Thyroid Disorders

Question 1

What does the Thyroid gland control?

Answer 1

• Growth & development
• Metabolism
• Cardiovascular
• Iodine metabolism
• Calcium homeostasis

Question 2

What does the Parathyroid gland control?

Answer 2

• Calcium homeostasis

Question 3

What is the anatomy of thyroid gland?

Answer 3

Located in the anterior neck, just below the larynx and close to the first part of the trachea

Two lobes on either side of the trachea (butterfly shape)

Each lobe is divided into many small lobules that contain thyroid follicles

Question 4

What are the cell types of the thyroid gland?

Answer 4

• Follicular cells
• Parafollicular cells (C cells)

Question 5

What hormone do Follicular cells produce?

Answer 5

Thyroid hormone (thyroxine and triiodothyronine)*

*: T4 is converted to T3 in the liver, kidney, and other tissues.

Biological activity: T4 < T3

Question 6

What is the function of Follicular cells?

Answer 6

• Growth and development
• Metabolism
• Cardiovascular
• Iodine metabolism

Question 7

What hormone do Parafollicular cells (C cells) produce?

Answer 7

Calcitonin

Question 8

What is the function of Parafollicular cells (C cells)?

Answer 8

Calcium homeostasis

Question 9

What doe thyroid hormones affect?

Answer 9

Thyroid hormones affect every cells and all organs of the body.

Question 10

What are the functions of thyroid hormones?

Answer 10

1. Growth and development
   - Bone: Promote normal growth and skeletal development in conjunction with growth hormone (GH)
   - Central nervous system: Promote normal brain development (important in utero and in early childhood)
2. Metabolism
   - Increase basal metabolic rate (BMR)
   - Increase oxygen consumption and heat production (ñbody temperature)
   - Increase sweating (due to increased body temperature, also due to increased activity of sympathetic nervous system)
3. Cardiovascular
   - Increase heart rate and cardiac output
4. Iodine metabolism
   - Iodine – An important component of thyroid hormones

Question 11

What is the regulation of thyroid hormone secretion?

Answer 11

Hypothalamus –TRH–> Anterior pituitary (Thyrotroph) –TSH–> Thyroid gland –> Thyroid hormone (Thyroxine (T4)
Triiodothyronine (T3))

Question 12

What is the function of TSH (Thyroid stimulating hormone)?

Answer 12

• To promote thyroid follicle development
• To stimulate the synthesis and secretion of thyroid hormones

Question 13

What happens when the Thyroid gland overproduces T4 & T3?

Answer 13

NEGATIVE FEEDBACK

INHIBITION of TRH, TSH, T4 & T3

= return to normal levels

Question 14

What happens when the Thyroid gland underproduces T4 & T3?

Answer 14

NEGATIVE FEEDBACK

STIMULATION of TRH, TSH, T4 & T3

= return to normal levels

Question 15

What are the primary vs. secondary failure?

Answer 15

Primary failure:
- damages Final endocrine gland (ex: Thyroid gland)

Secondary failure:
- damages Pituitary

Both lead to: Abnormal (increased or reduced) hormone secretion

Question 16

What are the HYPERthyroidism clinical manifestations?

Answer 16

Increased overall metabolism
- Increased basal metabolic rate (BMR)
- Weight loss with increased appetite
- Higher body temperature
- Heat intolerance (impaired ability to adapt to heat stress)
- Hot skin
- Increased sweating

Tachycardia (increased heart rate)
Palpitations

Question 17

Primary hyperthyroidism:

Answer 17

Defects in thyroid gland itself

Over-secretion of thyroid hormones by the thyroid

Question 18

Secondary hyperthyroidism (rare):

Answer 18

Defects in pituitary

Increased secretion of TSH

Question 19

What are the Hyperthyroidism causes?

Answer 19

1. Graves’ disease (most common cause of hyperthyroidism)
2. Toxic nodule
3. TSH-secreting pituitary adenoma (Secondary hyperthyroidism)

Question 20

Graves’ disease:

Answer 20

Autoimmune disease - increased production of TSH receptor antibody, thyroid stimulating immunoglobulin [TSI]
TSI binds to TSH receptor and mimics the action of TSH (stimulates thyroid hormone secretion)

Most common cause of hyperthyroidism

Graves’ disease-specific clinical manifestations
Exophthalmos: Inflammation of extraocular muscles and periorbital tissue leading to bulging of the eyes

Question 21

Toxic nodule:

Answer 21

Non-cancerous growth(s) develop in the thyroid and produce excessive amounts of thyroid hormone

Independent of the pituitary and secretes excess thyroid hormone

Question 22

TSH-secreting pituitary adenoma (Secondary hyperthyroidism):

Answer 22

Increased TSH secretion –> Increased thyroid hormone secretion

Question 23

How do you diagnose Hyperthyroidism?

Answer 23

Blood test (TSH) – Primary vs. secondary

Blood test (T4 and T3)

Question 24

How do you diagnose Graves’ disease (Exophthalmos) (hyperthyroidism)?

Answer 24

Blood test (TSI)
Radioactive iodine uptake test (elevated uptake of radioactive iodine spread evenly in the thyroid gland)

Question 25

How do you diagnose Secondary hyperthyroidism –THS-secreting pituitary adenoma?

Answer 25

Imaging analysis (MRI, CT) –confirmation of adenoma

Question 26

What is the treatment for hyperthyroidism?

Answer 26

1. Medication - Anti-thyroid medications -- Methimazole: Inhibition of thyroid hormone synthesis -- Propylthiouricil: Inhibition of thyroid hormone synthesis and peripheral conversion of T4 to T3 -- Beta–blockers: Hyperthyroidism speeds up many physiological functions 2. Radioiodine ablation therapy (radioiodine therapy) 3. Surgical removal of thyroid gland (thyroidectomy)

Question 27

What are the possible problems with HYPERthyroidism?

Answer 27

HYPOthyroidism - Over-response to anti-thyroid medication - Overkill of thyroid gland by radioiodine therapy - Excessive removal of thyroid gland by surgery

Question 28

What are the HYPOthyroidism clinicial manifestations?

Answer 28

Low overall metabolism - Low basal metabolic rate (BMR) - Weight gain - Low body temperature - Cold intolerance (impaired ability to adapt to cold stress) - Decreased sweating - Dry skin - Sleepiness and tiredness - Lower heart rate

Question 29

Primary hypothyroidism:

Answer 29

Defects in thyroid gland itself

Question 30

Secondary hypothyroidism (rare):

Answer 30

Defects in the pituitary Lack of or reduction of both thyroid hormone and TSH

Question 31

What are the causes of primary hypothyroidism?

Answer 31

Defects in thyroid gland itself 1. Hashimoto’s thyroiditis (most common) – Autoimmune disease - Production of abnormal antibodies against thyroid peroxidase (TPOAb), an enzyme important for the production of thyroid hormones 2. Iodine deficiency - Lack of adequate iodine in the diet 3. Surgical removal of thyroid gland 4. Over-response to anti-thyroid medication - Anti-thyroid drugs that inhibit thyroid hormone synthesis and conversion of T4 to T3.

Question 32

What are the causes of Secondary hypothyroidism?

Answer 32

Defects in the pituitary - Pituitary adenoma, pituitary damage

Question 33

What is the diagnosis of hypothyroidism?

Answer 33

TSH level – primary vs. secondary T4 and T3 levels Level of antibodies – Hashimoto’s thyroiditis (TPOAb) About 90% of cases People with thyroid function tests showing an abnormal TSH but normal T4 and T3 levels may have subclinical (or mild) hypothyroidism or hyperthyroidism. These people may have no signs or symptoms.

Question 34

What is the treatment for hypothyroidism?

Answer 34

Thyroid hormone replacement therapy Synthetic thyroxine (T4) – more stable form of thyroid hormone Iodine supplementation (if the cause is insufficient dietary iodine)

Question 35

What is Goiter?

Answer 35

Prolonged stimulation of thyroid gland by TSH (or TSH-like agent) --> Excessive growth of thyroid --> Diffuse thyroid enlargement (Goiter)

Question 36

What are the causes of Goiter?

Answer 36

- Iodine deficiency (by TSH) - Hashimoto’s thyroiditis (by TSH) - Secondary hyperthyroidism (by TSH) - Graves’ disease (by TSI)

Question 37

Goiter:

Answer 37

Prolonged stimulation of thyroid gland by TSH (or TSH-like agent)

Question 38

What are the 2 causes of Goiter and what do they result in?

Answer 38

1. Most common cause of goiter Iodine deficiency hypothyroidism A lack of iodine (insufficient iodine in the diet) 2. Hashimoto’s thyroiditis TPOAb both: decrease TSH secretion Excessive growth of thyroid (Goiter) Negative feedback increase TSH secretion lead to Excessive growth of thyroid (Goiter)

Question 39

What is the difference between Secondary hyperthyroidism and Grave's disease?

Answer 39

Secondary hyperthyroidism increase TSH secretion Graves’ disease increase TSI = Excessive growth of thyroid (Goiter)

Question 40

Thyroid disorders in children (pediatric):

Answer 40

Most thyroid diseases seen in adults also occur in children. Congenital hypothyroidism (1 in 2,000-4,000 newborn babies) Possible cause: Failure of the thyroid gland to grow before birth Neonatal screening by a thyroid blood test: High TSH and low T4 Growth retardation and mental disabilities No change in intelligence if hypothyroidism develops after two years of age Thyroid hormone treatment (normal growth and prevents mental disabilities) Hashimoto’s thyroiditis - Most common cause of hypothyroidism in both children and adults Thyroid hormone replacement therapy Graves’ disease - Extreme restlessness and short attention span - Anti-thyroid medication, thyroidectomy, and radioiodine therapy Diagnostic test (assessment of thyroid function) - Blood levels of thyroid hormone (T4) and TSH

Question 41

Thyroid disorders in elderly (geriatric):

Answer 41

Increased prevalence of thyroid disease with age Slightly lower thyroid function and slightly increased TSH in older people Hypothyroidism: Most common thyroid condition in individuals over 60 years of age Hypertyroidism Causes Graves’ disease - a common cause of hyperthyroidism (same as younger people) ***Toxic nodule - more frequent in older individuals than in younger individuals Difficulties in diagnosis - Individuals over 65 years show that thyroid illness is often undiagnosed. Symptoms are not always as widespread or obvious as those in younger patients.