what is thyroid gland ? thyroids hormone and diseases of thyroid gland

THYROID GLAND

introduction 

           thyroid gland is one the most important endocrine gland present in the body various releasing factors that are mainly produced from the pituitary gland  and the hormones that this gland produces are poured into the blood so that  they can be taken to the target site so that they can perform their specific functions this thyroid gland in present in the neck region structurally it consist of two lobes that are the left and the right lobes but in some few and rare cases there is a third lobe present that is known as the pyramidal lobe because this lobe is the remnant of the thyroglossal duct which usually waste away during the thyroid's gland descent . Its two lobes that are the left and the right lobe are connected to each other by the help of a structure known as isthmus from its front and upper view this gland looks like a butterfly having two lobes connected by isthmus if we talk about the length and the width of this gland than we can say that both of the lobes that are the left and the right lobe are about 5 cm long 3 cm width having a thickness of 2 cm whereas the connection between the two lobes isthmus is about 1.25 cm in both height and width this gland is larger in women as compared to men and in during during the condition of pregnancy the size of this gland increase because of many hormonal involvement of this gland in the process of pregnancy

position of thyroid gland 

        if we talk about the position of the thyroid gland in the human body than it is as following it is near the front of the neck lying against and around the front of the larynx and trachea thyroid gland is below Adam's apple and above the thyroid cartilage and the cricoid cartilage the connection between the two lobes that isthmus extends from the second to third ring of the trachea each of the lobe of the thyroid gland are embedded by parathyroid gland mainly on their posterior surfaces the tissues of the thyroid gland is mainly and mostly composed of thyroid follicles these follicles are made up of a central cavity filled with a sticky fluid called as colloid which is surrounded by a wall of epithelial follicle cells the colloid is the center of the thyroid hormone production and this production is very much dependent of the hormones whose main essential and unique component is iodine

function of thyroid gland 

      the main and the most important function of this endocrine gland is production of hormones such as 

• thyroxin or T4
• tri-iodothyronine or T3
• calcitonin

generally if we talk about some of the functions of the thyroid gland than we can say that some of its functions are following

• muscle strength
• breathing 
• menstrual cycle   
• cholesterol level check and balance
• body temperature
• body weight
• central and peripheral nervous system

in detail some of the functions of the thyroid gland is as following thyroid hormones are also mainly involved in metabolism such as thyroid hormones increases basal metabolic rate and it have its effect on almost all of the cells of the body such as absorption of substances and gut mobility are also influenced by thyroid hormones some of its other important functions are uptake of food by the cells breakdown of fats and increasing the number of free fatty acids in the body and despite of the increase of the number of free fatty acid in the body and that thyroid hormone on the other side controls and decrease the unnecessary cholesterol in the body by decrease it mainly by increasing the rate of secretion of cholesterol in the bile . Thyroid hormone also plays very important function in the developmental activities of the body such as the thyroid hormone somatotrophin play thyroid hormone is very crucial for the development of the young people . T3 and T4 play very vital role in brain maturation during fetal developing stage and it also very crucial role in maintaining normal sexual functions sleep and thought process . Thyroid hormone also plays a very important role in the increase and the strength of the heartbeat it also increases rate of breathing intake and consumption of oxygen and also increase the activity of the mitochondria all these factors when combine with each other increases blood flow in the body and also the body temperature

hormones of thyroid gland 

the main and primary function of the thyroid is the formation of iodine containing hormones and the hormones that thyroid gland produces are as following 

• thyroxin or T4
• tri-iodothyronine or T3
• calcitonin

the production and normal working of thyroid hormones are greatly affected by the iodine in the body production of thyroxin or T4 and tri-iodothyronine or T3 are regulated by thyroid stimulating hormone (TSH) that is in term released from the pituitary gland  thyroid stimulating hormone is stimulated by the thyrotrophic releasing hormone all of the thyroid hormones are created from thyroglobulin ( it is a protein that is present within the follicular space that is in-fact created in the rough endoplasmic reticulum of the follicular cells and than after the production is transferred in to the follicular space the thyroglobulin contains 123 units of tyrosine which reacts with iodine within the follicular space some of the applications of these hormones in the body are as following

thyroxin and tri-iodothyronine 

                                            thyroxin and tri-iodothyronine are both of thyroid hormones both of them are tyrosine based hormones and they are mainly responsible for the regulation of metabolism both thyroxin and tri-iodothyronine are partly composed up of iodine so therefor a deficiency of iodine in the body lead to decreased production of both of these hormones in human blood major form of thyroid hormone is thyroxin and thyroxin has a longer half life than tri-iodothyronine some of the functions of both of these hormones are 

• they act on basal metabolic rate by stimulating the breakdown of glucose and release heat and generation of ATP
• they function with somatotrophin hormone to control growth 
• they act directly on brain cells to differentiate 
• in amphibians they control process of metamorphosis if secretion of thyroid is deficient tadpole larvae of frog increases in size but does not metamorphose 
• excess thyroxin production causes a disease known as graves disease 
• under-secretion of thyroxin causes an abnormal condition called as cretinism 

calcitonin

            along with the production of thyroxin and tri-iodothyronine thyroid gland another hormone that is known as calcitonin and this hormone plays a very important role in the regulation of blood calcium level parafollicular cells produces calcitonin in response to high blood calcium level and so calcitonin decreases the release of calcium from the bone so therefore calcitonin effectively stimulates the movement of calcium into bones the effect and action of calcitonin is opposite to that of parathyroid hormone (PTH) released from the parathyroid gland calcitonin seems to be less essential than the parathyroid hormone as this is supported by the fact that calcium metabolism remains normal after the removal of the thyroid gland such as in case of thyroidectomy but same case is not with the parathyroid gland

      role of iodine in thyroid hormones 

                  iodine is very essential for the production of all of the thyroid hormones in the blood iodine travels in the form of iodide that is then taken up into the follicular cells by a sodium iodide symporter iodine than travels from within cells into the follicular space through the action of pendrin (it is also a iodide chloride antiporter ) when the follicle cells are stimulated by thyroid stimulating hormone the follicular cells reabsorb thyroglobulin from the follicular space the iodinated tyrosine are cleaved forming the thyroid hormone T3 and T4 the hormones secreted from the thyroid gland is about 80 -90% T4 and only 10 -20%

diseases of thyroid gland

some of the disease that are releases to thyroid gland are as following 

hyperthyroidism

• hypothyroidism 
• grave's disease
• thyroiditis
• thyroid nodules
• goiter 
• iodine deficiency

   thyroid nodules

                     thyroid nodules are often on the gland have a prevalence of 4 - 7% majority of the nodules do no cause any symptoms and are non cancerous nodules are more likely to occur in females who are exposed to radiation and in those who iodine deficient 

goiter
         goiter is a condition in which there is a enlargement of the thyroid gland goiters are present in some form in about 5% of people and are as a result of large number of causes sometimes in some cases no cause can be found and such a type of goiter is known as simple goiter some form of goiter can be associated with pain whereas many do not show any symptoms goiter may be associated with hyperthyroidism or hypothyroidism relating to underlying cause of the goiter
thyroiditis 
                             inflammation of the thyroid gland is also known as thyroiditis inflamed thyroid may cause symptoms of hyperthyroidism or hypothyroidism two types of thyroiditis initially hyperthyroidism and are sometimes followed by a period of hypothyroidism hashimoto's thyroiditis and postpartum thyroiditis
hashimoto's thyroiditis is a autoimmune disorder in which the thyroid gland is infiltrated with B and T lymphocyte cells whereas  postpartum thyroiditis occurs in some females following childbirth after delivery the gland becomes inflamed and the condition presents with a period of hyperthyroidism followed by hypothyroidism and usually a return to normal function the coarse of the illness place over several months and is characterized by a painless goiter
iodine deficiency 
                                          iodine deficiency predispose to goiter if it widespread than it is known as endemic goiter pregnant women deficient of iodine can give birth to infants with thyroid hormone deficiency
grave's disease
                                         grave's disease is an autoimmune disorder that is the most common cause of hyperthyroidism in this disease for an unknown reason auto-antibodies develop against the thyroid stimulating hormone receptors in addition gradual protrusion of the eyes may occur and is called as grave's opthalmopathy and there may be swelling of the front of the shins
hypothyroidism  
                                        an under-active thyroid gland result in hypothyroidism typical symptoms are abnormal weight gain tiredness constipation heavy menstrual bleeding hair loss cold intolerance slow heart rate iodine deficiency is the most common cause hyperthyroidism and a auto immune disorder known as hashimoto's thyroiditis is also one of its cause some forms of hyperthyroidism can result in myxedema and severe cause can result in myxedema comma