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The Thyroid (Human Anatomy): Position, Function, Thyroid Disease, thyroid hormones

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Thyroid gland: Introduction:

It is the largest and most famous endocrine gland in our body. This gland plays an important role in the functioning of the human body. 
In this post, we will know all the information related to the thyroid gland.

Thyroid Disease, thyroid hormones

Position of the Thyroid gland:- 

It is a brownish red, H-shaped bilobed gland, located in our neck, on the lateral parts of the thyroid and cricoid cartilages under the larynx. 

Structure of Thyroid gland:-

In adult humans, this gland is about 5 cm long and 3 cm wide. Its weight is on average 25 gm.
It is somewhat larger in women. 

The thyroid gland is made up of innumerable small vesicles on which are covered with cuboidal epithelium, which are interconnected by connective tissue. There is an ample supply of blood in them. 

These cells secrete a sticky secretion called a fibrous colloid and contain an iodine compound, the active substance of this compound being the thyroxine hormone.

Hormones of the thyroid gland:- 

The thyroid gland secretes two iodine-containing and one iodine-free (without iodine) hormone. 

(1) Iodine containing hormones:-

 (a) tetraiodothyronine or T4 
 (b) triiodothyronine or T3

(2) Iodine-free hormones:

Thyrocalcitonin hormone 


Tetraiodothyronine hormones are also called thyroxine hormones.
→ The thyroid gland secretes about 0.08 mg of T 4 and about 0.04 mg of T 3 per day.
→ T3 hormones are many times more effective than T4.

How much iodine should be in the daily diet:- 

The adult human body contains about 5-6 mg of iodine and most of it resides in the thyroid gland. 
The thyroid gland uses about 0.15 mg of iodine per day to secrete iodine-containing hormones, so about 0.15 mg (150 µg) of iodine should be obtained daily from food.

Iodine is usually obtained from green vegetables, dairy products, drinking water, seafood, etc. 
Exceeding amounts of iodine are often excreted in the urine. 

Control of secretion of thyroid gland hormones:- 

→ The secretion of hormones of the thyroid gland is controlled by the pituitary gland and the hypothalamus

→ Thyrotropin-releasing hormone (TRH ) from the brain hypothalamus stimulates the pituitary gland to secrete thyrotropin or thyroid-stimulating hormone (TSH ), which stimulates thyroid secretion. 

→ The secretion of TRH depends on the amount of TSH and thyroxine (T4) and glucose present in the blood and the metabolic rate of body cells. 

→ The secretion of these hormones increases in winter and in pregnant women.


Functions of thyroid gland's iodine-containing hormones (T3, T4):- 

1. These hormones of the thyroid are the catalysts of oxidation metabolism in all cells of the body except the central nervous system, retina, spleen, genitals, and lungs.
 Therefore, due to their effect, glucose and oxygen are consumed and the rate of energy production and the level of Basal Metabolic Rate (BMR) are maintained. The increase in their secretion increases the BMR, as a result of which the body temperature also increases due to the production of more ATP. 
2. Due to the metabolic effect of these hormones, the absorption of digestive products in the intestines, the rate of heartbeat, the synthesis of enzymes and other proteins in the cells, glycogen in the liver cells, and the synthesis of vitamin A from proteins and glucose and carotenes increases. 
3. The excitability increases due to the effect of these hormones and the effect of many other hormones also increase. 
4. These hormones regulate the amount of cholesterol.
5. These hormones are very important for healthy life and the growth of the body. 

Functions of thyrocalcitonin:-

This hormone is secreted by C cells found in the back of the thyroid gland. Its molecules are made up of polypeptide chains of units of 32 amino acids.
The function of the thyroid gland's iodine-free hormone (thyrocalcitonin) -  

1. This hormone stimulates the formation of bones.

2. Prevents disintegration of bones.

3. Also increases the excretion of calcium in the urine.

4. Due to its effect, the number of calcium ions in the ECF is reduced.

5. Increases calcium level in blood by absorbing calcium from food. 

Diseases caused by under secretion of thyroid gland hormones:-

This abnormality of the thyroid gland can be genetic or can be due to a lack of iodine in the diet. This irregularity is more often found in women. This causes the following diseases - 

1. Cretinism - 

This disease occurs due to under secretion of the thyroid in the fetal or infant stage. In this, the children remain dwarf. The shape of the body gets distorted. Due to being retarded, such dwarfs are called Critins. In this, the development of genitals also remains incomplete.

2. Myxoedema -

It is caused by under secretion of the thyroid in adults. In this, the metabolic rate is greatly reduced. There is weakness like old age before time. Blood pressure decreases. Hair starts falling out and drying out. The skin becomes pale and rough. The voice becomes low and heavy. Can't bear the cold. There is weakness in the muscles. Wisdom becomes weak. There is a decrease in infertility. The number of cholesterol increases. The body looks bloated but weak and lethargic. Protein synthesis is reduced. Weight increases. The temperature decreases. The pulse moves slowly. 
Giving thyroxine in the form of medicine to such a patient ends the disease.

3. Simple goiter - 

In this, the thyroid gland increases, due to which the neck also swells and starts appearing thick. 
Due to the lack of iodine in the diet, thyroxine cannot be produced due to the lack of iodine in the blood, as a result the secretion of thyroid-stimulating hormone (TSH) from the pituitary gland also increases to meet this deficiency. Due to the effect of TSH, the number of cells in the thyroid gland starts to increase in order to take more and more iodine from the blood, due to which this gland swells and becomes bigger. 
Due to this the size of the gland increases but the secretion remains normal.

4. Hashimoto's disease - 

Sometimes, due to old age, injury, infection, operation, etc., the hormones of the thyroid gland become so low that their receptor proteins present in the cells of the body do not recognize them, so the body's immune system considers them to be toxins and in the body. Antibodies are formed that destroy these hormones, which also destroy the thyroid gland itself. Thus it is an autoimmune disease. It is also called thyroid suicide. 
These diseases can be got rid of by increasing the amount of iodine in the diet.

Diseases caused by excessive secretion of thyroid gland hormones -

1. Thyrotoxicosis - 

It may be genetic. 
This disease can be caused by chronic infectious diseases like influenza, measles, tuberculosis, wholly cough or conception, overeating, etc.
In this, the metabolic rate increases very much due to which the body temperature, blood pressure, heartbeat, etc.
Due to this, unnecessary excitement in the body, insomnia, tiredness, irritability, nervousness, diarrhea and tremors, etc. Starts sweating more.

2. Expansive toxic goiter - 

In this, the over-secreting thyroid gland swells up and takes the form of an esophagus. 
Due to this, the body becomes lean and slim, and the metabolic rate increases.

3. Exophthalmic goiter - 

The accumulation of mucus under the eyeballs due to the over secretion of the thyroid gland causes the eyeballs to protrude outwards, which makes the vision look scary and staring, and the metabolic rate increases. 

4. Plumer's disease - 

 Due to excessive secretion in this disease, sometimes due to the formation of lumps in the thyroid gland of the patient, the gland swells irregularly. 

Treatment of diseases caused by over secretion of thyroid hormones:- 

1. By cutting and removing some parts of the gland, the patient gets benefits.
2. Taking medicines that stop the production of thyroxine hormones, the disease is cured.
3. Treatment using radioactive iodine.
4. Treatment by homeopathic and naturopathic medicine.

It is worth noting that by drinking water containing chlorine, there is a deficiency of iodine in the body, the body is not able to absorb the iodine taken in the food, this is the reason why drinking water containing chlorine causes the body to become fat, so drink it thoughtfully.


Thanks, friend!   We have told here the complete information about the thyroid gland, which is researched and certified. 

It is very useful for medical exams, science exams, for knowledge, for patients and doctors.

Sorry for any errors. Do share this topic.

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