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LSM3214 > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Where is the thyroid gland located?

A

In the neck

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2
Q

What is the colour of the thyroid gland and why?

A

Red, due to extensive blood supply and circulation

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3
Q

What is the function of the follicle cell?

A

Secretes thyroglobulin into the colloid

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4
Q

What is the function of the colloid?

A

An extracellular space where thyroglobulin with attached iodine atoms are stored

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5
Q

What is the thyroid follicle?

A

The combination of follicle cells and colloid, serving as the functional unit for thyroid hormone production

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6
Q

What makes up the thyroid hormone?

A

Tyrosine + Iodine

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7
Q

Where is tyrosine obtained from?

A

Synthesised by the body, cannot be obtained from diet

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8
Q

Where is iodine obtained from?

A

Must be obtained from dietary intake

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9
Q

What is the process of Thyroglobulin formation?

A

Follicle cells produce Tg with tyrosine incorporated.
Exported into the colloid via exocytosis

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10
Q

How is iodine absorbed?

A

Iodide from the blood is captured by the thyroid and transferred into the colloid by a Na+ K+ pump where Na+ and I- is coupled

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11
Q

What is the mode at which iodide is passed to colloids and why?

A

Active transport against its concentration to ensure full uptake

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12
Q

What transformation does iodide undergo and by which enzyme?

A

Iodide is oxidised into active iodide by membrane bound thyroperoxidase (TPO)

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13
Q

How is iodide attached to Tg?

A

Iodide enters the colloid via a channel and is attached to tyrosine within the thyroglobulin molecule by TPO

iodide + tyrosine in Tg = mono-iodityrosine
2 iodide + tyrosine = di-iodotyrosine

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14
Q

How does T3/T4 form?

A

Iodo-tyrosine molecuels are coupled!
MIT + DIT = T3, DIT + DIT = T4

MIT + MIT does not occur!

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15
Q

What is the mechanism of TH release?

A

With appropriate stimulation, follicular cells phagocytose a piece of colloid to internalise the Tg-hormone complex

Engulfed vesicle is attacked by lysosomes, splitting the iodinated products from Tg (i.e. MIT, DIT, T3, T4)

T3&4 diffuse through outer membranes of the follicular cells and into the blood

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16
Q

How is TH stored in the plasma?

A

Bound to plasma proteins

17
Q

How is TH stored in the colloid?

A

Bound to thyroglobulin

18
Q

Which TH molecule is more active?

A

T3 is active, derived from T4

19
Q

Where does T4 to T3 conversion occur?

A

Mainly in the liver, kidney and pituitary

20
Q

What is the feedback loop that TH has?

A

Negative feedback loop

21
Q

What is the function of the hypothalamus?

A

Secretes thyrotropin releasing hormone (TRH)

22
Q

What is the function of the anterior pituitary gland?

A

Secretes thyroid stimulating hormone (TSH)

23
Q

What is the effect of TH on metabolic rate and heat/sweat production?

A

High TH = High BMR due to:
- More O2 consumption & energy use under resting conditions (more mitochondria etc. for oxidative phosphorylation)
- Higher heat production due to increased metabolic effects

24
Q

What is the sympathomimetic effect of TH?

A

TH simulates sympathetic actions, such as increased heart rate and higher cell responsiveness to catecholamines

25
Q

What are causes of hypothyroidism?

A
  1. Failure of the thyroid gland
  2. Secondary deficiency of TRH, TSH or both
  3. Inadequate iodine supply
26
Q

What are common symptoms?

A

Weight gain (due to low BMR), extreme fatigue, intolerance to cold

27
Q

What is cretinism?

A

Infant hypothyroidism, which can lead to dwarfism and mental retardation

28
Q

What is myxedemia?

A

Adult hypothyroidism, causing low body temperature, lethargy, muscular weaknesses and slow reflex.

29
Q

What are causes of hyperthyroidism?

A
  1. Hypersecreting thyroid tumour
  2. Production of TSI (most common!!)
  3. Secondary excess of TRH, TSH or both
30
Q

What is TSI and how does it lead to hyperthyroidism?

A

TSI is an antibody which binds to TSH receptors, thereby mimicking TSH activity, leading to increased thyroid growth and secretion.

However, TSI is not subjected to the negative feedback inhibition by TH, so TH secretion continues!

31
Q

What is goitre?

A

Enlarged thyroid gland due to overstimulation

32
Q

In which cases of hyper and hypothyroidism is goitre present?

A

Hypothyroidism: Failure of thyroid gland, lack of dietary I- (because stimulation is still there!)

Hyperthyroidism: Presence of TSI, excess TSH/TRH secretion

33
Q

What is the mechanism of action of anti-thyroid drugs as a mode of treatment for hyperthyroidism?

A

Anti-thyroid drugs interfere with TH synthesis (e.g. block I- uptake or inhibits TPO which helps conversion)

34
Q

How does administration of radioactive iodine as a treatment for hyperthyroidism work?

A

Radioactive iodine is picked up by thyroid cells, enters the colloid and destroys the forming TH

LSM3214 (5 decks)

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