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Endocrine System: The Endocrine Glands
By Lhenn on Apr 26, 2010 with Comments 0
The endocrine system consists of special organs called glands. A gland is an organ of the body that makes and stores fluids that the body needs.
The endocrine glands are different from other glands in the body. They are also called the ductless glands. They have no tubes for their secretions to flow through. Instead, they release their fluids directly into the bloodstream. The fluids that are produced by the endocrine glands are called hormones.
A hormone is a chemical substance that controls the growth and development and other functions of the body. For example, the rate at which you grow is controlled by hormones. When an endocrine gland releases a hormone, the blood carries it into the target organ. The target organ is a part or a place in the body where a hormone acts. A hormone controls the production of energy in the body. Its target organs include all the body cells and tissue.
The Hypothalamus Gland
The hypothalamus gland is located at the base of the brain. It is a part of the brain. It serves as a high link between the endocrine system and the nervous system. It is found just above the pituitary gland. The pituitary gland is under the control of the hypothalamus gland.
The hormones secreted by the hypothalamus gland may either stimulate or inhibit the pituitary gland from releasing its hormones.
The hypothalamus senses when the level of a certain hormone is low. It transmits the information to the pituitary gland which regulates the hormone level needed. When the hormone supply is adequate, the hypothalamus switches off the action. For example, one hormone is stored in and released from the pituitary gland.
A hormone called oxytocin is released from the hypothalamus gland of the mother during childbirth. It stimulates the contraction of the uterus when the mother is in labor. It is responsible for the release of milk from the breasts of the mother for feeding the baby upon birth.
The Pituitary Gland
The pituitary gland is located in the lower part of the brain. It is only about the size of a pea. Despite its small size, it produces several hormones that control the function of the other glands. This is the reason why pituitary gland is often called the master gland. But the pituitary is directly under the control of the hypothalamus gland. Hormones from the hypothalamus either stimulate or inhibit the production of the hormones of the pituitary gland. The endocrine glands stimulated by the secretions of the pituitary gland are the sex glands, the adrenal cortex, and the thyroid glands.
The pituitary gland has two lobes, the anterior (front lobe) and the posterior (back lobe).
The anterior lobe of the pituitary gland secretes at least six different hormones including the growth hormone. The growth hormone stimulates growth and amino acid transport in the body. Amino acid is the building block of proteins. The growth hormone increases muscle mass and stimulates bone growth.
Another hormone secreted by the anterior pituitary gland is the thyroid-stimulating hormone. This hormone is brought by the blood to the thyroid glands where it regulates the secretion of its hormones. Too little of this hormone causes under activity of the thyroid glands. Too much of this hormone would result in the over activity of the thyroids. The thyroid hormones control metabolism and growth and development of the body.
The hormone prolactin is also secreted by the anterior pituitary gland. It promotes milk production in mothers. The other secretions of the pituitary gland stimulate the sex glands in males and females.
The Pineal Gland
The pineal gland is a small endocrine gland located near the center of the brain. It secretes the hormone melatonin. This hormone promotes the development of the ovaries and the testes.
The Thyroid Glands
The thyroid glands are butterfly-shaped glands located in the neck. They are found around the front and sides of the trachea just below the larynx. The thyroid glands are stimulated by the thyroid-stimulating hormone from the pituitary gland in order to produce the secretions. The thyroid glands secrete two hormones: the thyroxin and the calcitonin. The thyroxin hormone affects all the cells of the body. It controls or regulates how fast the body burns up food to produce energy or metabolic rate. It also stimulates the growth and mental development of a child.
The calcitonin hormone works together with a hormone from the parathyroid glands to regulate the amount of calcium in the blood. When the amount of calcium in the blood increases, calcitonin is released to increase the excretion of calcium by the kidneys. It also regulates the intestines to slow down absorption of calcium, and also prevents the bones from releasing more calcium into the blood. Thus, the level of calcium in the blood decreases.
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