Week 10 - Thyroid Gland, Disturbances to Thyroid Function Flashcards
What is the mechanism of action of carbimazole?
Inhibits the iodination of thyroglobulin by the enzyme thyroperoxidase
This prevents the formation of T3 and T4
Radioiodine is used to cause thyroid apoptosis in resistant cases of hyperthyroidism
What is the underlying pathology in Grave’s disease?
- Stimulating antibodies against TSH receptors on follicle cells- autoimmune condition
- Hyperthyroidism
- When these antibodies bind, they activate the receptor and this stimulates thyroid hyperplasia with increased T3/4 production
Why does T4 have a longer half life than T3?
Greater affinity for binding proteins
Which hormone is used to treat hypothyroidism? Why?
T4 (Thyroxine)
Easier to maintain constant blood concentration due to elevated half life
Outline the general effects of thyroid hormone on the body.
- Increases basal metabolic rate: Increases number and size of mitochondria, increases oxygen consumption, increases nutrient utilisation
- Stimulates metabolic pathways: Mainly catabolic - Glycogenolysis, glycolysis, lipolysis, proteolysis
- Promote normal growth and development of tissues: increases synthesis of specific proteins
- Increases responsiveness of tissue to the sympathetic nervous system (noradrenaline) and various hormones (metabolic and reproductive)
Outline the effects of thyroid hormone on the nervous system.
- Increases myelination of nerve fibres and development of neurons
- Increases speed of reflexes
- Increases mental activity (alertness, emotional tone, memory)
Outline the effects of thyroid hormone on the cardiovascular system.
- Increases cardiac output
- Direct effects on heart muscle
- Potentiates effects of noradrenaline
Outline the effects of thyroid hormone on skin and subcutaneous tissue.
- Increases turnover of proteins and glycoproteins (mucopolysaccharides)
What condition does hypothyroidism cause in the newborn? State some common signs and symptoms of this condition.
Cretinism
Symptoms:
- Severe mental retardation due to failure in CNS development
- Diminished linear growth
- Delayed sexual development
Signs:
1. Coarse features, protruding tongue
Outline some signs and symptoms of hyperthyroidism.
- Heat intolerance, increased perspiration, warm, moist hands
- Weight loss (lipid and protein)
- Tachycardia (noticeable heart beat) - often irregular: increased cardiac output
- Increased bowel movements: increased appetite
- Nervousness, irritability, emotional lability
- Hyper-reflexive: possible tremor of outstretched hands
- Eye signs: Exophthalmos
Name some possible treatments for hyperthyroidism.
- Carbimazole: inhibits incorporation of iodine into thyroglobulin
- Radioactive iodine: kill thyroid gland with irradiation
- Surgery: surgical removal of the thyroid gland - individuals can live on synthetic thyroid hormone alone
Name some signs and symptoms of hypothyroidism.
- Cold intolerance, decreased perspiration, cold, dry hands
- Mild weight gain
- Bradycardia: decreased cardiac output
- Constipation
- Mood swings: feeling anxious and depressed
- Poor concentration, poor memory, lack of initiative
- Oedema (Myxoedema: Dry, firm waxy swelling of skin and subcutaneous tissue)
- Dry skin, brittle nails, some hair loss
Describe the underlying pathology of Hashimoto’s disease. How is this condition generally treated?
Autoimmune disease:
- Destruction of thyroid follicles
- Production of antibody that blocks the TSH receptor on follicle cells
- Oral T4: 100-200 micrograms/day
Name some causes of hypothyroidism.
- Autoimmune disease
- Post-surgery
- Radioactive iodine
- Anti-thyroid drugs (e.g. carbimazole, PTU: propylthiouracil)
- Secondary: lack of TSH
- Congenital (1 in 4000)
- Iodine deficiency
- Rare inborn errors
Name some causes of hyperthyroidism.
- Autoimmune: Toxic multinodular goitre
- Autoimmune: Grave’s disease
- Solitary toxic adenoma
- Excessive T4 or T3 therapy
- Excess iodine: Amiodarone
- Ectopic thyroid tissue
