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Metabolism - Alex's Cards (ESA2) > Session 7 - Endocrinology > Flashcards

Session 7 - Endocrinology Flashcards

1
Q

What recognisable landmark is the thyroid CARTILAGE?

A

The Adam’s apple

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2
Q

How many lobes does the thyroid gland have - what are they connected by?
Where is the thyroid gland located?

A

2 lobes = left and right lobe connected by the ISTHMUS

The thyroid gland is just above the sternal notch (where there is dip in your skin at bottom of neck)

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3
Q

Explain the stages of embryological development of the thyroid

A
  1. Thyroid gland is first endocrine gland to develop
  2. It appears as an epithelial proliferation at the base of the tongue
  3. It descends through the thryoglossal duct in front of the hyoid bone
  4. The thyroglossal duct degenerates leaving the gland
  5. The thyroid gland continues moving to its final position
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4
Q

Describe follicular cells

A

They are stores of thyroid hormones
The thyroglobulin protein is secreted by the thyroid follicle into the extracellular colloid material (found inside the cell strangely!)

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5
Q

What are the 2 cell types in the thyroid?

A
  1. Thyroid follicular cells

2. Thyroid parafollicular cells

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6
Q

What do thyroid parafollicular cells produce?

A

They secrete the hormone calcitonin (which is involved in calcium homeostasis)

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7
Q

What cells are found in the parathyroid gland and what do they produce? (often described as 4 glands found at the base of the thyroid)

A 
Chief cells (or principal cells)
They produce parathyroid hormone
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8
Q

Describe the structure of moniodotyrosine

A

1 iodine on an aromatic ring

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9
Q

Describe the structure of diiodotyrosine

A

2 iodines on an aromatic ring

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10
Q

What is the structure of triiodothyronine?

A

A monoiodotyrosine and a diiodotyrosine linked together (total of 3 iodines on 2 aromatic rings)

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11
Q

What is the T3 thyroid hormone called?

A

Triiodothyronine

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12
Q

What is the T4 thyroid hormone called?

A

Tetraiodothyronine

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13
Q

What is tetraiodothyronine made up of?

A

Two diiodotyrosine linked together (total of 4 iodine molecules on 2 aromatic rings)

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14
Q

What 3 reactions does thyroid peroxidase regulate?

A
  1. Oxidation of iodide to iodine
  2. Addition of iodine to the tyrosine residues
  3. Coupling of tyrosine residues
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15
Q

Iodine is reduced to iodine and then absorbed by the small intestine. How is it taken up from the blood?

A

There is a symporter which allows iodide to be taken into the thyroid epithelial cells
This is the sodium-iodide symporter

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16
Q

What is the majority of thyroid hormone secreted as - T3 or T4?

A

90% is secreted as T4

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17
Q

What is biologically more active, T3 or T4? Where does conversion of the less active hormone to more active hormone take place?

A

90% of hormone secreted is as T4

T3 is 4 times more active than T4 so most of T4 is converted to T3 in the liver and kidneys

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18
Q

Are thyroid hormones lipid or water soluble?

How are they transported around the blood?

A

They are LIPID soluble so need to be transported around the blood
They are transported by thyroxine-binding globulin

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19
Q

Explain how negative feedback & regulation of thyroid hormones takes place

A

The hypothalamus secreted TRH (thyroid releasing hormone)
This acts on the anterior pituitary gland which secretes TSH (thyroid stimulating hormone)
TSH acts on the thyroid gland to release T3 and T4
When levels of one rise they negatively feedback on the others to reduce secretion

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20
Q

What is the TSH hormone comprised of?

A

A glycoprotein hormone made up of 2 non-covalently bound subunits (alpha and beta)
The beta subunit is what makes it unique to other anterior pituitary gland hormones (which all have the same alpha subunit)

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21
Q

What type of receptor does TSH bind to?

A

A GPCR - it can bind to EITHER GaS or GaQ GPCRs (i.e. it can produce a wide range of signalling effects)

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22
Q

Thyroid hormones increase BMR and heat production in all tissues except?

A

Brain, spleen and testes

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23
Q

Thyroid hormones have a sympathomimetic effect. What does this mean?

A

They impact upon the sympathetic nervous system

They do this by increasing target cell response to catecholamines by increasing receptor number on target cells

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24
Q

How do thyroid hormones impact upon the CVS?

A

Increased responsiveness to catecholamines
This means increased chronotropy and inotropy (rate and force) of heart = increased cardiac output
There is also increased vasodilation to carry extra heart to surface

25
Q

How do thyroid hormones impact upon the nervous system?

A

They are essential for development and function of the nervous system
Thyroid hormones increase myelination and development of neurones

26
Q

What class of receptors do thyroid hormones belong in?

A

Nuclear receptors
They are receptors bound to the DNA in the absence of thyroid and repress gene transcription
When thyroid hormone binds the DNA is no longer repressed and can begin transcription

27
Q

Thyroid hormone receptors are bound to DNA in the cell nucleus in the absence of thyroid
What are the specific sequences of DNA they bind to called?

A

Hormone response elements (in the promoter region of thyroid hormone regulated genes)

28
Q

Is the normal plasma level of thyroid hormones in the milli, micro, nano or picomolar range?

A

In the picomolar range (10 to the minus 12)

29
Q

Name a few possible causes of hypothyroidism

A
  1. Failure of thyroid gland
  2. TRH or TSH deficiency
  3. Inadequate dietary supply of iodine
  4. Autoimmunity
30
Q

What is Hashimoto disease?

A

An autoimmune disease resulting in destruction of thyroid follicles - leading to hypothyroidism
It is the most common disease of the thyroid gland and is more common in women than men

31
Q

Name the most common cause of hyperthyroidism

A

Graves’ disease

32
Q

What are some symptoms of hyperthyroidism?

A
  1. Bulging eyes
  2. Tachycardia
  3. Hot and sweaty
  4. Weight loss
  5. Increased appetite
  6. Increased bowel movements
  7. Irritability
33
Q

What is graves’ disease caused by?

What would the levels of TSH be like?

A

Production of thyroid stimulating immunoglobulin which stimulates the thyroid gland rather than the TSH hormone doing this and being regulated
Levels of TSH are very low as these do not stimulate the thyroid gland in this condition

34
Q

What is used during thyroid scintigraphy?

A

Technetium-99m is used for isotope scanning of the thyroid with a gamma camera

35
Q

What is the most common drug given to treat hyperthyroidism and how does it work?

A

Carbimazole
It is converted to methimazole in the body which prevents thyroid peroxidase from iodinating and coupling tyrosine residues on thyroglobulin

36
Q

Is it possible to feel a normal thyroid gland?

A

No

37
Q

The thyroid gland is attached to the trachea and larynx by what?

A

The pre-tracheal fascia

38
Q

What direction does the thyroid gland move when swallowing?

A

It moves up

39
Q

The thryoid gland during embrylogical development appears where exactly at the tongue?

A

At the foreman caecum of the tongue

40
Q

The thyroglossal duct during embryological development usually disappears. What happens if remnants of the epithelium remain?

A

It can form a thyroglossal duct cyst - in the front of the neck (always on the midline!)

41
Q

In what direction does a thyroglossal duct cyst move during tongue protrusion?

A

It moves upwards

42
Q

In hyperthyroidism - will TSH levels be high or low?

A

Low (suppressed)

This is because there is already plenty of thyroid hormone in the bloodstream (hyper = excessive production) so we don’t want TSH to be encouraging further production

43
Q

In hypothyroidism will TSH levels be high or low?

A

High (raised)

This is because in hypothyroidism the thyroid gland is underfuncitoning and there is not enough thyroid hormone in the bloodstream
The TSH levels raise to try and increase the amount of thyroid hormone production

44
Q

What are the 3 ways a goitre can be described?

A
  1. Diffuse (covers the whole of he thyroid gland)
  2. Multinodular
  3. Single nodule
45
Q

In which sex are goitres more common?

The reasoning is not clear but what is the suggested explanation?

A

Women (7% of females in U.K. compared to 1% of men)

It has been suggested that the oestrogen/progesterone ratio affects thyroid function

46
Q

When might you see a physiological (normal thyroid functioning) goitre in women?

A
  1. Menarche (before puberty)
  2. Pregnancy
  3. Menopause
47
Q

What is the most common cause of goitre globally?

What is the most common cause of goitre in the U.K.?

A
  1. Worldwide = iodine deficiency - in severe cases people may become hypothyroid
  2. In U.K. = multinodular goitre (normal thyroid function) - a very small percentage of people may develop hyperthyroidism
48
Q

What happens if the mother is iodine deficient and hypothyroid during pregnancy?

A

The child will be mentally retarded with an abnormal gait, short stature, deaf-mute, goitre and hypothyroidism

49
Q

How can a multinodular goitre cause tracheal compression?

A

It can enlarge into a retrosternal goitre (which pushes against the mediastinum and causes tracheal compression)

50
Q

Describe symptoms and signs of hypothyroidism

What is the one symptom you would not expect?

A
  • Tiredness
  • Brain may not function properly (memory problems, depression, psychosis)
  • Weight gain
  • Puffy eyes hands and feet with non-pitting oedema
  • Hair loss (particularly outer third of eyebrows)
  • Muscle weakness and cramps
  • Cold intolerance
  • Peaches and cream face
  • Bradycardia

Unusual symptom = menorrhagia (heavy periods)

51
Q

What 2 meanings can myxodema have?

A
  • It can mean non pitting oedema (particularly around the hands, eyes and feet)
  • It can also mean hypothyroidism (sometimes the 2 terms are used interchangeably)
52
Q

What is the autoimmune disorder called that can cause hypothyroidism?
What does it do?

A

Hashimoto’s disease

It produces antibodies against thyroglobulin and thyroid peroxidase

53
Q

What is the treatment for hypothyroidism?

A 
Oral thyroxine (T4) 
Adjust the dose until the levels of TSH in the body are normal
54
Q

What is thyrotoxicosis?

A

Excessive thyroid hormone in the bloodstream - can due to a number of reasons including hyperthyroidism

55
Q

What are the symptoms and signs of thyrotoxicosis?

What is the one more unusual symptom?

A
  • Hot and sweaty
  • Weight loss
  • Increased appetite
  • Increased bowel movements
  • Heat intolerance
  • Overactivity and tiredness
  • Palpitations
  • Shaking
  • Tachycardia
  • Lid lag
  • Staring eyes

One more unusual symptom = amenorrhea (missing periods)

56
Q

What is autoimmune disorder that can cause hyperthyroidism?

What does it do?

A

Graves’ disease

A circulating immuniglobulin called thyroid stimulating immunoglobulin (TSI) stimulates the TSH receptor

57
Q

What are 2 distinctive symptoms of Graves’ disease?

A
  1. Bulging eyes (exophthalmos)

2. Pre-tibial myxoedema (orange peel appearance of shins)

58
Q

What is the treatment for thryotoxicosis?

A

Carbimazole - this prevents thyroid peroxidase from iodinating or coupling tyrosine residues on thyroglobulin

Metabolism - Alex's Cards (ESA2) (8 decks)

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