Pharm Chapter 31

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Pharm Chapter 31
2011-05-01 00:05:36
Thyroid Parathyroid Hormones

Thyroid and Parathyroid Hormones
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  1. What does the Thyroid do?
    • Control metabolism
    • Promote normal growth and development
  2. What does the parathyroid do?
    • Regulates Ca++ homeostasis
    • Maintains normal bone mineralization
  3. What suggests that T4 is a precursor to T3?
    • T3 may exert most of the physiologic effects on tissues
    • (conversion occurs in peripheral tissues)
  4. How are thyroid hormones synthesized?
    • Adding iodine to residues of the aa tyrosine
    • Add 1 iodine atom= monoiodotyrosine
    • Add 2 iodine atoms= diiodotyrosine
    • T3(triiodotyrosine): monoiodotyrosine + diiodotyrosine
    • T4(thyroxine): diiodotyrosine + diiodotyrosine
  5. How are thyroid hormones regulated?
    • TRH from hypothalamus stimulates release of TSH from ant. pituitary
    • TSH goes to thyroid gland to stimulate production of T3 and T4
    • NEGATIVE FEEDBACK: increase inhibits TSH, prevents high levels of peripheral thyroid hormones
  6. What are some physiologic effects of thyroid hormones?
    • Can be direct or facilitate other hormones
    • Thermogenesis: ↑ basal metabolic rate and heat production
    • Growth/development: stimulates release and enhances effect of GH
    • Cardio: ↑'s HR and myocardial contractility, ↑ing cardiac output
    • Metabolic: ↑'s glucose availability and lipids for cellular activity
  7. What is Thyrotoxicosis?
    • Hyperthyroidism
    • treated w/drugs that attenuate thyroid hormones
    • Can be cause by tumors and endocrine regulation problems
    • Enlargement of thyroid or goiter
  8. What is Diffuse toxic goiter?
    • Graves disease
    • Type of Hyperthyroidism
    • Caused by problem of immune system
    • Rx: Remove thyroid or administer radioactive iodine
  9. What are drugs used to treat Hyperthyroidism?
    • Antithyroid agents
    • Iodide
    • Radioactive Iodide
    • Beta-adrenergic blockers
  10. How do Antithyroid agents work? Examples?
    • Inhibit thyroid hormone synthesis
    • Inhibit thyroid peroxidase enzyme
    • Prevent coupling of residues within thyroglobulin molecule
    • Block conversion of T4 to T3 (propylthiouracil)
    • Prophythioracil (Propyl-Thyracil), Methimazole (Tapazole)
  11. How does iodide treat hyperthyroidism?
    • Large doses cause rapid decrease in thyroid function (temporarily)
    • Diminishes after 2 weeks
  12. How does radioactive iodide work?
    • Emits beta radiation to destroy thryoid follicle cells
    • No damage to surrounding tissue in gland
    • Permanently ablates thyroid gland
  13. How do beta-adrenergic blockers help hyperthyroidism?
    • Don't directly decrease hormones
    • Suppresses symptoms such as tachycardia, palpitations, fever, restlessness
    • Propranolol
  14. What are types of Hypothyroidism?
    • Myxedema: adult
    • Cretinism: Child
    • Goiter (may be present in some forms of hypothyroidism): Lack of dietary iodine (endemic goiter)--->no negative feedback of TSH, so increase in thyroglobulin
  15. What are some thyroid hormones?
    • Natural and synthetic
    • Levothyroxine(Synthroid)
    • Liothyronine (Cytomel)
    • Used to treat Hypothyroidism
  16. What is the controlling factor of PTH?
    • Ca++ in the blood
    • Decrease in Ca++ activates receptor on cell membrane and increases PTH release
  17. How does PTH release Ca++ into the bloodstream?
    • Liberates Ca++ from bone--->increases bone turnover
    • Enhances osteoclasts
  18. What are the physiologic effects of PTH?
    • Liberates Ca++ from bone
    • ↑ renal reabsorption of Ca++ and ↑ phosphate excretion
    • ↑ Ca++ absorption from GI tract (increases conversion of Vitamin D to calcitriol which stimulates Ca++ absorption from intestine)
  19. What are the two primary fxns of bone?
    • 1.) Rigid framework
    • 2.) Provides Ca++ pool
  20. How do PTH levels affect bone?
    • High levels: accelerate bone breakdown (and fracture)
    • Low levels: enhance bone formation (stimulate osteoblastic activity)
  21. What regulates bone homeostasis?
    • PTH
    • Vitamin D
    • Calcitonin
    • GC's (catabolic effect)
    • Estrogens, androgens, insulin, thyroid hormone (enhance bone formation)
  22. How does Vitamin D affect bone?
    • Promotes muscle growth and increase strength and lean body mass
    • From diet or UV light on skin
    • ↑ supply of Ca++ and PO4 (GI absorption)
    • Suppresses PTH
  23. What is a PTH antagonist?
    • Calcitonin (from thyroid gland)
    • Lowers blood Ca++ by stimulating bone formation and ↑ incorporation of Ca++ into skeletal storage
  24. What happens when Blood Calcium levels are not maintained?
    • Falls below 6mg/100mL, then titanic muscle contractions ensue
    • Levels greater than 12mg/mL depresses nervous function
  25. What helps prevent bone loss?
    • Alone will not prevent osteoporosis but is helpful with other Rx's
    • Calcium carbonate (Tums)
    • Calcium citrate (Citracal)
  26. What does Vitamin D do?
    • Precurosr for cmpds that
    • ↑ intestinal absorption and decreases excretion of Ca++ and PO4
    • Enhances bone mineralization
    • Fat soluble, can lead to toxicity
  27. What are bisphosphonates?
    • (Disphosphonates)
    • Reduce bone resorption by inhibiting osteoclastic activity
    • Used in Paget disease
    • Used in neoplastic disease
    • Can help prevent bone loss associated with prolonged administration of GC's
    • Primary Rx's for osteoporosis (Improve bone health in women)
    • Alendronate(Fosamax)
    • Pamidronate(Aredia)
  28. How does Calcitonin work?
    • Decreases blood Ca++ levels and promotes bone mineralization
    • Used to Rx hypercalcemia and decrease bone resorption in Paget's
    • Human Calcitonin (Cibalcalcin)
  29. What can help treat postmenopausal osteoporosis?
    • ↑ bone mineral content and reduce risk of fractures
    • Combined with Ca++ supplements
    • Raloxifene (Evista)
  30. Teriparatide
    • (Forteo)
    • Synthetic form of PTH
  31. Cincacalcet
    • (Sensipar)
    • Calcimimetic agent (mimics endogenous Ca++)