Thyroid physiology and anatomy 1 (read)

Question 1

What is the innervation of the thyroid gland ?

Answer 1

• Parasympathetic from vagus nerve
• Sympathetic from superior middle and inferior ganglia of sympathetic trunk

Question 2

Describe the blood supply of the thyroid gland

Answer 2

Superior and inferior thryoid arteries +/- thyroida ima

Question 3

Describe the venous drainage of the thyroid gland

Answer 3

3 pairs of veins - superior/middle thyroid vein ==> internal jugular

inferior thyroid vein ==> brachiocephalic vein

Question 4

What is the thyroid gland supported by ?

Answer 4

Ligaments and strap muscles

Question 5

What is the main ligament which supports the thyroid gland ?

Answer 5

The posterior suspensory ligament (berry ligament)

Question 6

What is there a risk of injuring during surgery on the thyroid ?

Answer 6

• Injury to the vasculature
• Injury to the recurrent laryngeal nerve

Question 7

What are the 3 primary features of thyroid glands under the microscope ?

Answer 7

1. Follicles
2. Follicular cells
3. Parafollicular cells

Question 8

What are follicles in the thyroid ?

Answer 8

Small spherical groupings of cells that consist of a rim of follicular cells which surround the colloid

Question 9

What are parafollicular cells ?

Answer 9

Scattered amoung follicular cells and the spaces between follicles

Question 10

What is the colloid ?

Answer 10

Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

Question 11

What do follicles play a key role in ?

Answer 11

Thyroid function

Question 12

What is the function of follicular cells ?

Answer 12

1. When stimulated by TSH
2. Secrete thyroid hormones T3 and T4

Question 13

What is the function of parafollicular cells ?

Answer 13

Secrete calcitonin

Question 14

What is the overall idea of synthesis and secretion in the thyroid gland ?

Answer 14

Iodine (the fuel) comes in and then T3/T4 (products) come out

Question 15

Describe the stages of synthesis of T3 & T4

Answer 15

1. Iodine taken up by follicular cells
2. Iodine attaches to tyrosine residues on thyroglobulin to form MIT and DIT
3. MIT = monoiodotyrosine unit, DIT - Diiodotyrosine unit
4. Coupling of MIT and DIT = T3 (triiodotyrosine unit)
5. Coupling of 2 DIT’s = T4 (thyroxine)
6. T3 and T4 are then stored in colloid till required

Question 16

What is the major biologically acitve thyroid hormone ?

Answer 16

T3 - it is roughly 4 times more potnet but 90% of thyroid hormones secreted is T4

Question 17

Where is T4 converted to T3 ?

Answer 17

Converted in the liver and kidney

Question 18

What is the function of Deiodinase enzymes ?

Answer 18

To either activate or deactivate thyroid hormones

There is 3 types:

• D1
• D2
• D3

Question 19

Which Deiodinase enzyme converts T4 into T3 ?

Answer 19

D2 in the tissues