Thyroid Hormones Flashcards
What are some featurers of the structures of the thyroid?
Butterfly shape joined by the contolisthus,us, usually about 2-3 cm across and there are two cell types, the follicular and the parafolliuclar.
What are the features of the follicular cells of the thyroid gland?
Arranged in functional units called follicles, which contain thryoglobulin.
How is thyroid hormone secretion controlled?
It is under the control of the hypothalamus and the anterior pituarity gland, TRH is released into the hypothalmic pitaurity system, to catalyse the releaseof TSH. The realise of both hormones ic affected by negative feedback.
What are the three hormones released from the thyroid?
T3, T4( thryoxine) calcintonin
What are the actions of TSH?
Bind to receptors on follicle cells and stimulates all apsects of T3 and T4 secretion, it also has a trophic affect to increase the size of thyroid follicles, may result in a gotire.
How are T3 amd T4 synthesised?
Iodide is transported into epitheael cells against the concentration gradient, synthesis of a tyrosine rich protein in the epitheael cells, secretion of thyroglobulin into the lumen of s follicle, oxidation of iodide to produce an iodinating species, iodination of side chain of tyrosine residues in thyroglobulin, respectively produced in a ratio 1:10
How are T3 and T4 secreted?
Thryoglobulin, which is taken in by the process of endocytosis, proteolytic cleavage occurs to realesse T3and T4, and diffuse from the epithelium.
How are T3 and T4 transported?
Only a small amount is free in solution and biologically active, the rest is bounded to proteins such as thryonen binding globulin and prealbumin and albumin, t3 has a lower wffinity for the transporter and has a shorter half life in solution.
What are the mjor physilogical actions of T3 and T4??
Has an affect on the metabolic rate of most tissues, it increases the basal metabolic rate and all the process, it stimulates the neurotansmitter synthesis which can produce tachnhcardia,it is important in development especially in the CNS, where it is needed for the development of nerve cells cortical processes of nerves and the myelination of nerve fibres.
What is the mechanism lf action of T3 and T4?
It crosses the plasma membrane, it interacts with specific high affinity receptors in the nucleus p, which has a ten fold greater affinity for T3 then T4 , which leads to a conformational change of the transcriptor snd this increases the transcription of specific genes, stimulating oxidative energy metabolism.
What is the most common cause of hypothryoidism?
Hashimotos disease, where the is an autoimmune destriuction of thyroid follicles.
What are common symptoms of hypothroidism?
Weight gain, deep voice and cold intolerance, reduced BMR, tiredness and lethargy, tiredness and brachycardia, alopecia, dry skin, weakness in the muscle and arms
What is the most common cause of hyperthyroidism?
Graves disease, autoimmune, antibodies are produced that stimulate TSH release, and can be treated with carboimazule. Which inhibits thyroid perioxidases, which prevent coupling of tyrosine to thyroglobulin,
What are some features of the location of the thyroid?
It is infornt of the lower larynx and upper trachea, there are 3 veins and arteries supporting it, superior, middle, inferior and thyroid vessels, two nerves lie in close proximity the recurrent larengyl, external branch of the superior larengyl, and is only distinguishable or palpable when enlarged.
