The thyroid gland

Question 1

Where is the thyroid gland? Where are its attachments?

Answer 1

Anterior to the trachea and oesophagus. Attached to the thyroid cartilage and upper ends of trachea.

Question 2

What connects the two lobes of the thyroid?

Answer 2

The isthmus

Question 3

What lies on the posterior aspect of the thyroid?

Answer 3

The 4 parathyroid glands.

Question 4

What cells are present in the thyroid? What do they surround?

Answer 4

Follicular cells- produce thyroglobulin
Parafollicular cells- produce calcitonin
Colloids- store thyroid hormones.

Question 5

Describe the synthesis and release of thyroid hormones

Answer 5

Iodine in the diet is taken up from the bloodstream and brought into a follicular cell. Here it is transported into the colloid which triggers pinocytosis of the membrane releasing a vesicle of T3 and T4.
Lysozymes in the follicular cell break down the vesicle and it is released into the blood.

Question 6

What is the name for T3?

Answer 6

triiodothyronine.

Question 7

What is the name for T4

Answer 7

Thyroxine.

Question 8

How are T4 and T3 made using iodine?

Answer 8

Iodine attaches to the tyrosine residues on thyroglobulin to form MIT and DIT.
MIT- monoiodothyrosine- T3
DIT- diiodothyrosine- T4.

Question 9

What is secreted more, T3 or T4?

Answer 9

majority of secreted hormone is T4.

Question 10

What is more biologically active, T3 or T4?

Answer 10

T3

Question 11

What converts T4 to T3?

Answer 11

The liver and the kidneys.

Question 12

T3 and T4 are hydrophilic molecules. T or F.

Answer 12

F.

Question 13

Unbound thyroid hormones are in their active state. T or F.

Answer 13

True.

Question 14

What is the role of thyroid hormones in the body?

Answer 14

They control metabolism along with growth hormone. It can increase protein synthesis and increase plasma free fatty acid levels. .
Have a role in maintaining bone turnover and gut motility
Also involved in thermogenesis, CNS activity and brain development in neonates.

Question 15

How is thyroid hormone regulated?

Answer 15

The hypothalamus releases thyroid releasing hormone. This stimulates the anterior pituitary to release thyroid stimulating hormone. Thyroid stimulating hormone causes the thyroid gland to release T3 and T4 into the blood. T3 and T4 have a negative feedback effect on both the hypothalamus and pituitary.

Question 16

What would a patient with hyperthyroidism present as?

Answer 16

Increased heart rate and increased force. Palpitations and atrial fibrillation also.
Heat intolerance- skin could be moist and itchy.
Tendency to lose weight
Sweating
Agitated and irritable. Possible restlessness.
Sleep is disturbed
Irregular menstrual cycle
Diarrhoea

Question 17

Causes of hyperthyroidism

Answer 17

Graves disease (most common)
Toxic multi nodular goitre
DeQuervains thyroiditis.
Adenomas and sarcomas

Question 18

What is Graves disease?

Answer 18

An autoimmune condition where autoantibodies stimulate the TSH receptor and cause release of hormones.

Question 19

What would tests for TRH, TSH, T3 and T4 look like in graves disease?

Answer 19

TRH and TSH would both be low (they try to decrease levels of T3 and T4 by negative feedback but it doesn’t work).
T3 and T4 would be high.

Question 20

What antibodies are present in Graves disease?

Answer 20

Anti- TPO
TSH receptor antibody
sometimes anti-thyroglobulin.

Question 21

What a patient with graves disease present like?

Answer 21

Superficially-
Exopthalamus- protruding eyes
Pretibial myxoedoema
Goitre
Clinically- high circulating levels of antibodies.

Question 22

What causes exopthalamus and pretibial myxoedema in Graves disease?

Answer 22

Fibroblasts behind the orbit and overlying the skin express TSH receptors. Activation of these results in glycosaminoglycan build up, inflammation and fibrosis which leads to exopthalamus and pretibial myxoedema.

Question 23

What does pretibial myxoedema look like?

Answer 23

Bilateral plaque formation on the anterior surface of the leg. Orange peel like in appearance.

Question 24

What is the treatment for Graves disease?

Answer 24

Carbimazole- decreases production of thyroid hormones. Start at a high dose and reduce over 12-18months.
If carbimazole isn’t tolerated use propylthiouracil.

Question 25

What is toxic multi nodular goitre?

Answer 25

Nodules that secrete thyroid hormones. Usually found in the elderly and in thyroid deficient areas.

Question 26

What would a radio-isotope uptake scan look like for a patient with TMNG?

Answer 26

Patchy uptake- non symmetrical.

Question 27

What tumours are likely to arise in the thyroid gland and what treatment are they resistant too?

Answer 27

Adenomas are more likely to be found than sarcomas. They are very resistant to anti-thyroid medication so surgery is the best option.

Question 28

What is DeQuervains thyroiditis? How will a patient present?

Answer 28

Fever, malaise and local tenderness due to an acute inflammatory process. After a few weeks of this patient will experience transient hypothyroidism.

Question 29

What will a scintagraphy scan for DeQuervains show?

Answer 29

Low uptake.

Question 30

Treatment of hyperthyroidism?

Answer 30

Oral medication e.g. carbimazole or propylthiouracil. Radio-iodine- tends to be used for multi nodular goitre or relapsing graves disease. Surgery- however scar and anaesthetic risks.

Question 31

What are the conditions for living after having radio-iodine?

Answer 31

No pregnancy for 6 months | Avoid close prolonged contact with children for a few weeks.

Question 32

What is the risk of radio-iodine?

Answer 32

Hypothyroidism.

Question 33

How would a patient with hypothyroidism present?

Answer 33

``` Decreased heart rate Expressionless face and sparse hair Cold intolerance Lethargy and fatigue Loss of appetite and weight gain Increased soft tissue on the face Menorrhoea or oligomenorrhoea Constipation ```

Question 34

Describe the levels of TRH, TSH, T3 and T4 in a patient with hypothyroidism?

Answer 34

TRH and TSH would be high | T3 and T4 would be low or normal.

Question 35

What are the causes of hypothyroidism?

Answer 35

Primary autoimmune hypothyroidism Hashimotors thyroiditis Iodine deficiency Drug induced.

Question 36

What is primary autoimmune thyroiditis?

Answer 36

Lymphocytic infiltration into the thyroid gland leading to atrophy (death of tissue).

Question 37

What is Hashimotors thyroiditis? How do patients usually present?

Answer 37

The immune system attacks the thyroid gland damaging it. It is associated with anti-TPO antibodies. Patients usually present with goitre.

Question 38

What are people with Hashimoto's thyroiditis at more risk of?

Answer 38

Getting a non-Hodgkin lymphoma.

Question 39

What is the treatment for hypothyroidism?

Answer 39

Thyroxine to replace the T4.

Question 40

The dose requirement for thyroxine decreases by 25-50% in pregnancy. T or F.

Answer 40

False, it increases by 25-50%.