Thyroid Flashcards
Function of thyroid gland
basal metabolic rate
lipid, protein, and carb metabolism
Terms for decreased and increased secretion of thyroid hormone.
decreased: hypothyroidism
increased: hyperthyroidism
______ separates the lobes of the thyroid gland in the dog, cat, and horse.
isthmus
(T/F) The thyroid has a fibrous capsule than can be dissected from the organ.
True
What two vessels supply blood to the thyroid gland?
cranial thyroid artery
caudal thyroid artery
__________ cells line thyroid follicles and produce colloid.
follicular epithelial
What 2 things does colloid of thyroid follicles contain?
- thyroglobulin
- thyroid peroxidase
What is thyroglobulin? What does it contain?
glycoprotein
stores thyroid hormones + tyrosine
What does thyroid peroxidase do?
converts iodide –> intermediate form which binds to aromatic ring on tyrosine in thyroglobulin
What are the two possible intermediate forms produced when thyroid peroxidase converts iodide?
monoiodotyrosine OR diiodotyrosine
What is the full name for T3? T4?
T3 = triiodothyronine
T4 = tetraiodothyronine (thyroxine)
Monoiodotyrosine combines with diiodotyrosine to form _________ and ______.
T3 (triiodothyronine)
rT3 (reverse triiodothyronine)
When two diiodotyrosine come together, it forms ________.
T4
Parafollicular cells of the thyroid gland produce ________.
calcitonin
Calcitonin secretion increases as calcium (increases/decreases) which (stimulates/inhibits) osteoclasts.
increases
inhibits
All functions of the follicular epithelial cells of the thyroid gland dependent upon _______.
TSH (from pituitary)
Where is the protien portion of thyroglobulin synthesized in the follicular epithelial cell?
rough endoplasmic reticulum
_____ is added to the protein portion of thyroglobulin in the rough ER before it is transferred to _______.
mannose (carbohydrate)
golgi complex
An additional carbohydrate, _______, is added to thyroglobulin once in the golgi complex.
galactose
When entering the golgi complex, vesicles fuse with the (convex/concave) or (trans/cis) face of the golgi. When exiting, they bud from the (convex/concave) or (trans/cis) face.
convex
cis
concave
trans
Once secretory granules with thyroglobulin bud from the golgi, they fuse with apical membrane of __________.
follicular epithelial cell
Thyroglobulin is released into the lumen of the thyroid follicle via what process?
exocytosis
Circulating _______ is actively transported into the follicular epithelial cell.
iodide (I-)
What transports circulating iodide into the follicular epithelial cell?
Na+/I- symporter
Where is the Na+/I- symporter located?
basolateral membrane of follicular epithelial cell
What stimulates the Na+/I- symporter?
TSH (thyroid stimulating hormone)
_____ stimulates _____ which stimulates Na+/I- symporter to transport iodide into the follicular epithelial cell in the thyroid gland.
TRH (thyrotropin releasing hormone)
TSH (thyroptin)
_____ stimulates _____ which stimulates Na+/I- symporter to transport iodide into the follicular epithelial cell in the thyroid gland.
TRH (thyrotropin releasing hormone)
TSH (thyrotropin)
How is thyroid peroxidase synthesized?
by follicular epithelial cells
enters follicular lumen same as thyroglobulin
Iodide is transported to the follicular lumen by a transmembrane protein called ________.
pendrin
Pendrin is a transmembrane protein on the (apical/basolateral) membrane of follicular epithelial cells.
apical
___ and ___ are biologically active while ___ is inactive.
T3 + T4
rT3
____ stimulates follicular epithelial cells to ingest colloid by what process?
TSH
pinocytosis
Pinocytotic vesicles fuse with _______ to form _______.
primary lysosomes –> secondary lysosomes
What enzyme in secondary lysosomes digest thyroglobulin and liberate T3 & T4?
proteases (cathepsins)
From the follicular epithelial cell, T3 and T4 diffuse into _______ surrounding the follicle once liberated from colloid.
capillaries
What is meant by “free” T3 and T4?
not bound to plasma proteins
(T/F) Free T4 readily enters cells while T3 does not.
False - both readily enter
In the target cell, ___ is converted to ___, the active form.
T4
T3
What process occurs to convert T4 to T3?
deiodinated
What process occurs to convert T4 to T3?
deiodinated (remove iodide)
T3 binds to ______ receptors to alter ______.
nuclear (chromatin)
transcription
(T/F) TSH stimulates both the synthesis and release of T3 and T4.
True
As blood levels of T3 and T4 rise, what occurs with TSH and TRH?
inhibited (negative feedback) to both hypothalamus and pituitary
Distinguish between primary, secondary, and tertiary hypothyroidism.
Primary: problem with thyroid gland (no thyroid hormone production)
Secondary: problem with pituitary (no TSH to stimulate T3/T4 production)
Tertiary: problem with hypothalamus (no TRH –> down TSH –> down T3/T4)
Which type of hypothyroidism is uncommon in dogs? Which is common? Which is not reported in animals?
- secondary
- primary
- tertiary
(Cold/warmth) stimulate secretion of TRH, and therefore TSH, resulting in increased T3 and T4 release. (Cold/warmth) does the opposite.
cold
warmth
What are follicular epithelial cells derived from?
pharyngeal endoderm
What are parafollicular cells derived from?
neural crest ectoderm
Name the effect T3 and T4 have on each system:
- metabolism
- GI tract
- heart
- increase BMR
- maintain smooth muscle function
- increase B receptor synthesis
T3 and T4 maintain ______ synthesis and _____ gland function.
protein
sebaceous
Match each extreme to the diseased state of either hypo or hyperthyroidism:
- V+ & D+ | constipation
- tachycardia | bradycardia
- dry/dull coat | patchy/oily coat
- heat intolerant | cold intolerant
- weight loss | weight gain
- lethargy | nervousness
Hypo: constipation, bradycardia, dry/dull coat, cold intolerant, weight gain, lethargy
Hyper: V+ & D+, tachycardia, patchy/oily coat, heat intolerant, weight loss, nervousness
