Endocrine system III

Question 1

Anatomy of thyroid

Answer 1

• ventral surface of the thyroid
• comprised of 2 lateral lobes; pyramidial lobe and isthmus
• isthmus connects two lateral lobes

Question 2

Thyroid blood supply

Answer 2

• via the superior and inferior thyroid arteries

Question 3

Thyroid gland histology

Answer 3

-Structural units: follicle = acinus
Colloid and principal epithelial cells
-Principal cells = follicular cells
Formation of colloid = contains the prohormone thyroglobulin
Produce thyroid hormones (reabsorption thyroglobulin from colloid and split into)
Triiodothyronine (T3)
Thyroxine (T4)
-Parafollicular cells = C cells
Lie adjacent to follicles in basal lamina
Produce calcitonin

Question 4

Major thyroid hormone actions

BMR

Answer 4

• increased masal metabolic rate:
  Increased use of oxygen by cells to make more atp for energy
  increased ATP production increased use (carbohyfrates and lipids)
  protein synthesis increased

Question 5

Major thyroid hormone actions

increase heat production

Answer 5

• due to increased production of Na+/K+ ATP ase

- when active = enzyme releases heat due to ATP breakdown

Question 6

Major thryroid hormone actions

TH

Answer 6

critical for normal development of musculoskeletal system

Normal brain development

Question 7

Thyroid hormones

Answer 7

• lipophilic
• bind to the thyroid hormone receptor
  Thyroxine (T4): main with 4 iodine atoms
  Triiodothyronine: 3 iodine atoms

Question 8

Major sources of iodine

Answer 8

Iodine salt
Dairy products
Shellfish

Question 9

Production of thyroglobulin

Answer 9

Thyroglobulin: iodine + tyrosine
Dietary iodine is absorbed in the GI tract, then takem up to the thyroid gland
- the transport of iodide into follicular cells is dependent upon a Na+/I- cotransport system
- iodide taken up by thyroid gland oxidised by peroxide in the lumen of the follicle, can then be used in production of thyroid hormones

Question 10

Regulation of thyroid hormones

Answer 10

• vessels anterior pituitary
• TSH is released in response to disturbed homeostasis
• TSH binds to specific cell surface receptors in thyroid stimulates adenylate cyclase to produce cAMP
• TSH increases metabolic activity that is required to synthesis Thyroglobulin and generate peroxide
• TSH stimulates both iodine uptake and iodination of tyrosine residues on thyroglobulin