Thyroid Glands Functions and Abnomalities

Thyroid gland :

                       It consists of two lobes situated above the larynx In mammals. it produces following hormones:

1.Thyroxine (or tetraiodo-thryonine: T4)

2.Tri-iodothyronine or T3: . it has a structure similar to thryroxine with 3 iodine atoms rather than 4.

3.Calcitonin hormone



Thyroxine T4 and Tri-iodothyronine T3: 

The thyroid gland remains active continuously. But it produces higher levels of secretions during periods of rapid growth and sexual maturation and in stress situations such as cold and hunger.

These two hormones perform same function. They perform following functions:

1. Thyroxine and triiodothyronine act on the basal metabolic rate They stimulate the breakdown of glucose and release of heat and generation of ATP.

2. They also act with somatotropin and increase growth. They act directly on brain cells causing them to differentiate.

3. They affect the process of metamorphosis in amphibians. if there is deficiency of secretion of thyroxine the tadpole larva of frog do not metamorphose to develop into frog. Instead it grows to a large sized tadpole.

Calcitonin hormone:

High Ca ions concentration in 'the blood causes stimulation of the synthesis and release of calcitonin. The low levels of Ca ions suppress it secretion. Excess or deficiency of this hormone leads to a disturbance in calcium metabolism. It affects on nerve ,skeleton, muscle, blood etc.



Abnormalities of Thyroid Secretions:

l. Graves' Disease and Exophthalmic Goiter: 

Excess thyroxine produces a condition called Graves’ disease with exophthalmic goiter. it increases the basal metabolic rate. Prolonged disease can lead to cardiac failure. The cause of Graves’ disease is the production of an abnormal body protein. This protein continuously stimulates the thyroid to excessive secretion.

2.Cretinism: 

The congenital deficiency of thyroxin causes cretinism. In this case the individual fails to develop normally. There are following symptoms of this disease:

The affected persons have small coarse scanty hair,thick yellowish scaly skin.

Mentally retarded. The affected person also failed to develop sexually.

3.Myxoedema

Deficiency later in life produces a swelling of the neck (goiter). it is caused due to iodine shortage in diet. It may lead to deposition of excess fat. So weight is increased. This condition is _known as myxoedema. It is characterized by following changes:

Puffiness of hands and skin. All bodily and mental processes are retarded.

Table salt with iodine is recommended. So that there is no deficiency of iodine and thus no deficiency of thyroxin in the body.