Endocrinology Test 2

Question 1

Thyroid gland

Answer 1

• Largest pure endocrine gland
• Butterfly-shaped
• On trachea just inferior to cricoid of larynx
• Internally composed of follicles
• Follicle cells produce thyroglobulin, a glycoprotein precursor to Thyroid Hormone (TH)
• Parafollicular cells produce Calcitonin

Question 2

Thyroid Gland blood supply

Answer 2

Superior and inferior thyroid arteries

Question 3

Thyroid venous drainage

Answer 3

superior, middle, and inferior thyroid veins

Question 4

Thyroid hormone components

Answer 4

• 2 Iodine containing amine hormones
• T3 & T4
• T3 is 10X more active than T4
• Activates glucose oxidation enzymes
• Increases basal metabolic rate & heat

Question 5

Synthesis of thyroid hormone steps: 12

Answer 5

¥ TRH secreted by hypothalamus
¥ TSH secreted by thyrotropes of anterior pituitary & enters blood stream
¥ TSH is H₂O soluble
¥ Reaches follicle cells of thyroid
¥ Stimulates synthesis of thyroglobulin (transcription & translation)
¥ Thyroglobulin is discharged into lumen of follicle
¥ Thyroglobulin is broken down into amino acid tyrosine molecules
¥ At same time, Iodides (negative charged iodine ions) are actively up taken into follicular cells
¥ Iodides are oxidized (loose electron) to active form of iodine and enters lumen of follicle by facilitated diffusion
¥ In lumen, iodine is attached to tyrosine in colloid to produce MIT & DIT: Tyrosine + one Iodine atom = MIT; Tyrosine + 2 Iodine atoms = DIT
¥ MIT + DIT = T3 and DIT + DIT = T4
¥ Thyroid hormone (T3, T4) is lipid soluble