Biology: Insulin Structure and Deficiency
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Questions and Answers

What is the location of the α subunits in the insulin receptor?

  • In the nucleus
  • In the mitochondria
  • Extracellular (correct)
  • In the cytoplasm

    • What is a consequence of hyperglycemia on the kidneys?

  • Increased glucose reabsorption
  • Glucose is stored in the kidneys
  • Decreased glucose reabsorption (correct)
  • Excretion of glucose is unaffected

    • What is the effect of hyperglycemia on water intake?

  • No effect on water intake
  • Increased water intake (correct)
  • Decreased water intake
  • Water intake is variable

    • What is the purpose of measuring HbAIc concentration in diabetes?

    <p>As an integrated index of diabetic control</p> Signup and view all the answers

    What happens to amino acids in the liver during diabetes?

    <p>They are converted to glucose</p> Signup and view all the answers

    What is the effect of insulin deficiency on protein metabolism?

    <p>Increased protein catabolism</p> Signup and view all the answers

    What is the initial response to glucose in terms of insulin secretion?

    <p>Initial spike of insulin secretion</p> Signup and view all the answers

    What is the role of glutamate in insulin secretion?

    <p>It commits a second pool of secretory granules to the releasable form</p> Signup and view all the answers

    What is the effect of glucagon on glycogen in the liver?

    <p>It increases glycogen breakdown</p> Signup and view all the answers

    What is the effect of glucagon on ketone body formation?

    <p>It increases ketone body formation</p> Signup and view all the answers

    What is the role of the citric acid cycle in insulin secretion?

    <p>It increases glutamate production</p> Signup and view all the answers

    What is the feedback control of plasma glucose on insulin secretion?

    <p>It is a feedback loop with great precision</p> Signup and view all the answers

    What is a major long-term complication of diabetes in humans?

    <p>Atherosclerotic vascular disease</p> Signup and view all the answers

    What is the role of glucokinase in glucose-stimulated insulin secretion?

    <p>It phosphorylates glucose to pyruvate</p> Signup and view all the answers

    What is the result of ATP entering the cytoplasm in pancreatic B cells?

    <p>Inhibition of ATP-sensitive K+ channels</p> Signup and view all the answers

    What is the role of GLUT-2 transporters in glucose-stimulated insulin secretion?

    <p>They transport glucose into the B cell</p> Signup and view all the answers

    What is the effect of decreased lipoprotein lipase activity on lipoprotein metabolism?

    <p>Decreased removal of VLDL and LDL from the circulation</p> Signup and view all the answers

    What is the response to glucose in pancreatic B cells?

    <p>A biphasic increase in insulin secretion</p> Signup and view all the answers

    What term is used to describe the situation of extracellular glucose excess and intracellular glucose deficiency?

    <p>Starvation in the midst of plenty</p> Signup and view all the answers

    What is the result of accelerated atherosclerosis in diabetes?

    <p>Increased incidence of stroke and myocardial infarction</p> Signup and view all the answers

    What is the effect of weight reduction on insulin resistance?

    <p>Decreases insulin resistance</p> Signup and view all the answers

    What is characterized by high circulating triglycerides and low HDL?

    <p>Dyslipidemia</p> Signup and view all the answers

    What is the result of proliferative scarring of the retina?

    <p>Blindness</p> Signup and view all the answers

    What complication of diabetes affects the autonomic nervous system and peripheral nerves?

    <p>Diabetic neuropathy</p> Signup and view all the answers

    What is the effect of hypoglycemia on glucagon secretion?

    <p>It increases glucagon secretion</p> Signup and view all the answers

    What is the mechanism of the sympathetic effect on glucagon secretion?

    <p>Via β-adrenergic receptors and cAMP</p> Signup and view all the answers

    Which of the following hormones inhibits glucagon secretion?

    <p>Secretin</p> Signup and view all the answers

    What is the effect of somatostatin on insulin secretion?

    <p>It inhibits insulin secretion</p> Signup and view all the answers

    Which of the following stimuli increases pancreatic somatostatin secretion?

    <p>Glucose and amino acids</p> Signup and view all the answers

    What is the function of pancreatic polypeptide?

    <p>It is closely related to neuropeptide Y</p> Signup and view all the answers

    What percentage of the total cells are A cells?

    <p>20%</p> Signup and view all the answers

    Where is insulin synthesized in the B cells?

    <p>Rough endoplasmic reticulum</p> Signup and view all the answers

    What is the half-life of insulin in the circulation in humans?

    <p>5 min</p> Signup and view all the answers

    What is the effect of insulin on adipose tissue?

    <p>Increase glucose entry</p> Signup and view all the answers

    How are the contents of membrane-bound granules expelled from the cell?

    <p>Exocytosis</p> Signup and view all the answers

    What is the fate of insulin after it binds to insulin receptors?

    <p>It is destroyed by proteases in the endosomes</p> Signup and view all the answers

    What is the immediate effect of Ca2+ influx on insulin secretion?

    <p>Exocytosis of readily releasable pool of insulin-containing secretory granules</p> Signup and view all the answers

    What is the role of glutamate in insulin secretion?

    <p>Commits secretory granules to the releasable form</p> Signup and view all the answers

    What is the effect of glucagon on glycogen metabolism in the liver?

    <p>Increases glycogen breakdown</p> Signup and view all the answers

    What is the effect of glucagon on ketone body formation in the liver?

    <p>Increases ketone body formation</p> Signup and view all the answers

    What is the feedback control mechanism of plasma glucose on insulin secretion?

    <p>Negative feedback</p> Signup and view all the answers

    What is the effect of glucagon on lipolysis?

    <p>Increases lipolysis</p> Signup and view all the answers

    What is the primary effect of glucagon on lipid metabolism?

    <p>Increased ketogenesis</p> Signup and view all the answers

    What is the role of β-adrenergic receptors in the regulation of glucagon secretion?

    <p>Mediation of the sympathetic effect on glucagon secretion</p> Signup and view all the answers

    Which of the following hormones has a paracrine effect on the pancreatic islets?

    <p>Somatostatin</p> Signup and view all the answers

    What is the effect of cholecystokinin on glucagon secretion?

    <p>Increase in glucagon secretion</p> Signup and view all the answers

    What is the effect of somatostatin 28 on insulin secretion?

    <p>Inhibition of insulin secretion</p> Signup and view all the answers

    What is the relationship between pancreatic polypeptide and other amino acid polypeptides?

    <p>It is closely related to polypeptide YY and neuropeptide Y</p> Signup and view all the answers

    What is the primary effect of pancreatic polypeptide on digestion in humans?

    <p>It slows the absorption of food</p> Signup and view all the answers

    What is the typical pattern of plasma glucose levels seen in functional hypoglycemia?

    <p>A normal rise followed by a subsequent fall to hypoglycemic levels</p> Signup and view all the answers

    What is the primary cause of polyuria in diabetes mellitus?

    <p>Increased glucose levels in the blood</p> Signup and view all the answers

    What is the effect of fasting on the secretion of pancreatic polypeptide?

    <p>It increases the secretion of pancreatic polypeptide</p> Signup and view all the answers

    What is the typical outcome of chronic mild hypoglycemia in individuals?

    <p>Incoordination and slurred speech</p> Signup and view all the answers

    What are the two fundamental defects that contribute to the abnormalities seen in diabetes mellitus?

    <p>Reduced glucose entry into peripheral tissues and increased glucose liberation from the liver</p> Signup and view all the answers

    In muscle cells, what is the primary mechanism by which insulin stimulates glucose entry?

    <p>Increasing the number of glucose transporters in the cell membrane</p> Signup and view all the answers

    What is the primary difference in how insulin stimulates glucose entry in muscle and liver cells?

    <p>Insulin increases GLUTs in muscle cells but induces glucokinase in liver cells</p> Signup and view all the answers

    What is the structure of the insulin receptor?

    <p>A tetramer made up of two α and two β glycoprotein subunits</p> Signup and view all the answers

    In what tissues does insulin stimulate glucose entry by increasing the number of GLUTs?

    <p>Muscle, adipose, and some other tissues</p> Signup and view all the answers

    What is the effect of insulin on ketone body formation in the liver?

    <p>It decreases ketone body formation</p> Signup and view all the answers

    What is the effect of insulin on protein catabolism and gluconeogenic amino acid release in muscle cells?

    <p>It decreases protein catabolism and gluconeogenic amino acid release</p> Signup and view all the answers

    What is the effect of insulin on glucose entry into muscle cells?

    <p>Increases the number of glucose transporters in the cell membranes</p> Signup and view all the answers

    What is the function of glucokinase in the liver?

    <p>Phosphorylates glucose, increasing its entry into the cell</p> Signup and view all the answers

    What is the structure of the insulin receptor?

    <p>A tetramer made up of two α and two β subunits</p> Signup and view all the answers

    What is the effect of insulin on ketone body formation in the liver?

    <p>Decreases ketone body formation</p> Signup and view all the answers

    What is the effect of insulin on protein synthesis in muscle?

    <p>Increases protein synthesis</p> Signup and view all the answers

    What is the mode of glucose transport into intestinal and kidney cells?

    <p>Both facilitated diffusion and active transport with Na+</p> Signup and view all the answers

    What is the effect of glucagon on glycogen in the liver?

    <p>Breakdown of glycogen</p> Signup and view all the answers

    What is the role of glutamate in insulin secretion?

    <p>Stimulates release of insulin</p> Signup and view all the answers

    What is the effect of Ca2+ influx on insulin secretion?

    <p>Stimulates release of insulin</p> Signup and view all the answers

    What is the effect of glucagon on gluconeogenesis in the liver?

    <p>Stimulates gluconeogenesis</p> Signup and view all the answers

    What is the effect of glucagon on ketone body formation in the liver?

    <p>Increases ketone body formation</p> Signup and view all the answers

    What is a consequence of insulin deficiency in animals?

    <p>Selective destruction of the B cells of the pancreatic islets</p> Signup and view all the answers

    What is the feedback control mechanism of plasma glucose on insulin secretion?

    <p>Negative feedback control</p> Signup and view all the answers

    What is the effect of hyperglycemia on blood?

    <p>Hyperosmolality</p> Signup and view all the answers

    What is the fate of glucose molecules in the kidneys during hyperglycemia?

    <p>They are excreted in the urine</p> Signup and view all the answers

    What is the result of episodic plasma glucose elevation over time?

    <p>Formation of HbAIc</p> Signup and view all the answers

    What happens to amino acids in diabetes?

    <p>They are catabolized to CO2 and H2O at an increased rate</p> Signup and view all the answers

    What is the effect of insulin deficiency on glucose metabolism?

    <p>Increased glucose concentration in the blood</p> Signup and view all the answers

    What is the effect of insulin deficiency on the blood amino acid level?

    <p>It increases</p> Signup and view all the answers

    What is the result of decreased removal of triglycerides into the fat depots in uncontrolled diabetes?

    <p>Increased plasma triglyceride levels</p> Signup and view all the answers

    What is the effect of adrenal glucocorticoids on gluconeogenesis in severely ill diabetics?

    <p>They increase gluconeogenesis</p> Signup and view all the answers

    What is the reason for the increased formation of ketone bodies in diabetes?

    <p>Accelerated lipid catabolism</p> Signup and view all the answers

    What is the effect of insulin on the hormone-sensitive lipase in adipose tissue?

    <p>It inhibits the lipase</p> Signup and view all the answers

    What is the relationship between the plasma level of free fatty acids and the plasma glucose level in diabetes?

    <p>The FFA level is directly proportional to the plasma glucose level</p> Signup and view all the answers

    What is a consequence of intracellular glucose deficiency in many cells?

    <p>Starvation in the midst of plenty</p> Signup and view all the answers

    What is a long-term complication of diabetes?

    <p>All of the above</p> Signup and view all the answers

    What is associated with obesity and relates to insulin resistance?

    <p>All of the above</p> Signup and view all the answers

    What is the result of proliferative scarring of the retina in diabetic retinopathy?

    <p>Blindness</p> Signup and view all the answers

    What is characterized by high circulating triglycerides and low HDL?

    <p>Dyslipidemia</p> Signup and view all the answers

    What is affected by the neuropathic abnormalities in diabetes?

    <p>Autonomic nervous system and peripheral nerves</p> Signup and view all the answers

    Study Notes

    Diabetes and Insulin Regulation

    • Insulin deficiency leads to a situation where there is an extracellular glucose excess and an intracellular glucose deficiency, known as "starvation in the midst of plenty".
    • Diabetes is complicated by acidosis and coma, and long-standing diabetes leads to microvascular, macrovascular, and neuropathic disease.
    • Microvascular abnormalities include proliferative scarring of the retina (diabetic retinopathy) and renal disease (diabetic nephropathy), leading to blindness and chronic kidney disease.
    • Macrovascular abnormalities are due to accelerated atherosclerosis, leading to increased incidence of stroke and myocardial infarction.
    • Neuropathic abnormalities involve the autonomic nervous system and peripheral nerves.

    Obesity and Insulin Resistance

    • Obesity is increasing in incidence and relates to the regulation of food intake and energy balance.
    • As body weight increases, insulin resistance increases, decreasing insulin's ability to move glucose into fat and muscle cells.
    • Weight reduction decreases insulin resistance.
    • Associated with obesity are hyperinsulinemia, dyslipidemia, and accelerated development of atherosclerosis.

    Regulation of Insulin Secretion

    • Glucose acts directly on pancreatic B cells to increase insulin secretion.
    • The response to glucose is biphasic, with a rapid but short-lived increase in secretion followed by a prolonged increase.
    • Glucose enters B cells via GLUT-2 transporters and is phosphorylated by glucokinase, then metabolized to pyruvate in the cytoplasm.
    • Pyruvate enters the mitochondria and is metabolized to CO2 and H2O via the citric acid cycle, with the formation of ATP by oxidative phosphorylation.

    Glucagon Regulation

    • Glucagon is produced by the A cells of pancreatic islets and the upper gastrointestinal tract.
    • Glucagon is glycogenolytic, gluconeogenic, lipolytic, and ketogenic.
    • In the liver, glucagon increases breakdown of glycogen and plasma glucose, increases gluconeogenesis, and elevates the metabolic rate.
    • Glucagon secretion is increased by hypoglycemia, stimulation of the sympathetic nerves, protein meal, and infusion of various amino acids.

    Insulin and Glucagon Interaction

    • Insulin and glucagon have opposing effects on glucose metabolism.
    • Insulin increases glucose entry into cells, glycogen synthesis, and protein synthesis, while decreasing glucose output from the liver.
    • Glucagon increases glucose output from the liver, glycogenolysis, and gluconeogenesis.

    Other Islet Cell Hormones

    • Somatostatin is produced by D cells of pancreatic islets and inhibits the secretion of insulin, glucagon, and pancreatic polypeptide.
    • Pancreatic polypeptide is produced by F cells of pancreatic islets and slows the absorption of food in humans.
    • Its secretion is increased by a meal containing protein and fasting, exercise, and acute hypoglycemia.### Insulin Receptor Structure
    • α subunits of the insulin receptor are extracellular and bind insulin
    • β subunits of the insulin receptor span the membrane

    Consequences of Insulin Deficiency

    • Insulin deficiency is a common pathologic condition in humans
    • Can be produced in animals by pancreatectomy, certain toxins, drugs that inhibit insulin secretion, or anti-insulin antibodies

    Effects of Hyperglycemia

    • Hyperglycemia causes symptoms due to hyperosmolality of the blood
    • Leads to glycosuria as the renal capacity for glucose reabsorption is exceeded
    • Results in osmotic diuresis, dehydration, and polydipsia
    • Leads to non-enzymatic glycation of hemoglobin A, forming HbAIc, which is a clinical index of diabetic control

    Effects of Hyperglycemia on Protein Metabolism

    • Increases the rate of amino acid catabolism to CO2 and H2O
    • Increases conversion of amino acids to glucose in the liver (gluconeogenesis)
    • Adrenal glucocorticoids contribute to increased gluconeogenesis in severely ill diabetics
    • Decreased protein synthesis in muscle leads to increased blood amino acid levels

    Fat Metabolism in Diabetes

    • Accelerated lipid catabolism and increased ketone body formation
    • Decreased synthesis of fatty acids and triglycerides
    • Decreased conversion of glucose to fatty acids in adipose tissue due to intracellular glucose deficiency
    • Insulin's inhibition of hormone-sensitive lipase is absent, leading to increased plasma free fatty acid levels
    • Plasma triglyceride and chylomicron levels, as well as FFA, are increased in uncontrolled diabetes, often resulting in a lipemic plasma

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    Description

    Test your knowledge of insulin's structure, functions, and the consequences of its deficiency in humans and animals. Learn about the α and β subunits, insulin secretion, and its effects on the body.

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