Thyroid Hormones Flashcards
Describe the iodide pump mechanism from blood into the colloid, including the role of pendrin
50 mg of iodine (iodides such as sodium iodide) are required each year. Absorbed from gut tract in same manner as chlorides. Iodide pump: •Sodium—iodide symporter(2:1) in basal membrane of thyroid cell. •Energy for pump comes from a sodium-potassium ATPase pump. •Iodide can be concentrated inside the cell 30—250x plasma concentration. •Iodide is transported across apical membrane of cell into follicle via a chloride iodide counter—transporter = pendrin •Membrane enzyme, peroxidase, catalyzes conversion of iodide into iodine (I2).
Describe the synthesis of thyroid hormones
Organification of iodine: •Combining of iodine with tyrosine on thyroglobulin. •Catalyzed by peroxidase •Results in monoiodotyrosine (MIT) and diiodotyrosine (DIT) Recombination: •DIT + DIT = thyroxine (T4- more numerous) •DIT + MIT = triiodothyronine (T3- more active)
Describe the mechanism for the release of thyroid hormones.
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List causes and symptoms of hyperthyroidism, including Graves’ disease/adenoma
High concentrations of circulating thyroid-stimulating immunoglobulins: •IgG components •Mimic TSH and bind to TSH receptors •Result in high concentrations of circulating thyroxine and low levels of TSH Symptoms: •High state of excitability •Intolerance to heat •Increased sweating •Mild to extreme weight loss •Varying degrees of diarrhea •Muscle weakness •Nervousness or other psychic disorders •Extreme fatigue •Inability to sleep •Tremor in hands •Exophthalmos (Protruding eyes) Treatment: •Surgical removal of most of thyroid gland •Treatment with radioactive iodine
Thyroglobulin molecule has what components
… MIT, DIT, T3and T4 attached to it and is stored in the colloid until needed.
Each thyroglobulin contains about __ molecules of ___. The thyroid can store ____ supply of thyroid hormones.
30, thyroxine several months
List the physiological functions of thyroid hormones.
•Increased transcription of a large number of genes •Increased cellular metabolic activity •Effect on growth Effects on specific bodily mechanisms: •Stimulation of carbohydrate metabolism •Stimulation of fat metabolism •Effect on plasma and liver fats •Increased requirement for vitamins •Increased BMR •Decreased body weight Effects on cardiovascular system: •Increased blood flow and cardiac output •Increased heart rate •Normal arterial pressure •Increased respiration •Increased GI motility •Excitatory effects on CNS •Effects on muscle function •Muscle tremor •Effect on sleep •Effect on other endocrine glands •Effect on sexual function
Draw the pathway by which thyroid hormone activates target cells. Relate thyroid hormone to BMR and hypothyroidism and hyperthyroidism. List factors that are involved in regulation of thyroid hormone secretion.
T3 (or T4 converted to T3 intracellularly) enter the cytoplasm then migrate through the pores of the nuclear membrane. They bind to the thyroid hormone receptor. In combination with the Retinoid X receptor, gene transcription is activated to produce the TH response element. mRNA is produced and leaves the nucleus. New proteins are synthesized and go on to affect other systems, growth, CNS development, increase cardiovascular processes, and increase metabolism.
Relate thyroid hormone to BMR and hypothyroidism and hyperthyroidism.
As BMR increases above “normal” or 0, the amount of TH produced reaches hyperthyroid levels (>100 mg/day). As BMR decreases below “normal” or 0, the amount of TH produced reaches hypothyroid levels (<100 mg/day)
List factors that are involved in regulation of thyroid hormone secretion.
Refer to text for effects of the following on thyroid hormone secretion: •TSH •cAMP •TRH •Cold and other neurogenic stimuli •Thyroid hormone feedback (PIC)
List causes and symptoms of hypothyroidism, including Hashimoto disease, endemic goiter, and cretinism.
Causes: •Hashimoto disease (autoimmunity) •Endemic goiter •Cretinism (caused by extreme early hypothyroidism) Symptoms: •Generally opposite those of hyperthyroidism •Myxedema •Atherosclerosis Treatments: •Oral medication
Antithyroid Drugs Describe the concepts behind different therapies for thyroid disorders
Thiocyanate and perchlorate anions: •Inhibit iodine uptake (inhibit I –Na+cotransport) Propylthiouracil: •Inhibits peroxidase •Can be used to treat for hyperthyroidism Iodides: •Decrease thyroid activity when present in very high concentrations
TSH
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cAMP
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Cold and other neurogenic stimuli
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