21.3 Thyroid hormones Flashcards
What type of pump is the iodide pump?
2: 1 sodium:iodide symporter.
- sodium potassium ATPase pump
Where is iodide more highly concentrated?
in the cell (colloid gland). 30-250x that in the plasma
What is used to transport the iodide across the apical membrane?
pendrin: choride-iodide counter transporter
How does the thyroid hormone form?
- thyroglobulin from the thyroid binds up 70 Tyr with iodine to form thyroid hormones
Which form of iodide is able to bind with tyrosine directly?
nascent form binds directly (oxidized form)
What is the major hormonal product of teh thyroid?
thyroxine
What combinations will produce thyroxine?
- 2 diiodotyrosine joining
2. monoiodotyrosine and dioodotyrosine to form triiodothyronine (T3)
Explain the process of how thyroid hormones are released.
- apical surface pinches off to form the pinocytosic vesicles
- lysosome fuse with vesicels, digest thyroblogulin molecules, releases thyroxine and triiodothyronine
- thyroid diffuse into blood
What is the majority of thyroid hormone that is released?
- thyroxine, which slowly deiodinated to form triiodothyronine
What is the purpose of the deiodinase enzyme?
- helps to recycle the majority of iodinated tyrosine in the thyroglobulin during a recycling process
What plasma component has a high affinity for the thyroid hormones?
plasma proteins which maintains a high level in the blood and slow diffusion into tissues
How does thyroid hormone affect the cardiovascular system?
- increase blood flow and cardiac output
- increase heart rate
- normal arterial pressure (no change)
- increased respiration
How does thyroid hormone affect the nervous and muscular systems?
- increases excitation of CNS leading to muscle tremors
Does thyroid hormone affect the GI?
- yes, it will lead to increased GI motility
How will thyroid affect the metabolic system?
- initiate carbohydrate metabolism
- initiate fat metabolism
- requires increased vitamin in take
- increase BMR and decrease body weight
What type of signaling molecule is thyroid hormone?
- intracellular; lipophilic signaling. Both T3,T4 can cross membrane. T4 requires iodinase to enter into the nucleus
What compounds regulate thyroid secretions?
TSH, cAMP, TRH, cold(immune response), Thyroid hormone feedback
Causes of hyperthyroidism?
- Grave’s disease
2. Adenoma (benign glandular tumor)
What are common effects of hyperthyroidism?
- fatigue
- inability to sleep
- tremors
- exopthalmos (anterior bulging of the eye)
- psychic disorder
What are common causes of hypothyroidism?
- Hasimoto disease (autoimmune)
- Endemic goiter
- Cretinism
Cause: myxedema, atherosclerosis
What does thiocyanate ions Rx do?
inhibit iodine uptake by blocking the I, Na cotransporter
What is used to block the I, Na cotransporter system?
thiocyanate ion
What drug is used to inhibit peroxidase?
propylthiouracil
What is the effect of propylthiouracil?
inhibiting peroxidase uptake
What can low levels of deiodinase enzyme simulate or mimic?
similar to iodine deficiency
What effects will thyroid hormones have on teh cardiovascular system?
- increase cardiac output
- increase HR
- no effect on arterial pressure
- increase respirations
What will growth hormone do to the GI motility?
increase motility
What will growth hormone do to muscles and nerves?
- increase muscle function
2. increase CNS excitation
How will TSH (thyrotropin) affect thyroid hormone secretion?
- increase thyroid hormone secretion
How will cAMP affect thyroid hormone secretion?
- increase thyroid hormone secretions and prolong growth of thyroid glandular tissue
How will TRH affect thyroid hormone secretion?
1.Secreted from the hypothatlamus to stimulate secretion of TSH. which will increase thyroid hormone release
What affect do cold and neurogenic stimuli have on thyroid hormone release?
- cold/parasympathetic stimulation leads to increased TSH.
2. Sympathetic stimulation leads to decreases the TSH release
What does the thyroid hormone feedback system do to regulate the thyroid secretions?
- causes inhibition when circulating concentrations reach 1.75 times normal. inhibit TSH
What can cause hyperthyroidism?
- grave’s disease
2. adenoma
What are common symptoms of hyperthyroidism?
- highly excitable
- heat intolerant
- increased sweating
- weight loss
- diarrhea
- weakness
How is yperthyroidism treated?
- removal of thyroid gland or treat with radioactive iodine
What are commons causes of hypothyroidism?
- autoimmune (hashimoto) disease
- endemic goiter
- crteinism
Can myxedema and atherosclerosis be symptoms of hypothyroidism?
yes, corrected with supplemental thyroid
What is the effect of thiocyanate?
inhibits uptake of iodine, reducing thyroid T3,T4 production
What is the effect of propylthiouracil?
inhibition of peroxidases
What can iodides do in high concentrations?
decrease thyroid activity
