The thyroid gland, located immediately below the larynx on each side of and in front of the trachea, is one of the largest of the endocrine glands, normally weighing 15-20g in adults. The thyroid gland secretes to major hormones, Thyroxine “T4” and Triiodothyronine “T3” and also secretes calcitonin which is an important hormone for calcium metabolism.
Thyroid hormone functions:
- Both the T4 and T3 profoundly increase the metabolic rate of the body, without which the basal metabolic rate would fall 40 to 50 percent below normal.
- The thyroid hormone increases the transcription of Large numbers of Genes.
- It increases Active transport of Ions through cell membranes.
- It increases the number and activity of Mitochondria.
- It promotes the growth and development of the brain during fetal life and for the first few years of postnatal life.
- Thyroid hormones stimulate carbohydrate metabolism such as rapid glucose uptake, enhance glycolysis, enhance gluconeogenesis and increased the rate of glucose absorption from the gastrointestinal tract.
- It mobilizes lipids rapidly from fat tissues which decreases the fat stores and also fatty acids concentration in the plasma and its oxidation by cells.
- It increases the requirement for vitamins.
- It decreases body weight when secreted at an increased amount.
- It increases blood flow and cardiac output, heart rate, and heart strength.
- Thyroid hormones have effects on sexual functions which their normal secretion is very important for the normal function of sexual activities. Such as in men, lack of these hormones likely to cause loss of libido; and in women, lack of these hormones causes menorrhagia and polymenorrhea.
The normal level of Thyroid Hormones are:
factors affecting its secretion:
- Thyroid-stimulating hormone (TSH) secreted from the Pituitary gland has a direct effect on its secretion and synthesis.
- The thyrotropin-releasing hormone (TRH) secreted by Hypothalamus has indirectly effect on its secretion and synthesis as it causes secretion of TSH.
- Any type of stimulus that causes secretion of TRH and TSH such as cold and neurogenic stimulus.
- Increased thyroid hormone in the plasma will cause a decrease in the TSH secretion which in turn will decrease or normalize the amount of thyroid hormones in the plasma.
- Thyroid hormone secretion is also regulated by the availability of Iodin Ions in the body.
Thyroid Hormones Abnormalities:
It is a condition in which there is increased secretion of thyroid hormones above the normal level and the causes of hyperthyroidism are an autoimmune disease (Grave’s disease “the most common”), thyroid adenoma (tumors) that causes the thyroid gland hyperplasia and Goiter. The sign and symptoms which a patient of hyperthyroidism represents are:
- a high state of excitability
- intolerance to heat
- increased sweating
- mild to extreme weight loss
- varying degrees of diarrhea
- muscle weakness
- nervousness or other psychic disorders
- extreme fatigue but inability to sleep
- tremor of the hands (fine tremors)
- exophthalmos (protruded eyes)
The treatment for Hyperthyroidism
are surgical removal of most of the thyroid gland, administering propylthiouracil along with certain other drugs and also Radioactive Iodine Therapy.
It is a condition in which there is decreased secretion of thyroid hormone which can be due to autoimmunity against the thyroid gland (Hashimoto disease), infection of the thyroid gland, Iodine deficiency which leads to Endemic colloid Goiter, and Atherosclerosis in Hypothalamus. The sign and symptoms of Hypothyroidism are:
- Fatigue and extreme somnolence with sleeping up to 12 to 14 hours a day
- extreme muscular sluggishness
- slow heart rate
- decreased cardiac output and decreased blood volume
- sometimes increased body weight
- mental sluggishness
- failure of many tropic functions in the body evidenced by depressed growth of hair and scaliness of skin.
- development of a froglike husky voice
- myxedema (development of an edematous appearance throughout the body
Treatments of Hypothyroidism:
It can be treated by daily oral ingestion of a tablet or more containing thyroxine, and certain other treatments for autoimmunity and infectious thyroid gland.
Diagnosis of Hyperthyroidism and Hypothyroidism:
- Thyroid Profiling Test: which indicate all the plasma concentration of TRH, TSH, T3, and T4.
- Test for Basal Metabolic rate
- Plasma concentration of TSI