino acids, K, and Phos
Prolonged changes take place due to DNA transcription activation
When exercising, how do your muscle cells increase their glucose uptake?
When they contract it mobilizes GLUT 4 from intracellular storage to the depot, which increases glucose permeability
After eating, large amount of glucose is moved into the muscles. What happens to this glucose, assuming you don’t immediately exercise?
stored as muscle glycogen , which can be used later by the muscle for energy
Insulin causes most of the glucose absorbed after a meal to:
be rapidly stored in the liver as glycogen
Describe how insulin causes glucose uptake by the liver
- activates liver phosphorylase to stop any further breakdown of glycogen
- increases the activity of glucokinase, which phosphorylates glucose as it enter the cell so that it’s trapped inside the cell
- increases the activities of glycogen synthase to polymerize the units into glycogen
When blood sugar falls, how does glucose get released back into the blood from the liver?
by decreased amount of insulin
pancrease stops secreting insulin and the liver stops inhibiting glucose breakdown
What happens when the amount of glucose consumed is more than can be stored in the liver as glycogen?
insulin promotes the conversion of glucose into fatty acids
fatty acids are packaged as LDLs
LDLs are transported to the adipose tissue and deposited as fat
Which organ has a glucose level that is completely unaffected by insulin?
The brain!
Most brain cells are permeable to glucose and can use glucose without the intermediation of insulin
Why does insulin increase fat storage?
Insulin increases glucose use, which means less fat is used for energy
promotes fatty acid synthesis
What effect does insulin have on protein formation?
promotes formation
prevents degradation
An insulin deficiency has what effect on plasma fatty acids?
Plasma amino acids?
Increased (since glucose can’t be used)
Increased (more protein being broken down in the absence of insulin)
Insulin acts synergistically with ________ to promote growth
growth hormone
How do beta cells know when to secrete insulin?
have a large number of glucose transporters that keep glucose influx into the cell proportional with serum blood glucose levels
when glucose is phosphorylated in the cell if gets stuck and triggers closure of potassium channels
closing the K channels depolarizes the membrane, which causes an influx of calcium
calcium triggers vessicular release of insulin
How do sulfonylureas work?
stimulate insulin secretion by binding to the ATP-sensitive potassium channels (the same ones glucose binds to) in order to cause depolarization
depolarization releases insulin
What are incretins?
hormones that enhance the rate of insulin release from pancreatic beta cells
also inhibit glucagon release from alpha cells
prolonged secretion of which hormones can cause exhaustion of beta cells?
glucagon
GH
cortisol
progesterone and estrogen
Stimulation of the ______ nerves to pancrease can increase insulin secretion
parasympathetic
What is the effect of epinephrine on blood glucose levels?
causes glycogenolysis in the liver, releaseing large quantities of glucose into the blood
breaks down adipose cells and increases concentration of fatty acids
Glucagon is also called the ________ hormone
hyperglycemic
What is remarkable about the glycogenolysis pathway sparked by glucagon?
one of the most thoroughly studied examples of adenylyl cyclase - cAMP pathway
amplifying effect: each succeeding product of the pathway is produced in greater quantity than the preceding product
Glucagon raises blood sugar via _______ and _______
glycogenolysis in the lvier
gluconeogenesis in the liver after all available glycogen stores are utilized
Why is glucagon helpful in beta blocker overdose?
It increases heart rate and myocardial contractility by some mechanism other than the B1 recceptor that somehow bypases the need for beta receptor activation
An increase in blood glucose ______ glucagon
Increased blood amino acids ______ glucagon
Exercise ______ glucagon
decreases
increases
increases
What is the principle role of somatostatin?
extend the period over which food nutrients are assimilated into the blood
prevents rapid exhaustion of the food
Somatostatin is also the same chemical substance as _____
growth hormone inhibition hormone
Makes sense, since insulin and GH have dual roles in promoting growth
In severe hypoglycemia, low blood sugar in the cells of the ________ stimulates the SNS to release _______
hypothalamus
epinephrine from the adrenal cortex
Which organs rely on glucose ONLY and cannot use fats for metabolism?
the brain
retina
germinal epithelium of the gonads
Type 1 DM is associated with _____ insulin levels
Type 2 DM is associated with ______ insulin levels
decreased
increased
Why does obesity cause insulin resistance?
Likely isn’t due to a decreased number of insulin receptors, but rather an alteration in secondary signalling
likely that toxic lipid accumulation in cells causes this abnormal signalling
What are SgLT2 inhibitors?
Inhibit SGLT2 in the renal tubules, preventing reabsorption of glucose
HbA1c is useful for testing glucose levels over past three months. Why?
lifespan of a RBC is 120 days
Why is it problematic to try to just cut out carbs for patients with DM2?
It keeps BG low, but a lack of insulin still causes increased LDLs and protein deficiency.
It’s recommended to give diabetics a normo-carb diet and give enough insulin to cover the carbs eaten
______ calcium causes nervous excitability
_______ calcium causes nervous depression
decreased
increased
The anterior lobe of the pancreas, where endocrine action is most profound, is perfused by:
The posterior lob is perfused by:
superior mesenteric A
celiac A
Insulin facilitates the intracellular transport of which three ions:
potassium
phosphate
magnesium
What is amylin
cosecreted with insulin
regulates BG conentration by delaying gastric emptying and suppressing glucagon secretion after meals
satiety effect
ANTI-HYPERGLYCEMIC
How do glucose levels effect glucagon release?
high glucose –> decreased glucagon
low glucose -> increased glucagon
What is the difference between hypothalamic somatostatin and pancreatic somatostatin?
P somatostatin regulates islet cell function to inhibit secretion of insulin, glucagon, and polypeptide
essential in carbohydrate, fat, and protein metabolism
H somatostatin inhibits release of GH and TSH
Somatostatin has what effect on somatotropes?
Keeps them “static”
(inhibits)
