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Year 1: All Units > MEH: The Tyroid Gland > Flashcards

MEH: The Tyroid Gland Flashcards

1
Q

Describe the location of the thyroid gland.

A

Lies against and around the front larynx and trachea below the thyroid Cartilage (Adams apple)

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2
Q

Describe the structure of the thyroid gland.

A

2 lobes joined by the isthmus (it looks like a bow tie)

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3
Q

Describe the chemical structure of the thyroid hormones T3 and T4.

A

T3: iodine is at 3 potions n the aromatic ring
T4: iodine is at 4 potions n the aromatic ring

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4
Q

Describe how the thyroid hormones are produced.

A

T3: MIT (monoiodotyrosine) + DIT (diiodotyrosine)
T4: DIT (diiodotyrosine) + DIT (diiodotyrosine)

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5
Q

Describe how he thyroid hormones are stored.

A

Colloid cells store thyroglobulin which acts as a scaffold on which thyroif hormones are formed and stored.

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6
Q

Describe how the activity of the thyroid gland is controlled.

A

The presence of increased concentrations of thyroid hormone, causes an inhibition of the anterior pituitary and hypothalamus via a negative feedback mechanism.

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7
Q

Describe the consequences of over-secretion of thyroid hormones.

A

1

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8
Q

Describe the consequences of under-secretion of thyroid hormones.

A

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9
Q

How does the thyroid gland develop embryological?

A

It is the first endocrine gland to develop. It appears as an epithelial proliferation at the base of the tongue. It first descends through the thyroglossal duct which later degenerates one the gland has migrated down.

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10
Q

Is colloid considered intracellular or extracellular?

A

Extracellular

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11
Q

What do thyroid follicular cells produce?

A

Thyroid hormone

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12
Q

What do parafollicular cells produce?

A

Calcitonin

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13
Q

What are the 3 roles of thyroid peroxidase?

A
  1. oxidation of iodide to iodine
  2. addition of iodine
  3. coupling
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14
Q

How is iodine taken up into the thyroid gland?

A

sodium-ion symporter /iodine trap

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15
Q

Which thyroid hormone is mostly secreted?

A

T4 (90%)

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16
Q

Where is most T4 converted into T3?

A

Liver and kidneys

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17
Q

T3 and T4 are lipophilic hormones. How, therefore, are they transported in the blood?

A

Bound to thyroxine-binding globulin (not active when bound)

18
Q

Describe the structure of TSH.

A

Glycoprotein hormone which is composed of 2 non-covently bound subunits.

19
Q

Describe 3 general actions of thyroid hormone.

A
  1. Increase basal metabolic rate and hence heat production. They do this by increasing mitochondria size and enzyme synthesis
  2. Stimulation of metabolic pathways. Lipid metabolism and carb metabolism.
  3. Sympathomimetic effects. Increases the number of receptors on target cells
20
Q

What effects do thyroid hormones have on the cardiovascular system.

A
  • Increase cardiac output (by causing a chronotopic and inotropic effect)
  • Increase peripheral vasodilation to carry extra heat to the surface of the body
21
Q

What effects do thyroid hormones have on the nervous system.

A

increase in the myelination of nerves and development of neurons.

22
Q

What type of receptor is a thyroid hormone receptor?

A

Nuclear

23
Q

What range is the normal plasma concentration of thyroid hormones?

A

picamolar (1x10^-12)

24
Q

What is a goitre?

A

Enlargement of the thyroid gland when it is overstimulated

25
Q

What conditions can result from hypothyroidism?

A
  • Cretinism

- Myxedema

26
Q

In a patient with hypothyroidism, would the following hormones be raised, lowered or remain the same?

  • T3
  • T4
  • TSH
A

T3: lowered
T4: lowered
TSH: increased

27
Q

In a patient with hyperthyroidism, would the following hormones be raised, lowered or remain the same?

  • T3
  • T4
  • TSH
A

T3: increased
T4: increased
TSH: decreased

28
Q

What is Hashimoto’s disease?

A

An autoimmune disease resulting in thyroid follicle destruction and hence eventually hypothyroidism.

29
Q

What is Grave’s disease?

A

An autoimmune disease resulting hyperthyroidism caused by the production of thyroid stimulating immunoglobulin. (TSI)

This continuously stimulates thyroid hormone secretion outside of the negative feedback loop.

30
Q

What substance is used for thyroid scintigraphy?

A

Technetium-99m or iodine

Tc is faster as it can be given IV where iodine has to e given orally

31
Q

What is the most common anti-thyroid drug commonly used in the UK?

A

Carbimazole which is a pro-drug

32
Q

What is the pre-tracheal fascia?`

A

It is connective tissue that connects the thyroid gland to the trachea and larynx. Hence why the thyroid moves up on swallowing.

33
Q

Where does a thyroglossal cyst move on tongue protrusion?

A

upwards and in

34
Q

What is the majority of metabolic thyroid disease due to?

A

A primary abnormality of the thyroid land itself (98%)

35
Q

What hormone can be analysed as a way in which to test thyroid function?

A

TSH as it is v.rare for a pituitary adenoma to produce TSH and lead to thyrotoxicosis.

36
Q

When can physiological goitre occur?

A

Menarche, pregnancy, menopause.

37
Q

What are the commonest causes of goitre globally?

A
  1. Iodine deficiency (mainly in populations that live in mountainous areas)
  2. Multinodular goitre (affects western populations more)
38
Q

Describe some symptoms of hypothyroidism.

A 
– Excessive tiredness, feeling slowed down
– Memory problems, depression, psychosis (myxoedema medness)
– Weight gain
– Cold intolerance
– Gruff voice, croaky voice
– Puffy eyes , face hands and feet
– Dry, flaky skin
– Hair loss, particularly outer third of eyebrows
– Symptoms of carpal tunnel syndrome
– Constipation
– Menorrhagia
– Muscle weakness and cramps
39
Q

Describe some symptoms of hyperthyroidism.

A
  • Overactivity, tiredness
  • Nervousness, anxiety, insomnia
  • Shaking, trembling
  • Heat intolerance
  • Increased sweating – warm sweaty hands
  • Palpitations. Rarely angina
  • Weight loss in spite of increased appetite
  • Diarrhoea
  • Amenorrhea
  • Proximal muscle weakness
40
Q

Describe some signs of hypothyroidism.

A

• May be no obvious signs!
• Weight gain
• Dry skin, coarse brittle hair, loss of outer third of eyebrows
• Pallor. ‘Peaches and cream’ face
• Coarse facial features and periorbital puffiness
• Bradycardia
• Hyporeflexia with delayed relaxation
• Non pitting oedema – myxoedema. Due to deposition of
mucopolysaccharides, particularly around eyes, hands and feet
• Ascites or pericardial effusion (both uncommon)

41
Q

What is myxoedema?

A

As well as meaning non pitting oedema, particularly around the eyes, hands and feet, the term myxoedema is also used to mean hypothryoid in general.

42
Q

Describe some signs of hyperthyroidism.

A
  • Weight loss
  • Warm sweaty hands
  • Fine hand tremor
  • Tachycardia. Atrial fibrillation
  • Bounding pulse – wide pulse pressure
  • Proximal myopathy
  • Lid lag - Lid lag Lid lag 2
  • Staring eyes

Year 1: All Units (66 decks)

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