PBL 5: Slowed - Down Teacher Flashcards
What is the role of thyroid hormones?
Essentially increase metabolic rate:
- work on nuclear receptors
- modulate metabolic efficiency, energy expenditure and calorigenesis
- mitochondriogenesis as increase ATP demand
- increased uncoupling = non shivering thermogenesis
What is the effect of thyroid hormones on the heart?
- increased contractility and electrical activity as T3 binds to myocytes
- atrial fibrillation
What is the effect of thyroid hormones on glucose metabolism?
Insulin agonist and antagonists in different organs
Agonist: peripheral tissues such as muscle upregulates GLUT4 to increase glucose uptake
Antagonist: intestine absorption and hepatic gluconeogenesis/glycogenolysis
What is the effect of thyroid hormones on fats?
Deposits fat in adipose tissue and increases LPL to reduce lipid levels
How is thyroid hormone regulated?
TRH stimulates the release of TSH which stimulates the release of T4 which gets converted into T3
There is negative feedback so that the release of TSH is inhibited by high levels of T3 and T4 and the release of TRH is inhibited by high levels of T4.
Somatostatin and stress also inhibit TRH release
Somatostatin and dopamine can also inhibit TSH release
High iodine inhibits T4 release
What is the half life of thyroid hormone?
7-10 days
What are the main features of hypothyroidism?
low energy expenditure, weight gain, normocytic anaemia, cold intolerance
What are the 2 types of hypothyroidism?
PRIMARY: permanent loss/destruction of the thyroid
SECONDARY: insufficient pituitary stimulation of TSH
What are the features of primary hypothyroidism?
High TSH as low T3 and T4 so low inhibition
Hashimoto’s
Low glucose metabolism
Mental slowing
What is the mechanism of goitre?
Hashiomoto’s (primary hypothyroidism)
- immunocyte infiltration replacing parenchyma = thyroid enlargement = gland fibrosis and thyroid depletion
Why do you get goitre?
Iodine deficiency - hashimoto’s
What are the features of secondary hypothyroidism?
Pituitary adenoma
Low gluconeogenesis
Dyslipidaemia as low LPL
What are the features of hyperthyroidism?
Heat intolerance Weight loss (increase in LPL) Hyperglycaemic (increase in gluconeogenesis = insulin resistant) Bone resorption Tachycardia Hypermetabolism
What are the features of Grave’s?
Hyperthyroidism Thyroid gland enlarged = goitre antibodies (thyroid stimulating immunoglobulin) acts on TSH receptor mimicking T4 activity Exophthalmos Pretibial myxoedema
How do you treat hypothyroidism?
Levothyroxine
