thyroid Flashcards
Thyroid hormones are derived from ?
tyrosine
what does the thyroid gland produce
thyroid hormones & calcitonin
follicle cells produce ?
T3 + T4
C-cells produce?
calcitonin
what are the effects of thyroid hormone on the Cardiovascular system
↑ CO (↑HR, bp, contractility)
↑ O2 and E consumption
↑ erythropoiesis → ↑ O2 delivery
what is the main cause of primary hypothyroidism
Lymphocytic thyroiditis
inflammation and damage to thyroid gland –> can’t produce normal amounts of thyroid hormone
↑ circulating anti-thyroglobulin antibodies
what is another cause of primary hypothyroidism but very uncommon
Congenital hypothyroidism (usually terriers)
Autosomal recessive mutations in the thyroid peroxidase gene
what are the causes of Secondary Hypothyroidism
- Lots of other diseases / nutritional status
- Drug-induced!
what drugs have the potential to cause Secondary Hypothyroidism
- Trimethoprim / sulfonamides
- Glucocorticoids
- Phenobarbital
LEVOTHYROXINE is ?
T4
why is levothyroxine (T4) largely confined to vasculature
b/c it mostly binds to plasma proteins
what is the main risk w/ giving levothyroxine (T4)
causing Iatrogenic hyperthyroidism/thyrotoxicosis (gave too much drug)
levothyroxine is contraindicated in patients w/ what illnesses & why
- Thyrotoxicosis - producing too much thyroid hormone to begin with
- Acute myocardial infarction - T4 has cardiovascular effects (increase CO, increases O2 and E demand)
- Untreated adrenal insufficiency
what is the most common endocrine disorder of cats
hyperthyroidism
what is the cause of hyperthyroidism in cats
adenomatous hyperplasia of the thyroid;
Benign tumor in the thyroid gland that causes uncontrolled production of thyroid hormones
what other disease does hyperthyroidism often mask and how
Chronic Kidney Disease
b/c hyperthyroidism increases CO which increases perfusion of kidneys & GFR
↑ GFR can mask low GFR of CKD
treatment with METHIMAZOLE can often unmask what other illness
CKD
what drug forms antinuclear antibodies that in can lead to MS like syndrome
methimazole
why is iodine 131 an irreverisble treatment
Radioactive iodine concentrates in thyroid colloid
- causes death of follicle cells (but not C-cells)
how does propranolol work to treat hyperthyroidism
it promotes the inactivation of T4 by blocking type I+II monodeiodinases (which convert inactive thyroxine T4 into active triiodothyronine T3)
how can hyperthyroidism / thyrotoxicosis
cause tachycardia +/- arrhythmia
↑ sensitivity to sympathetic stim
↑ CO (↑HR, bp, contractility)
how can hyperthyroidism / thyroidotoxicosis result in blindness
Hypertension → retinal damage, blindness
