4) Hypothalamic Pituitary-Thyroid Axis Part 2

Which plasma protein is primarily responsible for transporting thyroid hormones in the blood?

Thyroid Binding Globulin (TBG)

What percentage of T4 in plasma is in the free, biologically active form?

Approximately 0.02%

What physiological change occurs during pregnancy that affects thyroid hormone levels?

Increased TBG and decreased free T4

Which enzymes convert T4 to T3 at the peripheral tissue level?

Deiodinases

Where are thyroid hormone receptors primarily located?

Cell nucleus

What type of transporter allows T3 to enter target cells?

Monocarboxylate and anion transporters

How does T3 exert its biological effects inside the nucleus?

Interacting with DNA and RXR heterodimers

Which of the following is a major physiological action of thyroid hormones?

Increase in basal metabolic rate

What is a likely symptom of hypothyroidism based on metabolic effects?

Bradycardia and feeling cold

Why are beta blockers used in the treatment of hyperthyroidism?

To block adrenergic effects of excess T3

What effect do thyroid hormones have on carbohydrate metabolism?

Increase gluconeogenesis and glycogenolysis

What developmental condition can result from untreated congenital hypothyroidism?

Cretinism