Endocrine System: Thyroid

Question 1

List 3 effects of thyroid hormone (KNOW THISSS)

Answer 1

1. Temp regulation
2. Increases metabolism
3. Helps regulate the way we use energy(changes in hair, skin and nails)
4. GI motility
5. Contractility of skeletal and cardiac muscle

Question 2

The follicles of the thyroid are filled with secretory substance called ___________. This substance is mostly a ___________ that is responsible for_______, _____ and ________ of TH

Answer 2

colloid, a glycoprotein-iodine complex thyroglobulin (TGB), synthesis, storage and secretion

Question 3

What is the function of the parafollicular cells (c cells) of the thyroid?

Answer 3

Secrete calcitonin which controls Ca++ regulation by lowering Ca++. Works by effecting bone resorption & osteoblastic activity

Question 4

Thyroid is highly efficient in the use of ______, daily consumption of 150-200 mcg is sufficient.

Answer 4

iodine

Question 5

Explain the biosynthesis of the thyroid hormone

Answer 5

iodide > trapped by active transport into follicular cell by NIS protein and pendrin. concentration 20-40x of blood > Iodide oxidation catalyzed by thyroid peroxidase (TPO) to facilitate its combination with tyrosine> organification of iodine> iodine binds with TGB and is incorporated with tyrosine to produce Monoiodotyrosine (MIT)
(1 molecule of iodine (T1)) and Diiodotyrosine (DIT) (2 molecules of iodine (T2)) > coupling > Triodothryonine = 1 MIT + 1 DIT = T3 > Thyroxine = 2 DIT = T4

Question 6

Our body loves ______. T1 + T2= _______

Answer 6

T3

Question 7

Coupling of T2+ T2= _______

Answer 7

T4

Question 8

Where is the 2-3 mo supply of T3 and T4 stored?

Answer 8

in TGB. > T3 & T4 cleaved and released from storage by pinocytosis into follicular cells > TGB hydrolized by lysosome and releases mostly protein bound T3/T4 into circulation

Question 9

_________ and 70% is reused

Answer 9

TH deiodinated

Question 10

T4 converts to T3 (80%) by _________ (80%) or __________ (20%)

Answer 10

5’deiodinase or inactive form Reverse T3

Question 11

Other 30% of the thyroid hormone is excreted via the __________

Answer 11

bililary tract

Question 12

What are the drugs that decrease the synthesis of release of TH?

Answer 12

Lithium, Steroids

Question 13

TH circulates in plasma bound to proteins. What are they?

Answer 13

1.Thyroxine-binding globulin (TBG)
2. Transthyretin (old name-Thyroxine-binding prealbumin or TBPA)
3. Thyroxine-binding albumin (TBA)

Question 14

Which TH is metabolically active?

Answer 14

free TH

Question 15

_________makes up the majorifty of circulating thyroid hromone

Answer 15

T4

Question 16

T4 has greater affinity for ________ than T3 so less T4 is free and active.

Answer 16

protein binding

Question 17

What is T4 synthesized from?

Answer 17

4 molecules of iodine (combination of 2 DITs)

Question 18

Most T4 converts to ________ in tissues

Answer 18

T3

Question 19

What is the half life of T4?

Answer 19

7 days

Question 20

T3 is less ___________ than T4 so more active T3 is circulating

Answer 20

protein bound

Question 21

T3 is most formed by _____________ rather than from synthesis in the thyroid

Answer 21

Deiodinated T4

Question 22

________ has 4x greater affinity for the receptors in the nucelus at tissues so more active

Answer 22

T3

Question 23

What is the half life of T3?

Answer 23

1 day

Question 24

TH hormone binds to the intracellular receptors on or near DNA in the nucleus. What does it do?

Answer 24

Activate & stimulate transcription process of mRNA> increase translation of RNA in ribosomes > increase synthesis of proteins (enzymes, structural proteins, transport proteins) > stimulate energy producing electron transfer in mitochondria

Question 25

What is the genomic function of thyroid hormone?

Answer 25

1. Regulation of gene expression
2. > 30 genes are regulated by thyroid hormone

Question 26

What is the non genomic function of thyroid hormone?

Answer 26

1. Direct effect on cells mitochondria, membrane, and cytosol
2. increase ATP formation
3. increase Na+ & K+ ATPase (which increases rate of membrane transport of these ions)
4. increase mitochondria number & size

Question 27

Thyroid hormone increases metabolism of all tissues EXCEPT

Answer 27

retina, spleen, testes, and lungs

Question 28

What are the functions of the thyroid homone?

Answer 28

1. Increases basal metabolic rate (BMR)
2. Regulates protein catabolism in muscle increase
3. Regulates Carbohydrate & fat metabolism
   increase glucose uptake by cells
   increase glycolysis and gluconeogenesis
   increase insulin secretion
   increase fat metabolism by increase free fatty acid concentration & oxidation
4. maintains body weight
5. Regulates thermogenesis
6. Controls excretion of cholesterol in bile & stimulate production of LDL receptors
7. Adjusts vitamin needs
8. sexual development

Question 29

What is the GI function of the thyroid hormone?

Answer 29

increase GI motility
increase glucose absorption in gut

Question 30

What is the cardio function of the thyroid hormone?

Answer 30

increase O2 demand
increase HR & contractility initially then decrease secondary to protein catabolism

Question 31

What is the Musculoskeletal function of thyroid hormone?

Answer 31

increase muscle reaction initially then decreases

Question 32

Thyroid hormone is necessary for growth in children for what 2 reasons?

Answer 32

Mental development
Psychomotor development

Question 33

T3 promotes _______ development

Answer 33

cochlear

Question 34

Thyroid Hormone Regulation: H-P feedback

Answer 34

Cerebral cortex >Hypothalamus release TRH>
Anterior pituitary release TSH > Thyroid synthesizes & secretes T3 & T4 > Blood levels of TH increase

Question 35

The negative feedback primarily to act on anterior pituitary to turn off _______ and secondary at hypothalamus to turn off _________ release

Answer 35

TSH secretion, TRH release