Thyroid Pathology

Question 1

What are the three endocrine cell populations present within the thyroid gland ?

Answer 1

follicular epithelial cells, secrete colloid and iodothyronines (T3)
interstitial C-cells (parafollicular cells), secrete calcitonin in response to hypercalcemia
parathyroid gland tissue

Question 2

Describe T3 synthesis

Answer 2

iodide ions enter the follicular epithelial cells
thyroglobulin is synthesized in RER
TG secreted into colloid
I- oxidised into I2
I2 attaches to TG tyrosyl residues through a series of reactions. it will form the bases of T3 and T4
colloid containing conjugated and iodinated TG is endocytosed by follicular epithelium
endocytic vesicles fuse with lysosomes where T3 and T4 are cleaved from TG
T3 and T4 are released into circulation

Question 3

Define primary thyroid hypoplasia

Answer 3

lack of formation of a normal thyroid gland

Question 4

Define secondary thyroid hypoplasia

Answer 4

systemic disease decreasing the amount of cells producing TSH

Question 5

List the 5 causes of thyroid hypofunction

Answer 5

lymphocytic thyroiditis
idiopathic follicular atrophy
bilateral non-functional thyroid tumours
goiter
secondary hypothyroidism

Question 6

Define lymphocytic thyroiditis

Answer 6

autoimmune disease, the production of autoantibodies against TF antigens
grossly, the gland is small due to massive atrophy

Question 7

Define idiopathic follicular atrophy

Answer 7

unknown origin, no inflammation present, see a small gland due to atrophy

Question 8

Define bilateral non-functional thyroid tumours

Answer 8

adenocarcinomas, can be adenomas
functional clinical effects occur with >75% loss of tissue
grossly, see masses and compression atrophy

Question 9

Define a goiter

Answer 9

a non-neoplastic enlargement of the thyroid gland, often associated with follicular hyperplasia/hypertrophy
grossly, large due to hyperplasia

Question 10

Define secondary hypothyroidism

Answer 10

caused by pituitary of hypothalamic disease resulting in decreased TRH or TSH
grossly, small due to atrophy

Question 11

What are the systemic consequences of HYPOthyroidism

Answer 11

gain in BW
integument changes (hyperkeratosis, hyperpigmentation, myxedema)
hypercholesterolemia
reproductive changes (libido loss, low sperm count)

Question 12

Name the causes of thyroid hyperfunction

Answer 12

disorders of growth, most commonly functional tumours

Question 13

Name the common thyroid tumours

Answer 13

adenocarcinomas in dogs (locally invasive and aggressive, resulting in destruction of remaining normal tissue)
thyroid adenomas in horses (can be very large, also can be very small. typically non-functional)
C-cell neoplasms in ruminants

Question 14

Systemic consequences of hyperthyroidism

Answer 14

thyrotoxic cardiomyopathy, hypertension, weight loss with increase appetite, vomiting, “thyroid slip” on physical exam