Thyroid follicular cells secretes
T4 inactive form, used as storage
stored as thyroglobulin
T3 is the active form
Parafollicular cells produce calcitonin
Thyroid glands is regulated by feedback loops
Only endocrine functions and highly vascularized
Produces T3 and T4 and Calcitonin via C cells
Positive feedback loop
Low t4 and t3 leads to the hypothalamus secreting TRH and stimulates the release of TSH from the anterior pituitary gland and leads to more Thyroid hormones released.
Negative feedback loop
High T3 and T4 leads to the inhibition of TSH and TRH through end product inhibition
Effects of T3 and T4 released
Increased metabolic rate of body cells
Rise in body temperature
T3 and T4 made by iodination of tyrosine residues on thyroglobulin
T4 stored form is converted to T3 by deiodination of T4
Liothyronine is the synthetic form of T3 used in urgent need of thyroid hormones
Graves disease
TSI thyroid stimulating immunoglobulins stimulates thyroid gland to keep overproducing T3 and T4 by mimicking TSH. Auto immune disorder
Faster metabolism and various symptoms
Nervousness, weight loss, broken hair, enlarged thyroid gland, arrhythmia
Hypothyroidism due to low iodine
No iodine due to diet deficiency and T3 and T4 remain low and no negative feedback
Thyroid storm
Sever hyperthyroidism
Increased heart rate, tremors, palpitations, and weight loss. Hyperthermia due to fever, hypotension and tachycardia. Dyspnea on exertion.
Myxedema coma
Long-standing hypothyroidism when left untreated
Confusing which can lead to coma
Hypothermia, Bradycardia, hypotension and low respiratory rate and potential respiratory failure
Facial edema
Diagnosis based on clinical presentation. history of hypothyroidism and low thyroid hormone levels.
Treatment: Immediate intravenous administration of thyroid hormones
