Within the bodies of all mammals, a complex network of glands (the endocrine system) is responsible for the production and secretion of special proteins and lipids (fats) called hormones.
In turn, these hormones serve to regulate many vital functions within the body, from growth and development to digestion and utilization of nutrients. Like the nervous system, the endocrine system assumes a regulatory role within the body, and its proper function is essential to the overall health of the animal.
Without the endocrine glands and their hormones, a state of chaos would quickly ensue within the body, as the functional harmony existing between the various organ systems would cease to exist.
Anatomy and Physiology
Hormones can be protein in nature, or they can be fashioned from special fatty components, known as steroids. “Steroid” is one of the most misused and widely misunderstood terms in today’s society.
Corticosteroids are a special group of steroids produced by the adrenal glands that are vital to many everyday functions within the body. Synthetic derivatives of this steroid group are commonly used, among other things, to reduce pain and inflammation resulting from musculoskeletal injuries.
Androgens (i.e., testosterone) and estrogens, the sex hormones that influence reproductive activity and secondary sexual characteristics, are also types of steroid hormones produced naturally within the body.
Anabolic steroids, probably the most notorious members of the steroid family, are actually synthetic derivatives of the male androgenic steroid hormones. This is the group that has been largely exploited by athletes for increased muscular strength and size.
Although all the different classes of steroids mentioned above, whether natural or synthetic, share a similar structural design, it is easy to see that their functions and effects differ greatly between each class.
Both protein and steroid-type hormones are secreted directly into the bloodstream from the glands or organs that produce them, and circulate to their specific target cells or organs, where they exert their effect.
The amount of hormone required to exert its particular effect is precise. If present in too great a quantity, or if supplies are deficient, abnormal function of its target cells or organs result.
As a result, hormonal activities within the body are governed by complex negative feedback mechanisms, which ensure proper blood levels at all times.
Unfortunately, certain disease conditions involving the endocrine glands and organs can disrupt this delicate balance, which can pose serious health problems.
The hypothalamus, located at the bottom portion of the brainstem, functions as an integration center between the nervous system and the endocrine system. Nervous system functions of the hypothalamus include regulation of body temperature, emotional behavior and sleep, and control of food and water intake.
As an endocrine organ, the hypo- thalamus secretes the hormone ADH (antidiuretic hormone), which controls the water balance within the body; oxytocin, which stimulates lactation and uterine contractions; and a variety of other hormones that exert control over the pituitary gland.
The pituitary gland produces hormones that have effects on other endocrine glands, such as the thyroid and adrenal glands. In addition, pituitary hormones also influence growth and reproductive patterns.
Hormones produced by the thyroid gland control the rate of growth and metabolism within the body, as well as decrease calcium levels within the bloodstream.
Closely associated with the thyroid gland are the parathyroid glands, which produce a hormone that counteracts the action of a certain thyroid hormone by increasing blood calcium levels.
This balance between the thyroid and parathyroid glands helps maintain proper blood levels of calcium at all time. Too much parathyroid hormone can result in excess resorption of bony tissue, resulting in metabolic bone disease.
The adrenal glands produce a variety of hormones, each exerting unique effects within the body. Among other things, adrenal hormones influence carbohydrate and protein metabolism and storage (cortisol, cortisone), help the kidneys regulate sodium and potassium levels (aldosterone), and control blood pressure and heart rate (epinephrine and norepinephrine).
Certain organs can double as endocrine glands. The pancreas is not just responsible for producing digestive enzymes; it secretes two hormones, insulin and glucagon, both involved in carbohydrate (sugar) metabolism within the body.
Insulin functions to lower blood sugar by increasing its uptake and utilization by the body organs. Counteracting the effects of insulin, glucagon increases blood sugar levels by decreasing its uptake into the liver and fatty tissue.
Diabetes mellitus is a disease in which not enough insulin is produced by the pancreas, prohibiting cells and organs from extracting carbohydrates out of the bloodstream.
Other organs exhibiting endocrine functions include the stomach, which produces hormones that regulate digestion; the ovaries and testicles, which, together with the adrenal gland and placenta (in pregnant females), produce the sex hormones; the kidneys, which secrete hormones that influence blood flow and filtration within the kidneys themselves; and the thymus gland, with hormonal activity that influences the cells of the immune system.