The endocrine system consists of a widely distributed group of glands that secretes regulatory substances called hormones. Because these substances are released directly into the blood, the endocrine glands are known as the ductless glands. Despite the fact that hormones in the blood reach all parts of the body, only certain tissues respond. The tissue that is influenced by a specific hormone is called the target tissue. The cells that make up this tissue have specific receptors on their membranes to which the hormone attaches, enabling it to act on the cells.
Hormones :Hormones are produced in extremely small amounts and are highly potent. By means of their actions on various target tissues, they affect growth, metabolism, reproductive activity, and behavior.
Chemically, hormones fall into two categories:
1 steroid hormones, made from lipids, and
2 hormones made of amino acids, which include proteins and protein-like compounds. Steroids are produced by the sex glands (gonads) and the outer region (cortex) of the adrenal glands. All of the remaining endocrine glands produce amino acid hormones. The production of hormones is controlled mainly by negative feedback. That is, the hormone itself, or some product of hormone activity, acts as a control over further manufacture of the hormone . endocrine system is a self-regulating system.
Hormone production also may be controlled by nervous stimulation or by other hormones.
1 steroid hormones, made from lipids, and
2 hormones made of amino acids, which include proteins and protein-like compounds. Steroids are produced by the sex glands (gonads) and the outer region (cortex) of the adrenal glands. All of the remaining endocrine glands produce amino acid hormones. The production of hormones is controlled mainly by negative feedback. That is, the hormone itself, or some product of hormone activity, acts as a control over further manufacture of the hormone . endocrine system is a self-regulating system.
Hormone production also may be controlled by nervous stimulation or by other hormones.
The Endocrine Glands:
Endocrine glands are glands that have no duct and release their secretions directly into the intercellular fluid or into the blood. A collection of endocrine glands makes up the endocrine system: the pituitary (anterior and posterior lobes), thyroid, parathyroid, adrenal (cortex and medulla), pancreas and gonads.
► The Pituitary:
The pituitary gland (hypophysis) is a small gland beneath the brain. It is divided into an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis). Both lobes are connected to and controlled by the hypothalamus, a part of the brain. The anterior pituitary releases six hormones. One of these is growth hormone somatotropin), which stimulates the growth of bones and acts on other tissues as well. The remainder of the pituitary hormones regulate other glands, including the thyroid, adrenals, gonads, and mammary glands. These hormones are released in response to substances (releasing hormones) that are sent to the anterior pituitary from the hypothalamus. They can be identified by the ending -tropin, as in gonadotropin. The adjective ending is -tropic. The posterior pituitary releases two hormones that are actually produced in the hypothalamus. These hormones, antidiuretic hormone and oxytocin, are stored in the posterior pituitary until nervous signals arrive from the hypothalamus to trigger their release. Antidiuretic hormone (ADH) acts on the kidneys to conserve water and also promotes constriction of blood vessels. Both of these actions serve to increase blood pressure. Oxytocin stimulates uterine contractions and promotes milk “letdown” in the breasts during lactation.
► The Adrenals:
The adrenal glands, located atop each kidney, are divided into two distinct regions: an outer cortex and an inner medulla. The hormones produced by this gland are involved in the body’s response to stress. The cortex produces steroid hormones, cortisol, aldosterone, and small amounts of sex hormones. Cortisol (hydrocortisone) mobilizes reserves of fats and carbohydrates to increase the levels of these nutrients in the blood. It also acts to reduce inflammation and is used clinically for this purpose. Aldosterone acts on the kidneys to conserve sodium and water while eliminating potassium. The adrenal cortex also produces small amounts of sex hormones, mainly testosterone, but their importance is not well understood.
Endocrine glands are glands that have no duct and release their secretions directly into the intercellular fluid or into the blood. A collection of endocrine glands makes up the endocrine system: the pituitary (anterior and posterior lobes), thyroid, parathyroid, adrenal (cortex and medulla), pancreas and gonads.
► The Pituitary:
The pituitary gland (hypophysis) is a small gland beneath the brain. It is divided into an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis). Both lobes are connected to and controlled by the hypothalamus, a part of the brain. The anterior pituitary releases six hormones. One of these is growth hormone somatotropin), which stimulates the growth of bones and acts on other tissues as well. The remainder of the pituitary hormones regulate other glands, including the thyroid, adrenals, gonads, and mammary glands. These hormones are released in response to substances (releasing hormones) that are sent to the anterior pituitary from the hypothalamus. They can be identified by the ending -tropin, as in gonadotropin. The adjective ending is -tropic. The posterior pituitary releases two hormones that are actually produced in the hypothalamus. These hormones, antidiuretic hormone and oxytocin, are stored in the posterior pituitary until nervous signals arrive from the hypothalamus to trigger their release. Antidiuretic hormone (ADH) acts on the kidneys to conserve water and also promotes constriction of blood vessels. Both of these actions serve to increase blood pressure. Oxytocin stimulates uterine contractions and promotes milk “letdown” in the breasts during lactation.
► The Adrenals:
The adrenal glands, located atop each kidney, are divided into two distinct regions: an outer cortex and an inner medulla. The hormones produced by this gland are involved in the body’s response to stress. The cortex produces steroid hormones, cortisol, aldosterone, and small amounts of sex hormones. Cortisol (hydrocortisone) mobilizes reserves of fats and carbohydrates to increase the levels of these nutrients in the blood. It also acts to reduce inflammation and is used clinically for this purpose. Aldosterone acts on the kidneys to conserve sodium and water while eliminating potassium. The adrenal cortex also produces small amounts of sex hormones, mainly testosterone, but their importance is not well understood.
The medulla of the adrenal gland produces two similar hormones, epinephrine (adrenaline) and norepinephrine (noradrenaline). These are released in response to stress and work with the nervous system to help the body meet challenges.
► THE PANCREAS:
The endocrine portions of the pancreas are the pancreatic islets, small clusters of cells within the pancreatic tissue. The term islet, meaning “small island,” is used because these cells look like little islands in the midst of the many pancreatic cells that secrete digestive juices. The islet cells produce two hormones, insulin and glucagon, that regulate sugar metabolism. Insulin increases cellular use of glucose, thus decreasing sugar levels in the blood. Glucagon has the opposite effect of increasing blood sugar levels.
► THE PANCREAS:
The endocrine portions of the pancreas are the pancreatic islets, small clusters of cells within the pancreatic tissue. The term islet, meaning “small island,” is used because these cells look like little islands in the midst of the many pancreatic cells that secrete digestive juices. The islet cells produce two hormones, insulin and glucagon, that regulate sugar metabolism. Insulin increases cellular use of glucose, thus decreasing sugar levels in the blood. Glucagon has the opposite effect of increasing blood sugar levels.
Other Endocrine Glands; The thymus, is considered an endocrine gland because it secretes a hormone, thymosin, which stimulates the T lymphocytes of the immune system. The gonads are also included because, in addition to producing the sex cells, they secrete hormones. Other organs, including the stomach, kidney, heart, and small intestine, also produce hormones.
Finally, prostaglandins are a group of hormones produced by many cells. They have a variety of effects, including stimulation of uterine contractions, promotion of the inflammatory response, and vasomotor activities. They are called prostaglandins because they were first discovered in the prostate gland.
staying hydrate Everytime, will help this system to work properly.
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