The Endocrine & Glandular System
The Body maintains a steady internal state, and it regulates itself. Pervading every activity is the influence of the brain, the master control, with its servants being, the endocrine and nervous systems.
The endocrine glands are found in various parts of the body, and are characterised by the fact that they release their hormones (chemical messengers) directly into the bloodstream. The hormones then travel to cells in all parts of the body. The membrane of each cell has receptors for one or more hormones, and the binding of a hormone to its specific receptor site begins to make particular changes in the internal metabolism of this ‘target’ cell.
Parts of the Endocrine System
Many glands make up the endocrine system. The Hypothalamus, Pituitary Gland and Pineal Gland are in the Brain. The thyroid and parathyroid glands are in the neck. The Thymus is between the lungs, the Adrenals are top of the kidneys, and the Pancreas is behind the stomach. The Ovaries (female) or Testes (male) are in the pelvic region.
- The Hypothalamus connects the endocrine system with the nervous system. Its main job is to tell the pituitary gland to start or stop making hormones.
- The Pituitary gland is the endocrine system’s master gland. It uses the information it gets from the brain to tell other glands in the body what to do. It makes many important hormones, including the growth hormone; prolactin, which helps breastfeeding mothers to make milk; and luteinizing hormone, which manages estrogens in women and testosterone in men.
- The Pineal gland makes a chemical called melatonin that helps the body to get ready to go to sleep.
- The Thyroid gland makes the thyroid hormone, which controls the body’ metabolism. If this gland doesn’t make enough (a condition called hypothyroidism), everything happens more slowly. The heart rate may slow down, and constipated is a possibility, and weight gain may occur. If it makes too much (hyperthyroidism), everything speeds up. The heart might race, diarrhoea may be a possibility. And weight may be lost without trying.
- The Parathyroid is a set of four small glands behind the thyroid. They play a role in bone health and control the levels of calcium and phosphorus.
- The Thymus. This gland makes white blood cells called T-lymphocytes; they fight infection and are crucial as a child’s immune system develops. The thymus starts to shrink after puberty.
- The Adrenals are best known for producing the “fight or flight” hormone, adrenaline (also these two glands also make hormones called corticosteroids. They affect the metabolism and sexual function, among other things.
- The Pancreas is part of both the digestive and the endocrine systems. It makes digestive enzymes that break down food. It also makes the hormones insulin and glucagon. These ensure there is the right amount of sugar in the bloodstream and cells. If insulin isn’t made, which is the case for people with type 1 diabetes, blood sugar levels can get dangerously high. In type 2 diabetes, the pancreas usually makes some insulin but not enough.
- The Ovaries (female) make oestrogen and progesterone. These hormones help develop breasts at puberty: regulate the menstrual cycle, and support a pregnancy.
- The Testes (male) make testosterone; these help males to grow facial and body hair at puberty. It also tells the penis to grow larger and plays a role in making sperm.
The activity of these glands is constantly regulated by the nervous, hormonal and chemical information being fed to them. Hormone production is controlled in many cases by a negative feedback system, in which overproduction of a hormone leads to a compensatory decrease in subsequent production until the balance is restored. The pituitary gland has a central role in this process of maintaining harmony.
In a small area of the forebrain, just above the pituitary gland is the hypothalamus, which is the main coordinating centre between the endocrine and nervous system. It functions as a monitor and regulator of the autonomic nervous system, as well as the body’s metabolism through eating, drinking, and temperature control, and also monitors the menstrual cycle. The anterior pituitary responds to hormones selected by the hypothalamus, which either stimulate or inhibit the secretion of its own hormones.
Integration of the bodily systems is possibly demonstrated best by the Endocrine and Glandular System, along with the control box that is the brain. These show how the body can manage itself, as long as we give it the tools to do just that.