Thyroid Physiology

Question 1

What is the feedback loop regulating thyroid hormones?

Answer 1

The TRH-TSH-Thyroid Hormones feedback loop between the thyroid gland, hypothalamus, and pituitary regulates thyroid hormone levels.

Question 2

Why is understanding the TRH-TSH-Thyroid feedback loop important in PICU?

Answer 2

It helps recognize both typical and atypical thyroid function presentations, which can be subtle and often missed in critically ill pediatric patients.

Question 3

What are the key steps in thyroid hormone synthesis?

Answer 3

Iodide trapping, oxidation, and hormone storage.

Question 4

Why is it important to know the steps of thyroid hormone synthesis in PICU?

Answer 4

It helps in understanding potential thyroid disorders and effects of medications that may interfere with these processes.

Question 5

What enzyme converts T4 to T3?

Answer 5

Deiodinases.

Question 6

Where does the conversion of T4 to T3 primarily occur?

Answer 6

In the liver and brain, among other tissues.

Question 7

Why is peripheral T4 to T3 conversion crucial in critical care?

Answer 7

Critical illnesses and medications can alter enzyme activity, impacting hormone levels and metabolic status.

Question 8

What proteins transport thyroid hormones in the blood?

Answer 8

Thyroxine-binding globulin (TBG), albumin, and transthyretin.

Question 9

What is the significance of understanding free vs. bound thyroid hormones?

Answer 9

It is vital for correctly interpreting lab tests, especially during illness where protein levels may change.

Question 10

How do T3 and T4 enter cells?

Answer 10

They enter cells through specific transport mechanisms and affect gene transcription via nuclear receptors.

Question 11

What is the role of nuclear receptors in thyroid hormone action?

Answer 11

They mediate the effects of T3 and T4 on gene transcription, impacting growth and development.

Question 12

Which lab assays are commonly used to measure thyroid function?

Answer 12

TSH and free T4 (FT4) assays.

Question 13

Why is assay sensitivity and specificity important in thyroid function tests?

Answer 13

It ensures accurate diagnosis and management of thyroid disorders in critically ill children.

Question 14

What role do thyroid hormones play in growth and development?

Answer 14

They regulate critical aspects of growth, development, and metabolism.

Question 15

How might critical illness affect thyroid hormone levels?

Answer 15

Critical illness can alter enzyme activity, protein levels, and feedback mechanisms, impacting hormone levels.

Question 16

Why is understanding thyroid physiology important for a PICU fellow?

Answer 16

It enhances the ability to diagnose, manage, and treat pediatric patients with thyroid-related issues that influence recovery and outcomes.

Question 17

What could interfere with thyroid hormone synthesis in critically ill patients?

Answer 17

Medications, iodine deficiency, or autoimmune conditions.

Question 18

What conditions might alter thyroid hormone transport in pediatric patients?

Answer 18

Hypoalbuminemia or changes in thyroxine-binding globulin levels due to illness.

Question 19

How does the TRH-TSH-Thyroid feedback loop respond to low thyroid hormone levels?

Answer 19

TRH and TSH levels increase to stimulate the thyroid gland to produce more hormones.

Question 20

What is the clinical significance of free T4 levels in critically ill patients?

Answer 20

Free T4 levels reflect the biologically active hormone and are crucial for assessing thyroid function in illness.

Question 21

What might cause abnormal TSH levels in a pediatric patient?

Answer 21

Hypothyroidism, hyperthyroidism, or pituitary disorders.

Question 22

How do critical illnesses impact the deiodination of T4 to T3?

Answer 22

Critical illnesses can inhibit deiodinase activity, reducing T3 levels and leading to ‘sick euthyroid syndrome.’

Question 23

What thyroid disorder is characterized by low T3, normal T4, and normal TSH levels in critical illness?

Answer 23

Sick euthyroid syndrome.

Question 24

How can thyroid hormone dysfunction influence metabolic status in pediatric patients?

Answer 24

It can lead to altered energy utilization, temperature regulation, and growth.

Question 25

Why is knowledge of thyroid function tests crucial in a PICU setting?

Answer 25

It aids in differentiating between primary thyroid dysfunction and illness-related thyroid changes, guiding appropriate management.