Role of Thyroid Gland in Our Body

Metabolism is a process that provides energy to the body, setting off chains of chemical reactions to perform vital life processes. One of the most crucial endocrine glands, the thyroid gland, plays a significant role in the body's metabolism, growth and development.

Iodine supplementation is essential for proper thyroid functioning. Studies show that the most common cause of thyroid disorders is iodine deficiency. An overactive or underactive thyroid gland can significantly affect metabolism. This article explains the role of the thyroid gland in regulating growth and energy expenditure and controlling the metabolic reactions occurring in the body.

What Is The Thyroid Gland?

The thyroid gland is an endocrine gland concerned with the smooth functioning of metabolic processes in the body. It secretes thyroid hormones to regulate body functions. Located just in front of the neck and below Adam's apple, this gland produces hormones required for brain and bone development. 

Thyroid Gland Anatomy

The thyroid gland, weighing about 15-20 grams in normal adults, is a highly vascular gland situated anteriorly in the neck. The following section describes the gland's location, basic anatomy and physiology.

Location of The Thyroid Gland

The thyroid gland's precise location is in the anterior part of the lower neck. It lies posterior to the neck muscles and below the laryngeal cartilage. The thyroid gland lies near important anatomical structures like the parathyroid glands and laryngeal nerves. 

Structure and Shape of The Thyroid Gland

The thyroid gland attaches itself to the trachea through a network of connective tissue known as Berry's ligament. It is a two-lobed (left and right) gland in the neck's visceral chamber. It has a centrally located isthmus connecting both lobes. 

The gland is an H- or U-shaped structure overlying the second to fourth tracheal rings. The thyroid gland comprises two lobes, with a middle section of thyroid tissue (thyroid isthmus) connecting them. This positioning gives it a butterfly-like appearance. 

The thyroid gland comprises structural and functional units known as the thyroid follicles, lined with follicular and parafollicular cells. These cells enclose a colloid-filled cavity or lumen. 

Blood Supply and Nerve Supply To The Thyroid Gland

The two main arteries that supply blood to the highly vascularised thyroid gland are:

• Superior Thyroid Artery - the first branch of the external carotid artery
• Inferior Thyroid Artery - branching from the subclavian artery

Both arteries offer a dual blood supply to the thyroid gland. The inferior thyroid artery, however, is the source of the principal blood supply. From the venous system, deoxygenated blood drains into the jugular vein via the superior and middle thyroid veins. It finally joins the superior vena cava draining deoxygenated blood into the heart.

The autonomic nervous system (parasympathetic division) is the prominent source of nerve supply to the thyroid gland. The left and right laryngeal nerves move across the thyroid gland, innervating it.

Thyroid Hormones

Just like any other endocrine gland, the thyroid gland also secretes hormones. These hormones are responsible for controlling several metabolic activities in the body. The following section talks about the types and functions of thyroid hormones.

Introduction To Thyroid Hormones

The hormones produced by the thyroid gland are collectively called the thyroid hormones. The chemical structures of these hormones reveal the presence of iodine as an essential part of their molecules. The thyroid gland synthesises these hormones through iodination or binding with proteins.

Types Of Thyroid Hormones

Thyroid hormones are of the following types:

• T3 or triiodothyronine - This hormone is essential for proper brain and heart function, digestion and bone health. It is an active thyroid hormone produced in trace amounts.

• T4 or tetraiodothyronine - It is commonly known as thyroxine. It regulates the rate at which the body utilises calories. T4 is produced in large quantities by the thyroid gland in an inactive form. This inactive precursor is converted into the active form, triiodothyronine (T3), in peripheral tissues.

• Calcitonin - It helps regulate the calcium levels in the body.

The follicular cells secrete T3 and T4 hormones, whereas the parafollicular cells secrete calcitonin.

Role Of Thyroid Hormones In The Body

Thyroid hormones affect the day-to-day working of many significant life processes. Here is a list of functions performed by the thyroid hormones:

• They stimulate the metabolism of nutrients like fats, carbohydrates and proteins.
• They regulate the basal metabolic rate.
• They can induce lipid synthesis or lipolysis.
• They affect ovulation and menstruation in women.
• They stimulate brain maturation during the prenatal stage.
• They help with protein synthesis and muscle growth.
• In children, these hormones work with growth hormones to enhance bone development.

Regulation Of Thyroid Hormones

Since the thyroid hormone correlates with body weight and energy expenditure, its regulation is crucial. The following section explains how the hypothalamus and pituitary regulate the thyroid hormone levels in the bloodstream.

Role Of The Hypothalamus and The Pituitary Gland

The hypothalamus and pituitary release the thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH), respectively, to regulate thyroid hormone levels. It involves a complex feedback mechanism.

• The hypothalamus releases TRH, triggering the anterior pituitary to secrete TSH.
• The anterior pituitary releases TSH, stimulating the thyroid gland to produce T3 and T4 hormones. The pituitary sends signals to the thyroid gland to secrete more or fewer hormones, depending on the current levels in the bloodstream.

Negative Feedback Mechanism

When T3 and T4 levels go below the normal range, the hypothalamus releases TRH. It stimulates the pituitary gland to secrete TSH, which then triggers the thyroid gland to produce more T3 and T4.

When sufficient T3 and T4 levels are present in the bloodstream, the hypothalamus stops releasing TRH and shuts itself off. Consequently, the pituitary stops secreting TSH, causing no more synthesis of T3 and T4. This negative feedback loop regulates the amount of thyroid hormones in the body.

Importance of Balanced Thyroid Hormone Levels

Maintaining a good balance of thyroid hormones keeps the metabolism in check, helps control weight and boosts energy levels. An unbalanced thyroid can be the onset of several thyroid disorders discussed in the following section.

Common Thyroid Disorders

Too high or too low levels of thyroid hormones in the bloodstream may lead to thyroid disorders. Some of them may turn chronic if not regulated early.

Hypothyroidism

Hypothyroidism condition occurs when the thyroid gland cannot release enough hormones to meet the body's physiological needs. An underactive thyroid may have effects on neurological, cardiovascular and metabolic systems.

Hyperthyroidism

In this condition, the thyroid gland secretes excessive thyroid hormones, disrupting the normal levels. Also known as overactive thyroid, hyperthyroidism accelerates metabolism causing weight loss, palpitations and irritability.

Thyroid Cancer

The growth of malignant or cancerous cells in the thyroid tissue causes thyroid cancer. According to reports, the incidence of thyroid cancer is increasing in India. 

Importance of Iodine in Thyroid Function

Specifically, iodine is present in T3 and T4 thyroid hormones and is crucial for synthesising the T3 and T4 hormones. Therefore, sufficient iodine intake is essential for the regular production of these hormones to control the metabolic processes.

Lifestyle Factors Affecting Thyroid Health

Since the thyroid gland controls metabolism, improper functioning can harm the entire body and its systems. Here are some lifestyle factors that can affect thyroid health and ways to manage them.

Importance Of Exercise

Including daily exercise can prevent thyroid disorders by increasing energy levels and lowering the risk of developing chronic diseases. Research has shown aerobic exercise can increase T3 and T4 hormone levels to the optimum range.

Sleep and Stress Management

Improper sleep schedules and stress may aggravate thyroid disorder symptoms like moodiness and anxiety. Exhaustion is another side effect. Getting adequate rest and managing stress levels can balance thyroid hormones.

Other Factors Affecting Thyroid Health

Additional factors influencing thyroid health are:

• Diet and nutrition
• Family history of thyroid disorders
• Associated autoimmune conditions
• History of radiation therapy
• Environmental factors like exposure to chemicals, heavy metals, toxins and high levels of fluoride (antagonistic to iodine)

Conclusion

The thyroid gland is a vital endocrine gland that may appear inconsequential in size but significantly affects body metabolism. The thyroid hormones released by this gland bring about growth and development. Taking care of it and ensuring a proper balance of thyroid hormones is essential to maintain the smooth functioning of the body.

FAQ

What are The Functions of The Thyroid Gland?

The principal functions of the thyroid gland are:

• Playing a crucial role in metabolism, growth and development.
• Releasing hormones into the bloodstream to help regulate several body functions.
• Affecting the functioning of all other physiological systems.

How are Thyroid Hormones Regulated?

The hypothalamus releases TRH which stimulates the anterior pituitary to release the TSH. Once the thyroid hormones (T3 and T4) get released into the bloodstream, they inhibit the synthesis of TSH and TRH. This negative feedback control mechanism helps in the regulation of thyroid hormones.

What is The Role Of Nutrition in Thyroid Health?

Both over- and under-consumption of some vitamins and minerals can affect thyroid health. Micronutrients like iodine and selenium can affect thyroid hormone synthesis and function. Nutritional deficiencies are one of the major causes of thyroid gland disorders.

How Does Pregnancy Affect Thyroid Health?

Thyroid hormone synthesis increases by 50% during pregnancy. The increased metabolic needs of the pregnant woman result in changes in the thyroid gland physiology. Both hypo and hyperthyroidism are possible outcomes. Therefore, there is an increased iodine requirement during pregnancy.