Recents in Beach

THYROID GLAND of Endocrine System notes

The thyroid gland is situated in the neck in front of the larynx and trachea at the level of the 5th, 6th and 7th cervical and 1st thoracic vertebrae.
It is a highly vascular gland that weighs about 25 g and is surrounded by a fibrous capsule.
It resembles a butterfly in shape, consisting of two lobes, one on either side of the thyroid cartilage and upper cartilaginous rings of the trachea. The lobes are joined by a narrow isthmus, lying in front of the trachea.
The gland is composed of cuboidal epithelium that forms spherical follicles. These secrete and store
colloid, a thick sticky protein material. Between the follicles, there are other cells found singly or in small groups: parafollicular cells, also called C-cells, which secrete the hormone calcitonin.
Hormone secreted by thyroid glands are: *CTEVT
a. Thyroxine (T4)
b. Tri-iodothyronine (T3)
c. Calcitonin.


Thyroxine and triiodothyronine
Iodine is essential for the formation of the thyroid gland hormones, thyroxine (T4) and triiodothyronine (T3).
The thyroid gland selectively takes up iodine from the blood, a process called Iodine Trapping.
Secretion of TSH is stimulated by the thyroid releasing hormone (TRH) from the hypothalamus and secretion of TRH is stimulated by exercise, stress, malnutrition, low plasma glucose and sleep.

Functions:-increases metabolic activity of most of the tissues of the body.
- Increases basal metabolic rate
- Increases heat production
- Increase metabolism of carbohydrates, fat and proteins
- Helps in growth and development of bone, muscles, nervous system, cardiovascular system
- It helps in protein synthesis.

-This hormone is secreted by the parafollicular or C- cells in the thyroid gland.

-It acts on bone and the kidneys to reduce the blood calcium (Ca2+) level when it is raised.
-It reduces the reabsorption of calcium from bones and inhibits reabsorption of calcium by the renal tubules.

-Its effect is opposite to that of parathyroid hormone (PTH, parathormone), the hormone secreted by the parathyroid glands.

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