The human body has a wide variety of hormnes, as mentioned in the later sections, Glands secrete the hormones.  they vary in their chemical nature, in site of production and release, and the effects they induce.

The mechanism is similar to that of a lock and key.

In response to a specific stimuli, the glands release hormones into the bloodstream.

These hormones then are carried via the blood to their target sites/ cells. ( The target cells for each hormone are characterized by the presence of certain molecules called receptors for the hormones )  On reaching a target site, hormone binds to the receptor. It is like a lock and key mechanism. Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action. Hormone receptors may be within the nucleus or on the surface of the cell.

Please Note :  The function or activity of cell is only modified after the interaction between the hormone and its receptor.  It is this interaction that triggers a series of  reactions in the target cells, which there by alters the activity of a cell.  Example, altered enzyme activity, gene activation or membrane permeability changes that alter the activity of that cell.

Let us enlist types of hormones secretd by our glands.  What all gland secrete which hormone, has already been discussed in types of Glands of Endocrine system.  Some hormones you may have heard of and same may sound like gibberish. The functions of some are relatively easy to understand, while others require a science major. We’ve assembled a list of some of the more commonly known hormones that are responsible for some of the most major functions of the body. It’s about time we got to know the hormones that we place the blame on, and know which one is to blame for what, so that next time your moody teenager talks back, you’ll know the serotonin is to blame.

Melatonin – Think of melatonin as your biological clock. This hormone is responsible for the way you feel throughout the day as far as alertness is concerned. All those drowsy feelings? Blame the melatonin.

Serotonin – This is the one you can blame for PMS and your moody teenager. Serotonin controls your mood, appetite, and your sleep cycles.

Thyroxin – A form of thyroid hormone, thyroxin increases the rate of your metabolism and also affects protein synthesis, which is the process that cells go through to build protein.

Epinephrine – This is one that you have most likely heard of; it’s also called adrenaline. Among a whole list of other things, epinephrine is responsible for what is known as the, "fight or flight" response. This is the hormone that tells you when to fight and when it’s best to run. Some of the bodily responses demonstrated when this hormone kicks in are dilated pupils, increased heart rate, and tensing of the muscles.

Norepinephrine – Also called noradrenaline, this hormone controls the heart and blood pressure. Norepinephrine also contributes to the control of sleep, arousal, and emotions. Obvious effects take place when there is too much or too little of this hormone. Too much gives you an anxious feeling while too little can leave you feeling depressed or sedated.

Dopamine – This controls the heart rate and also assists in perception; deciphering what is real and what is not.

Antimullerian Hormone – An inhibitor for the release of prolactin, the protein responsible mainly for lactation.

Adiponectin – This is a protein hormone, it regulates metabolic processes such as the regulation of glucose.

Adrenocorticotropic Hormone – This assists in synthesizing corticosteroids, which are responsible for stress response, blood electrolyte levels, and other physiologic systems.

Angiotensinogen – Responsible for the narrowing of blood vessels; a process known as vasoconstriction.

Antidiuretic Hormone – This hormone is also known by other names, but it is mainly responsible for retaining water within the kidneys.

Atrial Natriuretic Peptide – A peptide hormone secreted by the cells of the heart and other muscles, it’s mostly involved with the control of water, sodium, potassium, and fat within the body.

Calcitonin – Aids in constructing bone and reducing blood calcium.

Cholecystokinin – Aids in the release of digestive enzymes for the pancreas and acts as an appetite suppressant.

Corticotrophin-Releasing Hormone – Releases cortisol in response to stress.

Erythropoietin – Stimulates the production of erythrocytes, which are blood cells responsible for delivering oxygen.

Follicle-Stimulating Hormone – Stimulates the follicles within the sex organs of both males and females.

Gastrin – Secretes gastric acid.

Ghrelin – Hunger stimulant as well as aiding in the secretion of the growth hormone.

Glucagon – Helps to increase the blood glucose level.

Growth Hormone-Releasing Hormone – As its name clearly implies, this hormone releases the growth hormone.

Human Chorionic Gonadotropin – Keeps the immune system from attacking a forming embryo during pregnancy.

Growth Hormone – Helps to stimulate growth and the reproduction of cells.

Secretin – Inhibits gastric acid production.

Aldosterone – Mainly responsible for absorbing sodium in the kidneys to increase the volume of blood within the body.

Testosterone – The major male hormone, testosterone is responsible for sex drive, development of the sex organs, and the changes that take place during puberty.

Androstenedione – Essentially estrogen.

Estradiol – In males, this hormone is responsible for preventing what is basically known as cell death of the germ cells. In females, this hormone is in overdrive. Among other things, estradiol accelerates height and metabolism, maintains the blood vessels and skin, aids in water retention, and even aids in hormone-sensitive cancers.

Progesterone – A major contributor to the body’s support of pregnancy.

Insulin – Responsible for several anabolic effects, primarily glucose intake.

Insulin-Like Growth Factor – Has the same effects as insulin while also regulating the growth and development of cells.

Leptin – Slows down the appetite while simultaneously speeding up metabolism.

Luteinizing Hormone – Aids ovulation in women and testosterone production in men.

Melanocyte Stimulating Hormone – Produce melanocytes, which are responsible for the pigment in skin and hair.

Orexin – Increases the appetite while also increasing your alertness and energy levels.

Oxytocin – A hormone that plays a major role in reproduction, it aids in orgasm and is also responsible for the release of breast milk.

Parathyroid Hormone – Among other functions, this hormone is mainly responsible for the activation of Vitamin D.

Prolactin – A major contributor in sexual satisfaction and the production of breast milk.

Lipotropin – Stimulates the production of pigment by aiding in melanin production.

Brain natriuretic peptide – Aids in reducing blood pressure.

Histamine – A hormone based in the stomach, histamine aids in the secreting of gastric acid.

Endothelin – Controls muscle contractions within the stomach.

Enkephalin – Simply a pain regulator.

These are only examples of some of the hormones within the body; there are more complex hormones whose functions are not easily understood. Our bodies when not diseased, function like well-oiled machines, and the hormones are a major part of nearly every process.