Internal medicine (endocrine) Flashcards
what are the thyroid gland?
two distinct nodes either side of trachea
what are the two types of endocrine cells in the thyroid gland?
follicular
parafolliculuar (medullary)
what do follicular cells of the thyroid gland produce?
thyroid hormones
what do the parafollicular cells of the thyroid gland produce?
calcitonin
what regulates the thyroid hormone production?
hypothalamic pituitary thyroid axis
what produces the stimulation for the thyroid to produce hormones?
pituitary gland (TSH)
what does the thyroid gland produce when stimulated by TSH?
lots of T4 and small amounts of T3
what is T4?
thyroxine
what happens to T4 in peripheral tissue?
converted to T3
what effect does T3 have on the pituitary gland?
negative feedback causing less production of TSH
what structures does T3 have a negative feedback effect on?
hypothalamus and pituitary gland
what substance does thyroid hormone synthesis require?
iodine
which thyroid hormone is biologically active?
T3
what is the function of thyroid hormones?
increases metabolic rate and oxygen consumption of tissues
positive inotropc/chronotropic effects on heart
stimulate erythropoiesis
regulate cholesterol synthesis/degredation
what is the function of thyroid hormones?
increases metabolic rate and oxygen consumption of tissues
positive inotropc/chronotropic effects on heart
stimulate erythropoiesis
regulate cholesterol synthesis/degradation
catabolic effect on muscles/adipose tissue
is hypothyroidism more common in dogs or cats?
dogs
what are some possible causes of congenital hypothyroidism?
thyroid hypoplasia, aplasia, dyshormonogenesis
disproportionate dwarfism
what are the primary causes of acquired hypothyrodisim?
lymphocytic thyroiditis
idiopathic atrophy
aggressive thyroid neoplasia
what causes secondary/tertiary acquired hypothyroidism?
defects in the pituitary or hypothalamus
what are the clinical signs of hypothyroidism?
metabolic - lethargy, obesity, exercise intolerance
dermatology - hair thinning, alopecia, poor quality coat, skin hyperpigmentation, pyoderma
what are some changes in haematology that indicate hypothyroidism?
mild normocytic normochromic non-regenerative anaemia
hypercholesterolaemia
hypertriglyceridaemia
what is done to diagnose hypothyroidism?
thyroid hormone testing - increased TSH and decreased total/free T4
what measurements can be done for thyroid hormones?
total T4
free T4
total T3
TSH
what breeds is T3 a better test for thyroid function?
sighthounds and sled dogs
what can cause an artifactual increase of free T4?
storing at room temperature for prolonged period
