Thyroid Flashcards
TRH from the hypothalamus stimulates ___ secretion from the anterior pituitary gland
(control of thyroid hormone secretion)
TSH
Thyroid hormone synthesis/secretion occurs within the thyroid gland in the presence of __
(control of thyroid hormone secretion)
TSH
Negative feedback causes the hypothalamus to stop or slow production of TRH which then causes the ___ pituitary to stop or slow release of TSH
anterior
thyroid hormones, think:
T3, T4
Anything that increases cellular energy demand causes an increase in __ production (e.g., Cold environment, hypoglycemia, high altitude, pregnancy
)
T3/T4
Lateral lobes (wings) on each side of the trachea projecting upward to just below the ___
Lobes connected by an ___ located anterior to the trachea
(thyroid location)
larynx
isthmus
Largest of pure endocrine glands
Thyroid gland
A thyroid has an ___ blood supply
extensive
fer all them hormones
___ are the functional units of the thyroid
Follicles
A follicle is a sphere with its wall consisting of __ cells
follicular
This inside of this unit is called the __
thyroid micro
colloid
___ cells reside in between follicles
Parafollicular
produce calcitonin but not considered a thyroid hormone
The inactive form of thyroid hormone
Much more abundant, but less potent
Tetraiodothyronine (Thyroxine, T4)
The active form of thyroid hormone
Much more potent, less abundant
Triiodothyronine (T3)
Made in small quantities by parafollicular cells, helps to regulate calcium levels of the blood
(not a “thyroid hormone” only made in the thyroid)
Calcitonin
Follicular cells pull ___ ions from the blood stream
iodide
Follicular cells are also producing ____
thyroglobulin (TGB) (glycoprotein-carbon chain of many amino acids)
produced in endoplasmic reticulum
Packaged in the Golgi apparatus
Released by exocytosis into the lumen (colloid)
thyroglobulin (TGB)
glycoprotein-carbon chain of many amino acids – tyrosine
Iodide requires ___ to make iodine (the useable form for thyroid hormone synthesis)
____ oxidizes the iodide into iodine (I2)
oxidation
Perioxidase
(Insuffienct ___ lead to thyroid issues)
tyrosine, iodine, or peroxidase
(T3 and T4 are __ soluble)
lipid
At this point there is now TGB and iodine (I2) roaming in the colloid
Simultaneously TGB and ___ begin to react with each other forming bonds (at the tyrosine portions of TGB)
“middle step”
iodine
One iodine to one tyrosine
monoiodotyrosine (MIT)
Two iodines to one tyrosine
diiodotyrosine (DIT)
These MIT and DIT molecules continue to form bonds to one another
MIT + DIT = T3 (3 iodine molecules)
DIT + DIT = T4 (4 iodine molecules)
The colloid is then pulled back into the follicular cells by ___
pinocytosis
This colloid contains the T3 and T4
Once back in the follicular cell, this colloid is engulfed by a lysosome which digests the TGB and cleaves off the ___
T3 and T4
This T3 and T4 is sent out of the cell, into the interstitial space, into the bloodstream
Because they are weak in terms of water solubility, more than 99% of both T3 and T4 are then bound to transport proteins (thyroxine-binding globulin; TBG) in the blood stream
This is the “glue” binding the MIT, DIT, T3, T4
TGB – Thyroglobulin
This is the transport protein found in the blood stream that carries the T3/T4 to their target cells after synthesis of them is complete
TBG Thyroxine Binding Globulin
Actions of Thyroid Hormones (T3/T4)
Increase basal metabolic rate (BMR)
Stimulates synthesis of additional Na+/K+ pumps
Helps to regulate the metabolism
Can enhance actions of some catecholamines
Works with hGH and insulin to accelerate body growth
BMR is the rate of oxygen consumption under normal conditions
When increased, BMR causes metabolism of carbohydrates, proteins, and lipids
(Actions of Thyroid Hormones (T3/T4))
Increase basal metabolic rate (BMR)
This causes increased ATP production and consumption by the constant turnover of the Na+ and K+
These reactions release heat as a byproduct
This heat helps to raise and maintain the body temperature
Stimulates synthesis of additional Na+/K+ pumps
Stimulates protein synthesis
Increases use of glucose and fatty acid for ATP
production
Increases lipolysis and enhances cholesterol excretion
Helps to regulate the metabolism
T3 and T4 upregulate ____ in the presence of these substances
beta adrenergic receptors
The upregulation can explain why hyperthyroid patients experience increased heart rates, and blood pressure
____ of T3/T4 in fetal growth, infancy or childhood causes severe mental retardation and stunted bone growth
Deficiency
