Thyroid/Parathyroid Flashcards
Describe the hormones involved in the release of T3/T4 starting at the hypothalamus
thyroid releasing hormone (hypothalamus) causes release of thyroid stimulating hormone (pituitary) which in turn causes release of T3/T4
Is the release of thyroid releasing hormone and thus T3/T4 a negative or positive feed back system.
Negative
What are some factors that can increase T3/T4 production
Anything that requires increased cellular energy demand, examples:
cold, hypoglycemia, high altitude, pregnancy
What are the 3 macroscopic structures of the thyroid
R lateral lobe, L lateral lobe and the isthmus that connects the 2 lobes
-50% of thyroids have a 3rd lobe called the pyramidal lobe
What are the function units of the thyroid called
follicles
Describe the structure of follicles
colloid fluid surround by follicular cells
What thyroid hormone (T3 or T4) is the active form
T3, it is more potent
What thyroid hormone (T3 or T4) is the more numerous form
T4, inactive form, less potent
Describe the synthesis of T3/T4
- Follicular cells pull ioDIDE from the blood stream and oxidizes it to ioDINE (the usable form) using peroxidase, ioDINE is then released into the colloid
- Follicular cells are also producing thyroglobulin (TGB) and releasing into the colloid
- In the colloid TGB and Iodine react w/ each other to form monoiodotyrosine and diiodotyrosine
- In the colloid MIT and DIT form bound, MIT+DIT will form T3 and DIT=DIT will form T4
- Colloid is pulled back into the follicular cell by pinocytosis
- Vesicle containing colloid w/ MIT/DIT combo molecules fuses w/ lysosome which digest TGB and cleaves of T3 and T4
- Left over MIT/DIT is recycled
What AA does IoDINE react w/ on thyroglobulin (TGB)
Tyrosine
How many IoDINES are attached to tyrosine on DIT
2
How many IoDINES are attached to tyrosine on MIT
1
What proteins transport T3/T4 in the blood
Thyroxine binding globulin = 70%
Albumin=20%
Transthyretin=10%
All are made in the liver
What protein carries T3/T4 in the blood so it can be released in the cerebrospinal fluid CSF
Transthyretin
What is the actions of T3/T4
- increases basal metabolic rate/regulates metabolism
- increases action of catecholamines
- works w/ HGH and insulin to accelerate growth
What metabolic actions does T3/T4 cause
- stimulates protein synthesis
- increases lipolysis
- increases use of glucose and FFA of ATP production
- stimulates synthesis of Na/K pumps need for ATP production
How does T3/T4 raise body heat
stimulates synthesis of Na/K pumps need for ATP production, these rxns release heat as a byproduct thus increasing body heat
What is myxederma
unique phenomenon that produces puffy features, enlarged tongue, and joint stiffness in hypothyroidism
-caused by accumulation of negatively charged mucopolysaccharides in connective tissue which causes fluid and sodium to accumulate
What is hypothyroidism in children called and what is its usually caused by
Cretinism
usually caused by severe lack of iodine or immune dysfunction
characterized by stunted growth, mental retardation (b/c T3/T4 needed w/ HGH for growth)
Describe Hashimoto’s Disease
Auto immune disorder where antibodies attack and destroy TSH receptors at the thyroid and thyroglobulin
Describe Graves Disease
Autoimmune disorder caused by the production of thyroid-stimulating immunoglobulin which mimics TSH so thyroid gland is over stimulated and eventually burns out
What is exophthalmos
protrusion of the eyeballs caused by stimulation of TSH receptors on orbital fibrocytes, clinical sign of Graves dz
How is Graves Disease treated
Removal of thyroid and life time supplementation of T4
Will hypo/hyperthyroid be visible by the presentation of the pt
No, it is a spectrum disorder
What are the parafollicular cells and what do they do
Cells found between the follicles of thyroid that produce calcitonin
True or false calcitonin is a type of thyroid hormone
False
What is the only endocrine glad that stores its hormones in large quantities
Parafollicular cells , store ~100 days worth
What is the function of calcitonin
“tones” down the amount of calcium in the blood
by inhibiting osteoclast, increasing osteoblast, decreasing Ca absorption in intestine, and increasing Ca loss in distal convoluted tubule
What are the parathyroid glands and what do they do
4 small glands on the posterior surface of the thyroid that secrete parathyroid hormone
-Parathyroid hormone acts increase blood Ca
What is the functional component of the parathyroid hormone
Chief cells
