9 min read
Cecily Grace Morgan
The concept of homeostasis defines any self-regulating process by which biological systems maintain stability and balance. This physiological regulation is essential for maintaining a constant internal environment, allowing us to thrive, even in the face of changing external conditions.
Key takeaways
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Homeostasis is the term used to describe the self-regulation that keeps our internal conditions stable despite external changes.
Taken from the Greek words ‘homoios’, which means ‘similar to’ and ‘stasis’, meaning ‘standing still’, homeostasis is essential for maintaining the health of our bodies. It explains how an organism is able to maintain relatively constant internal conditions in the face of constantly changing, and even hostile, external environments.
This state of balance is required among all body systems for the body to function properly. In homeostasis, the body constantly regulates itself to maintain stable levels of pH (acidity), blood pressure, blood sugar, electrolytes, energy, hormones, oxygen, proteins, and temperature to respond to external changes and maintain a favourable internal environment.
Temperature regulation – when you’re too hot, the body sweats to lose heat. When you’re too cold, the body shivers to generate it.
Blood sugar levels – when blood sugar rises, the pancreas releases insulin to bring it back down. When it drops, the pancreas releases glucagon to bring it back up.
Water balance – when you’ve drunk too much liquid, you urinate more. When you haven’t drunk enough, your kidneys hold more water so you urinate less.
Beginning at the cellular level, homeostasis explains how the body’s functions operate so “as to not deviate from a narrow range of internal balance, a state known as dynamic equilibrium.” This narrow range must be maintained to prevent the death of cells, tissues, and organs. In favourable internal conditions, cells keep themselves alive and contribute to the tissues of which they are a part which, in turn, contribute to organs which themselves are part of wider systems in the body.
Disruption of these homeostatic mechanisms leads to a breakdown of the system and the organs and cells which contribute to them, resulting in illness and/or disease. So, how does homeostasis regulate body temperature, pH levels, and glucose concentration? Perhaps one of the clearest examples of the importance of homeostasis is thermoregulation.
Small temperature changes can be resolved through physiological responses: peripheral and central thermoreceptors sense a temperature change and send this information to the hypothalamus – a part of the brain that controls various processes, including body temperature, hunger, and sleep. The body has multiple responses to temperature changes. These processes are known as feedback controls.
If the body temperature is too high, the body responds with processes to dissipate heat:
Activating sweat glands to increase sweat production, leading to heat loss.
Widening of blood vessels to increase the flow of blood to the skin to increase heat loss.
Decreasing the release of catecholamines and hormones to reduce metabolic rate.
Triggering behavioural changes such as reducing movement, adopting an open body position and removing clothing.
If the body temperature is too low, the body responds with processes to generate heat:
Activating the sympathetic nervous system – causes the vasoconstriction of skin arterioles, causing blood to bypass the skin, and reducing heat loss.
Increasing the release of catecholamines and hormones to increase metabolic rate and heat production.
Activating the primary motor centre causes shivering and skeletal muscle contraction.
Triggering behavioural changes such as increased movements, adding clothing, and increased appetite.
The failure of an organism to regulate its internal temperature (in humans, body temperature remains constant at around 37℃), can lead to hypothermia (when temperatures are too low) or hyperthermia (when temperatures are too high). Extreme variations can result in organ failure, coma, and even death.
This example underscores the vital importance of maintaining homeostasis in the body. So, what factors can affect our body’s ability to do so?
Various factors can disrupt homeostasis. In the example of thermoregulation, these factors include exposure to the elements, hormones, metabolic rate, and disease, all of which can cause significant increases or decreases in body temperature, creating a hostile internal environment.
As we mentioned earlier, all the cells in our body also require a certain range of acidity levels, concentrations of minerals and blood glucose, among other factors, to survive and function effectively. Therefore, any external factors that affect these requirements have the potential to disrupt the body’s state of homeostasis, including external factors such as disease, injury, lifestyle, and mental health, and internal factors such as genetics.
While the examples we have explored so far largely focused on the physical requirements and effects of maintaining and disrupting homeostasis, self-regulatory processes play a role in every aspect of our lives and health.
Homeostatic disruption can not only lead to physical illness but also mental health issues such as anxiety and depression. Maintaining homeostasis is therefore vital not only for preventing physical disease, but also for ensuring our everyday physical and mental health. Several systems in the body play a role in mood regulation.
Mood regulation, or emotion regulation, is defined by our ability to effectively manage and respond to an emotional experience. Mood homeostasis is thought to be the instinct to choose mood-boosting activities, such as yoga or listening to music, when you’re feeling low and saving tasks like housework when you’re feeling happier and more up to it. A 2020 study found that mood homeostasis may be impaired in people with low mood and those with a history of depression.
Many anti-depressants act on chemical processes, increasing activity of chemicals including norepinephrine, serotonin or dopamine, while talking therapies focus on helping people develop habits that will help lift their mood when they’re down.
The endocannabinoid system is an internal network made up of endocannabinoids, CB1 and CB2 receptors, and metabolic enzymes. Endogenous cannabinoids, the most well-known of which are anandamide and 2-AG, interact with receptors known as cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2). This influences a number of physiological processes, including mood, memory and learning, temperature, appetite, metabolism, and sleep.
Activation of the ECS has been found to play a significant role in regulating many critical body functions. CB1 receptors are largely expressed in the brain, outnumbering many other receptors in this area. CB1 receptors are also found in the liver, reproductive and cardiovascular systems, skeletal muscles, and gastrointestinal (GI) tract. Preclinical and clinical data suggest that these receptors modulate synaptic neurotransmission in the limbic, or “emotional” brain, suggesting a role in the modulation of anxiety and depression.
CB2 receptors are predominantly expressed in immune cells, with a moderate presence in other peripheral tissues, including the cardiovascular system, GI tract, liver, adipose tissue, bone, and reproductive system. They have been found to play an active role in neurological activities, such as nociception (encoding and processing of harmful stimuli), drug addiction, and neuroinflammation.
While our bodies will always strive for homeostasis, there are some things we can do to support it in this endeavour. For example, regular exercise and a healthy diet can help support hormone balance and improve overall mental and physical health.
These roles have made cannabinoid receptors a target of interest in the treatment of a wide range of conditions, from chronic pain to epilepsy. A growing body of evidence indicates that phytocannabinoids found in cannabis, in particular THC and CBD, may have promising therapeutic applications, and researchers are exploring whether they may help restore homeostasis in a number of regulatory processes.
The concept of homeostasis can be traced all the way back to the ancient Greeks, who theorised that bodily regulation is required to maintain health. Alcmaeon of Croton (fl. 500 BC) referred to a “balance of opposites” to explain health and disease. The famous Greek physician Hippocrates later expanded on this theory (ca. 377 BC), proposing that health was the product of the balance and mixture of four body humours: blood, phlegm, yellow bile, and black bile.
These concepts were the basis of many medical practices; however, it wasn’t until the mid-19th century that systematic physiological investigation allowed for significant advancement in this area. In 1849, French physiologist Claude Bernard described the milieu intérieur, or ‘internal environment’ – his theory that organisms maintain a stable internal environment despite changing external conditions.
Crucially, Bernard was the first to recognise that mechanisms in the body are able to maintain relatively stable temperature and blood glucose concentration, and the importance of this regulation in the overall health of the organism. The term ‘homeostasis’ was later coined by American physiologist Walter B. Cannon in 1926.
In simple terms, homeostasis is the body’s way of keeping its internal balance, regardless of what’s happening outside. Whether you’re cold, hot, hungry or overhydrated, homeostasis helps ensure that everything inside your body stays at a healthy, consistent level.
A good example of homeostasis is shivering. When your body temperature drops, your skeletal muscles begin to contract to generate body heat, which causes mild shaking. It’s an involuntary response that maintains homeostasis.
Homeostasis is vital for our bodies to not only thrive but also survive. The self-regulation of physiological functions, from temperature and pH level maintenance to mood and sleep, is essential for our health and well-being. This has been the basis of medicine throughout history, leading to the development of countless therapies, medications, and holistic strategies.
Finally, although more research is needed, it’s thought that the endocannabinoid system plays a part in homeostasis, and researchers are exploring whether medical cannabis could support this.
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