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Garrett Flashcards
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  1. What are the cell types in the Islet of Langerhans, and what hormones are released by each cell type?
    • Alpha cells: located at the periphery of the islet; secrete glucagon
    • Beta cells: located throughout the islet; secrete insulin
    • Delta cells: few in number, located throughout islet; secrete somatostatin
  2. What is the functional significance of the vascularization of the Islets of Langerhans?
    • Rich vascularization for circulation of hormones secreted by the islet cells
    • Blood flows from the center to the periphery, so alpha and delta cells are exposed to high concentrations insulin from beta cells. This insulin inhibits glucagon release
  3. What is the effect of the Parasympathetic Nervous System on glucagon and insulin secretion from alpha and beta cells?
    Stimulates the secretion of insulin, glucagon, somatostatin, and pancreatic polypeptide
  4. What is the effect of the Sympathetic Nervous System on glucagon and insulin secretion from alpha and beta cells?
    Inhibits basal and glucose-stimulated insulin secretion and somatostatin release and stimulates glucagon and pancreatic polypeptide secretion
  5. Describe the synthesis of insulin via processing of proinsulin. Describe the mature form of insulin. Describe source of C-peptide and its use to assess the secretory function of the beta cells.
    • In the ER, the C-peptide is cleaved from proinsulin to generate the mature form of insulin.
    • Insulin is composed of an alpha chain and a beta chain held together by two disulfide bonds.
    • The liver does not readily degrade c-peptide (like insulin), so C-peptide levels can be used to assess the production of insulin.
  6. Describe the regulation of insulin secretion and electrophysiological mechanism of insulin secretion
    • **Glucose is the principal stimulus for insulin release
    • 1. Glucose leads to an increased ATP/ADP ratio from glycolysis and the Krebs cycle.
    • 2. This results in the inhibition and closure of ATP-sensitive K+ channels.
    • 3. K+ channel closure results in depolarization of the PM and opening of voltage-dependent Ca2+ channels.
    • 4. Increased [Ca2+] causes release of insulin
  7. What 4 hormones increase or stimulate insulin secretion?
    • ACH
    • CCK
    • Glucagon
    • GLP-1
  8. What 3 hormones inhibit insulin secretion?
    • Epinephrine
    • Norepinephrine
    • Somatostatin
  9. What is the biphasic release of insulin?
    There is an initial rapid release of preformed insulin followed by a more sustained release of newly synthesized insulin
  10. What does insulin stimulate within Carbohydrate Metabolism?
    • Glucose transport in adipose tissue and muscle
    • Rate of glycolysis in muscle and adipose tissue
    • Glycogen synthesis in adipose tissue, muscle, and liver
  11. What does Insulin inhibit in Carbohydrate Metabolism?
    • Glycogen breakdown in muscle and liver
    • Rate of glycogenolysis gluconeogenesis in the liver
  12. What does Insulin stimulate in Lipid Metabolism?
    • Fatty acid and triacylglycerol synthesis in tissues
    • Uptake of triglycerides from the blood into adipose tissue and muscle
    • Rate of cholesterol synthesis in the liver
  13. What does Insulin inhibit in Lipid Metabolism?
    • Lipolysis in adipose tissue, lowering the fatty acid level
    • Fatty acid oxidation in muscle and liver
    • Ketogenesis
  14. What does Insulin stimulate in Protein Metabolism?
    • Amino acid transport into tissues
    • Protein synthesis in muscle, adipose tissue, liver, and other tissues
  15. What does Insulin inhibit in Protein Metabolism?
    • Protein degradation in muscle
    • Urea formation
  16. What factors stimulate glucagon secretion?
    • High Amino Acid Levels
    • Epinephrine
    • Vagal Stimulation
  17. What factors inhibit glucagon secretion?
    • Hyperglycemia
    • Somatostatin
  18. What effeect does Glucagon have on Glucose-6-phosphatase, and what metabolic response does this induce?
    • Increased expression of Glucose-6-Phosphatase
    • Frees glucose to enter the circulation
  19. What effect does Glucagon have on Glucokinase, and what metabolic response does this induce?
    • Suppresses Glucokinase
    • Deceases glucose entry into the glycolytic cascade
  20. What effect does Glucagon have on Glycogen Phosphorylase, and what metabolic response does this induce?
    • Phosphorylates (activates) Glycogen Phosphatase
    • Stimulates glycogenolysis
  21. What effect does Glucagon have on Glycogen Synthase, and what metabolic response does this induce?
    • Inhibits Glycogen Synthase
    • Inhibits glycogen synthesis
  22. What effect does Glucagon have on Phosphoenolpyruvate Carboxykinase, and what metabolic response does this induce?
    • Stimulates its expression
    • Stimulates gluconeogenesis
  23. What effect does Glucagon have on Phosphofructokinase-2 (PFK-2), and what metabolic response does this induce?
    • Inactivates it
    • Inhibits Glycolysis
  24. What effect does Glucagon have on Fructose-6-Phosphatase, and what metabolic response does this induce?
    • Activates it
    • Stimulates Gluconeogenesis
  25. What effect does Glucagon have on Pyruvate Kinase, and what metabolic effect does this induce?
    • Suppresses its activity
    • Decreases Glycolysis
  26. Lung cancers commonly secrete what 3 hormones?
    • Parathyroid Hormone
    • Antidiuretic Hormone
    • ACTH
  27. What percentage of cholesterol for hormone synthesis comes from de novo synthesis, and what percentage comes from cholesterol in blood bound to LDL?
    • 20%
    • 80%
  28. Which form of the hormone is the active form?
    The free form -- the hormone must dissociate from the binding protein to be active
  29. What is it called when the effect of one hormone requires the presence of a second hormone (the effects of the second hormone allow the actions of the first hormone)?

    What is an example of this?
    • Permissive Action
    • Thyroid hormone has permissive effects in that it is needed for epinephrine to have its effects
  30. This is a hormone that stimulates the release of another hormone.
    Trophic Hormone
  31. What is the major integrative center for homeostatic control systems?
    Hypothalamus
  32. Are the circulating hormone levels in the endocrine system high or low?
    Very low
  33. What are the three general chemical classifications of hormones?
    • Amines
    • Steroids
    • Peptides
  34. What are the four amine-based hormones?
    • Dopamine (catecholamine)
    • Norepinephrine (catecholamine)
    • Epinephrine (catecholamine)
    • Thyroid Hormone (T3 &T4)
  35. Which form of Thyroid Hormone is the active form?
    T3
  36. What is the precursor to all amine-based hormones?
    Tyrosine
  37. What is the precursor to all steroid hormones?
    Cholesterol
  38. What is the specificity of the Endocrine System due to?
    Expression of hormone receptors on target tissues
  39. What are the 6 Steroid Hormones?
    • Aldosterone (mineralocorticoid)
    • Cortisol (glucocorticoid)
    • Testosterone (androgen)
    • Estradiol or Estrogen (androgen)
    • Progesterone (androgen)
    • Vitamin D
  40. What is the major steroid secreting gland?
    Adrenal Cortex
  41. Within the adrenal cortex, what hormone is secreted from the Zona Glomerulosa?
    Aldosterone
  42. Within the adrenal cortex, where is Aldosterone secreted from?
    Zona Glomerulosa
  43. Within the adrenal cortex, what hormones are secreted from the Zona Fasiculata?
    • Cortisol
    • Androgens
  44. Within the adrenal cortex, where are Cortisol and the Androgens secreted from?
    • Zona Fasiculata
    • Zona Reticularis
  45. Within the adrenal cortex, what hormones are secreted from the Zona Reticularis?
    • Cortisol
    • Androgens
  46. What hormones are secreted from the adrenal medulla?
    • Epinephrine
    • Norepinephrine
  47. Where are Epinephrine and Norepinephrine secreted from?
    Adrenal Medulla
  48. Other than the adrenal cortex and medulla, what are the steroid secreting glands?
    • Gonads (Testes & Ovaries)
    • Placenta
  49. How does the synthesis of Peptides take place?
    • Preprohormone: signal sequence is clipped in the ER
    • Prohormone: packaged in Golgi where further cleaved to the
    • Hormone: stored in vesicle, ready for release
  50. Proopiomelanocortin (POMC) is a pre-cursor for what important molecule?
    ACTH
  51. Proopiomelanocortin (POMC) is a preprohormone that can make multiple different hormones. How are different hormones cleaved?
    It is dependent on the enyzme doing the cleaving. Different tissues possess different enzymes, which is why different hormones are expressed there
  52. How do Catecholamines and most peptides travel through blood?
    The are water soluble so can travel in free form in blood
  53. How do Steroids, Thyroid Hormone, Growth Hormone, and Insulin-like Growth Factor (IGF-1) travel through blood?
    They are hydrophobic, so must be carried by being bound to proteins in blood. An equilibrium exists between bound and free forms of these hormones
  54. What are the two functions of the bound hormone?
    • Reservoir of hormone in blood: reduces the fluctuation of hormone levels -- helps buffer hormone release to maintain a stable level
    • Increases half-life of hormone: decreases metabolism, which increases half-life
  55. In general, proteins that have chronic long-term effects are in what state? Hormones with acute short-term effects circulate in what state?
    • Bound State
    • Free State
  56. Can protein-bound hormones be metabolized?
    No, only those in the free form can
  57. What are the three functions of Metabolism for hormones?
    • Inactivation: the metabolites are not biologically active
    • Activation: some hormones must be metabolized to be converted to their active form (i.e. T4 must be cleaved to T3)
    • Elimination: the metabolites (such as steroids) are more soluble in water and are excreted by the kidneys
  58. What are the three major sites of metabolism?
    • Liver
    • Kidney
    • Plasma -- catacholamines and peptides
  59. What is the major membrane-bound receptor for hormones?
    G-protein coupled receptor
  60. What is the major insulin receptor?
    Tyrosine Kinase
  61. What is the major Growth Hormone receptor?
    JAK-STAT Pathway
  62. In addition to fast effects, membrane bound receptors can also do what, which gives them long-term effects as well?
    Affect gene expression
  63. Steroids, Thyroid Hormone, and Vitamin D all bind to receptors in the cytoplasm and are then transported where? What can the hormone-receptor complex then do?
    • Taken to Nucleus
    • Binds to DNA and alters gene expression and protein synthesis
  64. Why is thyroid hormone required for epinephrine to have its metabolic effects (through permissiveness)?
    Because thyroid hormone is required for expression of beta receptors
  65. How does up regulation work?
    When don't have enough stimulus, get an up regulation of the system where we increase the number of receptors or level of responsiveness to compensate
  66. How does down regulation work?
    When there is too much stimulus, decrease the number of receptors or level of responsiveness to compensate (type II diabetes)
  67. What are the three patterns of hormone secretion?
    • Pulsatile: hormones are released in pulses (so don't get a down regulation)
    • Daily Cycles/Circadian Patterns: every 20-28 hours with GH and Cortisol
    • Monthly Cycles: menstruation
  68. What are the control inputs in hormone release?
    • Plasma Concentrations of mineral ions or nutrients: ie insulin secretion regulated by plasma glucose levels
    • Neuronal Control: hormone is released from hypothalamus into hypothalamo-pituitary system, which takes it to the anterior pituitary gland, then into circulation to target tissues.
    • Hormonal Control: GH, TH, and cortisol
  69. What are the two feedback systems for growth hormone?
    • Hypo releases GHRH (positive feedback molecule) and SS (negative feedback molecule).
    • Growth hormone is stimulated to be released (or not) from anterior pituitary, where it can move to target tissues
  70. What is the hormonal control mechanism for thyroid hormone?
    Hypo releases TRH, which is a positive feedback regulator of the release of TSH by the anterior pituitary gland, where TSH stimulates the release of thryoid hormone from the Thryoid.
  71. What is the hormonal control mechanism for cortisol?
    Hypo releases CRH, a positive feedback regulator of the release of ACTH by the anterior pituitary. ACTH then stimulates the release of cortisol from the adrenal cortex
  72. What is the major integrative center for homeostatic control systems?
    Hypothalamus
  73. ________ _________ are released from the hypothalamus and regulate the release of hormones from the anterior pituitary gland.
    Hypophysiotropic (Trophic) Hormones
  74. This is the base of the hypothalamus?
    Median Eminence
  75. This connects the hypothalamus with the pituitary, and contains the hypothalamo-pituitary portal system. The hypophysiotropic hormones travel from the hypothalamus to the anterior pituitary via the hypothalamo-pituitary portal system.
    Infundibulum
  76. How do the hypophysiotropic hormnes travel from the hypothalamus to the anterior pituitary gland?
    Through the hypothalamo-pituitary portal system in the infundibulum
  77. This is located in the sella trucica of the sphenoid bone, and is divided into two lobes.
    Pituitary
  78. This is an outgrowth of the hypothalamus, and is therefore neuronal tissue. Neurons from hypothalamus project here, and activation of those neurons causes release of hormones into the systemic circulation.
    Posterior Pituitary
  79. This is composed of tissue originating from Rathke's pouch in the pharynx. Hormones released from here enter the systemic circulation and travel to their target tissue. The target tissue can be another gland or a tissue that produces the final physiological response to the hormone.
    Anterior Pituitary
  80. Hypophysiotrophic hormones released from the hypothalamus travel to the anterior pituitary via the hypothalamo-pituitary portal vessels. Hypophysiotropic hormones bind to receptors on specific troph cells in the anterior pituitary and do what?
    Either stimulate or inhibit release of hormones from the troph cells.
  81. What is the main source of hormonal feedback control?
    Negative Feedback Loops: hormones inhibit the release of releasing and trophic hormones to help dampen hormone response. This keeps the hormone levels within a certain range
  82. This is a type of hyposecretion that is due to some abnormality in the gland. There can be destruction of the gland, such as the destruction of beta cells in Type I Diabetes, or defects in hormone synthesis or metabolism, such as an iodine deficiency, which can lead to thyroid disease.
    Primary Hyposecretion
  83. Hashimoto's disease is an example of what?
    Primary Hyposecretion
  84. This is a type of hyposecretion in which the gland is normal but there is too little stimulus from the pituitary or trophic hormone. An example of this is Kallman's Syndrome, in which there is no LH or FSH released due to a lack of GnRH hormones in the hypothalamus. Therefore, there is a lack of sex hormones even though the gonads are normal.
    Secondary Hyposecretion
  85. Kallman's Syndrome is an example of?
    Secondary Hyposecretion
  86. In this type of hypersecretion, an abnormality in the gland is commonly caused by the presence of a hormone-secreting tumor, such as a thyroid adenoma, which causes excess thryoid release.
    Primary Hypersecretion
  87. A thyroid adenoma is an example of?
    Primary Hypersecretion
  88. In this type of hypersecretion, the gland is normal but there is too much stimulus from the pituitary or trophic hormone. An example is Cushing's Disease, in which there is a defect or hormone-secreting tumor in the pituitary that causes excess release of ACTH, which stimulates hypersecretion of cortisol.
    Secondary Hypersecretion
  89. Cushing's Disease is an example of?
    Secondary Hypersecretion
  90. In this type of hormone responsiveness, hormone secretion is normal, but the target cell does not respond to the hormone. This can be caused by a deficiency or lack of hormone receptors (ie. androgen insensitivity syndrome), an abnormality in receptor-signal transduction coupling (type II diabetes), or an abnormality in metabolic activation (conversion of testosterone to dihydrotestosterone).
    Hyporesponsiveness
  91. What are three abnormalities leading to Hyporesponsiveness?
    • Deficiency or lack of hormone receptors: Androgen Insensitivity Sydrome
    • Receptor-signal transduction coupling is abnormal: Type II Diabetes
    • Metabolic activation is abnormal: Conversion of testosterone to dihydrotestosterone
  92. This type of response results in an up regulation of hormone receptors, for example there is one to epinephrine with hyperthyroidism due to an up regulation of beta-adrenergic receptors.
    Hyperresponsiveness
  93. What are the two types of Endocrine Function Tests?
    • Hormone Concentrations
    • Dynamic Hormone Secretion Measurements
  94. This Endocrine Function Test is measured in biological fluids (commonly plasma or urine). Radioimmune assays, immunometric assays or variations are most often used for measurements. Variations are due to pulsitile release, biological rhythyms and nutrition status. It is a static determination.
    Within this test, hormones should be measured along with their regulatory factors (i.e. insulin and glucose)
    Within this test, the target hormone should be measured with appropriate trophic hormones to determine is an ectopic site, such as a tumor, is causing elevations in hormone.
    Hormone Concentrations
  95. What are the two sub-types of Dynamic Hormone Secretion Measurements?
    • Stimulation Tests
    • Suppression Tests
  96. In this type of Dynamic Hormone Secretion Test, trophic hormone or another stimulant is given to determine the ability of the gland or tissue to secrete hormone. An example is a glucose tolerance test.
    Stimulation Tests
  97. In this type of Dynamic Hormone Secretion Test, drugs or hormones are administered to determine if the feedback systems are functional. For example, a synthetic analogue of cortisol is used to see if the subsequent release of cortisol is suppressed.
    Suppression Tests

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