Thyroid Gland Flashcards
Describe the location of the thyroid gland
Below the Larynx
What connects the thyroid glands anteriorly?
Isthmus - thyroid tissue
What are the hormones secreted by the thyroid gland?
- Thyroxine (T4)
- Triiodothyronine (T3)
_______________ are the follicular cells that line the thyroid follicles and are cuboidal shaped.
Thyrocytes
Parafollicle cells (C cells) secrete the hormone _________________
Calcitonin (thyrocalcitonin)
Which Thyroid hormone is the most active but with a short half life?
T3 - triiodothyronine
What do T4 and T3 bind to for travel in blood?
Bound to plasma proteins
What is the plasma protein that T4 and 3 bind to ?
Thyroxine-binding globulin (TBG)
What converts T4 to T3 once they enter target cells?
Deiodinase
T3 and T4 are made by ______________ after iodinization
Tyrosines
What is the precursor for tyrosine ?
Thyroglobulin (TG)
TG is the major protein component of what part of the follicular cells ?
Follicle colloid
What accumulates in thyroid follicles from the blood to then be secreted onto the colloid?
Iodide (I-)
Once Iodide enters the colloid through what process is it converted into iodine (I2)?
Oxidation
_____________ are attached to the AA ____________ within the T.
Iodines / tyrosine
One iodine + Tyrosine = molecule ?
Monoidotyrosine (MIT)
DIT (diiodotyrosine) is the attachment of how many iodines?
2
How many DIT molecules are needed to produce tetraiodothyronine or T4?
2
MIT + DIT = ?
Triiodothyronine T3
Where in the follicular cell does the TH synthesis occur?
Thyroid follicles
What is the process through which the thyroid follicles take up colloid volume when stimulated by TSH?
Pinocytosis
Which TH is lipophilic, meaning it can diffuse accross the plasma membrane?
T4
Which enzyme converts T4 into T3 in the cytoplasm?
Deiodinase
The hormone receptor complex that forms is due to the binding of T3 or T4 to non specific proteins?
T3 binds and enters the nucleus with NSP
Which receptors are needed to for the TH to activate gene expression?
TR (thyroid hormone Receptor) and RXR (retinoid X receptor)
The vitamin A derivative 9-cis-retinoic acid is associated with which receptor?
RXR
TH on metabolism can induce ________________, and thus ATP production
cell respiration
T/F TH can increase the basal metabolic rate
True
If food intake with an increased BMR does not increase, list some things that may happen
- lipolysis
- protein breakdown
- N2 excretion
TH on skeletal muscle can stimulate synthesis of what ?
Proteins (myosin heavy)
To Which muscle type fiber switch is stimulated by TH?
Fast-twitch fibers (white/type II)
With hypothyroidism, one can expect ____________________ to occur in relation to skeletal muscle
muscle weakness
With hyperthyroidism, one can expect the overcontraction of muscles and thus degeneration, which is termed:
Thyrotoxic myopathy
Do TH increase or decrease O2 consumption and CO?
Increase it, thus increase HR
The lack of TH during development can lead to __________________
Cretinism
TH can ___________ (increase or decrease) the sensitivity to catecholamines
Increase by increasing expression of the receptors
Thyrotropin (TSH) and TRH (thyrotropin releasing hormone) will do what to Th secretion?
It will augment it
Activation of T3 and T4 synthesis/secretion pathways is done by which hormone associated with TH?
TSH (thyrotropin)
An enlarged thyroid gland is termed:
Goiter
Goiter can be:
Endemic or toxic
Endemic goiter is due to a deficiency in what?
Iodine
In endemic goiter, are TSH secretion levels abnormally high or abnormally low?
Abnormally high
T/F TH levels are normal or a little low in a patient with endemic goiter
True - the abnormal growth of thyroid follicles compensate the inadequate TH production
What is another name for toxic goiter?
Thyrotoxicosis (Grave’s disease)
What is the cause for Grave’s disease/Thyrotoxicosis?
Autoantibody (TSI: thyroid stimulating immunoglobulin) binding to TSH receptor
T/F Toxic goiter can be found in animals
False
Which can be seen with thyrotoxicosis - hyper or hypo thyroidism?
Hyperthyroidism
What is the most common cause of feline hyperthyroidism?
Benign thyroid tumor
List clinical signs associated with feline hyperthyroidism
- weight loss
- hyperactivity
- palpable goiter
- unkempt coat
Lymphocytic Thyroiditis or Idiopathic thyroid gland atrophy are common cause of canine __________________
hypothyroidism
Obesity, Skin DZ, Lethargy and cold intolerance are signs associated with?
Hypothyroidism in dogs
