Endocrine system and disorders
The endocrine system is a control system of ductless endocrine glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. It does not include exocrine glands such as salivary glands, sweat glands and glands within the gastrointestinal tract.
Signal transduction of some hormones with steroid structure involves nuclear hormone receptor proteins that are a class of ligand activated proteins that, when bound to specific sequences of DNA serve as on-off switches for transcription within the cell nucleus. These switches control the development and differentiation of skin, bone and behavioral centers in the brain, as well as the continual regulation of reproductive tissues.
The nervous system sends electrical messages to control and coordinate the body. The endocrine system has a similar job, but uses chemicals to "communicate". These chemicals are known as hormones. A hormone is a specific messenger molecule synthesized and secreted by a group of specialized cells called an endocrine gland. These glands are ductless, which means that their secretions (hormones) are released directly into the bloodstream and travel to elsewhere in the body to target organs, upon which they act. Note that this is in contrast to our digestive glands, which have ducts for releasing the digestive enzymes.
Glands are of two types. Endocrine glands do not have a duct system and are called ductless glands. These glands release hormones directly into the blood or lymph. Exocrine glands such as the sudoriferous (sweat) glands contain ducts. Ducts are tubes leading from a gland to its target organ.
The endocrine system and the nervous system are so closely associated that they are collectively called the neuroendocrine system. Neural control centers in the brain control endocrine glands. The main neural control center is the hypothalamus, also known as the "master switchboard." Suspended from the hypothalamus by a thin stalk is the pituitary gland. The hypothalamus sends messages to the pituitary gland; the pituitary gland, in turn, releases hormones that regulate body functions.
The pituitary gland is called the "master gland" but it is under the control of the hypothalamus. Together, they control many other endocrine functions. They secrete a number of hormones, especially several which are important to the female menstural cycle, pregnancy, birth, and lactation (milk production).
Thyroid hormones regulate metabolism, therefore body temperature and weight. The thyroid hormones contain iodine, which the thyroid needs in order to manufacture these hormones. If a person lacks iodine in his/her diet, the thyroid cannot make the hormones, causing a deficiency. In response to the body's feedback loops calling for more thyroid hormones, the thyroid gland then enlarges to attempt to compensate.
Pancreas has two functions. It serves as a ducted gland, secreting digestive enzymes into the small intestine. The pancreas also serves as a ductless gland in that the islets of Langerhans secrete insulin and glucagon to regulate the blood sugar level.
Adrenal glands sit on top of the kidneys. They consist of two parts, the outer cortex and the inner medulla. The medulla secretes epinephrine and other similar hormones in response to stressors such as fright, anger, caffeine, or low blood sugar. The cortex secretes corticosteroids such as cortisone. Corticosteroids are well-known as being anti-inflammatory, thus are prescribed for a number of conditions.
Gonads (sex organs) are the testes and ovaries. The hormones produced are involved in the reproductive systems of the animal. These include testosterone, oestrogen and progesterone.
The pineal gland consists mainly of pinealocytes, but four other cell types have been identified: interstitial cells, perivascular phagocyte, pineal neurons and peptidergic neuron-like cells. It is responsible for the production of melatonin, which has a role in regulating the circadian rhythm. Melatonin is a derivative of the amino acid tryptophan. The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light. Light can be detected by the suprachiasmatic nucleus (SCN) which has directs connections to the retina.
Parathyroid glands secretes a parathyroid hormone, which affects calcium levels in the blood. The sole purpose of the parathyroid glands are to regulate the calcium level in our bodies within a very narrow range so that the nervous and muscular systems can function properly.
Hypothalamus is a region of the brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. The hypothalamus links the nervous system to the endocrine system by producing releasing hormones. HGH is a protein hormone secreted by the somatotropic cells of the anterior lobe of the pituitary gland. Human growth hormone secrets in a pulsatile manner throughout a 24-hour period. The pulsatile diurnal output of growth hormone is modulated by a pair of inner synergistic hypothalamus hormones.
Endocrine disorders include some of the most common health and medical conditions such as diabetes, high cholesterol and thyroid problems. These disorders involve the system of glands and hormones that help regulate our metabolism, growth and reproduction. Less common endocrine disorders include diseases of the pituitary, parathyroid and adrenal glands. Common diseases such as osteoporosis and reproductive disorders are managed jointly by endocrinologists and other specialists. Treating these disorders usually involves the help of a team of health care professionals, including physicians, trainees and dietitian and nurse educators.