Anatomy Week Eight

In this week we learned about the Endocrine system.  The nervous system and the endocrine systems work together to coordinate the functions of all the body systems.  At the synapses, nerve impulses trigger the release of the mediator molecules that are called neurotransmitters.  The endocrine system, as mentioned before, controls body activities by releasing these mediator molecules that are called hormones.  The means of control of these two systems are very different.

The hormone is a molecule that is released in one part of the body but regulates the activity of cells in other parts of the body as well.  The majority of the hormones enter the interstitial fluid and then the bloodstream.  As the blood circulates, it delivers these to the cells throughout the body.  Like neurotransmitters, hormones exert their effects by binding to receptors on or in their target cells.  There are, however, several mediator molecules that act as both hormones and neurotransmitters.  An important example of this is norepinephrine which is released by as a neurotransmitter by sympathetic postganglionic neurons, and also as a hormone by cells of the adrenal medullae.

The responses produced by the endocrine are often much slower than those of the nervous system.  Some hormones act within seconds, but most take several minutes or more to cause a response in the body.

There are two main kinds of glands in the body.  There are exocrine glands and endocrine glands.  The exocrine glands secrete their products into ducts that carry the secretions into body cavities, the lumen of an organ, or to the outer surface of the body.  Some examples of exocrine glands are the sebaceous glands, sudoriferous glands, mucous glands, and digestive glands.  

Endocrine glands in contrast secrete their products or hormones into the interstitial fluid surrounding the secretory cells, rather into ducts.   These hormones diffuse into capillaries and blood carries them to the target cells throughout the body.  The majority of hormones are required in very little dosages so the circulating levels are typically very low.  The glands that are endocrine are pituitary, thyroid, parathyroid, and pineal glands.  There are other glands that do not function exclusively as endocrine glands, but they do contain cells that are hormones.  These are the hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver,small intestine, skin, heart, adipose tissue, and placenta.  These and the endocrine glands act as the endocrine system.  

Without these hormones coursing through our blood, normal everyday functions of the body would not happen.  Something as simple as your body being able to sweat when you are overheating to cool you down, would not be able to happen without the endocrine system in place.