What systems does the endocrine system work with?

The endocrine system consists of organs known as glands which are ductless and produce secretions known as hormones, that are transported through the body by the circulatory system.

Hormones are chemical messengers which  bind to chemical receptors on cells which are known as target cells. One type of hormone is known as  a steroid hormone which can cross cell membranes and travel through to the nucleus, enter and switch genes on or off. There are also nonsteroid hormones which require secondary messengers to transport their message inside of target cells. 

Basically, the endocrine system helps to maintain homeostasis throughout the body and it works with all of the body's systems. Hormones work by feedback mechanisms.  If there is a high level of a hormone in the blood, this may trigger a gland to secrete less of the hormone in negative feedback, or to release more of the hormone in positive feedback.  Sometimes, two hormones with opposite effects help maintain homeostasis. An example is the hormone insulin secreted by the endocrine glands known as Islets Cells on the pancreas, which lowers blood sugar by causing excess sugar to be stored in liver and muscle cells and the hormone glucagon, which causes stored sugar to be released to the blood when needed. This example shows how the endocrine system works with the digestive system, the circulatory system and the muscular system to maintain sugar levels in the body.

Sex hormones released by the endocrine system glands--ovaries and testes, affect the reproductive system by regulating the female menstrual cycle which begins at puberty and allows a woman to release an egg each month. It also affects the male reproductive system to allow it to produce sperm cells. These hormones also produce secondary sexual characteristics that occur at puberty.

An endocrine system gland called the pituitary gland works with the skeletal system because when it produces human growth hormone (HGH) it stimulates the growth of bone cells to divide which increases a person's height. The pituitary gland has the name "master gland" because of the many hormones it makes which effect many systems of the body.

The thyroid gland makes the hormone thyroxin that affects metabolism. The metabolism involves many systems of the body--how fast foods are metabolized to release energy which involves the respiratory and digestive systems, along with the a which has to do with heart rate and blood flow.

Adrenal glands located on top of the kidneys secrete adrenaline, the flight or fight hormone which affects the skeletal and muscular systems to be ready during emergencies and the circulatory system which pumps more blood.

These are just a few examples of the many systems of the body, such as the nervous system, that are affected by the hormones produced by the endocrine system.