Hormones get a lot of attention. We attribute them to why teenagers are moody, and we’re wary of how they’re affecting the food we eat. Most people have a sense that they’re important players in sexual attraction, aggression, and pregnancy. But sometimes there are misconceptions about the complexity of hormones and just how cool they can be. Here are 5 things you might not have known about hormones!
1. Both men and women need estrogen and testosterone
It is common for people to think that estrogen is the “female” hormone and testosterone is the “male” hormone. However, both males and females make these hormones, and they are essential to health.
Testosterone and estradiol (which is the proper name for “estrogen”) are known as steroid hormones, and they derive from the molecule cholesterol. In fact, estradiol is made from testosterone by the enzyme aromatase. So, to make estradiol, the body must first produce testosterone. For example, the ovaries, the reproductive glands of females, have an abundance of aromatase, so testosterone made in the ovary is being primarily converted into estradiol. Conversely, the male reproductive glands, the testes, will primarily make testosterone which is released into the blood stream. Therefore, men have a higher amount of testosterone and women a higher amount of estradiol. But where is testosterone made in females and estradiol in males? Some testosterone from the ovaries isn’t converted into estradiol and can be released, and testosterone can also be produced from the adrenal glands that sit on the kidneys. The brain is also capable of making hormones. For both males and females, aromatase is expressed in the brain, and this is the largest known concentration of aromatase in the human male body which means that the male brain is a major source of estradiol production !
Figure 1 Steroids are defined by their four carbon rings chemical structure. Here, you can see how the chemical structure of both testosterone and estradiol are similar to cholesterol. Source: own figure adapted from public domain.
2. Women aren’t exactly “hormonal” when they are on their periods.
A common misconception in the media is that women are being “hormonal” when they have their period – also known as menses. During the menstrual cycle, there is a short time window when the ovary makes a lot of estradiol that triggers the release of an egg. When this egg is waiting to be fertilized, the other steroid hormone, progesterone increases. When fertilization doesn’t occur, both estradiol and progesterone levels dramatically drop. This lack of hormones is what triggers the uterus to contract and dispel its contents. So, when women have their periods, this is the lowest their hormones are in their cycle.
Figure 2 When estradiol and progesterone are at their lowest, menses occurs. Modified from an image by Isometrik.
3. Hormones can be made from more than just glands
So, you know hormones are made from the ovary and testes. This post may have been the first time you have heard that hormones can be made from the brain. But did you know that hormones can be made from almost anywhere in the body? You name it, and likely it makes a hormone. The intestines make a hormone called gastrin which is important in digestion. Fat cells make leptin which sends signals to the brain about hunger. Even bones can make hormones! The glands that make up the endocrine system are what are the primary synthesizers, but scientists are understanding a lot more about how other parts of the body are making these molecules on their own.
Figure 3 The endocrine system is made up of several glands in the body. Although glands produce a lot of hormones, other parts of the body can too! Source: NIH National Cancer Institute.
4. The great pheromone mystery
People throw around the term pheromone a lot, especially when discussing how to attract potential partners. While pheromones are important for a lot of animal reproduction, there is very little evidence that humans have the capacity to detect them. For mammals, detecting pheromones, which are chemicals that are released into the environment by one organism and detected by another, happens through the vomeronasal organ. This organ has never been found in humans, though there is something called “cranial nerve zero” which has been noted by anatomists but its function is still relatively unknown. Some literature indicates that it may aid in olfaction (sense of smell), and scientists have speculated it could have the ability to detect pheromones . However, there is minimal definitive evidence for this. Whatever the relationship is between humans and pheromones, we certainly do it in an odd way compared to other animals.
Figure 4 A way that animals get pheromones to their vomeronasal organ is through the Flehman response, which is curling of the upper lip and inhaling. The vomeronasal organ is located just above the roof of the mouth and a duct behind the teeth allows access to the organ. Source: Brandinian.
5. Oxytocin is more than just the “love” hormone
Calling oxytocin the “love” hormone is over simplifying its function, though there is a lot of science behind why it has been dubbed this. Oxytocin does a lot in the body. It’s essential for the contractions that happen in child birth, and is responsible for the “milk let down” in breast feeding. It is also an important hormone in forming monogamous bonds in animals that pair up for life (like the cute prairie vole!). Oxytocin in general has been characterized as “prosocial”, meaning that it promotes affiliative, or positive, social behaviors. It has been a focus of studies for autism and there are even clinical trials currently ongoing.
Figure 5 Prairie voles are one of the few species of mammals that practice monogamy. Males and females form long-term pair bonds and both will take care of young.
Now when you hear people talking about estrogens, testosterone, oxytocin, or pheromones, you can tell them why hormones are a lot cooler and more complicated than they may think.
Biegon A, DL Alexoff, S Won Kim, J Logan, D Pareto, D Schlyer, GJ Wang, JS Fowler. “Aromatase Imaging with [N-Methyl-11C]Vorozole PET in Healthy Men and Women” J Nucl Med (2015); 56:580-585.
Vilensky JA “The Neglected Cranial Nerve: Nervus Terminalis (Cranial Nerve N)” Clincal Anatomy (2014); 27:46-53.
Anagnostou E, L Soorya, J Brian, A Dupuis, D Mankad, S Smile, S Jacob “Intranasal oxytocin in the treatment of autism spectrum disorders: a review of the literature and early safety and efficacy data in youth.” Brain Res (2014); 1850:188-198.
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