thyroid gland
- It is largest endocrine gland situated in the neck close to the trachea. The gland is butterfly or H shape and consists of two elongated oval lobes joined by a narrow band called isthmus.
- It is highly vascular organ and contains many spherical or oval sac-like follicles. Cells lining the thyroid follicles secrete two thyroid hormones, thyroxine (T4) and trilodothyronine (T3).
- Both T4 and T3 iodinated forms of an amino-acid called tyrosine and remain stored in the jelly like semifluid material (colloidal) in the lumen of follicle. T3 is more active and several times more potent than T.
- From the thyroid, T4 is mainly secreted and converted to T3 in peripheral tissue e.g., liver.
- Thyroid is the only endocrine gland which stores its secretory product in large quantities. When necessary, the hormones are released from the colloid to the blood.
- In between thyroid follicles are present C- cells or parafollicular cells which release calcitonin or parafollices hormones. It is involved in calcium homeostasis.
- It is hypcalcemic and hyposphatemic. It is antagonistic to parathyroid hormone of parathyroid gland.
Functions of thyroid gland hormones
- Thyroid hormones greatly increase the metabolic rate of the body, consequently enhance heat production (calorigenic effect) and maintain BMR (basal metabolic rate).
- Thyroid hormones also promotes growth of body tissue- both physical growth and development of mental faculities are stimulated.
- They stimulate tissue differentiation. It is this action that promotes metamorphosis of tadpols into adult frogs.
- Enhanced actions of some neurotransmitters: adrenaline and nor- adrenaline is also seen.
- Metabolic Regulation
- Basal Metabolic Rate (BMR): Thyroid hormones significantly increase the basal metabolic rate, influencing how the body uses energy at rest. They enhance the metabolism of carbohydrates, fats, and proteins.
- Thermogenesis: These hormones stimulate heat production in the body, which is crucial for maintaining body temperature.
- Growth and Development
- Skeletal Growth: Thyroid hormones are essential for normal growth and development of bones. They stimulate the growth and maturation of skeletal tissues.
- Brain Development: They play a critical role in the development of the central nervous system, particularly during fetal development and early childhood. Adequate thyroid hormone levels are necessary for proper brain development and cognitive function.
- Cardiovascular System
- Heart Rate and Output: Thyroid hormones increase heart rate, cardiac output, and blood volume, thus enhancing overall cardiovascular function.
- Blood Pressure: They help regulate blood pressure by modulating the tone of blood vessels.
- Protein Synthesis and Degradation
- Protein Turnover: Thyroid hormones stimulate both the synthesis and degradation of proteins, balancing the overall protein metabolism in the body.
- Carbohydrate and Lipid Metabolism
- Glucose Utilization: They enhance glucose absorption from the gastrointestinal tract and increase the turnover of glucose in tissues, influencing blood sugar levels.
- Lipid Metabolism: Thyroid hormones stimulate the breakdown of fats (lipolysis) and regulate cholesterol levels, thereby influencing lipid profiles in the blood.
- Gastrointestinal Function
- Motility: They promote the motility of the gastrointestinal tract, affecting digestion and absorption of nutrients.
- Neurological Function
- Mood and Cognitive Function: Thyroid hormones influence mood, cognition, and overall neurological function. Imbalances can lead to symptoms like depression, anxiety, and cognitive impairments.
- Reproductive Health
- Menstrual Cycle: They play a role in the regulation of menstrual cycles and reproductive health. Thyroid dysfunction can lead to menstrual irregularities and fertility issues.
- Musculoskeletal Health
- Muscle Function: Thyroid hormones influence muscle strength and function. Abnormal levels can lead to muscle weakness and cramps.
- Skin and Hair Health
- Skin and Hair: They impact skin texture and hair growth. Imbalances can lead to dry skin, hair loss, or brittle hair.
Thyroid gland disorders can result from either an overproduction or underproduction of thyroid hormones, structural abnormalities, or inflammation. Here are some common thyroid disorders:
- Hypothyroidism
Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormones. It can be caused by several factors:
- Hashimoto’s Thyroiditis: An autoimmune condition where the body’s immune system attacks the thyroid gland.
- Iodine Deficiency: Lack of iodine in the diet, which is necessary for thyroid hormone production.
- Thyroidectomy: Surgical removal of the thyroid gland.
- Radiation Therapy: Treatment for cancers of the head and neck can damage the thyroid gland.
- Medications: Certain medications can interfere with thyroid hormone production.
Symptoms of Hypothyroidism:
- Fatigue and weakness
- Weight gain
- Cold intolerance
- Dry skin and hair
- Constipation
- Depression
- Slow heart rate
- Cognitive impairment
- Hyperthyroidism
Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. Common causes include:
- Graves’ Disease: An autoimmune disorder that stimulates the thyroid gland to produce excess hormones.
- Thyroid Nodules: Overactive nodules within the thyroid.
- Thyroiditis: Inflammation of the thyroid gland, which can temporarily cause hyperthyroidism.
Symptoms of Hyperthyroidism:
- Weight loss
- Heat intolerance
- Increased appetite
- Nervousness and irritability
- Tremors
- Rapid or irregular heartbeat
- Frequent bowel movements
- Insomnia
- Goiter
A goiter is an enlargement of the thyroid gland. It can be associated with both hypothyroidism and hyperthyroidism, or it can occur without any changes in thyroid hormone levels. Causes include:
- Iodine Deficiency: The most common cause worldwide.
- Graves’ Disease: Can cause a diffuse goiter.
- Hashimoto’s Thyroiditis: Can lead to thyroid enlargement.
- Thyroid Nodules: Benign or malignant growths can cause the gland to enlarge.
4. Thyroid Nodules
Thyroid nodules are lumps that can form within the thyroid gland. They are often benign but can sometimes be cancerous. Causes include:
- Iodine Deficiency: Can lead to the development of nodules.
- Genetic Factors: Family history can increase the risk.
- Radiation Exposure: Increases the risk of developing nodules.
Symptoms (if present):
- A visible lump in the neck
- Difficulty swallowing or breathing
- Hoarseness
- Thyroid Cancer
Thyroid cancer occurs when malignant cells form in the tissues of the thyroid gland. Types include:
- Papillary Thyroid Cancer: The most common type and generally has a good prognosis.
- Follicular Thyroid Cancer: Also common and has a good prognosis.
- Medullary Thyroid Cancer: Less common and can be associated with genetic syndromes.
- Anaplastic Thyroid Cancer: Rare and very aggressive.
Symptoms:
- A lump or nodule in the neck
- Swollen lymph nodes
- Pain in the neck
- Difficulty swallowing or breathing
- Hoarseness
- Thyroiditis
Thyroiditis is inflammation of the thyroid gland and can be caused by autoimmune conditions, infections, or certain medications. Types include:
- Hashimoto’s Thyroiditis: Chronic autoimmune thyroiditis leading to hypothyroidism.
- Subacute Thyroiditis: Painful inflammation, often following a viral infection.
Postpartum Thyroiditis: Occurs after childbirth, can cause temporary hyperthyroidism followed by hypothyroidism
Summary
Thyroid gland disorders can significantly impact overall health and well-being. These disorders range from hormone imbalances (hypothyroidism and hyperthyroidism) to structural issues (goiter, nodules) and malignancies (thyroid cancer). Proper diagnosis and management are essential for maintaining thyroid health and preventing complications.