Thyroid Symptoms, Causes, Hormones, Glands and Functions

Introduction:

• The thyroid gland is the largest gland of the endocrine system
• It originates from the ectoderm of the embryo.
• Thyrotropin or TSH(Thyroid Stimulating Hormone) is released from the pituitary gland's adenohypophysis into the thyroid gland, which stimulates its production.
• Located anterior to the thyroid cartilage of the larynx in the neck.
• Thyroid gland is the only gland that can store large quantities of hormones for about two months.
  
  
  
   

Topics covered:

• Hormones of thyroid gland
• Disorders of thyroid gland

Explanation
 

Structure of the thyroid gland:

• It is a bilobed organ roughly butterfly-shaped
• Lobes are connected by a narrow flap of connective tissue called the isthmus.
• The microscopic structure of the thyroid gland shows thyroid follicles and stroma tissue.
• The follicles of the thyroid are composed of cuboidal epithelium and are filled with a homogeneous substance called colloid.
• The thyroid follicular cells secrete thyroxine (tetraiodothyronine or T4) and triiodothyronine or T3.
• Stromal tissue is composed of loose connective tissue.
• Stroma is well supplied with blood capillaries.
• Small clusters of parafollicular cells or ‘C’ cells are present in the stroma.
• The C cells secrete the thyrocalcitonin hormone.
  
  
   

Hormones of the Thyroid Gland

• Three hormones are secreted by the thyroid gland.
  - Thyroxine (tetra iodothyronine or T4) by follicular cells
  - Tri iodothyronine or T3 by follicular cells
  - Thyrocalcitonin by parafollicular cells

1.  Iodothyronine

• tetraiodothyronine or T4) and Triiodothyronine (T4) are collectively referred to as Iodothyronine or thyroid hormones.
• Thyroxine/tetraiodothyronine contains four atoms of iodine hence named T4.
• Triiodothyronine contains three atoms of iodine hence named T3.
• T3 is produced in small amounts when compared to T4 but is more active and more potent.
• T4 and T3 have similar effects on the targeted organs.
• The liver, kidneys, and other targeted tissues can convert T4 into T3 by removing one iodine molecule.
• These hormones are stored by the thyroid gland in larger amounts.
• Iodine and tyrosine amino acid are linked together to synthesise these hormones and hence iodine is an essential micronutrient.

Functions of thyroid hormones (TH):

• Maintaining the Basal Metabolic Rate (BMR).
• Promotes tissue growth by stimulating protein synthesis.
• Maintain body temperature.
• Regulating the mental function.
• The activity of neurotransmitters such as adrenaline and noradrenaline is increased by TH.
• In animals such as frogs, they help with metamorphosis.

2. Thyrocalcitonin (TCT)

• It is also called calcitonin.
• It is involved in regulating the calcium level.
• TCT hormone is antagonistic in action to parathyroid hormone.
• High calcium levels in the blood stimulate the synthesis of thyrocalcitonin.
• It suppresses the release of calcium ions from the bones.

Disorders of thyroid gland

A) Hypothyroidism:

• Simple Goitre:

• Iodine deficiency results in enlargement of the thyroid gland.
• Common in hilly regions.
• It may lead to cretinism and myxoedema if ignored.
• Iodine supplements and even table salt prevent this disease.
  
  
   

• Cretinism:

• Hypothyroidism during pregnancy results in slow body growth and mental development in infants.
• Symptoms of this disease include sluggish metabolism, potbelly, protruding tongue, stunted growth, and retarded sexual development.
• Treatment involves early administration of thyroid hormone.
  
  
  
   

• Myxoedema/ Gull’s disease:

• Hypothyroidism in adults results in myxoedema.
• Symptoms seen are lack of alertness, intelligence and initiative, slow heart rate, puffy appearance due to accumulation of fat.
• The patient is treated with thyroid hormone administration.
  
  
  
   

• Hashimoto’s disease:

• An autoimmune disorder which destroys the thyroid gland and hence, hinders all types of thyroid function.
• Also termed as thyroid suicide

B) Hyperthyroidism:

Increased levels of thyroid hormone can be seen in the case of thyroid cancer or due to the development of nodules of the thyroid gland.

• Graves’ disease:

• Graves’ disease is also known as Exophthalmic goitre or Basedow’s disease or parry’s disease
• Exophthalmic goitre (enlarged thyroid gland) results in abnormally high levels of thyroid hormones.
• Symptoms include high protrusion of eyeballs, increased BMR and weight loss.
  
  
  
   

Frequently Asked Questions: FAQs

Q1. Which are the autoimmune disorders of thyroid gland ?
Ans :

• Grave disease
• Hashimoto

Q2. Which hormones are secreted by the thyroid gland ?
Ans :

• Three hormones are secreted by the thyroid gland.
  - Thyroxine (tetra iodothyronine or T4) by follicular cells
  - Tri iodothyronine or T3 by follicular cells
  - Thyrocalcitonin by parafollicular cells

Q3. Which hormone is antagonistic in action to the parathyroid hormone ?
Ans :

• Thyrocalcitonin hormone is antagonistic in action to parathyroid hormone as it suppresses the release of calcium ions from the bones which parathyroid hormone increases the level of calcium in the blood.

Q4. What are the symptoms of cretinism ?
Ans :

• Symptoms of cretinism disease include -
• Sluggish metabolism
• Potbelly
• Protruding tongue
• Stunted growth
• Retarded sexual development

Q5. Why Hashimoto’s disease is also termed as thyroid suicide ?
Ans :

• Hashimoto’s disease is also termed as thyroid suicide because it destroys the thyroid gland and hence, hinders all types of thyroid function.

Q6. What are the other names of Grave’s disease ?
Ans :

• Graves’ disease is also known as Exophthalmic goitre or Basedow’s disease or parry’s disease.

Q7. Which diseases are associated with hypothyroidism?
Ans :
The diseases which are associated with hypothyroidism are -

• Simple goitre
• Cretinism
• Myxoedema
• Hashimoto’s disease

Q8. What is the other name for Myxoedema ?
Ans : Gull’s disease