Thyroid Gland, Hormones and Thyroid Problems, Animation

January 14, 2020 0 By Jose Scott


The thyroid is a butterfly-shaped ENDOCRINE
gland located in the neck. It is wrapped around the trachea, just below
the thyroid cartilage –the Adam’s apple. The two major hormones of the thyroid are
triiodothyronine, T3 and thyroxine, T4. The numbers 3 and 4 indicate the number of
iodine atoms present in a molecule of each hormone. T3 and T4 are collectively referred to as
THYROID hormones. Thyroid hormone secretion is under control
of thyroid-stimulating hormone, TSH, from the anterior pituitary. TSH, in turn, is induced by thyrotropin-releasing
hormone, TRH, produced by the hypothalamus. The amount of circulating thyroid hormones
is regulated by a negative feedback loop: when their levels are too high, they SUPPRESS
the production of TSH and TRH, consequently INHIBITING their own production. Thyroid hormones act to INCREASE the body’s
metabolic rate. They stimulate appetite, digestion, breakdown
of nutrients and absorption. They also increase oxygen consumption, raise
the breathing rate, heart rate and contraction strength. As a result, the body’s HEAT production
is INCREASED. Thyroid hormone secretion usually rises in
winter months to keep the body warm. Thyroid hormones are also important for bone
growth and fetal brain development. There are 2 major groups of thyroid problems:
HYPOthyroidism: when the thyroid does NOT produce ENOUGH hormones, resulting in a LOW
metabolic rate, combined with SLOW respiratory and cardiovascular activities. Common symptoms include fatigue, weight gain
despite poor appetite, cold intolerance, slow heart rate, heavy menstrual bleeding and constipation. Iodine deficiency and Hashimoto’s thyroiditis
are the most common causes. Hashimoto’s thyroiditis is an autoimmune disease
in which the thyroid gland is gradually destroyed by the body’s own immune system. Hypothyroidism, especially when caused by
iodine deficiency, may lead to swelling of the thyroid gland, known as GOITER. In an attempt to fix the low levels of thyroid
hormones, the pituitary produces MORE TSH to further stimulate the thyroid gland. The thyroid, while UNable to make hormones
WITHOUT iodine, responds to TSH by GROWING in size. Hypothyroidism is managed with thyroxine hormone
replacement. HYPERthyroidism: when the thyroid gland produces
TOO MUCH hormones, resulting in a TOO ACTIVE metabolism, together with respiratory and
cardiovascular rates that are HIGHER than necessary. Common symptoms include irritability, insomnia,
weight loss despite good appetite, heat intolerance, heart racing and diarrhea. Hyperthyroidism is most commonly caused by
Graves’ disease, another autoimmune disorder characterized by presence of an antibody,
called thyroid stimulating immunoglobulin, TSI. TSI, similar to TSH, stimulates the thyroid
gland to produce hormones. Unlike TSH, however, TSI is NOT regulated
by negative feedback mechanisms, leading to UNcontrolled production of thyroid hormones. TSI also stimulates the thyroid gland to grow,
which MAY lead to formation of a goiter. Hyperthyroidism may be managed with drugs
that suppress thyroid function, radioactive iodine that selectively destroys the thyroid
gland, or surgery that removes part of the gland.