The Thyroid and Parathyroids

Question 1

what week of development does the thyroid descend?

Answer 1

4th week

Question 2

where does the thyroid descend from and to?

Answer 2

descends from the foramen caecum in the middle of the tongue in front of the larynx to the thyroglossal duct

Question 3

abnormalities of descent of the thyroid

Answer 3

lingual thyroid
retrosternal thyroid
thyroglossal duct cysts
pyramidal lobe

Question 4

what is the thyroid composed of?

Answer 4

follicles made of a central colloid surrounded by cuboidal epithelium cells

Question 5

what protein is found in the colloid?

Answer 5

thyroglobulin

Question 6

what are around the follicles?

Answer 6

C cells (parafollicular cells)

Question 7

what do parafollicular cells do?

Answer 7

secrete calcitonin

Question 8

what does the thyroid gland secrete?

Answer 8

T3/4

Question 9

what causes the thyroid to release T3/4

Answer 9

TSH binding

Question 10

what does the HPT axis involve?

Answer 10

hypothalamus > TRH
anterior pituitary >TSH
thyroid > T3/4

Question 11

role of T3/4

Answer 11

bind to target cells and this complex activates transcription

Question 12

T3/4 synthesis

Answer 12

• iodide ions (2I-) move into follicular cells and is oxidised allowing it to pass to the colloid
• iodine (I2) is linked to tyrosine from thyroglobulin to produce MIT (I-) or DIT (2I-)
• MIT + DIT forms T3
• DIT + DIT forms T4

Question 13

what is T3 called?

Answer 13

triiodothyronine

Question 14

what is T4 called?

Answer 14

thyroxine

Question 15

what do T3/4 bind to in the bloodstream?

Answer 15

TBG
TBPA
albumin

Question 16

thyroid hormone effects

Answer 16

increased BMR
thermogenesis
glycogenolysis
gluconeogenesis
lipolysis
proteolysis
GH
increased sympathetics (HR, BR, etc.)

Question 17

what are the parathyroids composed of?

Answer 17

chief cells supported by oxyphil cells

Question 18

what do chief cells secrete?

Answer 18

PTH