Pathophysiology of Carbohydrate Metabolism

Question 1

Glucose enters pancreatic beta cells via GLUT-2 receptors. How is the release of glucose then stimulated?

Answer 1

Glucose undergoes glycolysis in beta cells, producing ATP. Increased ATP closes potassium channels and depolarizes the cell. Calcium channels open and calcium influx-induced insulin exocytosis.

Question 2

This type of hypoglycemia occurs after eating a meal and is often due to rapid movement of food through shortened bowels.

Answer 2

Postprandial (Reactive) Hypoglycemia

Question 3

This molecule in produced from the cleavage of proinsulin and directly reflects insulin release.

Answer 3

C-peptide

Low c-peptide with high insulin indicates exogenous insulin injection

Question 4

This is the best maker of endogenous insulin secretion.

Answer 4

C-peptide

Question 5

True/False. Nearly half of all secreted insulin is filtered by the liver before entering circulation.

Answer 5

True - only 50% of secreted insulin enters circulation.

Question 6

Somatostatin (increases/decreases) insulin secretion and (increases/decreases) glucagon secretion.

Answer 6

Somatostatin inhibits both insulin and glucagon secretion

Question 7

These counter-regulatory hormones act similarly to glucagon to generate fuel for the body.

Answer 7

Catecholamines, cortisol, growth hormone, thyroid hormone

Question 8

What is the effect of epinephrine on skeletal muscle?

Answer 8

Epinephrine promotes glycogenolysis in skeletal muscle. Since muscle lacks glucose-6-phosphatase, lactate is produced

Question 9

These amino acids are coupled with sodium transporters that can induce beta-cell depolarization and insulin release.

Answer 9

Glycine, alanine, arginine

Question 10

A patient presents with symptoms of hypoglycemia. Blood test reveals high glucose levels. The patient fasts, but high insulin levels persist. What is the likely diagnosis?

Answer 10

Insulinoma - neuroendocrine tumor that secretes insulin

Question 11

This enzymatic pathway mediates the mitogenic functions of insulin.

Answer 11

MAP Kinase pathway

Question 12

Diagnosis of hypoglycemia requires fulfilling Whipple’s triad. What is Whipple’s triad?

Answer 12

Symptoms of hypoglycemia, low serum glucose, resolution of symptoms with supplemental glucose

Question 13

Diabetes is associated with an increased risk of cardiovascular complications. What is one reason for this?

Answer 13

Insulin is a vasodilator that increases NO synthesis. Diabetic patients lose this function due to low insulin, leading to increased vasoconstriction

Question 14

What medical condition contributes most to the pathogenesis of metabolic syndrome?

Answer 14

Insulin resistance

Question 15

True/False. Carbohydrates provide more energy than fatty acids.

Answer 15

False. Carbs and proteins provide 4kcal. Fats provide 9kcals.

Question 16

True/False. Insulin can cause hyperkalemia.

Answer 16

False. Insulin induces the Na/K ATPase and moves K+ into cells. Insulin is used in the treatment of life-threatening hyperkalemia

Question 17

What is the relationship between free fatty acids and insulin?

Answer 17

Insulin inhibits lipolysis to decrease free fatty acids. Excess free fatty acids contribute to the development of insulin resistance

Question 18

This is the functional endocrine part of the pancreas.

Answer 18

Islets of Langerhans

Question 19

What is the effect of sulfonylurea on blood glucose?

Answer 19

Sulfonylurea lowers blood glucose and may cause hypoglycemia

Question 20

This enzymatic pathway mediates the metabolic actions of insulin.

Answer 20

PI3K Pathway

Question 21

During periods of fasting, what is the progression of glucose use?

Answer 21

Plasma glucose –> glycogenolysis –> gluconeogenesis

Liver glycogenolysis can only provide glucose for approx. 16 hours

Question 22

What are the first symptoms of hypoglycemia?

Answer 22

Autonomic symptoms such as sweating, anxiety, palpitations, and dizziness. Neurologic symptoms follow due to continued low glucose

Question 23

This hormone functions to regulate energy balance and body weight. Resistance to this hormone is associated with obesity.

Answer 23

Leptin - produced by adipose tissue to suppress appetite

Question 24

What is the function of adiponectin?

Answer 24

Adiponectin inhibits gluconeogenesis and promotes beta-oxidation of fatty acids serving to decrease plasma glucose levels

Question 25

This is a dermatologic manifestation of chronically high circulating insulin levels.

Answer 25

Acanthosis nigricans - insulin promotes proliferation of keratinocytes and fibroblasts

Question 26

What are the primary target organs for glucagon?

Answer 26

Liver and adipose tissue. Glucagon has no direct effect on skeletal muscle

Question 27

How does glucagon mediate its effects on target tissue?

Answer 27

Glucagon increases cAMP, thus activating the PKA

Question 28

Diagnosis of metabolic syndrome requires 3 of 5 possible medical conditions. What are the 5 conditions?

Answer 28

Insulin resistance, dyslipidemia, hypertension, abdominal obesity, low HDL

Question 29

This type of hypoglycemia is due to glucose underproduction or excess insulin.

Answer 29

Fasting (Non-Reactive) Hypoglycemia

Question 30

What is the effect of norepinephrine and epinephrine on insulin secretion?

Answer 30

Inhibits insulin secretion and promotes glucagon secretion to increase plasma glucose