Thyroid Gland

Question 1

At what vertebral level is the Thyroid gland located?

Answer 1

C5 & T1

Question 2

What are the hormones released from the thyroid gland?

2

Answer 2

T3 = Triiodothyronie 
T4 = Thyroxine

Question 3

What are the cell types (and secretions) in the thyroid?

Answer 3

C (clear) cells - Calcitronin
Follicular cells - support hormone synthesis (surround hollow follicles)

Hollow follicles contain the inactive thyroid hormones

Question 4

What do the Follicular cells manufacturer?

Answer 4

Enzymes which make thyroid hormones

Thyroglobulin (rich in tyrosine residues)

Concentrate iodide from the plasma

Question 5

Where does the body receive Tyrosine and Iodide from?

Answer 5

The Diet

Question 6

How does Iodide get taken into cell?

Answer 6

Against the concentration gradient as it being taken up to concentrate
Symport system with Na

Question 7

What enzyme catalase the addition of Tyrosine and Iodine to make either T3 or T4 through oxidation

Answer 7

Thyroid Peroxidase

Question 8

How are T3 & T4 stored?

Answer 8

Bonded with thyroidgnobulin to stop it being lipophilic

Question 9

How are T3 & T4 released?

Answer 9

Thyroid stimulating hormone released from the pituitary
Endocytosis takes up Hormones in inactive form
Enzymes cut through thyroglobulin
Move into the blood as the active hormone
Bind to plasma proteins - Tyrosine binding protein (steroid hormones)

Question 10

How many months supply is kept in the follicles?

Answer 10

3-4 months

Question 11

What is the half life of T3 & T4?

Answer 11

T4 - 6 Days (binging protein has a higher affinity)

T3 - 1 Day

Question 12

Which thyroid hormone has a higher affinity for the receptors?

Answer 12

T3 (90%)

Question 13

What type of receptors are present for Thyroid hormones?

Answer 13

Intacellular

Question 14

What does a Deidonase enzyme do?

Answer 14

Removes an Iodine from T4 making it T3

Question 15

Where does T4 becomes deiodonated?

Answer 15

50% outside and 50% inside (means that T3 isn’t actually required to be secreted from the thyroid)

Question 16

What are the functions of thyroid hormones?

Answer 16

Raises metabolic rate 
Increases hepatic gluconeogenisis (but only is there is insulin present) 
Net increase in Proteolysis
Permissive to Growth hormones 
Net increase in Lipolysis

Question 17

What causes Hyperthyroidism?

Answer 17

Graves disease (antibodies mimic TSH)

• High levels of T3 & T4
• Negative feedback leads to very low actual TSH

Thyroid Adenoma

Question 18

What are symptoms of Hyperthyroidism?

Answer 18

Increase metabolic rate
- Weight loss and warm (heat intolerance)

Increase protein catabolism
- Muscle weakness/loss

Altered nervous system
- Hyper excitable reflexes

Elevated CV function (TH permissive to Epinephrine Beta receptors)
- Increased HR/Contractile force/ High output

Goiter formation

Question 19

What causes Hypothyroidism?

Answer 19

Hashmoto’s Disease
- Auto-imminue attack of thyroid gland

Iodine difficient
- Needed for synthesis of T3/4

Idiopathic (thyroiditis)

Question 20

What are symptoms of Hypothyroidism?

Answer 20

Increase metabolic rate
- Weight gain and cold intolerance)

Decresed protein catabolism
- Brittle nails and thin skin

Altered nervous system
- Slow speech and reflexes

Reduced CV function (TH permissive to Epinephrine Beta receptors)
- Slower HR/Weaker pules

Goiter formation

Question 21

What causes Goiter formation?

Answer 21

Both Hyper and Hypothyroidism causes over stimulation of thyroid gland causing Hypertrophy of the cells