Thyroid Gland and its Disorders MCQ - Practice Questions with Answers

• The thyroid gland is a butterfly-shaped organ and is composed of two cone-like lobes called the right lobe and left lobe, connected via the isthmus.
• It develops from the endoderm.
• It is located anterior to the thyroid cartilage of the larynx of the neck.
• It is composed of thyroid follicles made up of cuboidal epithelium and filled with homogeneous material called colloid.
• The stroma of the thyroid gland is made up of loose connective tissue.
• The stroma contains blood capillaries and parafollicular cells or C cells.
• It is the only gland that stores hormones in large quantities.
  

Hormones of the Thyroid Gland:

Thyroxine (T4) and Triiodothyronine (T3): 

• Thyroxine (T4) and Triiodothyronine (T3): 

• T4 contains four atoms of iodine and T3 contains three atoms of iodine.
• T3 is active and potent form and is formed by the removal of one iodine from T4 in liver, kidneys and other tissues.
• These are synthesised from tyrosine amino acids
• The functions are as follows:
• They regulate basal metabolic rate of the body and thus maintain basal metabolic rate (BMR)
• They stimulate protein synthesis and thus promote growth of the body tissues 
• They maintain body temperature
• They help in metamorphosis of tadpole into adult frog
• They increase action of neurotransmitters like adrenaline and noradrenaline

Thyrocalcitonin:

• It is secreted when calcium levels are high in the blood.
• It lowers the levels of calcium by suppressing the release of calcium ions from the bones.
• It is a peptide hormone.

Hyperthyroidism:

• Hypersecretion of thyroid hormone is also called Exophthalmic goitre or Graves’ disease or Basedow’s disease or Parry’s disease.
• It is a thyroid enlargement (goitre) in which the thyroid secretes excessive amount of thyroid hormone.
• It is characterised by exophthalmia (protrusion of eyeballs because of fluid accumu­lation behind them), loss of weight, a slight rise in the body temperature, excitability, rapid heartbeat, nervousness and restlessness.

Hypothyroidism:

• Cretinism: 
  • This disorder is caused by a deficiency of thyroid hormone in infants.
  • Affected infants have slow body growth and mental development, and reduced metabolic rate
• Myxoedema or Gull’s disease:
  • It is caused by a deficiency of thyroid hormone in adults. 
  • This disease is characterized by puffy appearance due to accumulation of fat in the subcutaneous tissue because of a low metabolic rate. 
  • The patient lacks alertness, intelligence and initiative. 
  • He also suffers from slow heartbeat, low body temperature and retarded sexual development.
• Simple Goitre:
  • It is caused by a deficiency of iodine in the diet because iodine is needed for the synthesis of thyroid hormone. 
  • It causes thyroid enlargement. 
  • It may lead to cretinism or myxoedema. 
  • This disease is common in hilly areas.
• Hashimoto’s disease:
  • In this disease all the aspects of thyroid function are im­paired. 
  • It is an autoimmune disease in which the thyroid gland is destroyed by autoimmunity.