Thyroid Gland Flashcards
Describe the shape of the thyroid gland.
Right and left lobes connected by a narrow isthmus.
What do c-cells secrete?
Calcitonin.
Which hormone is released by the hypothalamus to stimulate the pituitary to release TSH?
Thyrotropin releasing hormone (TRH).
What is the function of thyroid stimulating hormone (TSH)?
Stimulates the thyroid gland to produce T3 and T4.
Which cells produce T3 and T4?
Follicular cells.
What is the precursor to T3 and T4?
Thyroglobulin.
What enzyme binds iodine to tyrosine in thyroglobulin molecules? What are the products?
Thyroperoxidase.
Iodotyrosyl residues (MIT and DIT)
How do iodide ions enter the follicular cells?
Through the Na/I symporter (NIS).
Where is thyroperoxidase found?
On the apical membrane of the follicular cells.
Where are thyroid stimulating hormone receptors found?
On the basolateral membrane of the follicular cells.
Which enzyme couples iodotyrosyl residues?
Thyroperoxidase.
Where is mature thyroglobulin stored?
In the colloid.
Which enzyme is responsible for the mono-deiodination of T4 to T3?
Deiodinase (D1, D2 and D3).
Where is deiodinase found?
In most peripheral tissues.
List 3 plasma proteins that T3 and T4 bind to in the blood.
1 - TBG.
2 - Transthyretin.
3 - Albumin.
What are the 3 tests for thyroid function?
1 - Serum TSH.
2 - Serum free T4.
3 - Serum free T3.
What is goitre?
Enlargement of the thyroid gland.
List 6 possible causes of hyperthyroidism.
1 - Grave’s hyperthyroidism.
2 - Toxic nodular goitre.
3 - Thyroiditis (inflammation).
4 - Exogenous iodine.
5 - TSH secreting pituitary adenoma.
6 - Neonatal hyperthyroidism.
What is hyperthyroidism characterised by? What about hypothyroidism?
- *Increased serum free T4.
- *Increased serum T3.
- Decreased serum TSH.
- Hypothyoridism is the opposite.
List 4 cardiovascular symptoms of hyperthyroidism.
1 - Tachycardia.
2 - Atrial fibrillations.
3 - Shortness of breath.
4 - Ankle swelling.
List 3 gastrointestinal symptoms of hyperthyroidism.
1 - Weight loss.
2 - Diarrhoea.
3 - Increased appetite.
List 3 neurological symptoms of hyperthyroidism.
1 - Tremor.
2 - Myopathy.
3 - Anxiety.
List 5 symptoms of hyperthyroidism relating to the eyes and skin.
1 - Sore, gritty eyes.
2 - Double vision.
3 - Staring eyes.
4 - Itching (pruritis).
5 - Conjunctival oedema.
What is Grave’s disease?
- An autoimmune disorder characterised by pathogenetic TSH-R antibodies that stimulate TSH receptors on thyroid follicular cells.
- Accounts for 70% of cases of hyperthyroidism.
List 5 environmental factors that can contribute to Grave’s disease.
1 - Gender.
2 - Stress.
3 - Infection.
4 - Pregnancy.
5 - Drugs.
What is proptosis?
Bulging of the eyes.
What is opthalmoplegia?
Paralysis of the muscles surrounding the eyes.
List 3 symptoms of thyroid eye disease.
1 - Lid retraction.
2 - Proptosis.
3 - Opthalmoplegia.
How does neonatal hyperthyroidism develop?
TSH-R antibodies cross the placenta.
Other than measuring TSH, T4 and T3, give an example of how hyperthyroidism can be diagnosed.
PET scan
- Uptake of radioactive iodine.
List 3 treatment options of hyperthyroidism.
1 - Antithyroid drugs such as carbimazole or propylthioracil to block hormone synthesis.
2 - Surgical removal of thyroid.
3 - Radioiodine therapy.
How does propylthiouracil block thyroid hormone synthesis?
By inhibiting thyroperoxidase.
List 5 causes of hypothyroidism.
1 - Autoimmune - Hashimoto’s thyroiditis (TPO and Tg antibodies).
2 - Treatment for hyperthyroidism (iatrogenic).
3 - Thyroiditis.
4 - Iodine deficiency.
5 - Congenital - enzyme defects or thyroid agenesis (does not develop as an embryo).
What is cretinism?
Congenital hypothyroidism.
List 3 cardiovascular symptoms of hypothyroidism.
1 - Bradycardia.
2 - Heart failure.
3 - Pericardial effusion.
List 2 gastrointestinal symptoms of hypothyroidism.
1 - Weight gain.
2 - Constipation.
List 3 symptoms of hypothyroidism that relate to the skin.
1 - Myxoedema (swelling of the skin).
2 - Erythema (redness of the skin).
3 - Vitiligo (loss of skin pigmentation).
List 3 neurological symptoms of hypothyroidism.
1 - Depression.
2 - Psychosis.
3 - Carpal tunnel syndrome.
How is hypothyroidism treated?
Hormone replacement therapy using levothyroxine.
