The thyroid gland Flashcards
Where is the thyroid gland? Where are its attachments?
Anterior to the trachea and oesophagus. Attached to the thyroid cartilage and upper ends of trachea.
What connects the two lobes of the thyroid?
The isthmus
What lies on the posterior aspect of the thyroid?
The 4 parathyroid glands.
What cells are present in the thyroid? What do they surround?
Follicular cells- produce thyroglobulin
Parafollicular cells- produce calcitonin
Colloids- store thyroid hormones.
Describe the synthesis and release of thyroid hormones
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.
What is the name for T3?
triiodothyronine.
What is the name for T4
Thyroxine.
How are T4 and T3 made using iodine?
Iodine attaches to the tyrosine residues on thyroglobulin to form MIT and DIT.
MIT- monoiodothyrosine- T3
DIT- diiodothyrosine- T4.
What is secreted more, T3 or T4?
majority of secreted hormone is T4.
What is more biologically active, T3 or T4?
T3
What converts T4 to T3?
The liver and the kidneys.
T3 and T4 are hydrophilic molecules. T or F.
F.
Unbound thyroid hormones are in their active state. T or F.
True.
What is the role of thyroid hormones in the body?
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.
How is thyroid hormone regulated?
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.
What would a patient with hyperthyroidism present as?
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
Causes of hyperthyroidism
Graves disease (most common)
Toxic multi nodular goitre
DeQuervains thyroiditis.
Adenomas and sarcomas
What is Graves disease?
An autoimmune condition where autoantibodies stimulate the TSH receptor and cause release of hormones.
What would tests for TRH, TSH, T3 and T4 look like in graves disease?
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.
What antibodies are present in Graves disease?
Anti- TPO
TSH receptor antibody
sometimes anti-thyroglobulin.
What a patient with graves disease present like?
Superficially- Exopthalamus- protruding eyes Pretibial myxoedoema Goitre Clinically- high circulating levels of antibodies.
What causes exopthalamus and pretibial myxoedema in Graves disease?
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.
What does pretibial myxoedema look like?
Bilateral plaque formation on the anterior surface of the leg. Orange peel like in appearance.
What is the treatment for Graves disease?
Carbimazole- decreases production of thyroid hormones. Start at a high dose and reduce over 12-18months.
If carbimazole isn’t tolerated use propylthiouracil.
What is toxic multi nodular goitre?
Nodules that secrete thyroid hormones. Usually found in the elderly and in thyroid deficient areas.
What would a radio-isotope uptake scan look like for a patient with TMNG?
Patchy uptake- non symmetrical.
What tumours are likely to arise in the thyroid gland and what treatment are they resistant too?
Adenomas are more likely to be found than sarcomas. They are very resistant to anti-thyroid medication so surgery is the best option.
What is DeQuervains thyroiditis? How will a patient present?
Fever, malaise and local tenderness due to an acute inflammatory process. After a few weeks of this patient will experience transient hypothyroidism.
What will a scintagraphy scan for DeQuervains show?
Low uptake.
Treatment of hyperthyroidism?
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.
What are the conditions for living after having radio-iodine?
No pregnancy for 6 months
Avoid close prolonged contact with children for a few weeks.
What is the risk of radio-iodine?
Hypothyroidism.
How would a patient with hypothyroidism present?
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
Describe the levels of TRH, TSH, T3 and T4 in a patient with hypothyroidism?
TRH and TSH would be high
T3 and T4 would be low or normal.
What are the causes of hypothyroidism?
Primary autoimmune hypothyroidism
Hashimotors thyroiditis
Iodine deficiency
Drug induced.
What is primary autoimmune thyroiditis?
Lymphocytic infiltration into the thyroid gland leading to atrophy (death of tissue).
What is Hashimotors thyroiditis? How do patients usually present?
The immune system attacks the thyroid gland damaging it. It is associated with anti-TPO antibodies.
Patients usually present with goitre.
What are people with Hashimoto’s thyroiditis at more risk of?
Getting a non-Hodgkin lymphoma.
What is the treatment for hypothyroidism?
Thyroxine to replace the T4.
The dose requirement for thyroxine decreases by 25-50% in pregnancy. T or F.
False, it increases by 25-50%.
