Thyroid hormones - Dr.Park

Question 1

What are the physiological effects of thyroid hormones

Answer 1

Thyroid hormones play a role in growth and development, metabolic effects, thermogenesis, and cardiovascular effects.
- Thyroid hormones are essential in children and essential for brain development (if there is absence of T3 child can have cretinisim)
- can increase basal metabolic rate (BMR)
- starvation lowers both T3 hormone and thyroid receptor
- increase resting heat production
- inability to adjust to environmental temperature is a characteristic symptom of hyper- or hypothyroidism
- increase catecholamine sensitivity

Question 2

What are the differences between T3 and T4
What are the differences in their structures and activities

Answer 2

T4 also known as thyroxine is more commonly produced in the body and its structure differs from T3 because T4 had 4 iodines present

T3 also know as triiodothyronine is not as commonly produced in the body but is much more potent than T4. Its structure differs because it contains 3 iodines instead of 4.

Question 3

Identify the locations of particular reactions in thyroid hormone synthesis

Question 4

Distinguish toxic goiter from nontoxic goiter

Answer 4

Nontoxic goiter is related to Hypothyroidism and is when the thyroid gland is enlarged but has no disturbance on thyroid function

Toxic goiter is related to hyperthyroidism and it is enlargement of the thyroid gland that produces too much thyroid hormone

Question 5

Differentiate hyperthyroidism vs hypothyroidism

Answer 5

Hypothyroidism
- SKIN - pale cool and puffy
- EYES- drooping of eyelids
- CARDIOVASCULAR - Brachycardia, decreased cardiac output, and increased vascular resistance
- CNS- Lethargy (lack of energy)
- METABOLSIM - Decreased appetite and BMR, Hypoglycemia, increased cholesterol and triglycerides, decreased drug metabolism
Hyperthyroidism
- SKIN - warm, moist, sweating
- EYES- retraction of upper eye lid, and exophthalmos
- CARDIOVASCULAR- tachycardia, increased cardiac output, decreased vascular resistance
- CNS- nervousness
- METABOLSIM - Increased appetite, BMR, and drug metabolism. Hyperglycemia, and decreased cholesterol and triglycerides

Question 6

Describe the pathology of Hashimoto’s thyroiditis and Graves’ disease

Answer 6

Graves’ disease is correlated with hyperthyroidism and is an autoimmune thyroid stimulating IgG, enlargement of the entire thyroid gland

Hashimoto’s thyroiditis is related to hypothyroidism and is an autoimmune disease that destroys the thyroid and over time the patient will lose their thyroid gland

Question 7

Identify and explain the drugs used for thyroid hormone replacement therapy (hypothyroidism)

Answer 7

Natural thyroid hormone preparation
- desiccated thyroid and thyroglobulin from cattle and pig
Levothyroxine (T4)
- converted to T3 intracellularly
- slow onset and long half life (patients wait 6-8 weeks before they notice results)
Liothyronine (T3)
- rapid onset and short duration of action
- requires multiple daily doses
- difficult to monitor using conventional laboratory tests
Liotrix
- 4:1 mixture of T4 and T3
- more expensive , but not shown to be more effective than T4 administration alone

Question 8

What treatments are available for hyperthyroidism

Answer 8

Thioamides
- reduce synthesis and block production of hormone
- inhibit thyroid peroxidases
- slow onset (3-4 weeks)
131I
- radioactive iodine emitting beta particles and gamma rays
- localized destruction of thyroid follicles
- problems that arise when taking is that
Iodide
- Large dose of I- inhibits its own uptake, iodine organification
- beneficial effect is transient and thus not used for long term management
- lugol’s solution
- used for preparation for thyroidectomy and severe thyrotoxicosis