Thyroid

Question 1

type 1 (D1) deiodinases

Answer 1

predominantly expressed in liver and kidney. lower expression also occurs in the thyroid. contributes 24% of the circulating T3 converted from T4

Question 2

type 2 (D2) deiodinases

Answer 2

predominantly expressed in CNS, pituitary, thyroid, heart, brown fat, skeletal muscle. contributes 60% of circulating T3 converted from T4.

Question 3

intracrine vs. paracrine effects

Answer 3

intracrine affects thyroid signaling inside D2 expressing cells, paracrine effects are when D2 generated T3 also exits the cells to plasma and effects other tissues

Question 4

type 3 (D3) deiodinase

Answer 4

predominantly expressed in the brain and skin in healthy adults. also in placenta of pregnant women and in tissues in disease states. inactivates T3, converts T3 to T2 and reverse T3. prevents circulating T3 from entering the nucleus.

Question 5

diseases caused by defective sodium-iodide symporter

Answer 5

symporter gene mutation: causes congenital hypothyroidism.

Autoimmune thyroiditis: autoantibodies against symporter which affects iodide transport

Question 6

transportation of thyroid hormone into the target cells

Answer 6

1. through simple diffusion
2. through thyroid hormone transporters
   2a. monocarboxylate transporter family
   2b. organic anion transporting polypeptides.

the MCT and OATP are important for maintaining intracellular concentrations of thyroid hormones

Question 7

regulation of thyroid function

Answer 7

hypothal makes TRH, which causes anterior pituitary to make TSH, which causes thyroid to make T4 and T3. T4 and T3 stop production of TSH and TRH.

Question 8

regulation of gene expression

Answer 8

TR is a heterodimer made of TR and RXR. TR-RXR binds to thyroid hormone response element. T3 then binds to the complex and leads to regulation

Question 9

hypothyroidism symptoms

Answer 9

fatigue, depression, cold sensitivity, weight gain, goiter, muscle weakness, coarsening of skin, dry hair, muscle cramps, constipation, miscarriage

Question 10

types of hypothyroidism

Answer 10

iodine deficiency, hashiimoto’s thyroiditis, thyroid ablation. secondary hypothyroidism caused by disorder of pituitary or hypothal. myxedema, cretinism

Question 11

what are some problems with animal thyroid usage?

Answer 11

contains T3 which acts rapidly, varies in potency, some patients can be allergic.

Question 12

levothyroxine sodium

Answer 12

synthetic version of T4. preferred drug in treatment of hypothyroidism. longer half life compared with liothyronine. can be converted to T3 in peripheral tissues.

Oral administration, can do IV or IM.

Question 13

liothyronine sodium

Answer 13

synthetic version of T3. can be used in combo with levothyroxine in hypothyroidism. more rapidly effective. 4x as potent as T4. IV can be used in acute emergency conditions (myxedema coma). leads to transient high levels of T3 in serum if used constantly.

Question 14

precautions for thyroid hormone drugs

Answer 14

readjust after 4-6 weeks to keep proper levels. perform periodic tests to monitor T3 and T4 and TSH levels if chronic treatment. use with caution in ppl with heart problems. use low doses. give adequate dose to pregnant ladies to prevent fetal brain maldevelopment

Question 15

goiter

Answer 15

iodine deficiency

Question 16

hyperthyroidism symptoms

Answer 16

rapid heart beat, weight loss, nervousness and alertness, heat intolerance, fatigue, increased freq of bowel movements, loss of sleep, tremors, excessive sweating, eye changes

Question 17

graves disease

Answer 17

most common cause of hyperthyroid. autoimmune disease caused by thyroid stimulating antibodies, activate the thyrotropin receptor on thyroid cells.

Question 18

lab findings for hyperthyroidism

Answer 18

high T3 and T4, low TSH

Question 19

treatment strats for hyperthyroidism

Answer 19

subtotal thyroidectomy and replacement of T4. irradiate thyroid gland and replace T4. inhibit thyroid peroxidase activity. interfere with thyroid hormone facilitation of sympthetic activity.

Question 20

what drugs inhibit thyroid peroxidase activity

Answer 20

propylthiouracil, methimazole, carbimazole. inhibit organification of iodide and coupling of iodotyrosine, which prevents thyroid hormone synth.

Question 21

severe side effects of antithyroid drugs propylthiouracil and methimazole

Answer 21

agranulocytosis, hepatitis, lupus like syndrome. meth is safer than prop with regards to agranulocytosis. prop preferred in pregnancy since it is less likely to go through placenta.

Question 22

radioactive iodine

Answer 22

thyroid specific I131 isotope to destroy sufficient thyroid tissue to restore euthyroid. effects not seen for over 4 weeks. use in combo with drugz. used if relapse after drug therapy. dont use in pregnancy or breast feeding