Thyroid Gland

 

Endocrines : The glands of the body may be divided into those with an external secretion (exocrine glands) and those with an internal secretion (endocrine glands). Example of exocrine glands are the sweat, Lachrymal and mammary glands which pass their secretion along the ducts to the external surface of the body and the glands of the mouth, stomach, and intestine which pass their secretions along ducts into the alimentary tract. The endocrine or ductless gland on the other hand have no ducts or openings to the exterior.

The secretions are passed directly into the blood stream and transmitted to the tissues.

 

A hormone is a chemical substance produced by the endocrine glands and their overall function is to regulate the activities of various body organs and their functions. The first hormone was discovered by Bayliss in 1903.

The main endocrine glands in the body are :

 

Thyroid

 

Parathyroid

 

Islets of Langerhans

 

Adrenal gland

 

Pituitary and

 

Sex glands

 

THYROID GLAND

 

The largest of the endocrine glands is the thyroid, which is located in the neck region. The thyroid gland weighs 25 gms in a healthy adult. It has two oval parts called the lateral lobes on either side of the trachea. These two lobes are connected by a narrow band called isthumus. The entire gland is enclosed by a connective tissue capsule. This gland produces hormone, thyroxine rich in iodine.

 

Thyroid gets iodine from the blood stream. Iodine is formed by the reduction of iodide. It is then fixed with the amino acid tyrosine to form mono and di-iodo-tyrosine compounds. Two molecules of di-iodo-tyrosine combine to form thyroxine. By eating vegetables grown in iodine-containing soils or by eating sea-foods and iodised salt our diet will have enough iodine necessary for the production of thyroxine.

 

Thyroid stimulating hormone (TSH) produced by the anterior pituitary lobe increases the activity of thyroid gland. Whenever the thyroxine level falls below a particular level TSH is stimulated,

 

Functions of Thyroxine

 

Helps to regulate tissue growth and development.

 

Increases the B M R and thus raises the body temperature.

It controls the metabolism by regulating the anabolic and catabolic process.

 

Stimulates the cells to break down proteins for energy.

 

Decreases the breakdown of fats.

 

Increases the breakdown of body glucose and enhances the glucose absorption.

 

Calcium and phosphorus are removed from the bones and excreted in increased amounts.

 

Helps in the conversion of Beta-carotene into vitamin A.

Thyroid Disorders

 

It is of 3 types. They are:

 

Hypothyroidism

 

Hyperthyroidism

 

Simple goitre.

 

Hypothyroidism

 

It results due to lack of thyroid hormone secretion. It results in cretinism in children and myxoedema in adults.

 

Cause of Hypothyroidism

 

Failure or arrest of normal development of thyroid gland.

 

Failure to form genetic enzymes normally.

 

Deficiency of iodine in the body.

 

Administration of antithyroid drugs in excess.

 

After surgical removal of thyroid gland.

 

The Chief Features of Cretinism are as follows

 

Stunted growth

 

Broad nose

 

Thick lips

 

Lobling tongue

Muddy dry skin

Milestones of development in children get delayed e.g., Holding up the head, sitting, standing, walking gets delayed.

 

BMR is depressed.

 

This disease can be cured if thyroxine or iodine is administered sufficiently.

 

In adults hypothyrodism causes myxodema which is more common among females than in males.

The Chief features of hypothyrodism in adults (Myxoedema)

 

Decreased BMR

 

Sexual dysfunction

 

Lack of energy

 

Lack of memory

 

Loss of hair

 

Dullness

Loss of appetite

Slow heart rate

Gain in weight

 

Puffy face due to tissue fluid retention.

 

Hyperthyroidism

 

Occurs due to the excessive secretion or over action of thyroxine.

 

Symptoms of Hyperthyroidism

 

Enlargement of thyroid gland results in the protrusion of eye ball from the orbit.

Flushed skin and high temperature

 

Increased O₂ consumption and CO₂ output

 

Tendency to lose weight

 

The pulse and heart rate are high

 

Nervousness and irritability

 

Low resistance to withstand stress and strain

 

High blood pressure

 

Mild diabetes

 

Emotional restlessness

 

The clinical condition of hyperthyroidism is exophthalmic goitre in which the thyroid gland is usually enlarged and there is characteristic protrusion of eye balls from the orbit.

Simple Goiter

 

A lack of dietary iodine may cause endemic goiter. Thyroid gland is enlarged and has increased number of follicles. This leads to low level of thyroid hormone in the blood, and derangement of body functions.