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MBCHB3: Reproduction, Development and Ageing > Lecture 21: Thyroid > Flashcards

Lecture 21: Thyroid Flashcards

1
Q

What is the function of thyroid hormones:

A

Maintain metabolic activity and oxygen requirements esp. the brain

Regulate lipid and carbohydrate metabolism and thus body weight

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2
Q

Describe the location of the thyroid gland:

A
  • Deep to sternohyoid and sternothyroid muscles
  • Post. is trachea, recurrent laryngeal nerve
  • Sup. thyroid art. (ext carotid) and inf. thyroid art. (subclavian)
  • ANS innervation
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3
Q

What are markers for thyroid cancer?

A 
Colloid = Thyroglobulin
C-cells = Calcitonin
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4
Q

Describe the thyroid structure:

A

Thyroid follicles contains colloid.

C-cells exist around the follicles.

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5
Q

What does dietary iodine deficiency lead to?

A
  • Compensatory enlargement of thyroid
  • If in pregnancy can lead to cretinism (irreversible CNS damage)
  • Supplement iodine if planning pregnancy
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6
Q

Whats the role of iodine in T3,T4 formation?

A
  • Iodine conc. in plasma is extremely low
  • Iodide is trapped by Na-iodide symporter (NIS)
  • Active transport of two Na ions results in the entry of one I molecule against its concentration grafient
  • Thyroid gland contains ~8000 ug iodide

Radioactive iodine (hyperthyroidism?)

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7
Q

Describe the formation of T3,T4:

A

A) TSH dependent transport of iodide sodium iodide transporter. (NIS) (Cap-> follicule gland cell)
B) Iodide transported from the cell into the follicular lumen by pendrin (exchanges for Cl)
C) Iodide ions converted to an oxidised form of iodine, promoted by the enzyme peroxidase
D) Thyroglobulin synthesised in thyroid follicular cell and secreted into the follicular lumen
E) By pinocytosis thyroglobulin enters the thyroid follicular cell, proteases digest thyroglobulin and frees T3,4 and RT3 (enters circulation) - As this happens DIT or MIT (iodine) is cleaved and recycled in follicle cell. (deiodinase enzyme)

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8
Q

Describe iodide oxidation:

A
  • Oxidation of iodine is catalysed by thyroid peroxidase (TPO)
  • In the presence of H2O2, TPO iodinates tyorsine residues in thyroglobulin

TPO is inhibited by carbimazole

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9
Q

Write some notes on thyroglobulin:

A
  • Glycoprotein produced by thyroid follicle cells
  • 1 or 2 Iodine molecules attached (MIT or DIT)
  • T3/4 attached to TG and stored
  • Normally low levels in blood

Cancer marker after surgery

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10
Q

How is T3,4 stored and released?

A
  • ~50day supply T4/T3 incorporated into Tg
  • Degradation of Tg -> T4 or T3 released
  • Thyroid is only place T4 is synthesised. T3 can be formed peripherally by deionisation of T4.
  • T4 and T3 metabolised by many organs esp. liver and kidneys

T4 is main hormone

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11
Q

What can be a clinical issue with T3/4 storage?

A

Thyroiditis can lead to issues with release not production this is treated not with carbimazole

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12
Q

Describe the feedback loop of Thyroid

A

Insert slide 18

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13
Q

What is the most important marker for thyroid dysfunction:

A

TSH is the most important blood test for diagnosing thyroid disease.

(Beta HCG can also stimulate T3,4 because its alpha subunit is same as TSH)

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14
Q

What does TSH stimulate?

A

All aspects of thyroid hormone synthesis:

  • Increase iodide into follicular lumen
  • Increases blood flow
  • Increases Tg, TPO and H2O2
  • Increase3d endocytosis and degredation of Tg
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15
Q

Whats happening in graves disease?

A

TSH AB stimulates TSH receptor and increased T3,4 production (can hear thyroid pulse on stethoscope_

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16
Q

After a thyroidectomy how to you maintain pre-op T3 levels?

A

Give thyroxine (T4 supplement) to suppress TSH slightly

17
Q

Whats happening in thyrotoxicosis:

A

Low TSH, High T4 and T3

18
Q

What are the symptoms of Thyrotoxicosis:

A

Symptoms:

  • Nervousness, increased sweating
  • Weight loss
  • Heat sensitivity
  • Palpitations
  • Weakness
19
Q

What are the signs of thyrotoxicosis:

A
  • Bruit over thyroid, tachycardia
  • Goitre
  • Eye signs
  • Tremor
  • Skin change
20
Q

What are the causes of thyrotoxicosis:

A

Graves disease: Autoimmune production of an antibodu that stimulates TSH receptor

Multinodular goitre: Hyperfunctioning regions of thyroid gland, not suppressed by circulating thyroid hormone

Thyroiditis
Drugs - Iodine, thyroxine, amiodarone
Toxic nodule

21
Q

What is primary hypothyroidism:

A

High TSH, Low T4, +ve TPO ABs = Hashimotos disease

22
Q

Describe the signs of primary hypothyroidism:

A
  • Adult onset is slow
  • Can effect all organ systems
  • Decrease in energy metabolism - low basal metabolic rate +/- slightly low body temp
  • Decreased protein synthesis
23
Q

What happens in hypothyroidism?

A
  • Weight gain
  • Cold
  • Hair loss and dry skin
  • Constipation
  • Tired
  • Oedema

MBCHB3: Reproduction, Development and Ageing (24 decks)

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