The Thyroid Gland & Thyrotoxicosis Flashcards
1
Q
What is the function of the thyroid gland?
A
Produces hormones that regulate metabolic rate:
- triiodothyronine (T3) - active hormone, increases basal metabolic rate
- thyroxine (T4) - relatively inactive, decreases levels of T3
2
Q
How is thyroid hormone release regulated?
A
Negative feedback loop:
- hypothalamus senses low levels of T3/T4 > releases thyrotropin releasing hormone (TRH)
- TRH acts on anterior pituitary gland > releases thyroid stimulating hormone (TSH)
- TSH stimulates release of thyroid T3 and T4 from thyroid
- high levels of thyroid hormones prevent further release of TRH and TSH
3
Q
What are hypo- and hyper-thyroidism and thyrotoxicosis?
A
- Hypothyroidism = underactive thyroid gland
- Hyperthyroidism = overactive thyroid gland
- Thyrotoxicosis = clinical symptoms caused by high levels of thyroid hormones in the bloodstream
4
Q
What are the main symptoms of hyperthyroidism?
A
- intolerance to heat & sweating (vasodilation)
- weight loss despite increased appetite
- increased bowel movements
- irregular menstrual cycle
- rapid and irregular heartbeat (palpitations)
- tiredness & irritability
- tremor
- retraction of the eyelids - ‘staring’ appearance (proptosis)
- may have goitre
5
Q
Why are some hyperthyroidism symptoms mediated by the autonomic NS?
A
Thyroid hormones upregulate the number of adrenoreceptors in the body.
6
Q
Which treatments are used short-term for thyrotoxicosis?
A
- Non-selective beta-adrenoreceptor antagonists (e.g. Propanolol).
- Iodide (acute treatment): blocks release of stored thyroid hormone and decreases conversion of T4 to T3.
- Thiomides (acute and long-term treatment): inhibit thyroid hormone synthesis and iodination of of thyroid hormones.
Treatment usually required for 18 months.
7
Q
Which treatments are used long-term for thyrotoxicosis?
A
- Continuing medication (thiomides)
- Radioiodine treatment
- Surgery (thyroidectomy and long-term thyroxine replacement)
