5. Hyper/Hypo Thyroidism

Question 1

What percentage of hormone secreted by the thyroid is T4?

Answer 1

93%

Question 2

Which thyroid hormone is more biologically active?

Answer 2

T3

Question 3

Why are the actions of TH so sluggish?

Answer 3

Its actions are due to the transcription and translation of DNA, which is time consuming

Question 4

What are the general effects of TH?

Answer 4

1. Transcription of genes

2. Protein synthesis which increases the functional activity of the body

Question 5

What are the metabolic effects of TH?

Answer 5

1. Increases BMR
2. Calorigenic/heat producing effect
3. Synthesis and degradation of carbs, fat, protein

Question 6

What is the function of TH on the nervous system in children?

Answer 6

Myelination

Development of CNS

Question 7

What are the effects of TH on the cardiovascular system?

Answer 7

1. Increased blood flow and cardiac output
2. Increased heart rate
3. Peripheral vasodilation (due to heat producing effect)

Question 8

What are the effects of TH on growth?

Answer 8

1. Stimulates GH secretion
2. Increases production of IGF-1 by the liver
   These both affect protein synthesis and skeletal growth

Question 9

What effect does cold expose have on newborns?

Answer 9

Increases TRH secretion to increase calorigenic effect

Question 10

What are the causes of hypothyroidism?

Answer 10

1. Primary failure of the thyroid gland
2. Autoimmune disease (Hashimoto)
3. Deficiency of TRH or TSH
4. Inadequate iodine

Question 11

What are the symptoms of hypothyroidism?

Answer 11

1. Low BMR
2. Poor cold tolerance
3. Weight gain
4. Fatigue and drowsiness
5. Slow, weak pulse
6. Slow reflexes and mental responsiveness
7. Decreased hair growth
8. Scaly skin
9. Husky voice
10. Myxedema

Question 12

What is myxedema?

Answer 12

Total lack of TH function
Water retaining carbohydrates bound to protein form excessive tissue gel
The increased ECF gives the body a puffy appearance

Question 13

What is cretinism?

Answer 13

Hypothyroidism from birth

Presents as dwarfism, mental retardation

Question 14

What is congenital cretinism?

Answer 14

Lack of thyroid from birth

Question 15

What can endemic cretinism be caused by?

Answer 15

Genetic defect, thyroid doesn’t produce TH

Lack of iodine

Question 16

How can endemic cretinism be treated?

Answer 16

Administering iodine or thyroxine

Question 17

How is hypothyroidism diagnosed?

Answer 17

High TSH levels

Low thyroxine

Question 18

What are the causes of hyperthyroidism?

Answer 18

1. Graves’ disease
2. Excess TRH/TSH
3. Thyroid adenoma

Question 19

What is Graves’ Disease?

Answer 19

Autoimmune disease
Involves the production of TSI or LATS which target TSH receptors, stimulating secretion and growth of thyroid
TSI and LATS not susceptible to negative feedback

Question 20

What are the symptoms of hyperthyroidism?

Answer 20

1. High BMR
2. Increased heat production
3. Increased appetite
4. Decreased body weight
5. Net degradation of carbs, fat and protein
6. Increased HR and strength of contraction
7. Excessive mental alertness
8. Exophthalmos

Question 21

What is exophthalmos?

Answer 21

Inflammation and swelling of eye muscles and fat behind eyes
Eyeballs bulge forwards
Eyelids unable to close: causes dry eyes and corneal ulceration

Question 22

How is hyperthyroidism diagnosed?

Answer 22

Very low TSH

High thyroxine

Question 23

What is the cause of goitre in hypothyroidism?

Answer 23

Hashimoto disease or lack iodine
Decreased TH causes secretion of TSH
TSH overstimulates thyroid, leading to hypertrophy and hyperplasia of gland

Question 24

What is the cause of goitre in hyperthyroidism?

Answer 24

LATS promote thyroid growth

or excessive TSH is produced due to a hypothalamic or pituitary defect