The Endocrine Organs Of The Human Body-Thyroid Gland

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The endocrine organs of the human body

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Controlling system. it fluences metabolic activities of cells by chemical messengers called hormones

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The pineal gland

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The pineal gland is composed of glial cells nervous support cells and secretory pinealocytes

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Hormone

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The hormone melatonin is secreted from this gland into the bloodstream of the dural sinus supplied by the cerebrospinal fluid made from blood in the brain

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Levels of melatonin

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The levels of melatonin rise and fall daily with highest level at night and lowest levels around noon. It is stimulated by light from the eyes. It important in the body's day night cycle making us drowsy at night. Timing of puberty and sexual maturation. seasonally melatonin reproductive functions. They use light as a trigger to indicate season

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Thyroid gland

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found in the neck on the front of the trachea and below larynx consist of two lateral lobes, the left and right lobe connected by a central mass of tissue called the isthmus

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Thyroid gland

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Inside thyroid gland composed of follicles filled with a collid material which the two thyroid hormones are formed.

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Each hollow follicle is surrounded by simple cuboidal epithelial cells called the follicle cells. In the connective tissue between the follicles are parafollicular cells producing another hormone called calcitonin

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Functions

Thyroid gland receives blood supply from four thyroid arteries then drained by Thyroid veins that carry hormones into the body's circulation.

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2 Hormones secreted by the thyroid gland

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The follicle cells of thyroid gland produce a protein called thyroglobulin which is stored as colloid material inside each follicle

thyroglobulin based for two thyroid hormones. T4 or thyroxine and T3 or triiodothyronine. Thyroglobulin accumulates inside the follicles and stored iodine from the follicle cells and attached to it. When the hormones are required. the collid material is taken back up into the follicle cells where enzymes splittle of the thyroid hormones then pass into the bloodstream

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1 Hormones produce by thyroid glands affect nearly all body cells

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function

increased their metabolic rate, glucose oxidation and heat production. Promote normal tissue growth and maturity

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levels of thyroid hormones in the blood

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is maintained by a negative feedback loop involving the hypothalamus and pituitary gland. As blood levels of the thyroid hormones fall. TSH is released from the anterior pituitary gland. This stimulates the secretion of more thyroid hormone increasing blood levels of thyroid hormones feed back to the hypothalamus and anterior pituitary gland to inhibit TSH secretion from the pituitary gland

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The parafollicular cells

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The parafollicular cells of the thyroid gland produce the hormone calcitonin that assist in the regulation of calcium levels. calcitonin is released into the bloodstream when levels of calcium in the blood rise above normal. This stimulates the extra calcium to be deposited in bone.

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