THE thyroid is an important gland of the endocrine system. It has the shape of a butterfly and synthesizes two hormones: a T3 (triiodothyronine) and T4 (thyroxine), which act on metabolism. For the synthesis of these hormones, the thyroid requires iodine. To avoid a deficiency of this mineral in the population, common table salt is currently supplemented with sodium iodide.
Thyroid hormone secretion is controlled by a hormone secreted by the anterior pituitary called thyroid-stimulating hormone, or TSH. In addition to T3 and T4, the thyroid is also responsible for releasecalcitonin, a hormone that acts on calcium metabolism.
Read too: Organs of the Human Body - What They Are and Functions
What is the thyroid?
The thyroid is a endocrine gland consisting of two lobes, which are joined by a tape of glandular tissue (isthmus). The gland is located just below the larynx and each lobe is arranged on one side of the trachea. On a adult individual, weighs about 20 to 30 grams. It is worth saying that she is encapsulated by two layers of connective tissue.
The thyroid is made up of several thyroid follicles, which have a diameter of about 0.2 to 0.9 mm. Each follicle consists of a layer of cubic cells that surrounds a cavity, which has a gelatinous substance known as colloid.
Colloid is mainly made up of a glycoprotein called thyroglobulin, which contains the hormones T3 and T4. Follicular cells take up colloid by endocytosis and a series of reactions takes place, releasing T3 and T4 into the cytoplasm. You hormones they cross the cell membrane and diffuse into the capillaries.
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In the thyroid, the parafollicular cells or thyroid C cells, which are responsible for the production of the hormone calcitonin. The secretion of this hormone is activated when there is an increase in blood calcium concentration.
Read too: Importance of calcium in the body
Thyroid hormone secretion
The secretion of T3 and T4 hormones is increased due to the action of the hormone TSH, the thyroid stimulating hormone. When thyroid hormone levels in the blood fall below normal levels, the hypothalamus secretes thyrotrophin-releasing hormone (TRH), which acts on the pituitary, inducing it to secrete the TSH. TSH then stimulates the release of thyroid hormones. When there is an increase in thyroid hormones in the body and they return to normal levels, there is a reduction in TSH secretion by the pituitary and, in this way, the body's balance is maintained with adequate hormonal amounts.
Thyroid function
The thyroid is a endocrine gland that produces hormones thyroxine (T4), triiodothyronine (T3) and calcitonin. Hormones T3 and T4 are generally related to the regulation of metabolism in the body.
Thyroid hormones act, for example, on:
growth;
stimulation of the metabolism of carbohydrates and lipids;
increased basal metabolism;
reduction in body weight;
increased blood flow;
increased heart strength;
increased production of digestive secretions and gastrointestinal tract motility;
increased speed of thought, etc.
THE calcitonin is a hormone related to the reduction of blood calcium, with the main effect of inhibiting the reabsorption of bone tissue.
Read too: Feedback Mechanism - the responses produced by our body in situations of imbalance
Hypothyroidism and hyperthyroidism
The thyroid often doesn't work properly, may occur an increase in hormone production or a drastic reduction in the production of these hormones. When thyroid hormones are produced in insufficient amounts, we have a case of hypothyroidism, and when production is excessive, we have a case of hyperthyroidism.
O hyperthyroidism can have different causes, the most common being Graves' disease, an autoimmune disease that leads to thyroid malfunction. In the case of hypothyroidism, the main cause is also an autoimmune disease, known as tHashimoto's thyroiditis.
The Brazilian Society of Endocrinology and Metabology highlights as symptoms ofhypothyroidism:
slower heartbeat;
intestinal malfunction;
compromised growth;
memory reduction;
tiredness;
muscle and joint pain;
somnolence;
dry skin;
weight gain;
high cholesterol;
depression.
Still according to Society of Endocrinology and Metabolism, in the case of hyperthyroidism, stand out as symptoms:
weight loss;
rapid heartbeat;
diarrhea and frequent bowel movements;
agitation;
compromised sleep;
the person feels very energetic despite being tired all the time.
It is noteworthy that, in both hyperthyroidism and hypothyroidism, there may be an increase in the volume of the thyroid gland, leading to àgoiter formation.
By Vanessa Sardinha dos Santos
Biology teacher
Would you like to reference this text in a school or academic work? Look:
SANTOS, Vanessa Sardinha dos. "Thyroid"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/tireoide.htm. Accessed on June 27, 2021.
