Thyroid Physiology

Question 1

What are the follicles of the thyroid?

Answer 1

sites of thyroid where thyroid elements function

Question 2

What is thyroid fabrication (ie organification of iodide)?

Answer 2

conducted by thyroid peroxidase. Iodination of tyrosines on thyroglobulin. Synthesis of thyroxine(T4), triiodothyronine(T3), reverse T3.

Question 3

What two test do you use to differentiate whether thyroid abnormalities are autoimmune or not?

Answer 3

Antithyroglobulin and antithyroid peroxidase

Question 4

What is the function of the parafollicular “C” cells?

Answer 4

produce calcitonin that regulates calcium and phosphorus by decreasing bone osteoclast activity and inhibiting tubular reabsorption of calcium by the kidneys

Question 5

Describe the thyroid releasing hormone

Answer 5

secreted by the hypothalamus when blood levels of T3 and T4 are low. stimulates the pituitary gland to produce TSH.

Question 6

Describe the thyroid stimulating hormone

Answer 6

Secreted from thyrotrophs in the anterior pituitary.
TSH receptors of thyroid gland increase iodide uptake and iodination of thyroglobulin, thus stimulating the thyroid gland to synthesize and release thyroid hormones (T3 and T4). Secretion of TRH and TSH is inhibited by high blood levels of T3

Question 7

Describe characteristics of thyroxine (T4)

Answer 7

Production rate greater than T3 and lasts longer in blood than T3. T4 is converted to T3 in the peripheral tissue (especially liver and kidneys) before it can act physiologically.

Question 8

Describe characteristics of triiodothryonine (T3)

Answer 8

T3 is the active form of the hormone. 80% is produced by deiodination of T4 outside the thyroid and 20% by the thyroid. T3 is 4 times more potent than T4. T3 is degraded by deiodination more rapidly than T4

Question 9

What is thyroglobulin (Tg)?

Answer 9

Synthesized by thyroid cells and secreted into the follicle. Is a template for thyroid hormone synthesis and a storage form of inactive thyroid hormones and iodine

Question 10

What are the serum binding proteins of the thyroid hormones?

Answer 10

Thyroxine Binding Globulin (TBG) - binds in circulation. has the highest affinity for T3 and T4, but is present in the lowest concentration. Transthyretin (TTR) - serum and cerebrospinal fluid carrier of the thyroid hormone Thyroxine (T4)

Question 11

What happens when TBG concentration is increased?

Answer 11

Total serum T4 and T3 levels increase. Free T4, and free T3 levels remain unchanged.

Question 12

What happens when TBG concentration is decreased?

Answer 12

Total serum T4 and T3 levels decrease. Free T4 and Free T3 levels remain unchanged

Question 13

How do thyroid hormones effect metabolism?

Answer 13

Increases metabolism in all body tissues except retina, spleen, testes and lungs. Use of protein, fat and glucose increases. primary regulator of the Basal Metabolic Rate (BMR)

Question 14

How do thyroid hormones effect growth and development?

Answer 14

normal levels of thyroid hormone are essential to the development of the fetal and neonatal brain evidenced by growth retardation observed in thyroid deficiency.

Question 15

How do thyroid hormones effect cardiovascular hemodynamics?

Answer 15

As T3/4 increase BMR , vasodilation occurs to assist with increased heat removal. Cardiac output closely follows BMR . Heart rate increases.
Heart strength will diminish with excess T3/4. widening of pulse pressure

Question 16

How do thyroid hormones effect the plasma and liver fats?

Answer 16

Increased T3/4 decreases concentration of cholesterol, phospholipids and triglycerides in plasma. Decreased T3/4 increases the concentration of cholesterol, phospholipids and triglycerides in plasma and causes excessive deposits of fat in liver

Question 17

How do thyroid hormones effect the reproductive system?

Answer 17

Hypothyroidism may lead to menstrual disorders, infertility, risk of miscarriage, and pregnancy complications. Poor semen quality and poor testicular function

Question 18

What role does T3 play in the regulation of skeletal maturation at the growth plate?

Answer 18

regulates the expression of factors that contribute to linear growth in the growth plate. may participate in osteoblast differentiation and proliferation, and chondrocyte maturation leading to bone ossification

Question 19

What role does T3 play in the regulation of mitochondrial activity?

Answer 19

stimulates oxygen consumption by the mitochondria. A T3-dependent transcription factor of the mitochondrial genome induces early stimulation of transcription and increases transcription factor (TFA) expression