Thyroid Gland

Where is the thyroid gland located?

Anterior to the thyroid cartilage of the larynx

How are the two lobes of the thyroid gland connected?

By narrow isthmus

What does the thyroid gland do?

Stores and secretes thyroid hormones thyroxine (T4) and triiodothyronine (T3)

What does throxine contain?

4 iodide ions

What does triiodothyronine contain?

3 iodide ions

What do thyroid hormones do?

Increase sodium potassium ATPase production which is necessary for maintaining membrane potentials

What does the thryoid gland and surrounding strutures look like?

What are the effects of thyroid hormones?

• Increase oxygen and energy consumption

• Increase heart rate

• Increase sensitivity to sympathetic stimulation

• Stimulates red blood cell formation

• Affects activity of other endocrine tissues

• Increases bone turnover

What are thyroid follicles?

Hollow spheres lined by cuboidal epithelium, surrounded by capillaries

What do thryoid follicles contain?

Colloid which is a protein rich fluid

What do follicle cells synthesise?

Tyrosine rich thyroglobulin

What is iodine incorporated with to form thyroxine (T4) and triiodothyronine (T3)?

Iodine is incorporated into tyrosine residues of thyroglobulin to form thyroxine (T4) and triiodothyronine (T3). More T4 is produced but T3 tends to be more biologically active

Where is iodine found?

Naturally in the sea and in seafoods

What can an iodine deficiency cause?

Derbyshire Neck (furthest point from the sea in the UK), also called Goitre, is a swelling of the thyroid gland and is now known to be caused by lack of iodine. It is almost unknown today because iodine is added to drinking water (and salt)

What do C cells do?

• Produce calcitonin

• Important in calcium homeostasis

• Reduces serum calcium

• Deposition in bone

• Increased excretion by kidney

What is the role of calcitonin in regulation of calcium ion concentrations?

What is the role of PTH in regulation of calcium ion concentrations?

What are the parathyroid glands?

Small glands (1.6g) on the posterior of the thyroid

What do parathyroid (chief) cells produce?

Parathyroid hormone (PTH)

When is PTH released?

To increase serum calcium when levels decline

What does the parathyroid gland look like in relation to the thyroid gland?