Lecture 5 - Thyroid

Question 1

What do we see in thyroid cancer?

Answer 1

Parafollicular cells secrete calcitonin, large amounts of this secreted with cancer - Medullary cancer (tumour marker)

Differentiated thyroid cancer cells - produce thyroglobulin - this is a tumour marker in blood (also thyroiditis, goiter)

Question 2

How does iodine get to become thyroid hormones?

Answer 2

• Iodine transported into cell (iodine sodium transporter) from blood stream
• Iodine is attached to thyroglobulin with thyroid peroxidase enzyme at lumen interface (inhibited by carbimazole) to form MIT and DIT
• MIT and DIT will join and can form T3 and T4 (in the colloid)
• get endocytosis of colloid to bring T3 and T4 into the cells - fuse with lysosome

-Then T3 and T4 will separate from thyroglobulin in the follicular cells, and be released back into the bloodstream (under TSH regulation)

T3 - active form
T4 - mainly stored in thyroid as this
-Most bound to thyroid binding globulin and albumin in blood

Question 3

What does carbimazole do?

Answer 3

Can block dietary iodine getting into the cell

Used to treat an overactive thyroid gland

• Tyrosine residues will become iodinated to become thyroglobulin by thyroid peroxidase enzyme
• carbimazole can inhibit this

Question 4

Storage and release of thyroid hormone

Answer 4

• Thyroid hormone release involved endocytosis of Tg from follicular space
• degrade Thyroglobulin then form T4 and T3

Question 5

Regulation of thyroid hormone?

Answer 5

Hypothalamus - TRH
Pituitary - TSH
Thyroid - will bind to receptors and cause production of TG, iodine trapping and T4 and T3 synthesis
-also increases endocytosis of colloid, proteolysis of TG and therefor an increase in T4 and T3 secretion
-T4 and T3 will have negative feedback to the pituitary and hypothalamus

Question 6

hypothyroidism

Answer 6

Weight gain, cold, hair loss nad dry skin, consitpation, tired, odemea
-Low T4, T3 - high TSH

Question 7

Thyrotoxicosis
-symptoms
signs
causes

Answer 7

Low TSH, high T4, T3.
-symptoms - nervous, increased sweating, weight loss, heat sensitivitiy, tachycardia, weakness

Signs - goitre, skin changes, tremor, eye signs

Causes - graves disease - autoimmune production of an antibody that stimulates TSH receptor

• Multi nodular goitre - hyper functioning regions of the thyroid gland, not suppressed by circulating thyroid hormone
• thyroiditis

Question 8

Thyrotoxicosis

Answer 8

• too much Thyroid hormone in body - treatment can be radioactive iodine (causes dry eyes and mouth), also can treat with TPO enzyme
• low TSH and high T4, T3
• symptoms nervous, increased sweating, heat sensitivity, tachycardia, weakness
• signs goiter, skin changes, tremour, tachycardia
• Causes - graves disease - autoimmune production of antibody that stimulates TSH receptor
• Cause - mulitnodular goitre, hyper functioning regions of thyroid gland, not suppressed by circulating hormone
• also can be casued by throiditis

Question 9

thyroid hormone resistance syndrome

Answer 9

receptor mutations lead to pituitary insensitivity to T3, so tsh rises and causes rise in t4 and t3. -patient can presnet with hypo or hyperhtyroid features in different tissus and may have goiter

Question 10

Thyroditiis

Answer 10

• inflammation of thryoid gland (pre formed thyroid homrone is dumped from lumen with thryoglobulin)
• patient presents as thyrotoxic, then has a hypothyoid phase and usually recovers
• ciruclating thyroglobulin is increased and serves as a tumour maker

Question 11

Primary hypothyrodisim

Answer 11

high TSH, low T4, postive TPO antiboides

• Hashimotos disease
• audlt onset
• decrease in energy metbaolism, low basal metabolic rate, slightly low body temp
• decreased protein synthesis
• weight gain, cold, hair loss, dry skin