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Endocrine > Thyroid physiology > Flashcards

Thyroid physiology Flashcards

1
Q

What is the microanatomy of the thyroid?

A

Divided into segments called thyroid follicles

C cells are also present

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2
Q

What is the structure of a thyroid follicle?

A

Circular hollow ball.

Surface is made up of follicular cells

Centre is filled with colloid (protein rich material)

Surrounded by capillaries

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3
Q

What are the 2 hormones that the thyroid produces?

A

T3 - triiodothyronine

T4 - thyroxine

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4
Q

Which thyroid hormone does the thyroid produce the most?

A

T4 - thyroxine

90% of total amount

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5
Q

Which thyroid hormone is more potent (powerful)?

A

T3 - triiodothyronine

4X more potent

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6
Q

What is the purpose of the capillaries surrounding each follicle?

A

To deliver iodide molecules to the cells

Release site for the thyroid hormones once they’ve been produced.

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7
Q

Why are iodide molecules needed? And where do they come from?

A

Essential because both T3 and T4 need them as part of their structure.

Come from diet or tap water

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8
Q

How do iodide ions enter the follicular cells?

A

By a sodium-iodide symporter - iodide ions enter cells against their concentration gradient (active transport)

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9
Q

Describe what happens in the colloid of a thyroid follicle to produce T3 and T4?

A
  1. Iodide enters colloid and is oxidised into iodine
  2. Iodine attaches to rings of tyrosines within thyroglobulin
  3. Either 1 or 2 iodines are added forming T1 and T2 respectively
  4. The joining of two T2 molecules forms T4
    The joining of one T1 and one T2 forms T3
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10
Q

What is thyroglobulin?

A

A protein found in the colloid of the follicular cells

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11
Q

How are T3 and T4 molecules stored in the thyroid?

A

In the colloid bound to thyroglobulin

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12
Q

How does T3 and T4 get out of the colloid and into the blood?

A
  1. Endocytosis occurs so T3 & T4 bound with thyroglobulin go into a vesicle
  2. Lysosomes bind to the vesicle releasing T3 & 4 from thyroglobulin
  3. T3 & 4 is released from the vesicle and diffuses across the cell membrane into bloodstream
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13
Q

What does T4 - thyroxine do?

A

Regulates metabolism
Up regulates adrenergic receptors
Needed to produce growth hormone

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14
Q

What do the C cells produce?

A

Calcitonin

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15
Q

What does calcitonin do?

A

Acts to reduce calcium levels in the blood

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16
Q

How does calcitonin reduce calcium levels in the blood?

A

More calcitonin = less calcium

  • Decreases gut absorption of Ca
  • Inhibits osteoclast activity
  • Stimulates osteoblast activity

Endocrine (8 decks)

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