Thyroid Gland Flashcards
What do thyroid C (parafollicular) cells do?
secrete calcitonin in response to increased blood Ca (hypercalcemia)
What do thyroid follicular cells do?
Thyroglobulin –> monoiodotyrosine (MIT) and diiodotyrosine (DIT) –> biologically active hormones T3 and T4
under the influence of TSH and TRH
negative feedback on hypothalamus and adenohypophysis
regulate growth rate of metabolism and growth
what disorder of the C cells do we have to know?
C-cell (parafollicular cell) tumors
what disorders involving hypo function of the thyroid gland do we have to know?
hypothyroidism
congenital hypothyroidism (goitre, CHDS of foals)
what disorders involving hyper function of the thyroid gland do we have to know?
hyperthyroidism
nodular hyperplasia, follicular tumors
Hypothyroidism results in what pathophys thing?
decreased concentrations of thyroid hormones T3 and T4
what is one of the most common endocrinopathies of dogs? which breeds most affected?
hypothyroidism
beagles, daschunds
what are the causes of hypothyroidism
primary thyroid disease (idiopathic follicular collapse, lymphocytes thyroiditis)
rarely pituitary or hypothalamic lesion resulting in lowered TSH or TRH
what’s the lesion?
thyroid gland atrophy
thyroid atrophy makes the parathyroid glands more prominent (arrow)
what are the extra-thyroidal lesions of hypothyroidism?
reduction in BMR –> weight gain)
cutaneous
reproductive
hypercholesterolemia –> atherosclerosis
what are some examples of cutaneous lesions present in hypothyroidism?
bilaterally symmetrical alopecia
hyperkeratosis
hyperpigmentation
myxedema
what is goiter?
clinical term used to describe a non-neoplastic enlargement of the thyroid glands
what are some causes of goiter?
multiple cases, but have a shared pathogenesis
ex. iodine deficient diest, goitrogenic compounds, excess dietary iodine, genetic enzyme defects (Dyshormonogenetic goiter)
what is the pathogenesis of goiter, no matter the cause?
- inciting cause
- inadequate thyroid hormone synthesis
- decreased blood levels of T3 and T4
- increased TRH
- increased TSH
- hypertrophy/hyperplasia of follicular cells
- goiter
what’s the lesion?
goiter
thyroid gland. what’s the lesion?
goiter
what are the gross lesions of a thyroid gland with goiter?
bilaterally enlarged, dark purple thyroid glands
What does CHDS stand for?
Congenital Hypothyroidism-Dysmaturity Syndrome (in foals)
True or false: CHDS is common in western Canada
true
CHDS is characterized by ____ ____ and _____ _____.
Perinatal death, MSK malformations
with CHDS, there’s _____ gestation but foals appear _____.
prolonged
dysmature
what are the MSK abnormalities that come with CHDS?
contracted or ruptured tendons
mandibular prognathia
immature carpal and tarsal bones on radiographs
This goat has this lesion, plus contracted tendons and immature carpal and tarsal bones. what might this foal have?
congenital hypothyroidism-dysmaturity syndrome
with CHDS cases, why must you ALWAYS take the thyroid for histo?
grossly, the thyroid may look normal, but microscopic lesions are present
true or false: the etiology of CHDS is unknown
true
hyperthyroidism results in what pathophys thing?
elevated circulating levels of thyroid hormones (T3 or T4)
dogs commonly get ____ and cats commonly get _____
hypothyroidism
hyperthyroidism
true or false: hyperthyroidism is common in dogs
false! rare in dogs
what is one of the most common endocrine diseases of cats?
hyperthyroidism
what is the typical signalment for a cat with hyperthyroidism?
geriatric
why is hyperthyroidism rare in dogs?
they have more efficient enterohepatic excretion of thyroid hormones
if dogs get hyperthyroidism, how do they get it?
thyroid follicular tumors (Carcinoma > adenoma)
Hyperthyroidism results in what 2 important things clinically?
increased BMR
cardiac manifestations
hyperthyroidism causes increased BMR. what are the results of this?
weight loss despite ravenous appetite!!
PU/PD, nervous or hyper excitability, heat intolerance
hyperthyroidism causes cardiac manifestations. What are two clinical signs of this? what gross lesion can you see?
tachycardia, dysrhythmias
concentric hypertrophy of the heart (DON’T MISTAKE THIS FOR PRIMARY HYPERTROPHIC CARDIOMYOPATHY!)
Tell me which lesions are most common with hyperthyroidism
multifocal nodular hyperplasia and thyroid follicular adenomas > thyroid follicular carcinoma
Hyperthyroidism:
Cats most commonly get what lesions?
Dogs most commonly get what lesions?
Cats: multifocal nodular hyperplasia, thyroid follicular cell adenoma
Dogs: thyroid follicular carcinoma
What species/signalments do multifocal nodular hyperplasias occur in most commonly?
old horses, cats, dogs
what do multifocal nodular hyperplasias that cause hyperthyroidism look like grossly?
multiple, tan to brown, nonencapsulated nodules
this is from a cat with hyperthyroidism. what’s the lesion/cause?
multifocal nodular hyperplasia
what species do thyroid follicular cell adenomas occur in most commonly ?
cats
malignant thyroid tumors are more common in _____, benign thyroid tumors are more common in ____.
dogs, cats
what do thyroid follicular cell adenomas that cause hyperthyroidism look like grossly?
single, white to tan, well-defined and encapsulated mass
tell me the differences between multifocal nodular hyperplasia and thyroid follicular cell adenomas in terms of gross appearance?
Adenoma: single, encapsulated, white to tan
Hyperplasia: multiple, tan to brown, non encapsulated
thyroid follicular carcinomas:
1) can develop where?
2) invasive/non-invasive?
3) metastasize ____(early/late) to where?
1) ectopic thyroid tissue
2) non-invasive
3) early, lungs
what is the typical signalment of an animal with a thyroid c-cell tumor?
old bull
what is the cause of thyroid c-cell tumors?
unknown, but might be linked to high calcium diets
a bull with a thyroid c-cell tumor will have concurrent… what?
pheochromocytoma and pituitary tumors
true or false: thyroid c-cell tumors are only adenomas
false! both adenomas and carcinomas
