Thyroid gland and hormone

Question 1

cells of thyroid gland

Answer 1

1. Follicular cells -
   • Thyroxine - T4
   • Triiodothyronin - T3
2. Parafollicular cells -
   • Calcitonin - regulate calcium homeostasis

Question 2

Action of thyroid hormone

Answer 2

1. Increase Basal metabolic rate - increase rate of oxygen consumption, ATP production etc
2. Synthesis of additional sodium potassium pump -
   uses large amounts of ATP, heat is given off and body temp rises
   • important role in maintaining body temp
3. Stimulate protein synthesis, increase use of glucose and fatty acids for atp production
4. Enhance actions of catecholamines and upregulate B receptors
5. Accelerate body growth

Question 3

Mech of T3 and T4 upto entry into follicle

Answer 3

1. Follicular cells trap iodide I- from blood
2. Follicular cells synthesise thyroglobulin (TGB) and release it into lumen of follicle
3. Iodide ions are oxidised to form iodine and enter the lumen too
4. Iodine react with tyrosine amino acid of TGB
   • 1 iodine atom binding
   -> monoiodotyrosine (t1)
   • 2 iodine atoms binding
   -> diiodotyrosine (t2)
   TBG w iodine atoms becomes sticky material and stored in lumen as ‘colloid’.
5. Coupling
   • t2 + t2 = t4
   • t1 + t2 = t3

Question 4

Mech of t3 and t4 pt 2

Answer 4

6. Drops of colloid reenter follicular cells from lumen
7. Colloid merge which lysosome to cleave off t4 and t3 from TBG
8. t4 and t3 enter blood but lipid soluble so bind to THYROXINE BINDING GLOBULIN
   t4 - secreted in greater quantities
   -converted to t3 in body cells
   t3 - more potent

Question 5

Control of thyroid hormone secretion

Answer 5

1. Low levels of t3 AND t4 stimulate hypothalamus to secrete TRH
2. TRH stimulates thyrotrophs to secrete TSH
3. TSH stimulates follicular cell activity

Question 6

Calcitonin

Answer 6

1. Produced by parafollicular cells
2. Inhibits action of osteoclasts which break down bone matrix
3. Accelerates uptake of calcium and phosphate
4. Decreases calcium and phosphate level in the body