Serotonin Hormone Guide
What is Serotonin?
Serotonin is an important hormone that regulates a wide variety of functions in the body, and is most notable for its effects upon mood and well-being. Serotonin is found in a number of areas of the body, including the brain, central nervous system, platelets and digestive system. Serotonin is synthesized by the body from a hormone known as tryptophan, which most people recognize as the hormone in turkey and many other foods that makes us sleepy. Maintaining Serotonin balance is a vitally important aspect of promoting both the health of the brain and the health of the body.
Effects of Serotonin both Psychological and Physiological
Perhaps contrary to popular belief, the vast majority of serotonin that is produced by the body is secreted into the digestive system, in order to promote motility in the intestinal track. Around ninety percent of the serotonin released by the body serves this purpose.
When Serotonin is released by the digestive system, it acts upon the intestines and drains out into the blood stream over time. Platelets actually have the ability to absorb this Serotonin, and use it for their own purposes. Platelets are cells in the blood stream that don't have nuclei which are primarily used as a clotting mechanism. When the platelets begin to form a blood clot, they emit their stored serotonin, which shrinks blood vessels in the surrounding area in order to control blood flow and help stop circulatory leakage.
Serotonin also promotes cellular metabolism in certain types of tissue, and it is hypothesized that the hormone helps speed up healing in the case of injury.
Neurological Effects of Serotonin
Aside from the digestive system, the second most active area for Serotonin production is the central nervous system, where the hormone impacts physiological activity in a variety of ways. Serotonin impacts a number of regulatory systems in the brain, including sleep, appetite, and mood.
Serotonin also has some influences on learning, memory, and other cognitive abilities. There are a number of antidepressant medications that function by altering the way that the body responds to Serotonin, including Selective Serotonin Reuptake Inhibitors (SSRIs).
Serotonin in Nature
Serotonin is not only found in humans and animals, but also in plants and fungi. Serotonin actually has the ability to promote a pain response under some circumstances, and the hormone often coats the barbs of plants and is often a component of venom in insects. In fact, when Serotonin is administered via injection, it can sometimes cause pain to the patient, as if they were bitten or stung.
Serotonin and Digestive Health
There are also instances where Serotonin is produced by organisms within the digestive system. For example, there are amoeba which can replicate in the stomach and intestines, which release Serotonin, speeding up the digestive tract, which leads to diarrhea. Also, Serotonin is present in many fruits and seeds, which causes the digestive system to pass seeds more effectively.
Serotonin Produced by All Complex Animals
Serotonin is an important neural hormone and is produced by all animals with bilateral symmetry. Dependent upon the complexity of the organism, Serotonin serves an increasingly larger role in the nervous system. In simple animals like invertebrates, Serotonin primarily helps the organism to recognize the abundance of food in a particular area.
In more evolved animals, like vertebrates and arthropods, Serotonin not only evaluates food resources, but also plays a role in social interactions, including dominance and submission. Because reproduction and the viability of young depend on food availability, Serotonin contributes to the production of sex hormones and the motivation to breed. Serotonin also has a powerful impact on growth and mood.
Serotonin, Depression, and Obsessive Compulsive Disorder
Serotonin plays a complex role in maintaining healthy emotional balance in human beings. People that don't produce enough Serotonin are both more likely to suffer from depression and more likely to suffer from compulsive thoughts. Related to the mechanisms of Serotonin, people that don't produce enough Serotonin are more likely to engage in risky activities, including promiscuous sex and self-harm.
There is some clinical evidence that Depression inhibits the brain's ability to produce new neurons in the brain, which suppresses activity in certain parts of the brain, in particular, those related to mood stability and well-being. It is believed that SSRIs have the ability to restore Serotonin Levels in the brain, encouraging the rejuvenation of brain cells, which helps the mind recover from depression and generally improve quality of life from a psychological perspective.
It is unclear, however, whether Serotonin Deficiency leads to depression or if it is perhaps the other way around. Of course, depending on the particulars of the patient, either or both of these issues could be at play. In patients that experience chronic depression and OCD from an early age, the cause would primarily be neurological, whereas in patients that experience depression later in life, the cause is much more likely to be the result of circumstances in their lives.
How Do SSRIs Treat Psychological Disorders such as Depression and OCD?
One of the most common treatments for both OCD and Depression is the prescription of a Selective Serotonin Reuptake Inhibitor. These medications increase the activity of Serotonin in the brain by slowing down the rate at which neurons reabsorb Serotonin after releasing the hormone. The way that our body uses Serotonin is rather simple. A neuron receives a signal to release Serotonin, and it does so, releasing it a very short distance to the next neuron, where it remains active in the space between the neurons, exerting its function.
In many patients with OCD and Depression, Serotonin is released, but it may not be released in sufficient quantities, or it may not stay active for the appropriate amount of time before it is absorbed. SSRIs can treat both of these issues by increasing the Serotonin activity in the brain.
Functions of Serotonin in Humans
Serotonin and Appetite
Many animals use Serotonin as a mechanism to convince the animals to stay in the presence of food, but in humans, Serotonin is used as an appetite inhibitor. When you smell food, this causes your brain to release Dopamine, which is why you suddenly get more hungry when you smell an appetizing meal. Serotonin, on the other hand, is released when you actually eat the food, which suppresses the release of Dopamine by the brain.
There are receptors on cells in the brain that produce Dopamine, known as 5-HT2C. These points absorb Serotonin and subsequently cause the cells to cease the production of Dopamine. In fact, there are drugs and neurological disorders which cause these receptors to deactivate, which prevents the brain from recognizing when its full, which leads to overeating. Many people that feel uncontrollable urges to eat are born without a full array of these receptors.
Serotonin and Diet
As we mentioned earlier, Serotonin is synthesized by the human body from tryptophan. Interestingly enough, simply eating food with tryptophan as an ingredient, such as turkey, does not have a subsequent effect upon Serotonin Levels. On the other hand, eating pure tryptophan does lead to an increase in Serotonin Levels.
There is a reason for this. tryptophan can cross the barrier from the blood stream to the brain, but only under certain circumstances. Tryptophan only crosses the barrier when it is isolated from other proteins that are present in food. This encourages the body to only allow tryptophan produced by its own peripheral organs to pass into the system easily, although this can be bypassed by taking pure tryptophan.
There are studies that present evidence that a high-carb low-protein diet can result in an elevation in Serotonin levels, and it does so by promoting the release of Insulin. The issue with this, however, is that if this process is sustained for a long period of time, it may lead to conditions such as Type-2 Diabetes, obesity, and increasing resistance to insulin which ultimately suppress Serotonin production.
People with more muscle actually have more Serotonin than their leaner counterparts. This is because the muscles use all amino acids except tryptophan, which, because the brain absorbs more Tryptophan when there are lower concentrations of other amino acids, increases Serotonin production.
Serotonin and the Digestive System
When we eat, food passes through the digestive system. As food passes into the intestines, it encourages the release of Serotonin by what are known as enterochromaffin cells. This encourages motility because it stimulates the contraction of the intestines. There are veins which connect to the intestines, and platelets pass this area, absorbing unused Serotonin.
Serotonin is also one of the mechanisms which cause diarrhea. If the body recognizes an irritant or potential danger in the digestive system, production of Serotonin in the digestive system increases dramatically in order to pass the offending substance(s) out of the body more quickly.
If the digestive system creates more Serotonin than the platelets can transport, this increases the concentrations of free Serotonin in the blood stream. Free Serotonin then circulates through the body and encourages nausea and vomiting. There are drugs designed to block this response, and they are generally used in order to suppress vomiting and nausea which are often symptoms of chemotherapy and radiation.
Serotonin and Social Interaction
In many animal species, one's access to food is dependent upon competition. If an animal does not display enough aggression, it may not get as much food to eat. Based upon this inter-relationship between social hierarchy and food availability, Serotonin became involved in social interaction from an evolutionary perspective.
In many animals, Serotonin encourages the animal to engage with its social peers as an alpha. On the other hand, Serotonin impacts the fight-or-flight response dependent upon the social rank of the animal. In aeta-subordinate animals, Serotonin suppresses the urge to flee, whereas in alpha animals, Serotonin encourages flight, based upon a different distribution of Serotonin receptors.
When Serotonin is used by the brain, it is usually absorbed by neurons designed to transport Serotonin. Research has shown that much of the pathology related to anxiety in humans is related to how Serotonin is distributed after it has been absorbed by these transporters.
Serotonin and Aging
There are many ways that Serotonin impacts the aging process, as well as the cognitive capabilities of the brain. In many more primitive animal species, as Serotonin levels rise, it improves certain forms of memory. Serotonin levels falls as the creature ages, which inhibits these processes, but by blocking the re-uptake of Serotonin, it is possible to bolster cognitive memory capability in spite of aging.
In human beings as well as mammals, Serotonin levels do not rise with age in the same way, but they do start to fall as people reach the late stages of the life span, which does impact cognitive capacity.
Serotonin and Bone Mineral Density
Research has shown that in human beings, Serotonin concentrations in the blood stream play a role in controlling and regulating bone mineral density. In rodent subjects, individuals that have their ability to produce Serotonin turned off in the brain but not in the digestive system experience Osteopenia. On the other hand, those that have high levels in the brain, but do not have high levels in the digestive system have elevated bone mineral density.
Human research has not been as in depth, but there is strong evidence that individuals with elevated Serotonin levels in the blood are more likely to experience Osteopenia and Osteoporosis later in life. In the future, regulating Serotonin may be a way to treat patients with health conditions related to bone metabolism.
Serotonin and Human Development
In many animals, Serotonin plays a central role in encouraging normal growth and development into adulthood. Proper Serotonin levels during childhood and adolescence ensure that the body focuses the prime amount of resources into the developing child. If there is not enough food available, or there are other similar situations which can impact health and viability during development, Serotonin levels drop, which causes the child to develop more slowly.
Serotonin also promotes the production of HGH and its related growth factors, especially IGF-1. This is one of the mechanisms which helps encourage growth during puberty, and it also increases healing capacity in the case of injury.
Serotonin and the Cardiovascular System
As we mentioned earlier, Serotonin is released by the digestive system and eventually absorbed by the platelets in the cardiovascular system. When there is damage in the arteries or veins, Serotonin encourages the healing process as it is released from the platelets after they have formed a blood clot. This released Serotonin also emits signals to the immediate area to restrict blood flow, which helps to stem bleeding.
How Does the Human Body Make Serotonin?
There are two mechanisms by which human beings and other mammalian species produce Serotonin, both of which rely on the conversion of Tryptophan into Serotonin. One form of Tryptophan known as TPH1 is converted into Serotonin by the digestive system (the enterochromaffin cells) and the pineal gland, while a second form, TPH2 is converted into Serotonin by circulatory structures attached to the digestive system (the myenteric plexis) and neurons in the brain stem (the raphe nuclei)
In lab mice, TPH1 is shown to be vitally important to heart health, and without the ability to produce TPH1, the subjects have significant issues with heart strength and circulation and have significantly increased mortality.
On the other hand, mice without the ability to produce TPH2 are fine while they are in utero, but they don't grow at the same rate as their peers after birth causing them to be much more likely to die before they have been weaned from the mother. If they survive past five weeks, they end up as healthy as their normal peers, but have significant social issues related to aggression.
How Does Serotonin Deficiency Impact Infant Health?
In the case of human beings, there is some evidence that SIDS may be the result of a malfunction in the way that the infant body processes Serotonin. In animal research, when mice were programmed to produce less Serotonin than normal, it directly led to many issues related to Sudden Infant Death Syndrome, including cardiovascular insufficiency, which increased infant mortality rates. This is because Serotonin produced by the raphe nuclei play a role in breathing as well as heartbeat.
Serotonin Depletion and Mood Disorders
Serotonin is linked to a variety of disorders associated with mood. Serotonin Deficiency is strongly linked to both Depression and Obsessive-Compulsive Disorder. Interestingly enough, Serotonin Deficiency is also a temporary condition that occurs when someone falls for another, emotionally, and is associated with OCD tendencies that occur in the early parts of many relationships.
Serotonin and Alcohol
Moderate consumption of alcohol leads directly to a state of Serotonin Depletion resulting from a reduction in the concentration of tryptophan in the blood stream. This is one of the reasons that people that drink alcohol are more likely to engage in impulsive activities, including sex, because Serotonin has a modulating effect upon both self-control and libido.
Serotonin and Your Health
As you can see, Serotonin is one of the most physiologically complex hormones produced by the human body, and affects change in a wide variety of ways. Healthy Serotonin balance is a vital part of sustaining health and wellness, both psychological and physical.