Unit 2 - Thyroid gland Flashcards
What is the structure of the thyroid gland?
it is made up of follicular cells and parafollicular cells
What is in the lumen of follicular cells?
colloid
What do parafollicular cells produce?
calcitonin
What hormones are secreted from follicular cells?
thyroxine (T4) and triopdpthyronine (T3)
What is T3 and T4 synthesized from?
tyrosine and iodide
What are T3 and T4 bound to in colloid?
thyroglobulin
What is the main function of T3 and T4?
increase the basal metabolic rate (energy production at rest)
What is goiter?
Iodine deficiency that leads to the reduction in thyroid hormone production slowing the rate of oxidation of all cells which causes an enlarged thyroid gland
What synthesizes thyroglobulin?
follicular cells
What synthesizes ‘trap’ I?
follicular cells
When I- is released into the lumen of the follicle, what happens?
it is converted into highly reactive I^0
What does I^0 do?
it iodinates tyrosine molecules within the thyroglobulin protein
If iodinated tyrosinases are adjacent to one another what happens?
they condense and form T3 and T4
When T3 and T4 are needed, what occurs within follicular cells to free them?
TG containing T3 and T4 is taken up by phagocytosis and inside of follicular cells it is attacked by proteases, which free T3 and T4.
How is the secretion of thyroid hormones regulated?
deviations from homeostasis are detected by the hypothalamus and stimulate its release
When deviation from homeostasis is sensed, what is released by the hypothalamus?
TRH
What does TRH do?
it stimulates the release of TSH from the anterior pituitary
What does TSH do?
it enters the circulation which then tells the thyroid gland to release T3 and T4
How do thyroid hormones effect calorigenesis?
increase O2 consumption, increase BMR, increase heat dissipation, increase beta adrenergic receptors, increase vasodilation, increase cardiac output
How do thyroid hormones effect carbohydrate metabolism?
they provide more glucose
How do thyroid hormones effect lipid metabolism?
provide more fatty acids
How do thyroid hormones effect protein synthesis?
stimulates pre-adolescent growth and development and inhibits hyperthyroidism
How do thyroid hormones effect bone?
maintain growth and epiphyseal closure
How do thyroid hormones effect muscle?
they maintain muscle protein synthesis
How do thyroid hormones effect skin?
maintain protein synthesis and turn over, maintain hair coat, and sebaceous gland activity
How do thyroid hormones effect brain development?
increase fetal brain development, synapse formation, and myelination
In which species will you most likely encounter hyperthyroidism?
older cats
What are the most common causes of hyperthyroidism?
Thyroid gland tumors
What are common physical manifestations of hyperthyroidism?
poor hair coat, diarrhea, weight loss, heat intolerance, increased nail growth, goiter, vomiting, weak, and nervousness
What is hyperthyroidism treated with?
Methimazole, surgery, or radioactive I
What does Methimazole do?
inhibits T4 formation
In which species will you most likely encounter hypothyroidism?
dogs
Are there breeds which are predisposed for hypothyroidism?
yes, especially golden retrievers and doberman pinchers
What is primary hypothyroidism caused by and what happens after administering TSH?
it is a thyroid lesion; no increase in T4 after administering TSH
What is secondary hypothyroidism caused by and what happens after administering TRH?
pituitary lesion, no increase in TSH after administrating TRH
What is tertiary hypothyroidism caused by and what happens after administering TRH?
hypothalamic lesion, increase in TSH after administering TRH
What is the most common type of hypothyroidism?
primary
What is cretenism?
congenital hypothyroidism
how is hypothyroidism treated?
replacement therapy with synthetic thyroxine-levothyroxine
