Thyroid Gland

Question 1

The anatomy of the thyroid gland

Answer 1

In the neck above the clavicle
The left and right lobe joined by isthmus
Composed of follicular cells

Question 2

Function of thyroid gland

Answer 2

Increase heat production, oxygen consumption, metabolism of proteins, fats, and carbohydrates
Promotes normal growth
Required for normal CNS function

Question 3

Thyroid hormones

Answer 3

T4 = biologically active hormone – can be converted to T3
T3 = metabolically more active than T4
They contain iodine which is essential for their function and synthesis
Not very water soluble
Transported in circulation bound to proteins

Question 4

The regulation of the thyroid gland

Answer 4

Negative feedback control of T4 and T3
Free and not total, T4/T3 determine feedback
TSH and TRH involved in feedback

Question 5

The synthesis of the thyroid hormone (order)

Answer 5

Iodide oxidised to iodine in thyroid, follicular cells
Iodination of tyrosine on colloid thyroglobulin forms monolodotyrosine (MIT) and dilodotyrosine(DIT)
Coupling forms, T4 (DIT+DIT)and T3 (DIT+MIT)
Thyroid hormone, stored attached to colloid, thyroid globin
Thyroglobin taken up by follicular cells by pinocytosis
Lysosomes fuse with this droplets and proteases digest thyroglobulin to release thyroid hormone
the released thyroid, hormones transported in blood bound to thyroxine binding globulin

Question 6

Hypothyroidism

Answer 6

Weight gain, cold, intolerance, bradycardia, constipation
Management = replacement therapy with T4

Question 7

Hyperthyroidism

Answer 7

Weight loss, heat, intolerance, sweating, diarrhoea
Management = antithyroid drugs, thyroidectomy