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- Herausgeber: Clink Street Publishing
- Kategorie: Ratgeber
- Sprache: Englisch
The story about a body in continuous transformation. This book unravels the mystery surrounding women's biology and explains what is happening underneath the surface. We all know that the female body changes cyclically every month during the reproductive years, and that it completely transforms during puberty, pregnancy and menopause. However, most of us ignore the fascinating details. What triggers those changes and what are the sometimes unexpected consequences? The facts are as mind-blowing as entertaining. Based on the latest research, all information is presented in an easy to read manner with plenty of anecdotes; from historical prejudices to personal experiences, with some evolutionary ideas in between.
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Veröffentlichungsjahr: 2021
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Go Figure!
The astonishing science of the female body
Lisa Falco
This book is for scientific curiosity only and should not be used as medical advice.
All the facts in this book are collected to the best of the author’s ability and the scientific or literary source of the knowledge should always have been cited. If a source has fallen out in the editing process, this is an honest mistake that should be corrected for future editions. If you spot such a mistake, please don’t hesitate to inform the author.
To my family, close and far
Table of Contents
Introduction
The female body and mind are often portrayed as a mysterious temple that is impossible to understand. With this book I want to unravel some of the mysteries surrounding women’s biology and explain what is happening underneath the surface. With organisms as complicated as the human body, it is necessary to have a broad knowledge to understand how everything is interconnected. This book combines that overview with the captivating nitty-gritty details that demonstrate the ingenious construction of the female body, debunking a few myths along the way.
We all know that the female body changes cyclically every month during the reproductive years, and that it completely transforms during the major transition phases: puberty, pregnancy and menopause. However, most of us are not aware of the fascinating details. What triggers those changes, and what are the sometimes-unexpected consequences?
You will also learn many unexpected things:
How pregnancy is a temporary hijacking of the body and how this changes not only the body, but also the brain, everything directed by a new organ growing inside of it.Why women get more anxious as mothers and when they grow older.That men can breastfeed if given the right hormones.That vision and voice changes with the menstrual cycle.That women carry parts of their children (actual cells) with them forever after giving birth.How fertility can be even more complex than you thought.That sperm is being very well taken care of and are not at all the brave little swimmers that we always thought.Whether the mood swings before menstruation are real or a social construction (spoiler: they are real!).Why women are more robust towards infections than men while still suffering more frequently from autoimmune diseases?How does a regular menstrual cycle protect heart and bones?What happens when you age?Do menstrual cycles really synchronize?This book answers these questions and many more. It is based on science, but you should not shy away as I guide you gently through this fascinating journey. You can choose your itinerary since each chapter can be read independently. Our aim: comprehension, empowerment and fun. Whenever your memory needs a refresher, there is a list of the most common medical terms at the end of the book.
A body in continuous transformation
One thing that makes the woman’s body so extraordinary is its continuous changes. You not only have the major transitions – puberty, pregnancy, post-pregnancy, perimenopause and menopause, – but also the cyclic transformation happening each month.
The hormonal changes over the menstrual cycle can impact our mood, how we react to pain, how hungry we are, how strong our immune system is, and what our bodies look like, just to name a few examples.
For some women, the changes over the menstrual cycle can be a radical experience with many ups and downs, whereas other women can go through the cycle while hardly noticing any impact. The major transition phases are hard to go through without noticing. In puberty, oestrogen changes the body’s shape and function fundamentally. The breasts develop and the levels of fat increase under the skin, on the hips, thighs, and buttocks, all that accompanied by emotional storms, changing body odour, and hair growths. Everything is triggered by the new hormones.
Pregnancy might be the largest transformation of them all. The body is turned into a machine capable of producing and nourishing life. It is easy to observe the outer changes, such as the growing belly, the increasing size of the breasts and the additional fat needed to provide food for your growing baby, both inside and outside of your womb. Again, these changes are triggered by hormones, but this time released by the placenta, a new organ (you read correctly) formed inside the womb in the early pregnancy. On the inside, the placenta is not only releasing hormones, but also acting as a life support machine, providing the developing foetus with oxygen and nutrients while cleaning the foetus’ blood. At the same time the breasts are growing and changing their entire internal structure to be able to produce milk for the new baby.
The last major transformation in a woman’s life is the menopause. This is when her menstrual cycles stop once and for all. It marks the end of her reproductive life, and this is a transition that is dreaded by some and celebrated by others. The sudden removal of sexual hormones has a large impact, not only on the reproductive capacity, but it also affects metabolism, bone and muscle strength, ageing of the skin, and mental health. It might sound terrifying but it is a very natural part of growing older and a key to the successful evolution of humankind.
Later in this book you can read about the captivating details driving these transformations. This will allow you not only to observe what is happening, but also to understand it. Hopefully, this will help you feel more in control and able to enjoy those changes.
Understanding ourselves and others
We are often asked to believe and accept things as they are, without really understanding them. However, understanding is a cornerstone of tolerance, it is difficult to be tolerant about things we cannot relate to, or find logic. Women are often seen as difficult to understand, sometimes even by ourselves. This lack of understanding can in many cases lead to a lack of respect for our experiences, whether it is related to our physical or mental wellbeing.
A close friend said to me the other day: “This thing about PMS (premenstrual syndrome), isn’t it just an excuse for women to be bitchy?” I could not believe how she as a woman could say such a thing, but of course, she had never experienced PMS herself and could not relate to how it felt. This gave her the feeling that the whole thing was exaggerated.
Personally, I have no doubts that PMS exists. I never become ‘bitchy’, but I come home almost crying from work once a month, firmly convinced that everyone hates me, and that I am the most useless person on the planet. One day later, these feelings are gone and two days later, I get my next period. Same procedure, every month. Either PMS is true, or the world has synchronized itself with my menstrual cycle.
The purpose of this book is to try to explain in detail the physiological processes inside our bodies that influence us. One such subject is PMS, and the chain of events that may lead to depressed and anxious feelings. Hopefully, not only my friend, but also everyone else reading this book will get a better understanding of the experience many women have and thereby become more tolerant towards it.
I must admit that earlier in my life, I also had a problem respecting other women’s experiences. One in particular was the experience of menstrual cramps. I did not experience them myself, so somehow, I thought women who were incapacitated with pain were being overly sensitive. Unfortunately, in the past my own ignorance was shared with many medical professionals, and women’s pain has been ignored for much too long. Nowadays, we understand better which underlying issues cause the excessive pain. This both increases the tolerance for it, and helps women get treatment faster, whether it is PMS, period pain, emotional storms in puberty or hot flashes in menopause.
If you are a woman planning to get pregnant or experience problems with your health, it feels obvious to take an interest in your body and learn as much as possible. However learning about your body is relevant in all life stages. Your body will accompany you throughout your whole life, and many of the choices you make when you are young will have an impact later.
We are not victims of our hormones and our bodies, and we also should not exaggerate their effect. That being said, knowledge is power and being mindful about what is happening inside us can help us to either embrace it, or to put it aside and concentrate on other things.
Just another word before we start
The difference between you and science
What you will read in this book is based on science, but what does that really mean? A lot of medical science is based on clinical trials, where a group of people or animals are studied under different conditions. Clinical research can often seem a bit dodgy, and there are a few things that are important to know when you read about it. Mostly, the results are never black or white or straightforward to interpret, which is why statistics is needed.
Statistics can be seen as a ‘dark’ art before you get the hang of it. One joke about statisticians goes: “A statistician can have his head in the oven and his feet in the freezer and say that on average he is fine.” Statisticians often talk about averages, but it is also important to look at distributions. If we look at the statistician with the feet in the freezer, he will cover the entire distribution ranging from very cold (the feet) to very hot (the head). If you now imagine the statistician with a very large belly and with a small head and small feet you would get a good impression of a distribution. Only a very small portion of the body is at the extremes and the largest portion of the body is somewhere in the middle and experiences reasonable temperatures. This is a typical normal distribution; most things fall somewhere in the middle and a few things in the extreme areas. Very few people are exactly average, but most people fall within a distribution and it is the limits of the distributions that defines what is considered ‘normal’. The head and feet of the statistician would in this case not be considered ‘normal’. For instance, on average, women have a menstrual cycle that lasts 29 days, but it is completely normal to have anything between 24 and 35 days.1
Another important concept in statistics is that correlation is not causation. This means that just because researchers have managed to see a link between two phenomena, it does not mean that one causes the other. A famous example is the correlation between chocolate consumption and Nobel Prizes. In a study from 2012 it was shown that countries with a high consumption of chocolate produced more Nobel Laureates.2 The correlation between the two is very strong but that does not mean that there is a causation. Despite dark chocolate having many beneficial effects on your health, the most likely reason between chocolate consumption and Nobel Prizes is that economically wealthy countries spend more money both on education and luxury goods such as chocolate. Switzerland, which is the country with the most Nobel Prize winners per capita also happens to be very famous for its chocolate and therefore bias the results.
It is also important to realize that many scientific results do not have a direct impact on you as an individual. Many of the findings from clinical studies apply to a large population. It means that the results matter on a large scale but not necessarily to you. One example is the impact of breastfeeding. It has been shown that on average, breastfeeding increases the IQ score of babies by 3 points.3 First of all, it is very unlikely that you will be representative of the average effect. If the average increase is 3 points, it means that for your child, the effect of breastfeeding can be anywhere but probably somewhere between 0 and 6 points. Even though Einstein was allegedly breastfed until he was six years old, this was most likely not the reason he was so smart.
However, let us assume that you would be representative of the average effect. Your child will improve its IQ score with 3 points if you breastfeed it. An increase of 3 IQ points for your child will not bring it any additional advantages in life; for that, the difference is too small. However, on a society level it makes a big impact if the population has an IQ score that is 3 points higher on average, which is one of the many reasons it makes sense to promote breastfeeding.
I am a strong believer in science, but I remain aware of its many flaws. Despite that, I have just like most other people, a tendency in believing what confirms what I would like to believe in. This is called expectation bias. If you expect something to be true, or want it to be true, it is much more likely that you will find indications that confirm your beliefs. You also more likely refer to research results supporting your beliefs.
One such example is all the research supporting that a glass of wine a day is good for your health. That is a marvellous finding for a wine-lover like myself, so I am of course very prone to believe it and celebrate the finding with a nice glass of Cabernet Sauvignon. As it is not my domain of research, my own belief in the benefits of wine drinking is not harmful for anyone, except for myself in case it would turn out to be wrong. However, if I were researching the effects of alcohol, such a bias could be harmful.
An example of how bias has influenced research over the last centuries is the misogyny that has been directed towards women. This negative idea has pushed researchers towards findings demonstrating women’s inferiority to men. Even prominent thinkers like Darwin used his theories of evolution to justify the idea that women were intellectually inferior to men. This was a belief so deeply rooted in society that he did not manage to see beyond it.4 Luckily, things are evolving but it takes time to change such a well-established preconception, no matter how unfounded it is. As research in the past was mainly conducted by men, more focus has been on research on them, and women have not been studied properly. Having more women in science may lead to a better balance in the future.
It is easy to identify bias in the past, but it is difficult to say what type of biases we are carrying with us now. Trying to be aware of our own prejudices is just as important for researchers as it is to us as consumers of media and scientific communications.5
Another important thing to consider regarding clinical research is something called confounding factors. It is all the things that you have not examined, which might have an impact on your results and prevent you from seeing the real link between the input and output of the observations. This is also linked to correlation and causation, and it is basically what makes the difference between the two. If you have observed a correlation in your data, the confounding factors are what prevents you from finding the cause.
Again, wine studies are a good example of confounding factors and correlations. In many studies where the benefits of wine were shown, the participants were grouped depending on their drinking behaviour. People who drank nothing were in one group, people with moderate wine drinking (about one glass a day for women, two for men) in a second group, people who drank more in a third one. The studies could show that the group of people with a moderate consumption lived longer than, not only the group with a heavier drinking, but also longer than the group that did not drink any alcohol.
Can you draw the conclusion from this observation that wine drinking is good for you? Not really, many other factors influence the results. For example, there is a possibility that moderate wine drinkers have a higher socioeconomic standard, and such people tend to live longer. In this case, the researchers had done their homework and compensated for this, as well as many other factors. However, there was one thing that some of them had missed: in the group of people who did not drink alcohol, former alcoholics and people with chronic illness could have been included. As alcoholics and people with chronic illnesses have a shorter life expectancy, they would shorten the average lifespan of their group. Therefore, the conclusion that it is better to drink one glass a day than none may be biased.6
Temperature-box
Another fact that is even deeper rooted in our society is that our average body temperature is 37°C. Nowadays, that number has been adjusted to 36.6°C. The most probable cause is that we are much healthier and have less infections today, so our body temperature really is colder.7
Many truths have an expiry date. It is a common saying that a normal truth lasts 20 years and I suspect that this is correct, or maybe even shorter. Hopefully, most of the things you will read in this book will still hold in 10, 20 years’ time, but you must always be prepared to challenge what you have learned in the past, whether from school or in this book.
Certain things cannot be studied for ethical reasons. One such topic is, staying on the wine drinking theme, the effects of moderate alcohol consumption during pregnancy. We know that heavy alcohol consumption exposes the baby to a very high risk of birth defects for instance maternal alcohol exposure during early and late pregnancy can cause both structural and functional defects in long-term renal function.8 However, we do not know what would happen if you would only drink a little. It is also very likely that we will never know this. A woman with moderate alcohol consumption has no problem in stopping drinking for nine months and would therefore not take the risk to do any harm to her unborn baby. Nevertheless, such a study would never pass the various national ethical committees since the benefits of that knowledge is not in proportion to the risk the participants would expose their offspring to.
Most of the research cited in this book has been conducted in Europe and in the US. This might unfortunately bias some of the findings. Some studies have shown that there is a difference in what is considered ‘normal’ hormonal levels between women living in different areas of the world. For instance, studies of women in Bolivia have shown that they can conceive and go through healthy pregnancies at much lower hormonal levels than women living in Chicago.9 That being said, the fundamental biology does not differ between ethnicities. In the US, where they have better possibilities than in Europe to conduct studies on diverse populations, most of the differences seen between ethnicities can sadly be traced back to differences in socioeconomic status and precarious living conditions rather than biology. One thing to bear in mind is that being an ethnic minority can induce a lot of stress and that stress can have an impact on your health and your menstrual cycle. I will therefore rarely mention differences in ethnicities but rather refer to the factor that might change the data, such as body mass index, diet and stress. Wherever I have found differences in the data, this will be mentioned. Lifestyle is another bias in the data where European and North American is considered the norm. Not because I think that they should be, but because the research I found was conducted in those countries. If I rewrite this book in ten years, I hope the input data will be more diverse.
I am primarily a scientific writer but to make very dry and complex data understandable and interesting, I will sometimes simplify descriptions while trying to remain as scientific as possible.
And with those words, let’s get started on our learning journey. We start off by investigating what is a woman and how is she seen by science …
What makes a woman?
For centuries, women were seen by science as men, but with pesky hormones. When my son was four years old, he had a similar opinion but the other way around. His explanation of a man was: “It’s like a lady, but with balls. You could say that it is a ball-lady [Hodenfrau in German].”
For a long time, it was a joke in our family to refer to men as ‘ball-ladies.’ But just like my son has grown up to realize that men are not just women with testicles, science has now grown up to realize that women are not just men with odd or pesky hormones.
In which aspects are women so different? Many of the differences can indeed be traced back to the hormones which have a tremendous influence. People undergoing feminizing hormone therapy can immediately spot the changes that the hormones are doing to them. After three to six months of hormone therapy, the skin becomes softer, the muscle mass decreases, breast starts to grow, and the fat gets redistributed and accumulates around the hips and thighs.10 As those hormones trigger such huge changes, it is no surprise that women can both feel and look different as these very hormones change cyclically and even more during the major transformations that they go through in puberty, menopause and during pregnancy.
What else makes women so extraordinary and differentiates them from the other half of the planet’s population? At the time of writing, the definition of a woman on Wikipedia was as follows:
“Typically, a woman has two X chromosomes and is capable of pregnancy and giving birth from puberty until menopause. Female anatomy, as distinguished from male anatomy, includes the fallopian tubes, ovaries, uterus, vulva, breasts, Skene’s glands, and Bartholin’s glands. The female pelvis is wider than the male, the hips are generally broader, and women have significantly less facial and other body hair. On average, women are shorter and less muscular than men.”
According to Wikipedia, the things that distinguish the two sexes are mainly the attributes linked to making babies, having babies and feeding babies. Even though being able to create life is definitely one of the big marvels of the female body, there is of course more to the story and one can be a woman without being able to get pregnant and give birth. What may seem like an easy and uncontroversial distinction at first glance is in fact a rather complex question. First, we need to distinguish between gender and sex. Gender is related to identity and sex to biology, but even if we only consider the definition of sex, it is not straightforward. You can be a woman without having all the attributes that are typically linked to female biology, and you can be a man while having some of those attributes. There is no clearly defined line, and what one would think was a purely biological question cannot be answered without being political.11 The definition of sex is far beyond the scope of this book, in which the main issue is the effect of sex hormones. I will use the term ‘woman’ and ‘female’ in a broad sense without any attempt to classify individuals according to sex and gender.
Now, back to the pesky hormones, or the marvellous chemicals depending on how you see them, they are indeed to blame for a lot of things linked to the female biology. All the physical attributes in the Wikipedia definition have been created under the influence of hormones and they start playing a role even before birth. The very first job of the hormones is to turn women into men. Yes, you read that right. It turns out that my son’s early view on the world agrees with our current knowledge, namely that the default human is female and becoming a man is an active deviation from the default.
Switch-box
When we are just a foetus, a few weeks after our mother’s egg gets fertilized, there is no way to tell if we will become a man or a woman. Where there will later be our reproductive systems, there is just something called the gonads (or sex glands) and two systems of ducts, the Müllerian ducts and Wolffian ducts. Becoming a female means that the gonads will develop into ovaries, and the Müllerian tract will develop into the fallopian tubes, the uterus and the vagina. This will happen if there is no interference in the process.
However, there is a kind of master switch, which is a special gene situated on the Y-chromosome. If this is present, it will turn the foetus into a male by developing the gonads into testicles. This happens about seven weeks into pregnancy. Once the testicles have been developed, they start producing anti-Müllerian hormone (AMH) and testosterone. As you might guess from the name, AMH’s main job is to demount the Müllerian tracts; from the Wolffian tracts the connections between the testicles and other male genital parts are created. The clitoris and penis are formed from the same tissue but under the influence of sex hormones they develop in different directions.
Most of the external differences seen in men and women are secondary effects of these internal structures. The ovaries and testicles do not only produce eggs and sperm, but they also produce sexual hormones. The ovary produces oestrogen and progesterone, whereas the testicles produce testosterone. As already mentioned, these hormones have a huge impact on how the bodies develop and are the reasons behind many of the differences that can be observed in men and women when we reach puberty. Even though some hormones are strongly associated with men and others with women, both sexes produce all hormones but in different amount.
Asymmetry-box
For both males and females the gonad on the right side seems to be both heavier, larger and contains more proteins and DNA than that on the left side. This might be difficult to observe in women but easier to see in men.
Despite this difference in size, there is the same number of follicles (what will later develop to eggs) in both ovaries.
Women are not the norm
Whether biology agrees or not, women are not the norm in society. Most things, from how the workplace is organized, to how public toilets are planned, are designed for an average male.12 This is not only annoying but can even be dangerous in some aspects, one in particular is in drug development. For decades, medical research has focused on men as the standard human being. This has led to medicine being optimized for a typical white male, 70 kg, with way more muscles than a woman, and of course, without the pesky hormones. Men have a very different body composition than women, with around 18% of body fat compared to 25% in women. Women’s kidneys also take much longer to clear substances from the blood compared to men. It is therefore very common that drugs stay longer in women’s bodies, and if you keep filling up with more drugs at the same rate as men, the risk of getting a much higher dose of the drug than planned is very high. It is maybe important to note that the exclusion of women in clinical trials were not due to bad intentions but to a fear that clinical trials on women in the 70s had led to bad effects on foetuses.13
Drug-box
In an analysis of 163 new drug applications submitted to the U.S. Food and Drug Administration (FDA) between 1995 and 2000, drug concentrations in blood and tissues in 11 of the drugs varied by as much as 40% between men and women.14 In antidepressants and antipsychotics, women tend to have higher drug concentrations in their blood than men do.15
The FDA has also recently been forced to change recommended doses in drugs such as the sleep aid Ambien, since the concentration stayed high in the blood too long. This led to the women being drowsy until late in the morning which could even lead to car accidents.16 Women are also more likely than men to experience adverse reactions to drugs. Of all the drugs removed from the U.S. market between 1997 to 2001, 8 out of 10 caused more side effects in women.17
From 2016, the U.S. National Institute of Health requires that all new grant applications include both men and women, unless they provide a strong justification to exclusion of one sex.18 That is a great step forward, but this is still just for government funded research. As most of the research is done directly in the pharmaceutical companies, the problem is not solved, and it will take time until it has changed.
Despite all that, it is an exciting time to be a woman. Many norms are being challenged, both in society and in science. Many discoveries in women’s health have been made over the last decades. Some of them are astonishing, mainly because they were not known before. An example of such finding is the true size and shape of the clitoris, which was only discovered in the late 1990s. It was shown that what was seen of the clitoris was only the tip of the iceberg, and that in reality it is a large complex that surrounds both the vagina and the urethra.19 It is a similar story with the anatomy of the breasts and breastfeeding, which got new explanations in 2005.20 You will learn more about this in the pregnancy chapter.
It is a real concern that there is not enough research performed on women. It is, however, also important that the research that has been done is spread, implemented, and becomes common knowledge.
To really understand how the science works, let us start with the basics …
The mysterious chemicals
Hormones – the floating keys
Women often hear that they are ‘hormonal’, but what does that even mean? All humans, regardless of sex, are continuously influenced by hormones. They regulate most of our functions: our digestion and metabolism, how we breathe and sleep, if we get stressed, how we grow and develop, our mood, and of course how we reproduce.
Mostly, hormones act without us noticing anything, but sometimes we can feel the influence of some of them on our mood and on our wellbeing. As for me, getting ‘hormonal’ is synonym of being in high spirits and generally occurs when I have a high level of female sexual hormones, oestrogen. This is, however, not what most people refer to when they talk about being hormonal. They refer to this time of the month when women supposedly get cranky and difficult, just before their next period. In this phase of the menstrual cycle, all hormones that normally make us happy or calm are suddenly dropping from a high to a low level. Whereas the popular belief sees ‘being hormonal’ as being loaded with hormones, it is quite the opposite as we are rather on a hormonal detox.
Men also get hormonal, and this can sometimes be more problematic as it is less predictable and not cyclic in nature. There are links between aggressiveness and the male sexual hormone, testosterone.21 We witness this link mainly in sports, but just as men are not victims of their hormones, neither are we. But what are these ‘magical’ hormones that have such an impact on our lives?
The word hormone comes from Greek and means ‘setting in motion’ and this is exactly what they do. You can picture the hormones as keys floating around in the blood, and whenever they encounter the appropriate keyhole, they will turn on the ignition and trigger a reaction. The triggered reactions occur in cells, both close to where the hormones are produced and far away in other parts of the body. If the nervous system is the hardwired communication system of the body, then hormones would be the Wi-Fi.22 Hormones play a fundamental role in keeping the internal balance within the cells and within the whole body.
Most of the hormones are produced in glands, which together form the endocrine system. The endocrine glands in the body are situated in the brain (the hypothalamus, the pituitary gland and the pineal gland), the throat (the thyroid and parathyroid glands) and the abdomen (adrenal glands, the pancreas, the testes and the ovaries). Two of the most important glands which act as orchestrators for the other glands are the hypothalamus and the pituitary gland. They are situated in the brain and regulate how hormones are triggered in response to the world outside our bodies. The endocrine system oversees production of hormones and the regulation of how much of each hormone is released in the body. The level of hormones in the blood depends on levels of other substances in the blood, like the amount of calcium, and by factors, such as stress, infections, and the content of fluid and minerals in the blood.23
Hormones can either act locally, or they can be released in the bloodstream, where they circulate until they reach a receptor cell (‘keyhole’). When a hormone is captured by the receptor, the ‘ignition’ is turned on which triggers a reaction that changes how that cell behaves. By influencing millions of cells at the same time the hormones can induce large scale changes in the body.24 The main purpose of hormones is to regulate bodily processes, not to control mind and behaviour, but they do, however, influence them in many ways.
Each person reacts very differently to the same amount of hormones. Indeed, the influence of a hormone does not only depend to its quantity, but also to the duration of its action, how many receptor cells are available, and to how well the receptors are working. The number of receptors can change from day to day, or even from minute to minute.25
The hormones are produced in many different types of cells, which make them sometimes appear at places they are not normally produced.26 One example is oestrogen: in women oestrogen is mainly produced by cells in the ovaries, but it can also be produced in fat cells. As the hormonal world is complex, the fat cells produce different kinds of hormones depending on where they are located. If the fat cells are situated around a woman’s waist, they will produce more male hormones, so called androgens, which can lead to hormonal imbalance and disruptions of the menstrual cycle.
Understanding the action of hormones bring us closer to understanding the body but it still does not explain the full story. This body is way more complex than that. The truth is that we simply do not know or understand all the details. Most research in women looks at correlations between the amount of hormones and a certain phenomenon. But remember? Correlation is not synonym of causation and often elements will be missing in the story required to paint the full picture.
The hormonal axes
Hormones never act in isolation; they trigger chain reactions. Hormones released by glands in the brain will stimulate growth of cells in other parts of the body. As the cell grows, it will start producing another hormone which in turn will inhibit the hormones released by the glands. These types of interactions are called feedback loops, and the different glands affected by a certain feedback loop is called an axis.
Axis-box
One axis that is very relevant for women is the hypothalamic–pituitary–ovary axis (HPO axis) that coordinates the hormonal changes over the menstrual cycle.27 Other important axes are the hypothalamic–pituitary–adrenal (HPA) axis, which regulates how we react to stress, and the hypothalamic–pituitary–thyroid (HPT) axis, which regulates metabolism and also to some extent stress. As you can see, the hypothalamus and pituitary glands are very important players in all these axes, which is one of the reasons why our reproduction and menstrual cycles are closely linked to our general wellbeing.
The endpoint of the HPO axis is the ovaries which produce the egg cells but they are also endocrine glands secreting the most important female sexual hormones, oestrogen and progesterone. The name oestrogen comes from the word ‘oestrus’ which means sexual desire and ‘gene’ meaning to generate. Generating sexual desire is by no means the only effect of oestrogen, but it does play a very important role in reproduction. It also has many other beneficial side effects like protecting hearts, brains and bones. A general effect of oestrogen, as you will see many examples of in the following chapters, is to help the cells grow more and create more blood vessels. This ability has many interesting side effects apart from their role in reproduction.
Progesterone means pro-gestation. It is, as the name indicates, the hormone to promote a pregnancy. It prepares the body for pregnancy by building up the wall of the uterus and making it ready for implantation of the embryo. After implantation, it maintains the pregnancy by preventing the uterus to contract and thereby expulsing the growing foetus. It has a general effect of relaxing smooth musculature and acts calming.
Testosterone on the other hand, simply means that it is a hormone produced in the testes, i.e., the testicles. This is obviously not the case in women, but the hormone was named before scientists discovered that women produce testosterone as well.
