Thyroid Gland Flashcards
At what vertebral level is the Thyroid gland located?
C5 & T1
What are the hormones released from the thyroid gland?
2
T3 = Triiodothyronie T4 = Thyroxine
What are the cell types (and secretions) in the thyroid?
C (clear) cells - Calcitronin
Follicular cells - support hormone synthesis (surround hollow follicles)
Hollow follicles contain the inactive thyroid hormones
What do the Follicular cells manufacturer?
Enzymes which make thyroid hormones
Thyroglobulin (rich in tyrosine residues)
Concentrate iodide from the plasma
Where does the body receive Tyrosine and Iodide from?
The Diet
How does Iodide get taken into cell?
Against the concentration gradient as it being taken up to concentrate
Symport system with Na
What enzyme catalase the addition of Tyrosine and Iodine to make either T3 or T4 through oxidation
Thyroid Peroxidase
How are T3 & T4 stored?
Bonded with thyroidgnobulin to stop it being lipophilic
How are T3 & T4 released?
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)
How many months supply is kept in the follicles?
3-4 months
What is the half life of T3 & T4?
T4 - 6 Days (binging protein has a higher affinity)
T3 - 1 Day
Which thyroid hormone has a higher affinity for the receptors?
T3 (90%)
What type of receptors are present for Thyroid hormones?
Intacellular
What does a Deidonase enzyme do?
Removes an Iodine from T4 making it T3
Where does T4 becomes deiodonated?
50% outside and 50% inside (means that T3 isn’t actually required to be secreted from the thyroid)
What are the functions of thyroid hormones?
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
What causes Hyperthyroidism?
Graves disease (antibodies mimic TSH)
- High levels of T3 & T4
- Negative feedback leads to very low actual TSH
Thyroid Adenoma
What are symptoms of Hyperthyroidism?
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
What causes Hypothyroidism?
Hashmoto’s Disease
- Auto-imminue attack of thyroid gland
Iodine difficient
- Needed for synthesis of T3/4
Idiopathic (thyroiditis)
What are symptoms of Hypothyroidism?
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
What causes Goiter formation?
Both Hyper and Hypothyroidism causes over stimulation of thyroid gland causing Hypertrophy of the cells
