What is Endocrine Signaling?

Elite HRT

Written by Elite HRT on March 13, 2021

Medically reviewed by

Camille Frecking, Regulatory Affairs Specialist, MEDICAL ADVISOR

The human body has over 10 organ systems that work together to keep the body working efficiently. One of the most under recognized systems is the endocrine system. By understanding the inner workings of the endocrine system you can learn about endocrine signaling, but most importantly discover how your body manages to communicate with itself. 

This article will work to describe what the endocrine system is, the various glands and hormones that it produces, and finally endocrine signaling. Endocrine signaling does not happen the same with all hormones, so there will also be an explanation of the two types of signaling. 

The Endocrine System

The endocrine system is often ignored to be understood because it seems complex and overwhelming. When you take it step by step you can make it an understandable topic that you can use to better understand yourself. 

So let’s begin with what the endocrine system is. An organ system is a group of different organs that work together for a common goal or function. Endocrine is referring to glands that create hormones to travel through the blood and signal for a function. Therefore, the endocrine system is an interconnected system of glands and organs that signal to each other to do something.

Glands of the Endocrine System

Keeping the endocrine system in mind you can learn about the individual parts of the system which are the glands. For each gland there will be an explanation of what hormones it sends out and which organ or gland it is “talking to.”

> Pituitary Gland

The pituitary gland is special because not only does it release over 7 hormones, it tells other glands when to release their hormones. Because of this the pituitary is called the master gland. For the most part, instead of working on the organ itself to carry out a function it tells other glands to release hormones that do the work. 

One common hormone that belongs to the pituitary gland is luteinizing hormone (LH). This hormone is released by the front part of the pituitary gland and sends a message to the Leydig cells in the testicles. The testicles then go on to create testosterone. 

The pituitary gland also creates the following hormones:

  • Adrenocorticotropic hormone – signals to the adrenal glands to make cortisol.
  • Follicle stimulating hormone (FSH) – signals to the ovaries to make estrogen and to the testicles to make sperm.
  • Growth hormone (GH) – signals to the body to maintain its fat, muscle, and bones.
  • Prolactin – signals to the body to create breast milk after childbirth.
  • Thyroid-Stimulating hormone (TSH) – signals to the thyroid to make thyroid hormones.
  • Oxytocin – stimulates the body to release the flow of breastmilk, cause contractions in labor, and promote bonding between a mother and infant (or whoever you’re making physical contact with!)
  • Antidiuretic hormone – signals to the body to balance water and sodium. 

> Pineal Gland

The pineal gland is a very small gland located in the brain that’s main function is to maintain the sleep-wake cycle of the body. The pineal gland releases the hormone melatonin which works on the body to cause a sleepy feeling. The pineal gland is triggered if there is light or dark coming into the eyes. When darkness occurs the pineal takes that as it being night time so it releases melatonin to help you fall asleep, with light (both sunlight or artificial light) blocking the release of melatonin so you can stay awake. 

> Thyroid Gland

The thyroid gland is another biggie when it comes to body functioning. The thyroid gland is a butterfly shaped gland in the neck that responds to TSH by releasing triiodothyronine (T3) and thyroxine (T4). These hormones act on the body to manage metabolism. It can play a role in speed of digestion, mood, heart rate,  maintaining body weight, and even body temperature. If thyroid hormones are out of the normal balance there will be significant symptoms that need to be addressed by a healthcare provider. 

> Parathyroid Glands

The four parathyroid glands are often overlooked because of their small stature and location. They are located on the back side of the thyroid gland in a square shape. These glands are responsible for releasing parathyroid hormone also known as PTH. This hormone signals to the body to take calcium from the bones and put it into the blood. It does this if the calcium levels in the blood are too low. Overall, these four small glands have an important job of maintaining the calcium levels in the body. 

> Adrenal Glands

The two adrenal glands sit on top of the kidneys like a little hat. The adrenal glands release cortisol, epinephrine (adrenalin), norepinephrine, small amounts of estrogen and testosterone, and much more. The adrenal glands release hormones that act on almost all organ systems of the body so it is very important that they are working properly.

> Testicles

The testicles are only in men and have two main roles: one as a gland and one as an organ. As a gland the testicles are responsible for creating testosterone, the main male sex hormone testosterone. Testosterone helps the male body to have a healthy sex drive, maintain muscle mass, have bone strength, have healthy hair, balance their mood, and even more. As an organ the testicles are used to produce sperm for reproduction.

> Ovaries

The ovaries are only in women, and just like the testes, they have two roles: as both an organ and gland. The ovaries function as a gland to produce estrogen and progesterone. These hormones work together to balance the menstrual cycle, bone health, mood, sexual desire, and more. The ovaries also is where egg cells are created and matured for reproduction. 

Cell Communication

The term “signalling” keeps being said in regard to hormones signaling to another gland or organ. But what exactly is this signaling? You can think of this as how the body is communicating to itself. There are many ways that the body talks to itself including electrical signals from the nerves and muscles and of course hormones. 

The hormones themselves are chemical messengers that are sent from the gland, through the blood and to the organ or gland it is trying to reach. Hormones are so great because they can travel far distances, like all the way to your brain from your adrenal glands. But how does it know when it is in the right place?

The places that are meant to receive these hormones have specific receptors on them that can only accept certain hormones. Think of it as a house key. The key hole is the receptor and the key is the hormone. The door will only open if the right key comes inside. So only if the right hormones come along will the receptor “open” to do the determined function. This process is called endocrine signaling and is how hormones work with organs to make big things happen in the body. 

Depending on the type of hormone will determine if the receptors for the hormone is on the inside or the outside of the cell that it is trying to reach. The main difference is if the hormone will dissolve in water (water soluble) or in fat (lipid soluble). The word “soluble” just means “can be dissolved in.” 

Signaling With Internal Receptors

For lipid soluble hormones, they have to be received by receptors that are inside of the cell it is trying to reach. Lipid soluble hormones are ones that have a structure similar to fat and include hormones that are considered steroid hormones. This just means that they have a four-carbon ring structure with a special tail that makes them unique. Some steroid hormones are testosterone, estrogen, and progesterone. 

They are able to get to a receptor inside of the cell because the outside of a cell (cell membrane) is made out of the same lipid structure. Therefore, they can easily pass through to get to an inside receptor. 

Signaling With External Receptors

Water soluble hormones do not have the luxury of being able to pass through the cell membrane because fats repel water like vinegar and oil. Because water soluble hormones cannot pass through the membrane they can easily attach to receptors on the outside of the cell it is trying to reach. Some hormones that communicate like this are epinephrine, prolactin, and growth hormone

Conclusion

See? The endocrine system does not have to be big and intimidating! When broken down into simple pieces it is easy to see how the big puzzle fits together. 

From each individual gland to the hormone to the receptors, this system is able to effectively endocrine signal to make things happen in the body. It is also super interesting to think that medications and hormone replacement therapy work similarly to endocrine signaling by attaching to the same specific receptors and carrying out the same function!

Resources

Pituitary Gland: What Is It & Definition – Cleveland Clinic

Physiology of the Pineal Gland and Melatonin – Endotext – NCBI Bookshelf

Endocrine Signaling – Protocol