Thyroid Glands Flashcards
Name the 4 roles thyroid hormone has
1- increases cardiac output/heart rate
2- increases metabolic rate
3- neurological role
4- growth and development
How does thyroid hormone increase cardiac heart rate
By working synergistically with epinephrine(adrenaline)
= upregulating adrenergic receptors (binding to epinephrine and norepinephrine produced in adrenal medulla for increase HR)
What 2 ways does thyroid hormone increase metabolic rate
1- allows production of erythropoietin in kidneys which produces more RBCs for more oxygen carrying
2- increases respiratory rate of oxygen intake
= allows glycolysis etc
How does thyroid hormone have importance in neurology
Allows mental stability
Better reflexes and alertness
How does thyroid hormone have effect on growth and development
It increases growth hormone production = growth of bones etc
Name the 3 thyroid hormones produced
T3 - triiodothyronine
T4- tetraiodothyronine
Calcitonin
What is calcitonin important for
Calcium homeostasis
What type of hormone is T4 and T3 and what is it produced by
Amino acid hormones
(Thyroxine)
Tyrosine residue is iodinated by 4 iodine residues in T4 and T3 has 3 iodine residues
Name the 3 blood vessels at the thyroid gland
Thyroid arteries
Thyroid veins
Carotid artery (important for HR)
Why is it important for thyroid glands to have rich blood supply
For AA and iodine provided via blood
And also to transport T3 and T4
Where are 2-4 parathyroid glands found and what hormones do they produce
At the back on the thyroid glands
Produce calcitonin again for calcium homeostasis
Explain the intracellular structure of the thyroid glands and where is hormone stored
Single layer of follicle cells surrounding a colloid protein
Hormone is stored in the colloid protein
Within follicle cells there are C cells for calcitonin production
What is thyroglobin and where is it synthesised and then released
Glycoproteins rich in tyrosine residues
Produced by dna from the follicle cells
They then release them to the colloid proteinase
Which enzyme allows iodination (adding of iodine 1 or 2) to thyroglobins at the apical membrane between colloid and follicle cells
Thyroperoxidase
What produces thyroperoxidase enzyme which produces T1 and T2 from thyroglobin
The follicle cells via their dna
How is iodine actually transported to follicle cells ready to produce T1 and T2
The I/Na + transporter from the blood to the follicle cells
What is needed to couple with 2x T2 to produce T4 or 1x T1 and 1xT2 to produce t3
Thyroperoxidase enzyme
Adds iodine to tyrosine residues on thyroglobin
What is the proper name for precursors T1 and T2 which produce thyroxines
T1 = monoiodotyrosine (1 iodine)
T2= di iodotyrosine (2 iodine)
Explain the steps of how T3 and T4 from thyroglobin in the colloid reach the blood stream
Some colloid is taken up by follicle cells in PINOCYTOSIS
lysosomes in the cell then degrade thyroglobin
Releases T1,T2,3 and 4
T3 and T4 then transport into the blood freely as they can pass membrane (tyrosine= hydrophobic)
They then associate with thyroid binding proteins because they are hydrophobic so need protection
What happens to T1 and T2 when thyroglobin is digested by lysosomes
They are recycled back into tyrosine for the next production of T3 and T4
How much free form T3 or T4 is there in the blood which then act on receptors
0.4%
What happens when there is less free form Thyroxine in the blood
Equilibrium- the bound proteins dissociate to allow new free form thyroxine
Name the 3 thyroid binding proteins and their properties
1- thyronine binding pre albumin - binds with high affinity to both T3 and T4
2 thyronine binding albumin - binds more to T4
3- albumin - rapid dissociation of both hormones
Which thyroid binding protein allows for free hormones to be produced
Albumin
Explain the steps of thyroxine production from the hypothalamus
Hypothalamus reciebes signal to produce more thyroxine hormone
Parvocellular neurones produce and release thyrotropin release hormone which goes down hypophyseal blood vessel to anterior pituitary
Anterior pituitary releases TSH
Released into blood
Causes T3 and T4 increase in blood
= negative feedback where hypothalamus will then stop thyrotropin release hormone
How does TSH from anterior pituitary allow release of T3 and T4
Increases iodine uptake by increasing channels
Then increases thyroglobin production via upregulating transcription in follicle cells
Increases amount of thyroperoxidase which increases iodination of thyroglobin tyrosine residues
This then allows more T3 and T4 production by the coupling of T1 and T2 by thyroperoxidase
Increased pinocytosis of colloid into the follicle cells
T3 and T4 is then released due to increased lysosome digestion of thyroglobin in colloid
What increases follicle cell size into cuboid shape
More T3 and T4 (when lysosome degrades the colloid thyroglobin)
How is most of T3 produced and why is it produced that way
T4 metabolism (deiodinated into T3)
Because more T4 is produced than T3
Which 2 enzymes produce T3 from T4 by removing 1 iodine
1 5’ deiodinase = more t3 in blood
2 5’ deiodinase = more t3 in the CNS (brain) eg for neural activity
Which enzyme inactivates thyroxine by converting T4 into rT3
3 5’ deiodinase
Why is rT3 inactive compared to T3
Iodine residues removed is on the inner ring compared to outer ring of T3
= receptors don’t recognise it
Which type of receptors does thyroxine bind to
Intracellular receptors (hydrophobic)
Name the 4 thyroid binding receptors and what they bind to
Alpha 1 and 2 (alpha 2 is only one that binds to T4 better)
Beta 1 and 2 (both bind to T3 most)
Why is T3 preferred
Because alpha 1 and beta 1 and 2 receptors recognise it most
What happens when T3 is bound to intracellular receptors (usually bound to dna to stop transcription) and what effects
It changes the amount of protein expression via transcription allowance
This is for things like increasing transcription of mitochondrial coupling proteins
For heat and energy
For increased metabolic rate
Increased heart rate
