The Endocrine System

Functions

Regulation, regulation, regulation. The endocrine system is all about regulation - it regulates everything from growth to mineral levels to toxicity to metabolism. This is all accomplished through useful little things known as hormones. 

Hormones

Hormones are simple, chemical messengers that find receptor cells and trigger various mechanisms for regulation. To do their job, however, they need to find their cells, and this is done through two ways. Hormones will be secreted by either an exocrine gland or an endocrine glands. Exocrine Glands travel along specific paths known as ducts to get to their cells. Endocrine glands, on the other hand, are released directly into the blood stream. The two most well-known examples of this difference are the tear ducts and adrenaline: tear glands send tears through the ducts to the eyes, whereas the adrenal glands drive adrenaline right into the bloodstream. 

Hypothalamus

The hypothalamus is the main gland that regulates metabolism, temperature, and appetite. Located in the central part of the brain, it can send out hormones not only to regulate it's own functions, but to regulate the pituitary glands as well. Some of the hormones are carried directly to the pituitary gland where they then trigger the subsequent release of other hormones, or can stop hormones. Somatostatin is an example of this, coming from the hypothalamus into the pituitary gland and shutting down production of growth hormone. 

Pituitary Gland

Located just under the hypothalamus is the tiny pituitary gland, split into two parts: the anterior lobe and the posterior lobe. The anterior lobes functions are further regulated by the hypothalamus, while the poster lobe functions are simply pituitary functions. The anterior lobes functions includes the creation of growth hormone, to stimulate growth, sex-differentiation hormones, and stimulation hormones for both the adrenal and thyroid glands. The posterior lobe is actual more of a routing regions for hormones that are created by the brain and sent through the pituitary. 

Thyroid Gland

This gland is located towards the outside of the lower part of the throat, wrapped around the trachea. It's main responsibility is metabolism regulation, which is done with the hormone thyroxine, but it also stimulates development of the nervous system and bone growth specifically in children. Minor regulatory operations for the whole life span also include maintenance of blood pressure, heart rate, digestive functions, muscle tone, and reproductive functions. 

Parathyroid Glands

These are two small glands that lie across the two sides of the thyroid and help simply regulate blood-calcium levels and bone metabolism. 

Pineal Body

Located in the middle of the brain. Though the function of this small gland is unsure, it releases melatonin which may regulate biological sleep cycles.

Adrenal Glands

This pair of glands lies across the kidney's, one on each organ, and each one has two parts: the adrenal cortex and adrenal medulla. The cortex has a variety of basic regulatory functions, including metabolism, salt-water balances, immune system, and sexual functions. The medulla has one function only, coping with various stressors, which is handled by hormones known as catecholamines. Catecholamines respond to these stressors in various ways, such as changing heart rate, blood pressure, etc. 

Pancreas

One of the larger glands, the pancreas is an elongated structure lying behind the stomach in the abdominal region. Like other glands, it has two parts: the endocrine pancreas and exocrine pancreas. The endocrine part solely regulates blood sugar levels through glucagon and insulin. The exocrine pancreas is mainly for digestion, secreting various enzymes (not hormones) to aid in digestion. 

Reproductive Glands

Male Reproduction: Testes

Located in the scrotum in males, the testes are in charge of secreting various sex hormones, namely testosterone, which are in charge of secondary sex characteristics and sperm production. 

Female Reproduction: Ovaries

Females produce many of the same hormones as males, but in different proportions and quantities. The main female hormone is estrogen. Female hormones are in charge of secondary sex characteristics as well as female reproductive functions.