Hormone.

« women is called a follicle-stimulating hormone.

When a follicle-stimulating hormone binds to an ovary cell, it stimulates the enzymes needed for the synthesis ofestradiol, a female sex hormone.

Another gonadotropin called luteinizing hormone regulates the production of eggs in women and the production of the male sexhormone testosterone.

Produced in the male gonads, or testes, testosterone regulates changes to the male body during puberty, influences sexual behavior, and playsa role in growth.

The female sex hormones, called estrogens, regulate female sexual development and behavior as well as some aspects of pregnancy.

Progesterone, afemale hormone secreted in the ovaries, regulates menstruation and stimulates lactation in humans and other mammals. Other hormones regulate metabolism.

For example, thyroxine, a hormone secreted by the thyroid gland, regulates rates of body metabolism.

Glucagon and insulin,secreted in the pancreas, control levels of glucose in the blood and the availability of energy for the muscles.

A number of hormones, including insulin, glucagon,cortisol, growth hormone, epinephrine, and norepinephrine, maintain glucose levels in the blood.

While insulin lowers the blood glucose, all the other hormones raise it.In addition, several other hormones participate indirectly in the regulation.

A protein called somatostatin blocks the release of insulin, glucagon, and growth hormone,while another hormone, gastric inhibitory polypeptide, enhances insulin release in response to glucose absorption.

This complex system permits blood glucoseconcentration to remain within a very narrow range, despite external conditions that may vary to extremes. Hormones also regulate blood pressure and other involuntary body functions.

Epinephrine, also called adrenaline, is a hormone secreted in the adrenal gland.

Duringperiods of stress, epinephrine prepares the body for physical exertion by increasing the heart rate, raising the blood pressure, and releasing sugar stored in the liver forquick energy. Hormones are sometimes used to treat medical problems, particularly diseases of the endocrine system.

In people with diabetes mellitus type 1, for example, thepancreas secretes little or no insulin.

Regular injections of insulin help maintain normal blood glucose levels.

Sometimes, an illness or injury not directly related to theendocrine system can be helped by a dose of a particular hormone.

Steroid hormones are often used as anti-inflammatory agents to treat the symptoms of variousdiseases, including cancer, asthma, or rheumatoid arthritis.

Oral contraceptives, or birth control pills, use small, regular doses of female sex hormones to preventpregnancy. Initially, hormones used in medicine were collected from extracts of glands taken from humans or animals.

For example, pituitary growth hormone was collected fromthe pituitary glands of dead human bodies, or cadavers, and insulin was extracted from cattle and hogs.

As technology advanced, insulin molecules collected fromanimals were altered to produce the human form of insulin. With improvements in biochemical technology, many hormones are now made in laboratories from basic chemical compounds.

This eliminates the risk of transferringcontaminating agents sometimes found in the human and animal sources.

Advances in genetic engineering even enable scientists to introduce a gene of a specificprotein hormone into a living cell, such as a bacterium, which causes the cell to secrete excess amounts of a desired hormone.

This technique, known as recombinantDNA technology, has vastly improved the availability of hormones. Recombinant DNA has been especially useful in producing growth hormone, once only available in limited supply from the pituitary glands of human cadavers.Treatments using the hormone were far from ideal because the cadaver hormone was often in short supply.

Moreover, some of the pituitary glands used to makegrowth hormone were contaminated with particles called prions, which could cause diseases such as Creutzfeldt-Jakob disease, a fatal brain disorder.

The advent ofrecombinant technology made growth hormone widely available for safe and effective therapy. B Invertebrate Hormones In invertebrates, hormones regulate metamorphosis (the process in which many insects, crustaceans, and mollusks transform from eggs, to larva, to pupa, and finallyto mature adults).

A hormone called ecdysone triggers the insect molting process, in which these animals periodically shed their outer covering, or exoskeletons, andgrow new ones.

The molting process is delayed by juvenile hormone, which inhibits secretion of ecdysone.

As an insect larva grows, secretion of juvenile hormonedeclines steadily until its concentrations are too low to prevent the secretion of ecdysone.

When this happens, ecdysone concentrations increase until they are highenough to trigger the metamorphic molt. In insects that migrate long distances, such as the locust, a hormone called octopamine increases the efficiency of glucose utilization by the muscles, while adipokinetichormone increases the burning of fat as an energy source.

In these insects, octopamine levels build up in the first five minutes of flight and then level off as adipokinetichormone takes over, triggering the metabolism of fat reserves during long distance flights. Hormones also trigger color changes in invertebrates.

Squids, octopuses, and other mollusks, for example, have hormonally controlled pigment cells that enable theanimals to change color to blend in with their surroundings. C Plant Hormones Hormones in plants are called phytohormones.

They regulate most of the life cycle events in plants, such as germination, cell division and extension, flowering, fruitripening, seed and bud dormancy, and death ( see Plant: Growth and Differentiatio n).

Plant biologists believe that hormones exert their effects via specific receptor sites in target cells, similar to the mechanism found in animals.

Five plant hormones have long been identified: auxin, cytokinin, gibberellin, abscisic acid, and ethylene.Recent discoveries of other plant hormones include brassinosteroids, salicylates, and jasmonates. Auxins are primarily responsible for protein synthesis and promote the growth of the plant's length.

The most common auxin, indoleacetic acid (IAA), is usually formednear the growing top shoots and flows downward, causing newly formed leaves to grow longer.

Auxins stimulate growth toward light and root growth. Gibberellins, which form in the seeds, young leaves, and roots, are also responsible for protein synthesis, especially in the main stem of the plant.

Unlike auxins,gibberellins move upward from the roots.

Cytokinins form in the roots and move up to the leaves and fruit to maintain growth, cell differentiation, and cell division.Among the growth inhibitors is abscisic acid, which promotes abscission, or leaf fall; dormancy in buds; and the formation of bulbs or tubers, possibly by preventing thesynthesis of protein.

Ethylene, another inhibitor, also causes abscission, perhaps by its destructive effect on auxins, and it also stimulates the ripening of fruit. Brassinosteroids act with auxins to encourage leaf elongation and inhibit root growth.

Brassinosteroids also protect plants from some insects because they work againstsome of the hormones that regulate insect molting.

Salicylates stimulate flowering and cause disease resistance in some plants.

Jasmonates regulate growth,germination, and flower bud formation.

They also stimulate the formation of proteins that protect the plant against environmental stresses, such as temperaturechanges or droughts. V COMMERCIAL USE OF HORMONES Hormones are used for a variety of commercial purposes.

In the livestock industry, for example, growth hormones increase the amount of lean (non-fatty) meat in bothcattle and hogs to produce bigger, less fatty animals.

The cattle hormone bovine somatotropin (BST) increases milk production in dairy cows.

Hormones are also used inanimal husbandry to increase the success rates of artificial insemination and speed maturation of eggs.. »