HYPOTHYROIDISM Flashcards
what is the largest endocrine gland?
thyroid
where is thyroid located?
below larynx and wraps around the anterior and lateral sides of the trachea
what does the thyroid consist of?
2 large lobes connected by narrow anterior isthmus
what secretes t3 and t4?
thyroid follicles
what do the thyroid follicles consist of?
it is filled with colloid and lined by follicular cells
where are parafollicular thyroid cells (C cells) located?
between the follicular cells
what do parafollicular cells secrete?
calcitonin which lowers blood calcium levels
what does the hypothalamus release when there are low levels of t3/t4 and low metabolic rate or decreased body temp?
TRH
what does pituitary gland release after hypothalamus’s release?
TSH (thyrotropin stimulating hormone)
when the thyroid releases t3 and t4 what happens in a person who has low levels, low metabolic rate and so on?or decreased body temperature?
increases t3 and t4
increases metabolic rate
increases temperature
when are thyroid hormones produced?
when thyroid gland is stimulated by TSH from the anterior pituitary
80% t4 and 20% t3
what is the primary active thyroid hormone?
T3
200-300X MORE ACTIVE THAN T4!
what does t4 wait to do?
it circulates through body and waits to be converted on demand by your cells into the active t3 hormone
where are stored thyroid hormones in the follicular lumen bound to?
a protein called TG (thyroglobulin)
can bound hormones diffuse into cells?
no
what can unbound hormones bind to?
and what do they do
they can bind to thyroid receptors and exert effects on metabolic rate and temperature regulation
what are reasons for the inhibition of the conversion of t4 to t3?
aging, fasting/calorie restriction, any type of inflammation, lack of sleep, stress, acute and chronic conditions (Kidney and liver), IBD (intestinal probs), obesity, alcohol
what meds are responsible for the inhibition of the conversion of t4 to t3?
amiodarone, propranolol, propylthiouracil
how do the thyroid hormones increase metabolism?
- increases transcription of cell membrane Na+/K+ ATPase-> oxygen consumption
- enhances fatty acid oxidation and heat generation
- gluconeogenesis, glycolysis, lipolysis
how do the thyroid hormones aid in growth and development?
- protein synthesis
- regulates cholesterol and triglyceride metabolism
- affects brain, reproductive system, and bone development and growth
how do the thyroid hormones have interrelated actions with catecholamines?
- thyroid hormones enhance responsiveness to catecholamines (“fight or flight response”)
- increase expression of catecholamine receptors
what are the 3 catecholamines?
…
what is one additional function of thyroid hormone that is huge and hasnt been mentioned yet?
regulating pituitary hormone synthesis (feedback loop)