Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

RDA > Lecture 17 - 2018/2017 > Flashcards

Lecture 17 - 2018/2017 Flashcards

1
Q

What are the functions of the thyroid?

A
  1. Normal growth and development.
  2. Maintain metabolic activity (heat production) and oxygen requirements - determines your metabolic rate and critical for brain development.
  3. Regulate lipid and carbohydrate metabolism and thus body weight.
  4. Increased HR, SV, CO, peripheral vasodilation, increased pulse pressure when increased thyroid hormone.
  5. Control of thyroid hormone is by the HPO axis.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the thyroid consist of?

A

2 lobes (20g per lobe) that are connected by the isthmus. The thyroid is 4cm long and 2cm wide.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where is the thyroid located?

A

In front of the larynx in the neck.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What supplies the thyroid blood supply?

A

Superior (external carotid) and inferior (subclavian) thyroid artery.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What innervates the thyroid?

A

ANS innervation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the thyroid deep to?

A

Sternohyoid muscle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is posterior to the thyroid?

A

Recurrent laryngeal nerve and tracheal cartilage ring 2 and 3.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is to the left of the thyroid?

A

Oesophagus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the embryology development of the thyroid?

A

It originates from the pharyngeal gut. The thyroid descends down from the pharynx to its final location in front of the larynx.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

When is the thyroid functional?

A

By 12 weeks of gestation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When is the thyroid independent of the mother’s thyroid functions?

A

By 20-26 weeks gestation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Describe the embryology development of the thyroid in weeks?

A

Week 4 - thyroid starts to appear.
Week 5 - thyroglossal duct breaks down and gland descends.
Week 7 - the thyroid migrates anterior to the trachea.
Week 10 - the thyroglossal duct disappears.
Week 12-20 - thyroid is functional.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is a lingual thyroid?

A

When there is a little residual thyroid at the back of the tongue (failure to migrate). It can also be when the thyroglossal duct remnants are left behind. It is not uncommon to get cystic structures in the thyroglossal duct remnants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What do patients with a thyroglossal cyst present with?

A

Lump in the midline which moves with swallowing/poking tongue out (because thyroglossal duct is attached to the back of the tongue).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the thyroid full of?

A

Colloid - viscous clear colloured fluid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is colloid?

A

Colloid is mostly glycoprotein and full of glycoprotein thyroglobulin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe thyroid histology?

A

A follicle is formed by a single layer of hormone producing cuboidal epithelial cells forming a circle with lumen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How many follicles are in a gland?

A

20-40 follicles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is thyroglobulin?

A

It is a protein that stores thyroid hormone (T3/T4). The thyroid hormone attaches to thyroglobulin and sits in the thyroid ready for action.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How much T3/T4 does the thyroid store?

A

Around 50 days worth of thyroid hormone.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What do parafollicular cells secrete?

A

Calcitonin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is thyroiditis?

A

Inflammatory condition of the thyroid. The thyroid is inflamed therefore it has elevated levels of thyroglobulin hence an increase in T3/T4 (thyroid hormone). Pts with this would have high levels of thyroglobulin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What do patients with differentiated thyroid cancer present with?

A

Lump in the neck and elevated serum thyroglobulin. The thyroglobulin can be used as a tumour marker.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is factitious thyrotoxicosis?

A

This is where someone is taking thyroid hormone deliberately and subsequently making themselves thyrotoxic.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What does someone with factitious thyrotoxicosis present with?

A

Weight loss and typical features of an overactive thyroid. Serum thyroglobulin levels are very suppressed because the thyroid has gone to sleep.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are the follicular cells?

A

These are the cells in the thyroid that are filled with colloid. They are cuboidal, but when TSH is secreted (active thyroid) the cells become columnar and the lumen side becomes scalloped due to endocytosis of hormone containing colloid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How do you determine malignancy of the thyroid?

A

Fine needle aspiration.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are parafollicular cells (C cells)?

A

These are cells next to follicular cells (between them). They produce calcitonin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What happens to calcitonin when the thyroid is removed?

A

Calcitonin levels decrease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is medullary thyroid cancer?

A

Aggressive thyroid cancer that metastasises and doesn’t respond to radioactive iodine. It is a cancer of the parafollicular cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What does a patient with medullary thyroid cancer present with?

A

High calcitonin levels (tumour marker) and a lump in the neck.

32
Q

How much dietary iodine do we need per day?

A

150 micrograms.

33
Q

Where does our dietary iodine come from?

A

Soil and secondarily through dairy - iodine in soil, cows eat grass, we drink cows milk etc.

34
Q

What can iodine deficiency lead to?

A
  1. Compensatory enlargement of the thyroid (endemic goitre).
  2. In pregnancy, the maternal iodine levels are low so the fetal levels will drop as well. This may lead to the fetal thyroid not developing properly and it can cause irreversible damage to the developing CNS e.g. cretinism.
35
Q

What is thyroid hormone also known as?

A

T4 (4 molecules of iodine). T4 is then converted to T3 (3 molecules of iodine).

36
Q

Describe thyroid hormone synthesis?

A

90% of thyroid hormone produced in the thyroid gland is T4 with the remaining as T3. Most T3 bound to proteins such as thyroid binding globulin and albumin acts as a buffer against acute changes in T4 production and for iodine recycling.

37
Q

What is the concentration of iodide in plasma?

A

Extremely low - 10-15 micrograms per mL.

38
Q

How does the thyroid take up iodide?

A

The thyroid takes up the iodide by a sodium/iodide symporter (NIS). NIS takes up 2 sodium ions and 1 iodide ion (against its conc gradient - goes from low to high).

39
Q

How much iodide does the thyroid gland contain?

A

8000 micrograms - the store of iodide in our thyroid protects us from severe iodide deficiency.

40
Q

What is pendred syndrome?

A

Where a person has a genetic mutation of the pendrin transporter. They present with hypothyroidism and deafness.

41
Q

What does the pendrin transporter do?

A

It’s a transporter in the lumen surface membrane (membrane separating the cell and colloid) that takes tyrosine molecules and moves it from the cell and into the colloid.

42
Q

Describe iodine oxidation?

A

Iodide that is transported into the follicular cell is converted to iodine by thyroid peroxidase (TPO). In the presence of hydrogen peroxide TPO iodinates tyrosine residues on thyroglobulin (Tg) in colloid. Iodine attacges to tyrosine residues and iodinates them into monoiodotyrosine (MIT) and di-idotyrosine (DIT). MIT and DIT are still attached to the thyroglobulin.

43
Q

How is T3 and T4 are made?

A

Thyroid hormone is manufactured by puitting bits of MIT and DIT - T3 and T4 are stored in the colloid bound to the thyroglobulin.

  1. MIT + DIT = T3 (active) + reverse T3 (no function).
  2. DIT + DIT = T4 (most of the time you make T4 in your thyroid).
44
Q

What are patients with an overactive thyroid given?

A

Carbimazole - it inhibits the peroxidase enzyme, thus reducing the uptake of iodine into the thyroid.

45
Q

What is sick euthyroid syndrome?

A

Where metabolism to T3 is altered - there is a lot more reverse T3 being produced (iodine is taken off at the 3 prime position), so the circulating T3 levels are low. However, because there are high levels of reverse T3 in the blood, the pituitary thinks everything is normal so TSH will be normal.

46
Q

Describe the release of T4/T3?

A

This is under the regulation of TSH.

  1. T3/T4 release involves endocytosis of thyroglobulin (colloid) from the follicular space. 2. Endosomes fuse with lysosomes.
  2. Degradation of thyroglobulin in thyroid (T4 or T3 is released.
47
Q

What happens when T4 is released from the thyroid?

A

It circulates around the body in the blood and when it reaches the target organ (especially the liver and the kidney) it locally turns into T3.

48
Q

How is the thyroid hormone excreted?

A

It is metabolised, broken down and excreted by the liver and the kidneys.

49
Q

Summarise thyroid hormone being made?

A
  1. Dietary iodine gets into the follicular cell via the NIS.
  2. Iodine in the colloid attaches to tyrosine residues via TPO forming DIT and MIT (still attached to thyroglobulin).
  3. T4/T3 colloid droplets are pushed into the cell.
  4. T4/T3 are separated from thyroglobulin.
50
Q

What is amiodarone used for?

A

It is used in patients with malignant heart arrhythmia e.g. VT. It contains around 75mg of iodine (3 months supply of iodine). It is not uncommon for patients to develop an iodine induced thyroiditis and iodine induced thyrotoxicity.

51
Q

What are iodine supplements used for?

A

Used for patients with under-active thyroid. Do not give patients with hyperactive thyroid iodine as it makes their condition worse.

52
Q

What are anti-TPO antibodies?

A

This is when a person’s body will develop antibodies against TPO.

53
Q

What is radioactive iodine?

A

It is used to treat hyperthyroidism.

54
Q

What is thyroid hormone (T3/T4) controlled by?

A

TSH (thyroid stimulating hormone).

55
Q

Describe thyroid hormone control mechanisms?

A

T3 is also produced locally at target organs, which includes the pituitary. T3 and T4 have negative feedback at the hypothalamus and has a direct effect on the pituitary.

56
Q

Describe low TSH and high T4?

A

The thyroid is inappropriately producing a high amount of T4. The normal response is for the T4 to negatively feedback (inhibit) on the pituitary to produce less TSH.

57
Q

What can cause low TSH and high T4?

A

Hyperthyroidism - overactive thyroid.

58
Q

Describe high TSH and low T4?

A

This is when the thyroid is not working or removed - TSH is normally being produced however if thyroid is not working it won’t produce as much T4 (low). The pituitary is normal but the thyroid isn’t. This is hypothyroidism.

59
Q

Describe ‘normal’ TSH and low T4?

A

Low T4 will cause the pituitary to release more TSH. However, this TSH is supposedly normal. this indicates that the pituitary is not reacting properly to the low T4. The thyroid is normal but the pituitary has a problem.

60
Q

Describe high TSH and high T4?

A

High TSH and high T4 levels potentially indicate a tumour in the pituitary e.g. TSHoma.

61
Q

What are other causes of high TSH and high T4?

A

Thyroid hormone resistance syndrome can cause high TSH and high T4. There is a genetic mutation of the beta receptor for T3 - results in pituitary not being able to resorb and ‘see’ this T3 and so it thinks there is not enough thyroid hormone. This causes the pituitary to produce and release more TSH, which results in the thyroid producing more T4/T3.

62
Q

What does TSH do?

A
  1. Increases iodine in follicular lumen (where the colloid is).
  2. Increases blood flow to the thyroid.
  3. Increases production of the thyroglobulin, thyroid peroxidase and hydrogen peroxide.
  4. Increases endocytosis and degradation of thyroglobulin.
  5. Increases release of T4.
63
Q

Describe the effect hCG has on the thyroid?

A

Beta-hCG has an action on the thyroid via the alpha subunit - it can bind to receptors on the thyroid. when it binds to these receptors the thyroid thinks that it is actually TSH that has bound. Thus hCG can stimulate the thyroid to make more thyroid hormone.

64
Q

What does the patient with thyrotoxicosis have?

A

This patient has an overactive thyroid - hyperthyroidism. They have high T4/T3 and low TSH.

65
Q

What are the symptoms of thyrotoxicosis?

A
  1. Nervousness (psychiatric illness).
  2. Increased sweating (vasodilation).
  3. Weigh loss.
  4. Heat sensitivity (T4/T3 causes vasodilation - feeling hot and sweaty constantly).
  5. Tachycardia (increased heart rate).
  6. Weakness.
66
Q

What are the signs of thyrotoxicosis?

A
  1. Bruit over thyroid.
  2. Goitre.
  3. Skin changes (inflammatory, retroperitoneal fibrosis).
  4. Tremor.
  5. Eye signs (e.g. lid retraction, itchy eyes, oedematous eyes and gradually eye disease).
67
Q

What are the causes of thyrotoxicosis?

A
  1. Graves disease.
  2. Multi-nodular goitre.
  3. Thyroiditis.
  4. Drugs.
  5. Toxic nodule.
68
Q

Describe graves disease?

A

It is autoimmune production of an antibody that stimulates TSH receptor. It is more common in women. The antibody that binds to the TSH receptor causes the thyroid to think it needs to produce more T4/T3. Not uncommon for patient to end up with goitre, tremor, lid lag/lid retraction (eyes that bulge).

69
Q

Describe multi-nodular goitre?

A

Hyper-functioning regions of the thyroid gland are not suppressed by circulating hormone. Some of the nodules become autonomous and overproduce thyroid hormone uncontrollably. Common cause of thyrotoxicosis in older people.

70
Q

What drugs can cause thyrotoxicosis?

A
  1. Amiodarone.
  2. Iodine.
  3. Thyroxine.
71
Q

Describe a toxic nodule?

A

A single nodule in the thyroid becomes autonomous and overproduces thyroid hormone. It is due to a constitutive activation of TSH receptor due to a mutation in the nodule. It responds well to surgical removal of the toxic nodule or treatment with radioactive iodine. The thyroid nodules will move when swallowing because the thyroid is attached to the pre-trachial fascia.

72
Q

What is primary hypothyroidism?

A

This is a patient with an underactive thyroid - disease of the thyroid only.

73
Q

What is secondary hypothyroidism?

A

This is a patient with a disease of the pituitary.

74
Q

What are the signs and symptoms of primary hypothyroidism?

A
  1. Reduction in muscle strength.
  2. Hair loss and dry skin.
  3. Constipation.
  4. Oedema due to low thyroid hormone.
  5. Low body temperature.
  6. Low basal metabolic rate.
  7. Weight gain.
  8. Tiredness.
  9. High TSH and low T4.
  10. Decreased protein synthesis.
  11. Positive TPO antibodies.
75
Q

What are the causes of primary hypothyroidism?

A

Hashimoto’s disease - most common cause of hypothyroidism. The patient has an autoimmune process that shrinks and destroys the thyroid and the thyroid gets smaller and smaller.

RDA (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions