A Single Cell Magic
Our bodies are indeed equipped with super mechanisms to adjust to changes, from the long daylight hours of summer to the chilly nights of winter. While these changes do affect our overall health and mood as well as even immune functions, how cells in the body can sense and respond to them is a very intriguing scientific research. Cells are far more intricate than what one would imagine.
Within these basic units, there exist various internal systems interacting with the surroundings to indicate changes in season that would eventually affect the process within the body. It turns out there’s “magic” in this single-cell treatment as evidence of how our bodies have evolved to somehow synchronize with Earth’s cycles.
Suprachiasmatic Nucleus (SCN): The Brain’s Clock
For example, circadian rhythms as controlled by the brain is a simple way in which our body responds to changes in seasons. The SCN (suprachiasmatic nucleus), which is in the hypothalamus, is known as the master clock, where it controls rhythms in accordance with light and dark stimuli. When we are awake, exposure to light triggers the SCN to send signals through the pineal gland that suppresses melatonin, the chemical causing sleep. Conversely, when the days are short and daylight hours are decreased, it provides less stimulation for SCN to produce lesser amounts of melatonin, which affects more than sleep patterns, to prepare the body for the colder months ahead.
The SCN is therefore the central coordinating hub of peripheral clocks which are present in virtually all cell types. These clocks modulate various metabolic and cellular processes so that even though individual cells cannot visually perceive changes due to seasonal events they still believe in signals orchestrated by the SCN that would keep them in tune with these changes.
Photoperiodism: How Light Influences Cells
Seasonal changes are also felt by cells via photoperiodism-the biological reaction to changes in the duration of light throughout the seasons. This phenomenon is not limited to mankind but rather involves countless other animals and plants. Photoreceptors in the retina can be specialized and measure changes in daylight hours, passing this information along to the SCN, which-as described above-regulates the body’s general response. Therefore, for instance, shorter days will cause the biological processes responsible for metabolism, hormone production, and immune response to be activated in order to get the body ready for the seasonal changes.
Cells of the body, in most tissues but more specially in skin, respond to light exposure by creating vitamin D. Lowered sunlight in winter means vitamin D production is decreased and cellular functions are affected as the body relates less efficiently with the absorption of calcium or the immune response. Similarly, brain cells respond to shorter days with increased melatonin production, affecting sleep patterns and mood among many other things. Thus, the body can change with seasons without use of technology.
Hormonal Responses and Their Cellular Consequence
Hormones are the messengers in the body whose job is to deliver seasonal messages to cells in most types of systems. The effects of daylight duration not only impact melatonin, cortisol, and serotonin-but these hormone changes affect the way cells respond to seasonal environmental changes.
Melatonin: The creasing fall of night means the hormone levels of melatonin rise up, accelerating the fall into sleep by dusk since there is less sunlight. Melatonin attaches to specific receptors on the cells of the body and initiates an uninterrupted wave of messages to the cells that it is time to get restful, repair themselves, and boost up their immune systems during colder climates.
Cortisol: Cortisol is a hormone produced by the adrenal glands; levels will vary with seasonal changes. Increased cortisol during winter due to reduced daylight also interacts with other receptors on cells in various organs to impact immune responses, metabolism, and even emotions.
Serotonin: Commonly referred to as the “happiness hormone,” serotonin is positively correlated with sunlight exposure and strongly influences mood levels. The reduced exposure of sunlight in winters reduces serotonin production, hence generally influencing mood.
These hormones maintain cellular processes through sticking to receptors on the cell membranes, enabling the cell to “feel” changes and respond accordingly. The fluctuations of these hormones in the two seasons is important because it makes sure that cells within a biological system remain well-balanced and ready for sudden changes in their surroundings.
Seasonal Fluctuations on Immune Cells
It is very sensitive to seasonal changes, and the majority of immune cells have their activities at various levels throughout the year. For instance, immunological activities generally peak with the colder months when infections such as colds and flu are more readily available. Immune cells can sense seasonal changes through a few key avenues:
Temperature and Daylight Exposure: The immune cells react to the reduced temperatures as well as the shorter daylight exposures by modulating the production of inflammatory molecules in the body to prepare to fight the infections.
Vitamin D Receptors: Many immune cells are vitamin D receptors. Hence, with less sunlight exposure in winter, the vitamin D decreases, which affects the immune system. Fewer levels of vitamin D may make the immune cells more vulnerable to infections, thus partially explaining why most occur in winter.
These adaptations better enable our bodies to fight seasonal infections and respond to the demands placed on the immune system throughout the year.
Gene Expression and Epigenetics: A Cellular Memory of Seasons
Seasonal changes even affect gene expression inside the cells, it has been found that there are some genes which the cells are active at specific times of the year. For example, those genes that are part of inflammation processes are more active during the winter months, thus giving immunity a head start by having higher rates of seasonal illnesses. These cells thus have an “epigenetic” memory of the environment allowing them to prepare and adapt to seasonal patterns without any annual stimulation.
Cells may even alter what they do in response to signals from their neighboring cells and tissues, adjusting gene expression to adapt to the seasonal needs of the organism. This is particularly relevant to cells making up organs or systems directly impacted by seasonal variations, like cells in the skin, immune cells, and even neurons in the brain.
