Thyroid Gland Pathology Flashcards
What is an ectopic thyroid?
Thyroid tissue can extend all the way to the diaphragm
What are the three endocrine populations present within the thyroid?
- Thyroid gland follicular epithelium
* Secrete colloid and iodothyronines - Interstitial C-cells/ Parafollicular cells
* Located in the interstitium, between follicles
* Secrete calcitonin - Parathyroid gland tissue
What is the main function of T3/T4?
Maintaining metabolic activity
What do thyroid C cells secrete?
They secrete calcitonin in response to hypercalcaemia
What is the main function of calcitonin?
Reduces blood calcium by inhibiting osteoclasts
* increased renal PO4 3- and Ca 2+ secretion
polypeptide hormone
opposes the effect of PTH
What is the function of the thyroglossal duct?
connects ventral tongue to the thyroid
What is primary thyroid hyperplasia?
No formation of the thyroid (rare)
What is secondary thyroid hyopoplasia?
Pituitary gland produces less TSH
therefore the thyroid is less stimulated to produce T3/T4
leading to eventual hypothyroidism
What is lymphocytic thyroiditis?
autoimmune disease
production of autoantibodies against other antigens
What is goiter?
- non neoplastic enlargement of the thyroid gland
- associated with follicular hyperplasia/ hypertrophy
not common in carnivores
Where does the thyroid originate?
It originates on the floor of the pharynx- intimately related to the aortic sac
What is a thyroglossal duct cyst?
fluctuant mass (potentially full of fluid if it persists)
between the tounge and thyroid
Name 4 sequelae for thyroid hypofunction
- Gain in body weight
- Integument changes
- Hypercholesteraemia -> Atherosclerosis
- Reproductive changes
What is lymphocytic thyroiditis?
an autoimmune disease in which thyroid cells are destroyed via cell and antibody-mediated immune responses
What can cause goiter?
- Iodine deficiency/ iodide excess
- defective synthesis of thyroid hormones
- Goitrogens -> white clover, linseed meal, sulfonamides
What disorders of growth can cause thyroid hyperfunction?
Hyperplasia, adenoma, carcinoma
* common lesion in cats, dogs and horses
What usually causes thyroid hypofunction?
idiopathic follicular atrophy
Why is clinical hyperthyroidism common in cats?
- T4 is excreted into the bile via glucorinidation
- cats are bad at this
- therefore less T4 is excreted
- Therefore more likely to develop clinical hyperthyroidism
What are some sequelae for thyroid hyperfunction
- Hypertension
- Weight loss with increased appetite
- Vomiting
- Physical exam- thyroid slip
- Thyrotoxic Cardiomyopathy (saddle thrombi)
What is the most common thyroid disorder in a horse?
Thyroid adenoma
What is a common thyroid disorder in ruminants?
C-Cell Neoplasm
Explain the steps of iodothyronine synthesis
- I- enters the follicular cell on the basal side then exits into the colloid
- Thyroglobulin is synthesised in the RER
- Thyroglobulin is then secreted into the colloid
- I- is then oxidised to I2
- I2 then attaches to tyrosyl residues (forms either monoiodotyrosine or di-iodotyrosine
- TG is then conjugated to form either T3 or T4
Name 5 things that cause thyroid hypofunction
- Lymphocytic thyroiditis
- Idiopathic follicular atrophy
- Bilateral, Non-Functional thyroid tumour
- Goiter
- Secondary hypothyroidism
What is Hashimotos thyroiditis?
Immune system attacks your thyroid so it cannot produce as many thyroid hormones
What is the pathogenesis of lymphocytic thyroiditis?
Production of autoantibodies against TG
What is the gross pathology of lymphocytic thyroiditis?
Massive atrophy
In what animal species do bilateral non-functional tumours mostly occur in?
Mainly in dogs and horses
over 75% loss of tissue
What is the embryology of the thyroid gland?
Originates on the floor of the pharynx- intimately related to the aortic sac
Ectopic thyroid tissue can occur anywhere along this route all the way to the diaphragm
What are the main sequelae for thyroid hypofunction?
- Gain in body weight
- Integument changes-> bilaterally symmetric alopecia, hyperkeratosis , hyperpigmentation, myxedema
- Hypercholesterolemia -> atherosclerosis, renal glomerular and corneal lipidosis
- Reproductive changes (libido loss, low sperm count, altered oestrus cycle)
What is the pathogenesis of lymphocytic thyroiditis?
- Production of autoantibodies against T
- Gross path= massive atrophy
What is goiter not common in?
- Not common in carnivores
- Foetuses and neonates are most severley affected
What is the most common thyroid disorder of growth in dogs?
Adenocarcinomas
* often locally invasive and aggressive, resulting in the destruction of remaining normal tissue
How are carcinomas formed in cows?
C-Cell stimulation -> hyperplasia -. Adenoma -> Carcinoma
