89 Questions
What is the primary function of insulin and glucagon in the regulation of metabolism?
Regulation of carbohydrate metabolism
How many distinct cell types are present in the islets of Langerhans in humans?
Four
What is the role of somatostatin in the pancreas?
Regulation of islet cell secretion
What is the name of the hormone concerned primarily with the regulation of ion transport in the intestine?
Pancreatic polypeptide
What is the name of the cells in the islets of Langerhans that are also called α cells?
A cells
What is the term for the collections of cells in the pancreas?
Islets of Langerhans
What is the effect of hyperglycemia on the body's water balance?
Dehydration due to osmotic diuresis
What is the result of hyperglycemia on hemoglobin A?
Non-enzymatic glycation of hemoglobin A to form HbA1c
What is the effect of hyperglycemia on protein metabolism?
Increased rate of amino acid catabolism
What is the clinical significance of HbA1c measurement?
It is an integrated index of diabetic control for the past 4-6 weeks
How can hyperglycemia be induced in animals?
By administration of anti-insulin antibodies
What is the result of the body's response to dehydration caused by hyperglycemia?
Increased thirst and polydipsia
What is the primary reason for the increase in blood amino acid levels in severely ill diabetics?
Decreased protein synthesis in muscle
What is the effect of insulin on the hormone-sensitive lipase in adipose tissue?
It inhibits the hormone-sensitive lipase
What is the primary reason for the increased plasma concentration of triglycerides and chylomicrons in uncontrolled diabetes?
Decreased removal of triglycerides into the fat depots
What is the relationship between the plasma level of free fatty acids and the plasma glucose level in diabetes?
The plasma level of free fatty acids is directly proportional to the plasma glucose level
What is the effect of insulin on the conversion of glucose to fatty acids in the depots?
It increases the conversion of glucose to fatty acids
What contributes to the increased formation of ketone bodies in diabetes?
Accelerated lipid catabolism
What is the effect of insulin binding to its receptor?
Phosphorylation of β subunits on tyrosine residues
What is the cause of type 1 diabetes?
Autoimmune destruction of the B cells in the pancreatic islets
What is the term for the constellation of abnormalities caused by insulin deficiency?
Diabetes mellitus
What is the effect of treating diabetic acidosis with insulin?
Hypokalemia
What are the two subunits of the insulin receptor?
α and β
What is associated with obesity?
Hyperinsulinemia and dyslipidemia
What is the effect of insulin on skeletal muscle cells?
It increases the number of GLUT-4 transporters in the cell membranes
What is the effect of insulin on K+ levels?
It decreases the extracellular K+ concentration
What is the effect of insulin on Na, K ATPase in cell membranes?
It increases the activity of Na, K ATPase
What is the effect of weight reduction on insulin resistance?
It decreases insulin resistance
What is secreted by the pancreas?
Four polypeptides with hormonal activity
What percentage of cells in the islets are B cells?
60-75%
What is the process by which insulin is released from the B cells?
Exocytosis
What is the approximate half-life of insulin in the circulation in humans?
5-10 minutes
What is the structure of insulin?
Two chains of amino acids linked by disulfide bridges
What is the site of insulin synthesis in the B cells?
Rough endoplasmic reticulum
What is the percentage of the pancreas that is composed of β-islets?
1-2%
What is the effect of insulin on protein synthesis in skeletal muscle?
Stimulation of protein synthesis
What is the effect of insulin on glucose entry in adipose tissue?
Increase in glucose entry
What is the effect of insulin on ketone bodies in diabetic individuals?
Decrease in ketone bodies
What is the effect of insulin on amino acid uptake in muscle cells?
Increase in amino acid uptake
What is the effect of insulin on glycogen synthesis in muscle cells?
Increase in glycogen synthesis
What is the effect of insulin on lipoprotein lipase in adipose tissue?
Activation of lipoprotein lipase
What is the primary function of the islets of Langerhans in the pancreas?
Regulation of the intermediary metabolism of carbohydrates, proteins, and fats
Which of the following hormones is NOT produced by the islets of Langerhans in the pancreas?
Adrenaline
What is the function of the B cells in the islets of Langerhans?
Production of insulin
Which of the following is a consequence of hyperglycemia?
Increased plasma concentration of triglycerides and chylomicrons
What is the term for the cells in the islets of Langerhans that are responsible for producing glucagon?
A cells
What is the function of pancreatic polypeptide in the islets of Langerhans?
Regulation of ion transport in the intestine
What is the effect of pancreatic polypeptide on the absorption of food in humans?
It slows the absorption of food
What is the cause of chronic mild hypoglycemia in humans?
Uncontrolled diabetes mellitus
What is the characteristic of functional hypoglycemia?
The plasma glucose rise is normal after a test dose of glucose
What is the term for the constellation of abnormalities caused by insulin deficiency?
Diabetes mellitus
What is the effect of somatostatin on the secretion of pancreatic polypeptide?
It decreases the secretion of pancreatic polypeptide
What is the effect of a meal containing protein on the secretion of pancreatic polypeptide?
It increases the secretion of pancreatic polypeptide
What is the primary cause of type 1 diabetes?
Autoimmune destruction of the B cells in the pancreatic islets
What is the term used to describe the condition characterized by a large urine volume and sweet-tasting urine?
Diabetes mellitus
What is the characteristic of type 2 diabetes?
Dysregulation of insulin release from the B cells and insulin resistance in peripheral tissues
What is the term reserved for conditions in which there is a deficiency of the production or action of vasopressin?
Diabetes insipidus
What percentage of cases of diabetes mellitus is accounted for by type 1 diabetes?
3-5%
What is the usual age of onset for type 1 diabetes?
Only children
What is the primary function of the two hormones secreted by the islets of Langerhans in the pancreas?
Regulation of carbohydrate, protein, and fat metabolism
How many types of cells are present in the islets of Langerhans in humans?
Four distinct cell types
What is the role of somatostatin in the pancreas?
Regulation of islet cell secretion
What is the function of pancreatic polypeptide in the pancreas?
Regulation of ion transport in the intestine
What is the term for the collections of cells in the pancreas that produce hormones?
Islets of Langerhans
Which of the following cells are responsible for producing insulin?
B cells
What percentage of the pancreas is composed of β-islets?
2%
How many cells types are present in the islets of Langerhans in humans?
4
What is the half-life of insulin in the circulation in humans?
5 minutes
Where is insulin synthesized in the B cells?
Rough endoplasmic reticulum
What is the structure of insulin?
Two chains of amino acids linked by disulfide bridges
What is secreted by the D cells in the islets of Langerhans?
Somatostatin
What is the effect of pancreatic polypeptide on food absorption in humans?
It slows down the absorption of food
What is the cause of chronic mild hypoglycemia in humans?
Functional hypoglycemia
What is the term for the constellation of abnormalities caused by insulin deficiency?
Diabetes Mellitus
What is produced by F cells in the islets?
Pancreatic Polypeptide
What is the characteristic of functional hypoglycemia?
All of the above
What increases the secretion of pancreatic polypeptide?
Fasting, exercise, and acute hypoglycemia
What is the effect of Ca2+ influx on insulin secretion?
It produces the initial spike of insulin secretion
What is the effect of increased intracellular glutamate on insulin secretion?
It commits a second pool of secretory granules to the releasable form
What is the effect of glucagon on glycogen in the liver?
It activates phosphorylase to break down glycogen
What is the effect of glucagon on plasma glucose levels?
It increases plasma glucose levels
How does the feedback control of plasma glucose on insulin secretion operate?
With high precision and consistency
What is the function of glucagon in the body?
It is glycogenolytic, gluconeogenic, lipolytic, and ketogenic
What is the consequence of polyuria in diabetes?
Dehydration
Which of the following is a long-term complication of diabetes?
Diabetic retinopathy
What is the result of increased liberation of glucose into the circulation from the liver?
Extracellular glucose excess
What is the term for the situation where there is an extracellular glucose excess and an intracellular glucose deficiency?
Starvation in the midst of plenty
What is the consequence of accelerated atherosclerosis in diabetes?
Increased incidence of stroke and myocardial infarction
What is the term for the abnormalities involving the autonomic nervous system and peripheral nerves in diabetes?
Diabetic neuropathy
Study Notes
The Pancreas and Carbohydrate Metabolism
- The pancreas produces four polypeptides with regulatory activity: insulin, glucagon, somatostatin, and pancreatic polypeptide.
- These hormones regulate the intermediary metabolism of carbohydrates, proteins, and fats.
Insulin
- Insulin is a polypeptide containing two chains of amino acids linked by disulfide bridges.
- It is synthesized in the rough endoplasmic reticulum of the B cells in the pancreatic islets.
- Insulin increases the entry of glucose into cells, induces glucokinase, and increases the number of GLUT-4 transporters in cell membranes.
- It also causes K+ to enter cells, lowering extracellular K+ concentration.
- Insulin increases the activity of Na+, K+ ATPase in cell membranes, pumping more K+ into cells.
Fate of Secreted Insulin
- The half-life of insulin in circulation is about 5 minutes.
- Insulin binds to insulin receptors and is internalized.
- It is destroyed by proteases in endosomes formed by the endocytotic process.
Effects of Insulin
- Rapid actions (seconds): increases transport of glucose, amino acids, and K+ into insulin-sensitive cells.
- Intermediate actions (minutes): stimulates protein synthesis, activates glycolytic enzymes, and inhibits phosphorylase and gluconeogenic enzymes.
- Delayed actions (hours): increases mRNAs for lipogenic and other enzymes.
Insulin and Adipose Tissue, Muscle, and Liver
- In adipose tissue, insulin increases glucose entry, fatty acid synthesis, and triglyceride deposition, and inhibits hormone-sensitive lipase.
- In muscle, insulin increases glucose entry, glycogen synthesis, amino acid uptake, protein synthesis, and K+ uptake, and inhibits protein catabolism.
- In liver, insulin increases glucose uptake, glycogen synthesis, and protein synthesis, and inhibits gluconeogenesis and glycogenolysis.
The Pancreas and Carbohydrate Metabolism
The pancreas produces four polypeptides: insulin, glucagon, somatostatin, and pancreatic polypeptide, which regulate carbohydrate, protein, and fat metabolism.
Glucagon
- Glucagon is a 29-amino acid polypeptide hormone produced by the pancreatic islet alpha cells.
- It raises blood glucose levels by stimulating the liver to break down glycogen to glucose, which is then released into the bloodstream.
- Glucagon counteracts the action of insulin, promoting gluconeogenesis and glycogenolysis, thereby increasing glucose production in the liver.
- Its release is stimulated by low blood glucose levels, stress, and sympathetic nervous system stimulation.
- In addition to its role in glucose metabolism, glucagon also has a role in lipid metabolism, stimulating the breakdown of triglycerides in adipose tissue.
is a polypeptide hormone composed of 29 amino acids, synthesized in the pancreatic islet cells (also known as islets of Langerhans).
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Its primary function is to raise blood glucose levels, counteracting the effects of insulin.
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Glucagon stimulates the liver to convert stored glycogen into glucose, which is then released into the bloodstream.
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Additionally, glucagon promotes the breakdown of fatty acids and the synthesis of ketone bodies, providing an alternative energy source when glucose is scarce.
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Glucagon is produced by A cells in the pancreatic islets and the upper gastrointestinal tract.
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It is glycogenolytic, gluconeogenic, lipolytic, and ketogenic.
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In the liver, glucagon activates adenylyl cyclase, increasing intracellular cAMP, protein kinase A to activation of phosphorylase and therefore to increased breakdown of glycogen and an increase in plasma glucose
Diabetes Mellitus
Diabetes mellitus is characterized by polyuria, polydipsia, weight loss, and hyperglycemia.
It is caused by insulin deficiency, which can be due to autoimmune destruction of B cells in the pancreatic islets (Type 1 diabetes) or dysregulation of insulin release from B cells and insulin resistance in peripheral tissues (Type 2 diabetes).
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Complications of diabetes include microvascular, macrovascular, and neuropathic disease.
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Pancreatic Polypeptide
-
Produced by F cells in the islets
-
Closely related to polypeptide YY (gastrointestinal peptide) and neuropeptide Y (found in brain and autonomic nervous system)
-
Secretion increased by:
- Meal containing protein
- Fasting
- Exercise
- Acute hypoglycemia
-
Secretion decreased by:
- Somatostatin
- Intravenous glucose
-
Slows absorption of food in humans
Hypoglycemia
- Common in type 1 diabetics
- Occasional episodes are the price of good diabetic control in most diabetics
- Chronic mild hypoglycemia can cause:
- Incoordination
- Slurred speech
- Can be mistaken for drunkenness
Functional Hypoglycemia
- Plasma glucose rise is normal after a test dose of glucose
- Subsequent fall overshoots to hypoglycemic levels, producing symptoms 3-4 hours after meals
- Pattern sometimes seen in individuals who develop diabetes later
Diabetes Mellitus
- Constellation of abnormalities caused by insulin deficiency
Test your knowledge of the endocrine system, focusing on the pancreas and its role in carbohydrate metabolism, including insulin secretion and regulation, glucose transporters, and diabetes mellitus.
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