Thyroid hormones

Question 1

Thyroid hormones

Answer 1

T3, T4 and calcitonin

Question 2

Synthesis of thyroid hormones

Answer 2

Tyrosine (attached as part of thyroglobulin in cells) is iodinated by thyroid peroxidase to form mono-iodotyrosine (MIT) and di-iodotyrosine (DIT). DIT + MIT = T3, DIT X 2 = T4.
Lysosomes split T3/4 off from thyroglobulin

Question 3

Actions of thyroid hormones

Answer 3

T3/4 is stored in the thyroid colloid attached to thyroglobulin
About six weeks store is present.
Released by the aftion of TSH on thyroid cells much of T4 is converted to T3 by liver and kidneys as T3 is more active form.
T3 is a major factor in controlling basal metabolic rate in tne body. It jncreases cells responsiveness to Adr and NA, therefore increased HR and FOC, permissive effecf on GH action.

Question 4

Hyperthyroidism (Graves’ disease)

Answer 4

Nervousness 
High temp
Increased appetite
Protruding eyes
Weight loss
Tachycardia
Treatment via surgery or gibing radio-iodine leading to hypothyroidism which is then treated with thyroxine.
Alternative treatment - using thioureas to block thyroxine synthesis (as it inhibits thyroid peroxidase)

Question 5

Hypothyroidism (myxoedema)

Answer 5

Sleepiness
Mental slowness
Cold
Puffiness
Thin hair
Weight gain
Constipation
Treat with HRT, thyroxine via mouth/nasal spray

Question 6

Goitre

Answer 6

Enlarged thyroid, can be fojnd jn nith hypothyroidism and hyperthyroidism, caused by excess TSH