Hormones
Hormones are organic substances that are secreted by plants and animals and that function in the regulation of physiological activities and in maintaining homeostasis. They carry out their functions by evoking responses from specific organs or tissues that are adapted to react to minute quantities of them. The classical view of hormones is that they are transmitted to their targets in the bloodstream after discharge from the glands that secrete them. This mode of discharge (directly into the bloodstream) is called endocrine secretion. The meaning of the term hormone has been extended beyond the original definition of a blood-borne secretion, however, to include similar regulatory substances that are distributed by diffusion across cell membranes instead of by a blood system. . Among animals, the hormones of the vertebrates--particularly those of humans and other mammals--are the best known. Most vertebrate hormones originate in specialized tissues, called endocrine tissues, and are carried to their targets through the bloodstream. Endocrine glands. A major endocrine gland in vertebrates is the pituitary, which consists of two distinct sections: the anterior pituitary (or adenohypophysis) and the po
sterior pituitary (or neurohypophysis). The anterior pituitary is sometimes called the "master gland," because it secretes several hormones that affect the other endocrine glands. For example, the anterior pituitary hormones thyrotropin and adrenocorticotropic hormone (ACTH) regulate endocrine activity in the thyroid and the outer region (cortex) of the adrenal glands, respectively. The anterior pituitary also secretes hormones that affect the sex glands. One of these is follicle-stimulating hormone (FSH), which stimulates egg production in the ovaries and sperm production in the testes. Another is luteinizing hormone (LH). In females, LH works in conjunction with FSH to regulate the female reproductive cycle and the secretion of female sex hormones. In males, LH controls the production of the male sex hormones. Other hormones produced in the anterior pituitary include growth hormone, which is responsible for normal body growth, and prolactin, which promotes milk production in female mammals. Its designation as the master gland notwithstanding, the anterior pituitary itself is regulated by substances called releasing hormones that are secreted by the hypothalamus, the part of the brain located directly above the pituitary. These hypothalamic hormones stimulate--or, in some cases, inhibit--the secretions of the anterior pituitary. The posterior pituitary stores and releases two hormones: oxytocin, which causes the uterus to contract during birth, and vasopressin, which acts on the kidneys to restrict the output of urine. These two hormones are actually produce
Some common words found in the essay are:
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Approximate Word count = 1057
Approximate Pages = 4 (250 words per page double spaced)
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