Explaining and maintaining homeostasis

What is homeostasis?

Homeostasis refers to self-regulating processes that maintain balance within biological systems. Taken from the Greek words ‘homio’, 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 acid, blood pressure, blood sugar, electrolytes, energy, hormones, oxygen, proteins, and temperature to respond to external changes and maintain a favourable internal environment.

The history of a major physiological concept

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, Barnard 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 neurologist Walter B. Cannon in 1926.

Homeostasis in action

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. 

Homeostatic mechanisms and 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?

Factors that affect homeostasis 

Various external 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 acid 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. 

Homeostasis and Wellness

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. 

Why is homeostasis important in everyday 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. 

Homeostasis and mood regulation

Mood regulation, or emotion regulation, is defined by our ability to effectively manage and respond to an emotional experience. A recent study found that mood homeostasis may be impaired in people with low mood and those with a history of depression. Hormonal or neurotransmitter imbalances, such as a depletion of norepinephrine, serotonin or dopamine, have also been linked to the development of depression. Many therapies therefore focus on restoring healthy levels of these neurotransmitters - or achieving homeostasis. 

Homeostasis and the endocannabinoid system

The endocannabinoid system (ECS) consists of neurotransmitters, receptors, and enzymes that are expressed throughout the central nervous system and immune system. Endogenous cannabinoids - the most well-known of which are anandamide and AEG - interact with receptors - known as cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2) - to influence a number of physiological processes, including mood, memory and learning, temperature, appetite, metabolism, and sleep.

How is the endocannabinoid system (ECS) involved in regulating these homeostatic functions?

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.

What holistic practices support or assist with homeostasis?

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. 

Medical cannabis and homeostasis

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 - have promising therapeutic applications, many of which may be associated with their ability to restore homeostasis in a number of regulatory processes. 

Final thoughts

Homeostasis is vital for our bodies not only to thrive but also to 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. 

The vital role of the endocannabinoid system in maintaining homeostasis has led to the development of many cannabis-based medical products. As a result, medical cannabis can now be prescribed in the UK and many other conditions around the world when conventional therapies have been ineffective. This growing interest in the medicinal potential of cannabis and its derivatives builds upon millennia of human interaction with the plant, and the evolution of our understanding of the importance of homeostasis.