pack Flashcards
(22 cards)
What are the three main cell types of the islets of langerhans?
The beta cells (~60% of all the cells of the islets), lie mainly in the middle of each islet and secrete insulin and amylin (function unclear).
- The alpha cells (~25% of the total), secrete glucagon.
- The delta cells (~10% of the total), secrete somatostatin.
Where is insulin preprohormone cleaved?
preprohormone is then cleaved in the endoplasmic reticulum to form a proinsulin
Where is insulin prohormone cleaved?
Most of the proinsulin is further cleaved in the Golgi apparatus
What enzyme degrades insulin in the liver and to a lesser extent kidneys, muscles, and other tissues?
insulinase
What is the mechanisim of insulin secretion from B-cells?
Remember MOL (Catalyst university)
The basic cellular mechanisms for insulin secretion by the pancreatic beta cells in response to increased blood glucose concentration which is the primary controller of insulin secretion.
● The beta cells have a large number of glucose transporters (GLUT 2) that permit a rate of glucose influx that is proportional to the blood concentration in the physiological range.
● Once inside the cells, glucose is phosphorylated to glucose-6-phosphate by glucokinase. (rate limiting step)
● The glucose-6-phosphate is subsequently oxidized to form adenosine triphosphate (ATP), which inhibits the ATP-sensitive K+ channels of the cell.
● Closure of the K+ channels depolarizes the cell membrane, thereby opening voltage-gated calcium channels, which are sensitive to changes in membrane voltage.
● This produces an influx of Ca++ that stimulates fusion of the docked insulin-containing vesicles with the cell membrane and secretion of insulin into the extracellular fluid by exocytosis
https://youtu.be/5SsS_PCrDTo?si=fu1brrJSQlAxEU_e
What are two examples of sulfonylurea drugs and how do they work?
Examples: glipizide or Glucotrol
Mechanisim: inhibit K+ channels in the beta cell which depolarizes the membrane eventually causing insulin secretion
What is the pattern of insulin release in a patient that was fasting and then had a sudden rapid increase in blood glucose? (increased to a level 2-3X normal)
It is released in two stages.
Stage 1: Plasma insulin concentration increases almost 10X within 3-5 minutes after the acute elevation of the blood glucose (results from dumping of preformed insulin).
Stage 2 happens within 15-20 minutes and is gradual bc new insulin being formed.
What kinase activity do insulin receptors in tissues use for stimulation of glucose uptake?
Tyrosine kinase activity
What are excess carbohydrates that cannot be converted to glycogen converted into?
converted under the stimulus of insulin into fats and stored in the adipose tissue
Why does insulin release result in a decrease in ketobody synthesis?
because insulin causes decreased fatty acid degradation which means that less acetyl coenzyme A (acetyl CoA)
substrate will be available for the formation of ketoacids.
What does insulin do in relation to K+?
Insulin promotes K+ uptake into cells (at the same time that it promotes glucose uptake) by increasing the activity of the Na+-K+ ATPase.
There is extra information in the slides, reading through them quickly is advised.
Ok buddy
What happens when the blood glucose falls too low (20-50 mg/100 ml?
symptoms of hypoglycemic shock develop
characterized by progressive nervous irritability that leads to fainting, seizures, and even coma.
What 4 hormones other than insulin play a role in “Switching” Between Carbohydrate and Lipid Metabolism?
- Growth hormone (hypoglycemia) from the anterior pituitary gland.
- Cortisol (hypoglycemia) from the adrenal cortex.
- Epinephrine from the adrenal medulla.
- Glucagon from the alpha cells of the islets of Langerhans in the pancreas.
Does epinephrine increase blood glucose or fat levels more? Explain.
● Epinephrine is important in increasing plasma glucose concentration during periods of stress when the sympathetic nervous system is excited. However, epinephrine acts differently from the other hormones in that it increases the plasma fatty acid concentration at the same time. The reasons for these effects are as follows:
1. Epinephrine has the potent effect of causing glycogenolysis in the liver, thus releasing within minutes large quantities of glucose into the blood.
2. It also has a direct lipolytic effect on the adipose cells because it activates adipose tissue hormone-sensitive lipase, thus increasing the blood concentration of fatty acids as well. Conclusion: Quantitatively, the enhancement of fatty acids is far greater than the enhancement of blood glucose. Therefore, epinephrine especially enhances the utilization of fat in such stressful states as exercise, circulatory shock, and anxiety.
how does glucagon work?
- Glucagon activates adenylyl cyclase in the hepatic cell membrane
- Which causes the formation of cyclic adenosine monophosphate (cAMP),
- Which activates protein kinase regulator protein,
- Which activates protein kinase,
- Which activates phosphorylase b kinase,
- Which converts phosphorylase b into phosphorylase a,
- Which promotes the degradation of glycogen into glucose-1-phosphate,
- Which is then dephosphorylated; and the glucose is released from the liver cells.
What is the signaling pathway of Glucagon and Epinephrine?
Adenylate cyclase/cAMP
What is the signaling pathway of insulin?
Phosphoinositide 3-kinase
pathway
What is diabetic ketoacidosis?
What is hyperosmolar hyperglycemic state?
What do the alpha and beta adrenergic receptors do?
