copy 3 Flashcards
What are the thyroid follicles surrounded by?
Thyroid follicles are enveloped by a layer of epithelial
cells, called follicular cells, which in turn are
surrounded by parafollicular cells.
What is the function of follicular cells?
Synthesize and store thyroid hormones
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What type of epithelium do the follicular cells have?
Simple Cuboidal epithelium that becomes columnar when active and squamos when inactive
What are the two major hormones that the thyroid secretes?
Thyroxine (T4) an Triiodothyronine (T3).
What role does the pituitary gland have in regulating the thyroid?
It releases thyroid stimulating hormone that regulates Thyroid secretion.
What else does the thyroid secrete?
Calcitonin which plays a role in regulating calcium metabolism
What is the structural difference between T3 and T4?
The two active thyroid hormones are triiodothyronine
(T3) and tetraiodothyronine, or thyroxine (T4). The
structures of T3 and T4 differ only by a single atom of
iodine, as shown in Figure 9.16. Although T3 is more
active than T4, almost all hormonal output of the
thyroid gland is T4. This “problem” of secreting the less
active form is solved by the target tissues, which
convert T4 to T3. A third compound, reverse T3
What is the functional difference between T3 and T4?
T3 is more active than T4
But T4 has a longer half life and is synthsized in greater amounts
What are 2 causes of hyperthyroidism?
Autoimmune disease where antibodies (Thyroid-Stimulating Immunoglobulins: TSI) bind to the TSH receptor and induces continual activation (12 hours) of cAMP system. High levels of Thyroid hormone caused by TSI depress the pituitary gland secretion of TSH that drop to zero.
Thyroid adenoma: cancer within a region of thyroid gland that secrete large quantities of thyroid. The healthy part of the gland will show reduction in thyroid secretion due to the feedback mechanism exerted on the pituitary gland (less TSH secretion).
What are some symptoms of hyperthyroidism?
1- High state of excitability
2- Intolerance to heat
3- Increased sweating
4- Mild to extreme weight loss
5- Varying degrees of diarrhea
6- Muscle weakness
7- Nervousness
8- Extreme fatigue but inability to sleep
9- Tremor of the hands
