Week 2 - Thyroid Disorders

State the structure and location of the thyroid

Consists of a left and right lobe connected by the isthmus, located inferior to the larynx, wrapped around the trachea

Explain the 2 types of cells that make up the thyroid

• Follicular cells - epithelial cells that line thyroid follicles which secrete thyroid hormone

• Parafollicular cells - next to follicular cells that secrete calcitonin

Explain the roles of thyroid hormone

• Increase basal metabolic rate, producing heat and increasing body temp

• Required for growth and development

• Increases heart rate through NS stimulation

Explain the pathway of hormones that regulates metabolic rate

• Decreased metabolic rate

• Stimulates hypothalamus to release TRH (thyrotropin-releasing hormone)

• Stimulates anterior pituitary to release TSH (thyroid-stimulating hormone)

• Stimulates thyroid gland to produce and release thyroid hormone (T3 & T4)

• Thyroid hormone increases metabolic rate

Explain the negative feedback loop

Circulating T3 and T4 inhibits the hypothalamus and anterior pituitary from releasing TRH and TSH to reduce

Differentiate between primary and secondary hyperthyroidism/thyrotoxicosis

• Primary - dysfunction of the thyroid that causes hypersecretion of thyroid hormone

• Secondary - dysfunction of the anterior pituitary that causes hypersecretion of TSH and therefore thyroid hormone

Explain Grave’s disease

An autoimmune disease characterised by the presence of thyroid stimulating antibodies that stimulate the thyroid gland to produce thyroid hormone regardless of negative feedback and low TRH/TSH levels.

Explain why sweating and heat intolerance are symptoms of hyperthyroidism

Thyroid hormone increases cellular metabolism in which heat is a by-product. Therefore increasing amounts of thyroid hormone increases metabolism rate and therefore heat production within the body.

Explain why weight loss and increased appetite are symptoms of hyperthyroidism

Thyroid hormone increases BMR, increasing macronutrient breakdown and the amount of energy burned. Therefore increasing amounts of thyroid hormone would increase metabolism and energy burned faster then energy being consumed, causing weight loss and increased appetite.

Explain why fatigue and decreased concentration is a symptoms of hyperthyroidism

Thyroid hormone increases BMR, therefore decreases the amount of energy available in the body, leading to fatigue and decreased concentration

Explain why tachycardia and increased BP are symptoms of hyperthyroidism.

Thyroid hormone up-regulates beta-adrenergic receptors found in the heart, increasing effects of adrenaline and noradrenaline. Therefore increases heart rate and contractility, increasing blood pressure.

Explain why nervousness and irritability are symptoms of hyperthyroidism

Thyroid hormone up-regulates beta-adrenergic receptors, increasing the effects of adrenaline and noradrenaline. This increases stress levels and induces shakiness, nervousness and irritability.

Explain why increased bowel movements are a symptom of hyperthyroidism

Thyroid hormone up-regulates beta-adrenergic receptors, increasing smooth muscle contractility in the gut, increasing motility and decreasing transit time through the GIT.

Explain why hair loss and week nails are symptoms of hyperthyroidism

Thyroid hormone increases BMR, therefore increases protein breakdown down, reducing the amount of protein available for hair and nail production, causing them to weaken.

Explain why menstrual problems and infertility are symptoms of hyperthyroidism

Thyroid hormone increases BMR, decreasing the amount of energy available for reproductive regulation.

Explain why a toxic goiter is a symptom of hyperthyroidism

A toxic goiter is an enlarged thyroid gland due to increased stimulation from TSH, leading to increased production and hypersecretion of thyroid hormone

Explain why exopthalmos is a symptom of Graves Disease

Antibodies from Graves Disease mistakingly attack cells around the eye causing fluid accumulation that pushes the eyeballs forwards.

State some of the reasons causes of primary hypothyroidism

• Iodine Feficiency

• Hashimotos Thyroiditis

• Congenital Defects

• Thyroidectomy

Explain why iodine deficiency leads to hypothyroidism

Iodine is essential for thyroid hormone production. Therefore iodine deficiency leads reduction in thyroid hormone production.

Explain Cretinism

A congenital defect caused by severe hypothyroidism due to either abnormal thyroid gland development or iodine deficiency during pregnancy. This causes stunted skeletal growth, weak muscle tone, umbilical hernia, myxedema etc.

Explain Hashimoto’s thyroiditis

Autoimmune disease characterised by anti-peroxidase and anit-thyroglobulin antibodies that damages thyroid tissue, inhibiting thyroid hormone production.

Explain why dry, brittle hair and nails and dry, flaky skin are symptoms of hypothyroidism

Decreased thyroid hormone slows down BMR, therefore decreasing the amount of energy available and required for protein synthesis and cell turnover, therefore causing dry flaky skin and brittle hair and nails.

Explain why a non-toxic goiter is a symptom of hypothyroidism

Low thyroid hormone levels works as negative feedback to increase TRH and TSH levels. Increased TSH stimulating the thyroid causes a goiter however it is non-toxic as there is no production of thyroid hormone.

Explain myxedema

A severe and advanced form of untreated hypothyroidism. Causing symptoms such as puffy face, hands and feet, a deep voice, slowed speech, cognition, lethargy and confusion.

Explain why puffy face, hands and feet occurs in myxedema

Decreased BMR decreases the break down carbohydrates for metabolism. This increases the amount of carbohydrates in tissues, drawing water in causing fluid retention

Explain why a deep voice occurs in myxedema

Decreased BMR decreases the breakdown of carbohydrates for metabolism. This increases the amount of carbohydrates in tissues, causing swelling and fluid retention that compresses on vocal cords, changing the pitch of voice.

Explain why slowed speech, lethargy, depression and anxiety occurs in myxedema

Decreased BMR decreases the amount of carbohydrates used for metabolism. This increases the amount of carbs within tissues, causing swelling and fluid retention that compresses on nerves, causing NS depression.