BLD 402 THYROID EXAM QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS GRADED A++
Folicular cells
Synthesize T3 and T4
Colloid
thyroglobulin (with T3, T4) storage
Regulation of thyroid hormone synthesis
Hypothalamus-(TRH)-Pituitary-(TSH)-Thyroid-(T3,T4)- Target cells
thyroglobulin
tyrosine rich protein
Thyroid hormone synthesis
- Many steps induced by TSH
Step 1. there is enough dietary iodine in blood flow
Step 2. Follicular cells take I- in, and move it into colloids
Step 3. Follicular cells take amino acids into cells to make thyroglobulin rich protein,
Thyroglobulin is moved out to colloid by exocytosis
Step 4. Thyroperoxidases catalyzes production of H2O2, which will be sent to colloid
Step 5. Thyroidperoxidases oxidases iodide to iodine. The iodine reacts with tyrosine of
thyroglobulin (organification)
Step 6. Now there are mixture of monoiodotyrosine and diiodotyrosine within
thyroglobulin
, Step 7. One phenol group of MIT or DIT is added to another phenol group of DIT within
thyroglobulin
Step 8. T3 and T4 within thyroglobulin (with unused MIT, DIT) stored in colloid
Step 9. T3 and T4 within thyroglobulin (w/ unused MIT, DIT) will come back in follicular
cell by endocytosis when thyroid hormone is needed
Step 10. Lysosomal proteases hydrolyze thyroglobulin into T3, T4 iodide and other AAs
Step 11. Iodide and other amino acids will be recycled
Step 12. T3 and T4 are secreted from follicular cells
T3 and T4
Ratio: the biosynthesis process produces much more T4 than T3
Protein binding: most of both are bound to protein while circulating in blood. Binding to
protein will prevent them from reacting with other enzymes or renal excretion
- Thyroxine binding globulin: about 80% is bound to this
- Free T3 and T4: both are inactive while binding to proteins. those unbound free ones
have effect
Potentness: T3 is 10x more potent than T4 so free T3 is the most potent
Conversion of T4 to T3: In target tissues (liver, kidney, brain, muscle), T4 is converted
to T3 or rT3 by deiodinase. Some T3 will be used right away: some T3 will be used right
away: some T3 will go to blood flow. The reverse T3 (rT3) inactive.
Nongenomic action
receptor is on cell membrane
Genomic action
COMPLETE SOLUTIONS GRADED A++
Folicular cells
Synthesize T3 and T4
Colloid
thyroglobulin (with T3, T4) storage
Regulation of thyroid hormone synthesis
Hypothalamus-(TRH)-Pituitary-(TSH)-Thyroid-(T3,T4)- Target cells
thyroglobulin
tyrosine rich protein
Thyroid hormone synthesis
- Many steps induced by TSH
Step 1. there is enough dietary iodine in blood flow
Step 2. Follicular cells take I- in, and move it into colloids
Step 3. Follicular cells take amino acids into cells to make thyroglobulin rich protein,
Thyroglobulin is moved out to colloid by exocytosis
Step 4. Thyroperoxidases catalyzes production of H2O2, which will be sent to colloid
Step 5. Thyroidperoxidases oxidases iodide to iodine. The iodine reacts with tyrosine of
thyroglobulin (organification)
Step 6. Now there are mixture of monoiodotyrosine and diiodotyrosine within
thyroglobulin
, Step 7. One phenol group of MIT or DIT is added to another phenol group of DIT within
thyroglobulin
Step 8. T3 and T4 within thyroglobulin (with unused MIT, DIT) stored in colloid
Step 9. T3 and T4 within thyroglobulin (w/ unused MIT, DIT) will come back in follicular
cell by endocytosis when thyroid hormone is needed
Step 10. Lysosomal proteases hydrolyze thyroglobulin into T3, T4 iodide and other AAs
Step 11. Iodide and other amino acids will be recycled
Step 12. T3 and T4 are secreted from follicular cells
T3 and T4
Ratio: the biosynthesis process produces much more T4 than T3
Protein binding: most of both are bound to protein while circulating in blood. Binding to
protein will prevent them from reacting with other enzymes or renal excretion
- Thyroxine binding globulin: about 80% is bound to this
- Free T3 and T4: both are inactive while binding to proteins. those unbound free ones
have effect
Potentness: T3 is 10x more potent than T4 so free T3 is the most potent
Conversion of T4 to T3: In target tissues (liver, kidney, brain, muscle), T4 is converted
to T3 or rT3 by deiodinase. Some T3 will be used right away: some T3 will be used right
away: some T3 will go to blood flow. The reverse T3 (rT3) inactive.
Nongenomic action
receptor is on cell membrane
Genomic action
