Thyroid Disease Flashcards
What are the functions of thyroid hormones ?
- increase heat production
- increase oxygen consumption
- increase metabolism of proteins, fats & carbs
- promotes normal growth
What are the thyroid hormones?
- thyroxine = T4
- Tri-iodothyronine = T3
Describe the conversion of T4 into T3
- occurs in most tissues - particularly the liver
- conversion of T4 to T3 is reduced in systemic illness & drugs
What are the reference ranges for Total & Free T4 ?
Total = 60-150 nmol/L
Free = 9-26 pmol/L
What are the references ranges for total & free T3 ?
Total = 1.2-2.9 nmol/L
Free = 3.0-8.8 pmol/L
Describe the regulation of thyroid hormones
- negative feedback control of T4 & T3
- free T3 & T4 determines feedback
- thyroid stimulating hormone & thyroid releasing hormone also involved
What 2 hormones are involved in regulation ?
- Thyroid stimulating hormone
- Thyroid releasing hormone
Describe the beginning of thyroid hormone synthesis
- dietary iodide absorbed by small intestine
- 1/3 of this iodide is concentrated in thyroid glad & rest is excreted
What is the main binding protein for T3 & T4 ?
- thyroxine binding globulin
(albumin secondly)
What happens to the iodide in the thyroid gland?
- iodide is oxidised to iodine in thyroid follicular cells
- iodination of tyrosines on colloid thyroglobulin forms monoiodotyrosine(MIT) & diiodotyrosine (DIT)
- coupling forms t4 (DIT+DIT) & T3 (DIT+MIT)
How are thyroid hormones stored?
- attached to colloid thryoglobulin
- thyroglobulin is taken up by follicular cells via pinocytosis
How are stored thyroid hormones released ?
- lysosomes fuse with stored droplet & proteases digest thyroglobulin to release the thyroid hormones
What is the incidence of hypothyroidism in the UK?
- Men = 0.2%
- Women =2.0%
What age group is most affected by hypothyroidism ?
- 50/60 year olds
What are some of the primary causes of hypothyroidism ?
- Hashimoto’s thyroiditis
- post- thyroidectomy
- anti-thyroid drugs
- iodine deficiency
- congenital hypothyroidism
What is a secondary cause of hypothyroidism ?
- pituitary/hypothalamic effect
What are some of the clinical features of Hypothyroidism ?
- weight gain
- puffy face, hands & feet
- reduced appetite
- bradycardia
- cold intolerance
- menstrual abnormality
- deep hoarse voice
What are some ways to manage hypothyroidism ?
- Replacement therapy with T4
- monitoring of therapy with TSH
What are some pros to T4 replacement therapy ?
- readily available
- safe
- inexpensive
Define hypothyroidism
Under active thyroid gland
Define hyperthyroidism
overactive thyroid gland
What’s the incidence of hyperthyroidism ?
1% female
0.1% male
What are some common causes of hyperthyroidism ?
- graves disease
- toxic nodules
- thyroid hormone intake
What are some rare causes of hyperthyroidism ?
- ectopic thyroid tissue
- ash secreting tumours
What are the clinical features of hyperthyroidism ?
- weight loss
- increased sweating
- tachycardia
- heat intolerance
- menstrual abnormalities
How can hyperthyroidism be managed ?
- anti thyroid drugs = carbimazole
- radioiodine therapy - 131 I therapy
- thyroidectomy
Describe T3 & T4 in hypothyroidism
- Free T4 is low
- Free T3 can be normal
Describe T3 & T4 in hyperthyroidism
- Free T4 is high
- Free T3 is highly raised
Describe Thyroid Stimulation hormone in hypo/hyper-thyroidism
- high in hypothyroidism
- low in hyperthyroidism
Describe Non-thyroidal Illness
(Sick euthyroid syndrome)
- thyroid regulation& metabolism disturbed in systemic illness
- increased conversion of T4 to reverse T3
- TSH may be normal or low
- wait till patient recovers from illness before testing thyroid function
Describe T3 Toxicosis
- patients have very high T3 but T4 is within ref range
- TSH often very low or undetectable
- often presents with clinical hyperthyroidism
