MEH: The Tyroid Gland

Question 1

Describe the location of the thyroid gland.

Answer 1

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

Question 2

Describe the structure of the thyroid gland.

Answer 2

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

Question 3

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

Answer 3

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

Question 4

Describe how the thyroid hormones are produced.

Answer 4

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

Question 5

Describe how he thyroid hormones are stored.

Answer 5

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

Question 6

Describe how the activity of the thyroid gland is controlled.

Answer 6

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

Question 7

Describe the consequences of over-secretion of thyroid hormones.

Answer 7

1

Question 8

Describe the consequences of under-secretion of thyroid hormones.

Answer 8

1

Question 9

How does the thyroid gland develop embryological?

Answer 9

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.

Question 10

Is colloid considered intracellular or extracellular?

Answer 10

Extracellular

Question 11

What do thyroid follicular cells produce?

Answer 11

Thyroid hormone

Question 12

What do parafollicular cells produce?

Answer 12

Calcitonin

Question 13

What are the 3 roles of thyroid peroxidase?

Answer 13

1. oxidation of iodide to iodine
2. addition of iodine
3. coupling

Question 14

How is iodine taken up into the thyroid gland?

Answer 14

sodium-ion symporter /iodine trap

Question 15

Which thyroid hormone is mostly secreted?

Answer 15

T4 (90%)

Question 16

Where is most T4 converted into T3?

Answer 16

Liver and kidneys

Question 17

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

Answer 17

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

Question 18

Describe the structure of TSH.

Answer 18

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

Question 19

Describe 3 general actions of thyroid hormone.

Answer 19

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

Question 20

What effects do thyroid hormones have on the cardiovascular system.

Answer 20

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

Question 21

What effects do thyroid hormones have on the nervous system.

Answer 21

increase in the myelination of nerves and development of neurons.

Question 22

What type of receptor is a thyroid hormone receptor?

Answer 22

Nuclear

Question 23

What range is the normal plasma concentration of thyroid hormones?

Answer 23

picamolar (1x10^-12)

Question 24

What is a goitre?

Answer 24

Enlargement of the thyroid gland when it is overstimulated

Question 25

What conditions can result from hypothyroidism?

Answer 25

- Cretinism | - Myxedema

Question 26

In a patient with hypothyroidism, would the following hormones be raised, lowered or remain the same? - T3 - T4 - TSH

Answer 26

T3: lowered T4: lowered TSH: increased

Question 27

In a patient with hyperthyroidism, would the following hormones be raised, lowered or remain the same? - T3 - T4 - TSH

Answer 27

T3: increased T4: increased TSH: decreased

Question 28

What is Hashimoto's disease?

Answer 28

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

Question 29

What is Grave's disease?

Answer 29

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.

Question 30

What substance is used for thyroid scintigraphy?

Answer 30

Technetium-99m or iodine | Tc is faster as it can be given IV where iodine has to e given orally

Question 31

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

Answer 31

Carbimazole which is a pro-drug

Question 32

What is the pre-tracheal fascia?`

Answer 32

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

Question 33

Where does a thyroglossal cyst move on tongue protrusion?

Answer 33

upwards and in

Question 34

What is the majority of metabolic thyroid disease due to?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

When can physiological goitre occur?

Answer 36

Menarche, pregnancy, menopause.

Question 37

What are the commonest causes of goitre globally?

Answer 37

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

Question 38

Describe some symptoms of hypothyroidism.

Answer 38

``` – 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 ```

Question 39

Describe some symptoms of hyperthyroidism.

Answer 39

* 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

Question 40

Describe some signs of hypothyroidism.

Answer 40

• 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)

Question 41

What is myxoedema?

Answer 41

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.

Question 42

Describe some signs of hyperthyroidism.

Answer 42

* 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