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Endocrinology > 6 - The thyroid and iodothyronines > Flashcards

6 - The thyroid and iodothyronines Flashcards

1
Q

How many lobes does the thyroid gland have?

A

2

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2
Q

Where is the thyroid gland located?

A

On the trachea at the front of the neck.

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3
Q

What are the 2 physical structures in the middle of the thyroid gland called?

A

The pyramid

Isthmus

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4
Q

Where are the parathyroid glands found? What do they release?

A

At the top and bottom of each lobe.

They release PTH (parathyroid hormone)

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5
Q

How are the cells in the thyroid arranged?

A

Follicles - Follicular cells arranged around the colloid.

Parafollicular cells are arranged around the follicles

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6
Q

What do parafollicular cells secrete?

A

Calcitonin

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7
Q

What receptor does TSH bind to?

A

TSHR

TSH receptor

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8
Q

What does this TSH stimulate?

A
  • Iodine uptake into the follicular cell through the basolateral membrane.
  • Synthesis of thyroglobulin (TG)
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9
Q

What happens to the iodine that inters the follicular cell?

A

It leaves through the apical membrane into the colloid.

It is added to amino acids (tyrosine).

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10
Q

What is iodination?

A

When iodine is added to amino acids (tyrosine)

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11
Q

What are MID and DIT?

A

MID - monoiodotyrosine

DIT - diiodotyrosine

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12
Q

What is a coupling reaction?

A

When MID and DIT bind:

MID + DIT = T3 (tri-iodothyrine)

DIT + DIT = T4 (tetra-iodothyrine)

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13
Q

What happens to T3 and T4?

A

They are secreted into the blood through the basolateral membrane?

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14
Q

What must happen to T4?

A

It must be converted into an active form of T3 (deiodinated).

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15
Q

Why is there an active and inactive form of T3?

A

The iodines are in the incorrect position in the inactive T3.

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16
Q

What is the mechanism of action of T3?

A
  1. Enters cell
  2. Stimulates metabolic activity in mitochondria
  3. THR receptor
  4. Transcription & protein synthesis
17
Q

How are thyroid hormones transported in the blood?

A

Bound to plasma proteins

  • Thyroid binding globulin (TBG)
  • Albumin
  • Prealbumin

Some are unbound (bioactive components)

18
Q

What are the actions of TH?

A
  • Fetal growth & development
  • Untreated congenital hypothyroidism: cretinism
  • TH and TSH measured in new borns heel prick test.
  • Increase basal metabolic rate
  • Protein carb and fat metabolism
  • Potentiate actions of catecholamines (tachycardia, lipolysis)
  • Effects on GI, CNS, reproductive system.
19
Q

What are the latent periods for T3 an T4?

A

T3: 12 hours
T4: 72 hours

20
Q

What are the half lives of T3 and T4?

A

T3: 2 days
T4: 7-9 days

21
Q

Draw the control of TH production axis.

A

Drawing

Endocrinology (18 decks)

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