Thyroid

What is the primary cellular composition of the thyroid gland responsible for the synthesis and secretion of thyroid hormones?

Follicular cells

Thyroglobulin is synthesized in ____ cells

thyroid follicular

Adequate ____ intake (diet) is required for normal thyroid hormone production

iodine

What effect do thyroid hormones have on the activity of D1, D2, and D3 deiodinases?

Thyroid hormones increase the activity of D1 and D2, while decreasing the activity of D3

What is the primary function of deiodinases in the metabolism of thyroid hormones?

Convert T4 to T3, the biologically active form of thyroid hormone

Which clinical condition is associated with D2 deficiency?

Myxedema

What clinical conditions are associated with D3 deficiency?

Neurodevelopmental disorders like autism and ADHD

What is the function of deiodinases in the metabolism of thyroid hormones?

Converting T4 to T3

Which type of deiodinase is the most abundant in the body?

Type 1 deiodinase (D1)

Where is Type 3 deiodinase (D3) primarily located?

Brain and pituitary gland

What is the principle regulator of T3/T4 synthesis and release?

TSH

What is the primary feedback mechanism that regulates the synthesis and release of thyroid hormones (T3 and T4) in the thyroid gland?

Negative feedback by thyroid hormones T3 and T4

Increased _____ of almost all tissues occurs with secretion of T3/T4

metabolic activity

How do thyroid hormones affect cardiac function?

They increase the heart's contractile force, leading to an increase in stroke volume and cardiac output

What is the major hormone produced by the thyroid gland?

Thyroxine (T4)

How do thyroid hormones influence metabolism?

They increase the rate at which the body converts food into energy, leading to an increase in heart rate and cardiac output

Which gland produces thyroid-stimulating hormone (TSH)?

Pituitary gland

How do T3 and T4 impact heart rate?

They increase heart rate by stimulating the pacemaker cells

What is the role of thyroid hormones T3 and T4 in regulating cardiac function?

They increase heart rate and contractility

Thyroid follicles are composed of closed rings of cells (100-300 µm diameter) lined by ____ epithelium filled with colloid

simple cuboidal

The colloid in thyroid follicles is mostly composed of what?

thyroglobulin

Which of the following is true in regards to calcitonin?

Parafollicular cells within the thyroid secrete calcitonin to decrease serum calcium levels

For follicular cells of the thyroid, the apical surface faces and the basal surfaces faces .

colloid, interstitium

93% of total secretion (~80 µg/day) from the thyroid is ____

Tetraiodothyronine (Thyroxine; T4)

7% of total secretion (~5 µg/day) is ____

Triiodothyronine (T3)

T3 is ____ potent than T4

4x more

Which of the following plays an important role in the synthesis and storage of thyroid hormone?

Thyroglobulin

The Sodium/Iodide Symporter (NIS) uses Na+ driving force to move iodine, while ____ is Na+ independent iodide/chloride transporter

pendrin

In the circulation, what percent of thyroid hormone is found in each of the following states?

Free (unbound) = ~1% Thyroxine-binding globulin (TBG) = ~70% Transthyretin (prealbumin) = ~15% Albumin = ~15%

With increased levels of estrogen during pregnancy, which of the following occurs, leading to decreased levels of free T3/T4?

increased synthesis of TBG

Where is Type III deiodinase (D3) primarily found?

Thyroid gland, liver, and some brain regions

What is the role of Type I (D1) and Type II (D2) deiodinases in thyroid hormone metabolism?

Convert T4 to T3

How is the activity of deiodinases regulated in the body?

By thyroid-stimulating hormone (TSH) and thyroid hormones (T3 and T4)

What is the clinical significance of Type III deiodinase (D3)?

Associated with metabolic disorders

What is the primary function of Type I and Type II deiodinases in thyroid hormone metabolism?

Converting T4 to T3

How do post-translational modifications like phosphorylation and ubiquitination affect deiodinase activity?

Decrease deiodinase activity

Which clinical condition results from a deficiency of T3 due to reduced deiodinase activity?

Hypothyroidism

What role do deiodinases play in fine-tuning thyroid hormone levels?

Inactivating T3 and T4

In which tissues do deiodinases help concentrate T3 and T4?

Brain, kidneys, and liver

What clinical condition can result from mutations impairing the function of deiodinases?

Thyroid hormone resistance

How does TSH affect enzymes involved in T3/T4 synthesis such as TPO?

upregulates

Where are thyroid receptors located within a cell?

cytoplasm

Basal metabolic rate (BMR) can increase _____% above normal when large quantities of T3/T4 are secreted

60-100