Thyroid gland
Structure, function, and role of the thyroid gland
Structure thyroid gland.
Thyroid gland (glandula thyroidea) – vessel gland, a component of endocrine system, synthesizes a number of hormones essential for homeostasis of the body.
Thyroid gland – a symmetric organ composed of two lobes and isthmus. Right and left lobes are directly adjacent to trachea, isthmus is located on the anterior surface of trachea.
Some authors distinctly outline pyramidal lobe of the thyroid. In healthy (euthyroid) condition the weight of the thyroid ranges from 20 to 65 g, while the lobe sizes depend on gender and age and can vary in rather wide range. The size and weight of the thyroid increase in puberty and decrease in senile age. Temporary enlargement of the thyroid is also observed in women during the pregnancy, which is spontaneously reversible within 6-12 months after the delivery.
In the thyroid gland two iodine-containing hormone – thyroxin (T4) and triiodothyronine (T3) and one peptide hormone – calcitonin are synthesized. In the thyroid tissue amino acid tyrosine is accumulated, which is deposited and stored as a protein – thyroglobulin (construction material for the thyroid hormone synthesis). In the event of molecular iodine availability and engagement of the enzyme thyroid peroxidase (TP), hormones T3 and T4 are synthesized. Thyroxin (T4) and triiodothyronine (T3) are synthesized in the apical thyroid epithelium. Calcittonin (thyrocalcitonin) is produced by the parathyroid glands and C-cells of the thyroid gland.
In the human organism thyroid hormones play essential role in homeostasis regulation. They are directly involved in principal metabolic processes in tissues and organs; formation of new cells and their further differentiation; and genetically preprogrammed death of the old cells (apoptosis). The other equally important function of the thyroid hormones in the organism is the maintenance of constant body temperature and energy production (so called calorigenic effect). Thyroid hormones regulate oxygen consumption by the tissues, oxidation and energy production processes, and control generation and neutralization of the free radicals. Throughout the lifetime thyroid hormones have the impact on mental, intellectual and physical development of the organism. Hormone deficiency in the early age results in the growth retardation, and may provoke the abnormalities of the bone tissue, while hormone deficiency during the pregnancy considerably increases the risk of kretinism for the unborn child due to the brain underdevelopment during the intrauterine period. Thyroid hormones are also responsible for normal immune function – they stimulate so called T-cells, which protect the organism from the infection.
Prevalence of thyroid diseases
According to the World Health Organization (WHO), thyroid diseases have the second-highest prevalence among all endocrine disorders, right behind diabetes mellitus. Over 665 million people suffer from endemic goitre or other thyroid diseases worldwide; 1.5 billion people are at risk for developing an iodine-deficient condition. Statistical data show that the annual increment in the number of thyroid disease cases is 5 %.
More than 20 million people live with diagnosed thyroid disorders in Russia. In particular, statistically one out of two Moscow Region inhabitants suffers from a thyroid disease. And in some Russian regions as much as 95 % of the population are afflicted!!!
There are numerous causes of this situation: from iodine deficiency and unfavourable ecology to stress and genetic abnormalities.
Diagnostics of the thyroid gland diseases
Diagnostics of the patients with abnormal conditions of the thyroid should include physical, instrumental, and laboratory methods enabling to assess its morphology and functional activity. For instance, palpation (tactile examination with fingers) of the thyroid enables to determine its dimensions, consistency of the thyroid tissue and absence or presence of nodular lesions. Today enzyme immunoassay accomplished by the standard test kits is the most informational laboratory method for determination of the thyroid hormone concentration. In addition, functional status of the thyroid can be assessed from incorporation of the isotope 131I or Technecium 99mTc. Modern approaches to evaluation of the thyroid gland structure also include ultrasound diagnosis (echography), computed tomography (MRT), thermography and scintigraphy. These methods enable to gain information on the dimensions of the organ and the pattern of radiocontrast media accumulation in the different parts of the gland. Fine needle aspiration biopsy is used for the thyroid cells collection for the analysis and further investigation.
It should be noted that despite wide diversity of the laboratory methods, the assays for free/bound forms of T3 and T4 hormones, for anti-thyroglobulin antibodies (anti-TG-AB) and for anti-thyroid peroxidase antibodies (anti-TPO AB), as well as the assay of plasma thyroid stimulating hormone (TSH) level are the fastest methods of laboratory control. In addition, sometimes urine iodine excretion is determined. This investigation enables to learn, whether the thyroid gland disease is related to iodine deficiency.
The most common diseases of the thyroid gland
There are a lot of various abnormalities of the thyroid gland. Almost all of them, depending on the specific alteration of the thyroid functional activity, can be divided into 3 large groups.
- Diseases, associated with increased synthesis and/or secretion of the thyroid hormones. These abnormalities have common name thyrotoxicosis.
- Diseases associated with decreased synthesis of the thyroid hormones (Т3, Т4) and/or low blood level of these hormones. These abnormalities have common name hypothyroidism.
- Thyroid gland diseases not associated with alteration of functional activity, for which only morphological changes of the gland structure are typical (formation of goiter, nodules, hyperplasia etc.).
Hyporthyroidism (hypofunction) – this condition characterized by the low level of the thyroid hormones is found in 19 of 1000 females and 1 of 1000 males. Hypothyroidism often can not be revealed for a long period of time, because the symptoms develop very slowly, and in this period the patients have mo complaints. Furthermore, hypothyroidism symptoms can be non-specific, and the disease can be masked by a number of other diseases, and this, in turn, results in wrong diagnosis and administration of inappropriate therapy for this abnormalities.
Chronic thyroid hormone deficiency in the human body results in slowing down of all metabolic processes, which leads to diminished energy and heat production. Clinical manifestations of hypothyroidism include:
- fatigue,
- weakness,
- performance impairment,
- memory impairment,
- feeling cold,
- swelling,
- fast weight gain,
- skin dryness,
- dull and fragile hair.
In women hypothyroidism can cause menstrual disorders and lead to early menopause. Depression is one of the common symptoms of hypothyroidism and the reason for visiting psychologist or mental specialist.
Thyrotoxicosis (hyperfunction) – this clinical condition is characterized by persistent elevation of blood thyroid hormone levels leading to acceleration of all metabolic processes in the organism. Classic thyrotoxicosis symptoms include:
- irritability and hot temper,
- decrease in body weight (associated with good increased appetite),
- palpitations (sometimes associated with rhythm disturbance),
- sleep disorders,
- constant huperhydrosis,
- increased body temperature.
Sometimes, especially in elderly persons, these symptoms are not pronounced, and the patients explain their condition by the natural age-specific changes of the organism. Thus, for example, feeling hot, “flashes”, which are typical signs of thyrotoxicosis, may be considered by women as manifestations of menopause.
Goiter formation – the organ enlargement beyond acceptable size (thyroid gland volume is 9-25 ml in healthy males and 9-18 ml in healthy females) is a rather common phenomenon. In euthyroid condition some enlargement of the thyroid is observed in adolescents, in pregnant women and then in menopausal women. The goiter is categorized into diffused or nodular goiter depending on enlargement of the whole organ or of some part of the thyroid.
The causes of thyroid gland diseases
It is no doubt that genetic factors predisposing the person to one or another disease are of paramount importance in the development of the thyroid gland disease. However, the role of various external stress factors in development of thyroid abnormalities is also unquestionable. Among them:
- psychoemotional overstrain,
- imbalanced diet leading to vitamin and/or trace mineral deficiency (including iodine deficiency),
- unfavourable environmental and radiation situation,
- infections,
- chronic diseases,
- therapy with some drugs, etc.
Just these factors trigger the diseases of the thyroid gland.
More simply, the human organism is constantly exposed to some factors compelling the thyroid to produce hormones in either greater or less amounts. This results in “outwearing” or “blanching” of this endocrine organ, which becomes incapable to synthesize optimal amount of theT3 and T4 hormones for the body needs. Eventually, either chronic functional disorders of the thyroid (hypo-, hyperthyroidism), or morphological structure alterations develop (goiter formation, node formation, hyperplasia, etc.).
Conventional therapeutical agents and methods used for the disease of the thyroid gland
Generally, for the thyroid hormonal disorders manifested as hypo- or hyperthyroidism chemotherapeutic agents are administered. For structural changes of the thyroid including nodular forms, especially if malignant neoplasms are suspected or in the case of difficult swallowing or respiration, surgical intervention is employed (resection, thyroidectomy).
In Russia monoproducts of the thyroid hormones are most commonly used, including pharmacotherapeutics triiodothyronine, thyroxin and their combinations and compexes with inorganic iodine (Iodthyrox, Thyreotom, Thyreocomb). These pharmaceuticals compensate for deficiency of the endogenous thyroid hormones and, as a rule, are used for the lifetime. This method of the thyroid gland therapy has been called hormone replacement therapy (HRT). Main drawback of this method is that it results in inhibition of the synthesis of endogenous thyroid hormones, and the patient becomes dependent on hormone replacement therapy and cannot live without the tablets. Other side effects of HRT include allergic reactions to synthetic hormones, cardiac rhythm disturbance, and nervous disorders.
Thyrostatics, i.e. the agents disturbing the processes of synthesis, formation or release of thyroid hormones to the blood, are the second class of the products, which are widely used for the therapy of thyroid gland diseases. This group comprises thiamazole derivatives (Thyrosol, Mercazolyl), thiouracyl derivatives (Propycil) and also diiodotyrosine. Conventionally the thyrostatics are used to suppress elevated production of the thyroid hormones. However, it should be taken into account that such corrective therapy leads dystrophy of the thyroid gland tissue, considerable diminishment of the functional activity of the organ, and after a time the patient is imposed to transfer to hormone replacement therapy.
Promising products for the thyroid gland diseases
In addition to chemotherapeutics in Russia a number of herbal products are available, mainly, as approved biologically active supplements, which are used for complex therapy of the thyroid gland disease. Based on the composition of the supplements, this group of the products can be classified as follows:
- iodine monoproducts (containing only organic or inorganic iodine);
- iodine-containing products in combination with herbal components;
- all-herbal products.
Iodine-containing complexes demonstrate the narrow range of therapeutic activity, and thus their use is limited.
In the promotional materials and in pharmacies various forms of biologically active supplements containing finely ground parts of the medicinal herb are often offered. Such form of vegetable raw materials processing is inefficient for a number of reasons. It is well-known that the content of biologically active ingredients (BAI) in extract is 5-10 fold compared to raw material, which is used for the product manufacture. Hence, it is necessary to intake mass units (mg, g) of raw material in the amount 5-10-fold exceeding the mass units of extract. Furthermore, unfair manufacturers add to the product finely ground parts of the plants knowingly lacking pharmacological effect. The phenomenon of organ-specific BAI accumulation is well-known in phytopharmaceutics; for example, high level of active ingredients in roots with zero level of the same BAI in aboveground portions of the plants. Such technique of the biosupplement manufacturers is the certain willful misrepresentation aimed on uninformed customers. Furthermore, it should be noted that ingestion of biosupplements containing ground parts of the plants is often dangerous (due to high microbial contamination of the raw material leading to dyspeptic events: abdomen heaviness, flatulence, meteorism, nausea, colic, aggravation of the gastrointestinal disease – constipation, dysperistalsis, appendicitis). Perhaps, the main disadvantage of such products is the low bioavailability of biologically active ingredients from the whole plant raw material and high level of ballast ingredients, resulting in drastic deterioration of the pharmacological effect of these products.
Today ENDONORM® is the most interesting product for the clinicians, especially for endocrinologists and endocrinologists-gynecologists. Due to clinically validated extracts of the medicinal herbs in the composition of this product it is highly effective for the thyroid gland diseases, such as hypo- and hyperthyroidism, autoimmune thyroiditis, nodular/multinodular goiter, and for other thyroid gland disorders.
Detailed information about ENDONORM® is available here.
