The thyroid gland is a butterfly-shaped endocrine gland. It is brownish-red that rich in blood vessels. Vital nerves that are responsible for voice quality also pass through the thyroid gland.
The thyroid gland is found in all vertebrate, but they are quite variable to shape and anatomical position. In some lower vertebrates, only thyroid follicles are present.
In human, the thyroid gland consists of two lobes that lie on either side of the roof of the trachea and are usually connected by a thin isthmus extending over the anterior surface of the second, third and fourth tracheal rings.
Two layers of fibrous connective tissues cover the thyroid. The gland is about two inches (5 cm) long. The weight of the normal thyroid gland of the adult people ranges from 20-60 gm. The gland is actually situated in front of the throat just below the thyroid cartilage, known as the Adam`s Apple.
The thyroid consists of two fairly symmetrical lateral lobes. Each lobe measures about 5 x 2 x 2 cm in size. The two lobes are connected by a strip of tissue, known as the isthmus. Each lobe consists of many follicles of variable size. Each follicle is lined by a single layer of granular cubical epithelium and filled with protein material, called colloid. Thyroid follicles contain a lesser number of high cubical mitochondria rich-cells. These are called parafollicular cells.
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Hormones of Thyroid Gland
The thyroid gland contains two types of cells found in the thyroid follicles and secretes the following three types of hormones:
Thyroxine: It is also known as T4, which is secreted by principal cubical epithelial cells.
Tri-iodothyronine: It is also known as T3, which is also produced by principal cubical epithelial cells.
Thyrocalcitonin: It is produced by the parafollicular cells.
Thyroxine and Tri-iodothyronine
These two hormones are iodinated derivatives of tyrosin (amino acid). They are generally referred to as thyroid hormones. Thyroid gland performs the following functions through these two hormones. It has been observed that tri-iodothyronine is more active than thyroxin.
Functions of Thyroid Hormones
Hypofunction of Thyroid Gland or Hypothyroidism
Less secretion of thyroid gland produces cretinism in infancy or childhood and myxoedema in adults.
It is the condition in children due to severe thyroid deficiency. It is also known as congenital iodine deficiency syndrome. It hampers both mental and physical development, if untreated. It mainly occurs due to dietary iodine deficiency. Many people suffer from this congenital iodine deficiency syndrome around the world. It is a significant public health problem in many countries of the world. Many developed countries already have eliminated through iodine supplementation of food.
The most characteristic features of this defect are:
This disease generally occurs more in adult female than male due to decrease or absence of thyroid hormone. It is also known as severely advanced hypothyroidism. It happens when the body does not make sufficient thyroid hormone. If untreated or undiagnosed, it causes severe advanced hypothyroidism. Critically advanced hypothyroidism can lead to Myxedema crisis, a life-threatening situation.
Causes of Myxedema (hypothyroidism)
Symptoms of Myxedema
Hyperfunctions of Thyroid or Hyperthyroidism
This clinical syndrome due to hypersecretion of the thyroid gland is known as exophthalmic goitre or Graves disease.
It is also known as calcitonin. It is a protein hormone secreted from the parafollicular cells or C-cells (mitochondria-rich cells) of the thyroid gland. It is also secreted from the cells of the glandular ultimobranchial bodies in fishes, birds, and other non-mammalian vertebrates.
Functions of Thyrocalcitonin
The thyroid gland is a very important endocrine gland that is situated in your neck region. It produces three hormones such as thyroxine (T4), tri-iodothyronine (T3) and thyrocalcitonin. Among them, T3 and T4 are the most important hormones which play an important role to do normal function in your body.
There are many thyroid disorders due to abnormal secretion from the thyroid gland. These disorders occur in babies, children, teenagers and adults. It is estimated that about one in 20 people suffer from some kind of thyroid disorder. If untreated or undiagnosed, it can lead to a severe, life-threatening situation.