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Block 1 Week 1 > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

How many lobes does the thyroid gland have and what joins them together?

A

2 lateral lobes joined together by an isthmus.

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2
Q

Is the thyroid gland in front of or behind the trachea? Which tracheal ring is it near?

A

In front, next to the third tracheal ring.

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3
Q

When a patient swallows, why will the thyroid also move?

A

Because it is attached to/enclosed by the pretracheal fascia.

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4
Q

What are the 3 main arteries supplying the thyroid?

A
  1. Superior thyroid artery
  2. Inferior thyroid artery
  3. Sometimes by the thyroid ima artery
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5
Q

What is the superior thyroid artery a branch of?

A

External carotid artery.

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6
Q

What is the inferior thyroid artery a branch of?

A

Thyrocervical trunk.

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7
Q

What are the 3 main veins of the thyroid?

A
  1. Superior thyroid vein
  2. Middle thyroid vein
  3. Inferior thyroid vein
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8
Q

What are 2 benefits of the thyroid gland having 2/3 main arteries and 3 veins? I.e. quite an extensive blood supply?

A
  1. It means you can do partial thyroidectomies without the undamaged/healthy parts of the thyroid being affected.
  2. It means you should be able to leave the parathyroid glands intact and functioning, even with a total thyroidectomy.
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9
Q

In terms of the microstructure of the thyroid, what is it made of?

A

Follicles.

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10
Q

Which cells surround/create the thyroid follicles?

A

Follicular cells.

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11
Q

What are the size and number of thyroid follicles dependent on?

A

The activity of the thyroid gland.

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12
Q

What is another name for the parafollicular cells of the thyroid? What do they produce?

A

C cells, which produce Calcitonin.

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13
Q

What is the centre of the follicles of the thyroid glands called?

A

Colloid.

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14
Q

What do the follicles of the thyroid gland allow the thyroid to do in terms of hormones?

A

Store large amounts of thyroid hormones ready to secrete when required.

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15
Q

How many hormones does the thyroid gland make and secrete? What are they?

A
  1. Thyroxine
  2. Tri-iodothyronine
  3. Calcitonin
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16
Q

The thyroid hormones are iodinated derivates of what?

A

Tyrosine.

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17
Q

How many iodine molecules are in thyroxine?

A

4 iodine molecules - T4.

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18
Q

How many iodine molecules are in tri-iodothyronine?

A

3 iodine molecules - T3.

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19
Q

Are thyroid hormones lipophilic or lipophobic? What does this mean in terms of how they travel in blood?

A

Lipophilic. They can’t readily dissolve in blood and so need to be bound to proteins.

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20
Q

What are the proteins which bind to thyroid hormones so they can travel in blood, and their relative percentages?

A
  • 70% thyroxine binding globulin (TBG)

- 30% albumin.

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21
Q

What are the 6 broad steps in the synthesis of thyroid hormones?

A
  1. Thyroglobulin synthesis.
  2. Uptake and concentration of iodide (I-).
  3. Oxidation of iodide (I-) to iodine (Io).
  4. Iodination of thyroglobulin.
  5. Coupling of 2 iodinated tyrosine molecules to form MIT and DIT (T4 or T3).
  6. Secretion (and recycling MIT and DIT).
22
Q

Via what mechanism is iodide transported into the follicular cells of the thyroid?

A

Sodium iodide symporter (NIS).

23
Q

Where within the thyroid is iodide oxidised to form iodine?

A

Colloid.

24
Q

Which transporter carries iodide into the colloid/lumen of the thyroid follicles?

A

Pendrin.

25
Q

What is the recommended daily intake of iodine for adults?

A

150 micrograms.

26
Q

What does MIT and DIT stand for once iodine has been conjugated with thyroglobulin?

A

mono-iodotyrosine and di-iodotyrosine.

27
Q

MIT + DIT = ?

DIT + DIT = ?

A

MIT + DIT = T3

DIT + DIT = T4

28
Q

Which enzyme oxidises iodide to form iodine?

A

Thyroid peroxidase.

29
Q

In relation to the hypothalamic-pituitary-thyroid axis, which hormone does the hypothalamus produce in response to a stimulus such as cold?

A

Thyrotropin-releasing hormone (TRH).

30
Q

Where is TRH transported to once it is secreted by the hypothalamus? Once here what does it stimulate the production and secretion of?

A

Transported to the anterior pituitary to stimulate secretion of thyroid stimulating hormone (TSH).

31
Q

How do thyroid hormones enter target cells? Which transporter greatly aids in the uptake of thyroid hormone into the cells?

A

Through diffusion and transporter MCT8(10).

32
Q

What happens to T4 once inside its target cell?

A

It is converted into T3 by the enzyme deiodinase.

33
Q

What happens to T3 once inside target cells?

A

It binds to receptors and moves into the nucleus.

34
Q

By what week of gestation is the foetus making and secreting thyroid hormone?

A

Week 12.

35
Q

Can congenital hypothyroidism be reversed? How is this investigated?

A

It can be reversed within the first 2 years of life, but not after that. In the UK there is a TSH heel prick test for babies.

36
Q

List 3 ways thyroid hormones affect cellular/ enzyme activity in adults.

A
  1. Within the cell membrane - Na+K+ATPase.
  2. Within the mitochondria - respiratory enzymes.
  3. Within the cell nucleus.
37
Q

Thyroid hormones affect the activity of enzymes in the body. What 3 effects does this have?

A
  1. Increased metabolic rate
  2. Increased energy production
  3. Increased O2 consumption
38
Q

In primary hyper/hypothyroidism, where is the problem?

A

With the thyroid or iodine supply.

39
Q

In secondary hyper/hypothyroidism, where is the problem?

A

With the anterior pituitary gland or hypothalamus.

40
Q

What type of diseases are Graves’ disease and Hashimoto’s thyroiditis?

A

Autoimmune diseases.

41
Q

List some symptoms of hyperthyroidism.

A
  1. Heat intolerance, sweating, moist hands, warm
  2. Weight loss despite high appetite
  3. Diarrhoea
  4. Palpitations/ rapid pulse
  5. Tiredness/ weak muscles
  6. Nervousness, irritability, mood swings, shakiness
  7. Thirst and polyuria
  8. Goitre
42
Q

What is the pathology Graves Disease?

A

The body produces an auto-antibody which binds to the TSH receptor.

43
Q

What will you expect to see in the diagnosis of hyperthyroidism in terms of T3/T4 and TSH levels?

A

High levels of T3/T4

Low levels of TSH

44
Q

List some symptoms of hypothyroidism.

A
  1. Fatigue and tiredness
  2. Sensitivity to the cold
  3. Constipation
  4. Dry skin and hair (alopecia)
  5. Low mood and mental slowness
  6. Goitre
  7. Overweight/obese
  8. Heavy periods and fertility problems
45
Q

What will you expect to see in the diagnosis of hypothyroidism in terms of T3/T4 and TSH levels?

A

Low levels of T4 and T3.

Usually high levels of TSH.

46
Q

What is a goitre?

A

A swelling of the neck resulting from enlargement of the thyroid gland.

47
Q

What are 3 causes of a goitre?

A
  1. Iodine deficiency (low levels of T4)
  2. Graves disease (high levels of T4).
  3. Tumour (benign or cancer).
48
Q

What is the first step in a thyroid function test? What is the next step after this if the results are abnormal?

A

Measure serum levels of TSH. If abnormal then measure levels of free T4 and T3.

49
Q

What do both low TSH and T4 levels indicate as the diagnosis?

A

Secondary hypothyroidism - pituitary problem.

50
Q

What are 3 treatment options for hyperthyroidism?

A
  1. Drugs which inhibit production of thyroid hormones.
  2. Radioactive iodine to destroy the gland
  3. Surgery
51
Q

What are the treatment options for hypothyroidism?

A

Replacement hormones - levothyroxine (synthetic T4) and liothyronine (synthetic T3). Most commonly used is levothyroxine.

Block 1 Week 1 (10 decks)

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