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Cell Biology > Thyroid Glands > Flashcards

Thyroid Glands Flashcards

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1
Q

Name the 4 roles thyroid hormone has

A

1- increases cardiac output/heart rate

2- increases metabolic rate

3- neurological role

4- growth and development

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2
Q

How does thyroid hormone increase cardiac heart rate

A

By working synergistically with epinephrine(adrenaline)

= upregulating adrenergic receptors (binding to epinephrine and norepinephrine produced in adrenal medulla for increase HR)

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3
Q

What 2 ways does thyroid hormone increase metabolic rate

A

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

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4
Q

How does thyroid hormone have importance in neurology

A

Allows mental stability

Better reflexes and alertness

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5
Q

How does thyroid hormone have effect on growth and development

A

It increases growth hormone production = growth of bones etc

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6
Q

Name the 3 thyroid hormones produced

A

T3 - triiodothyronine

T4- tetraiodothyronine

Calcitonin

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7
Q

What is calcitonin important for

A

Calcium homeostasis

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8
Q

What type of hormone is T4 and T3 and what is it produced by

A

Amino acid hormones

(Thyroxine)

Tyrosine residue is iodinated by 4 iodine residues in T4 and T3 has 3 iodine residues

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9
Q

Name the 3 blood vessels at the thyroid gland

A

Thyroid arteries
Thyroid veins

Carotid artery (important for HR)

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10
Q

Why is it important for thyroid glands to have rich blood supply

A

For AA and iodine provided via blood

And also to transport T3 and T4

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11
Q

Where are 2-4 parathyroid glands found and what hormones do they produce

A

At the back on the thyroid glands

Produce calcitonin again for calcium homeostasis

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12
Q

Explain the intracellular structure of the thyroid glands and where is hormone stored

A

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

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13
Q

What is thyroglobin and where is it synthesised and then released

A

Glycoproteins rich in tyrosine residues

Produced by dna from the follicle cells

They then release them to the colloid proteinase

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14
Q

Which enzyme allows iodination (adding of iodine 1 or 2) to thyroglobins at the apical membrane between colloid and follicle cells

A

Thyroperoxidase

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15
Q

What produces thyroperoxidase enzyme which produces T1 and T2 from thyroglobin

A

The follicle cells via their dna

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16
Q

How is iodine actually transported to follicle cells ready to produce T1 and T2

A

The I/Na + transporter from the blood to the follicle cells

17
Q

What is needed to couple with 2x T2 to produce T4 or 1x T1 and 1xT2 to produce t3

A

Thyroperoxidase enzyme

Adds iodine to tyrosine residues on thyroglobin

18
Q

What is the proper name for precursors T1 and T2 which produce thyroxines

A

T1 = monoiodotyrosine (1 iodine)

T2= di iodotyrosine (2 iodine)

19
Q

Explain the steps of how T3 and T4 from thyroglobin in the colloid reach the blood stream

A

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

20
Q

What happens to T1 and T2 when thyroglobin is digested by lysosomes

A

They are recycled back into tyrosine for the next production of T3 and T4

21
Q

How much free form T3 or T4 is there in the blood which then act on receptors

A

0.4%

22
Q

What happens when there is less free form Thyroxine in the blood

A

Equilibrium- the bound proteins dissociate to allow new free form thyroxine

23
Q

Name the 3 thyroid binding proteins and their properties

A

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

24
Q

Which thyroid binding protein allows for free hormones to be produced

A

Albumin

25
Q

Explain the steps of thyroxine production from the hypothalamus

A

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

26
Q

How does TSH from anterior pituitary allow release of T3 and T4

A

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

27
Q

What increases follicle cell size into cuboid shape

A

More T3 and T4 (when lysosome degrades the colloid thyroglobin)

28
Q

How is most of T3 produced and why is it produced that way

A

T4 metabolism (deiodinated into T3)

Because more T4 is produced than T3

29
Q

Which 2 enzymes produce T3 from T4 by removing 1 iodine

A

1 5’ deiodinase = more t3 in blood

2 5’ deiodinase = more t3 in the CNS (brain) eg for neural activity

30
Q

Which enzyme inactivates thyroxine by converting T4 into rT3

A

3 5’ deiodinase

31
Q

Why is rT3 inactive compared to T3

A

Iodine residues removed is on the inner ring compared to outer ring of T3

= receptors don’t recognise it

32
Q

Which type of receptors does thyroxine bind to

A

Intracellular receptors (hydrophobic)

33
Q

Name the 4 thyroid binding receptors and what they bind to

A

Alpha 1 and 2 (alpha 2 is only one that binds to T4 better)

Beta 1 and 2 (both bind to T3 most)

34
Q

Why is T3 preferred

A

Because alpha 1 and beta 1 and 2 receptors recognise it most

35
Q

What happens when T3 is bound to intracellular receptors (usually bound to dna to stop transcription) and what effects

A

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

Cell Biology (21 decks)

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