Thyroid Hormone

Question 1

What are the hormones which are the major determinants of growth in normal postuterine life?

Answer 1

GH and IGF-1

growth hormone and insulin-like-growth factor

Question 2

What do changes in linear growth normally occur with simultaneously?

Answer 2

Changes in body mass

Question 3

What are the 2 main hormones which regulate body mass?

Answer 3

Leptin and Ghrelin

Question 4

Describe the function of Leptin

Answer 4

Helps inhibit the hunger response and regulates energy balance.

Plasma leptin levels is directly proportional mass of adipose tissue

Question 5

Describe the function of Ghrelin

Answer 5

Promotes the hunger response

Levels are low in lean humans

Question 6

What are the 2 thyroid hormones?

Answer 6

T3, T4

Question 7

What is the name for T4?

Answer 7

Thyroxine

Question 8

What is the name for T3?

Answer 8

Triiodothyronine

Question 9

What are thyroid hormones essential for?

Answer 9

Thyroid hormones are essential for normal development, growth and metabolism

Question 10

What does not exist for thyroid hormones?

Answer 10

No cell membrane receptors exist for these hormones

Question 11

As no cell membrane receptors exist for thyroid hormones, what happens instead?

Answer 11

They instead act via nuclear receptors and regulate transcription of cell proteins

Question 12

How many steps are there in the synthesis of thyroid hormones T4 and T3?

Answer 12

7

Question 13

Describe the first step - trapping.

Answer 13

TSH increases activity of Na/I cotransporter on follicular cell basal membrane.

Increased I in follicular cell than in interstitial space

Question 14

Describe the second step

Answer 14

Iodide leaves follicular cell into lumen, with thyroglobulin. Thyroid peroxidase oxidises I^- to I^0

Question 15

Describe the third step - iodination

Answer 15

TSH stimulates the iodination of thyroglobulin in the colloid

Question 16

Describe the fourth step - conjugation

Answer 16

TSH stimulates the conjugation of iodinated tyrosines, linked to thyroglobulin

Question 17

Describe the fifth step - endocytosis

Answer 17

TSH stimulates the endocytosis of iodinated thyroglobulin back into the follicular cell

Question 18

Describe the sixth step - proteolysis

Answer 18

TSH stimulates the proteolysis of iodinated thyroglobulin into T4 and T3

Question 19

Describe the seventh step - secretion

Answer 19

TSH stimulates the secretion of T4 and T3 into circulation

Question 20

Describe the function of TRH or Thyrotropin-Regulating Hormone

Answer 20

• produced by neurons in hypothalamus
• regulates synthesis and secretion of TSH from thyrotrophs in A. Pituitary
• stimulated by cold/stress.

Question 21

Describe the function of TSH or Thyroid-Stimulating Hormone

Answer 21

• synthesised and secreted by thyrotrophs in A. Pituitary
• released and enters into systemic circulation
• reaches thyroid gland, binds to receptors and promotes synthesis and secretion of TH
• TH function in Negative Feedback Loop to inhibit TRH and TSH so that not too much TH is made

Question 22

Describe the function of TSI or Thyroid-Stimulating Immunoglobulin

Answer 22

• found in cases of GRAVES disease
• interferes with Negative Feedback Loop
• Acts like TSH and promotes secretion of TH - but with no control so hyperthyroidism results!
• Graves = goiter and exophthalmos

Question 23

What are the 3 main causes of HYPOthyroidism?

Answer 23

1-Primary failure of thyroid gland to produce TH
2-Seondary to anterior pituitary or hypothalamus failure
3-Lack of dietary iodine (anaemia)

Question 24

What are the 3 main causes of HYPERthyroidism?

Answer 24

1-Abnormal presence of TSI - Graves disease
2-Secondary to EXCESS hypothalamic or anterior pituitary secretion
3-Hyper-secreting thyroid tumour