HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

CHAPTER 2. BIOGEOCENOTIC LEVEL OF ORGANIZATION OF LIFE AND THE PLACE OF HUMAN IN IT

2.8. BIOSPHERE AND HUMAN

The Concept of Biological Rhythms

Biological rhythms are periodically recurring cyclic Changes in the intensity and nature of biological processes and phenomena. They emerged in the course of evolution as an ADAPTATION OF ORGANISMS to cyclic changes in inanimate nature, meaning they possess adaptive significance. They occur in almost all organisms, including humans, and at all Levels of biological Organization—from molecular-genetic to biospheric. Examples include the diurnal movements of leaves and petals in plants. Biological rhythms are also inherent in individual biochemical enzymatic reactions. The phenomenon of the "biological clock"—the ability of organisms to navigate in time—is closely linked to biological rhythms. For instance, roosters crow and bats fly out to hunt at precisely the same time.

Daily, monthly, tidal, seasonal, annual, and multi-year biological rhythms are distinguished. The most thoroughly studied are daily (circadian) rhythms. They are associated with the alternation of day and night resulting from the Earth's rotation around its axis. Approximately 300 human physiological Functions undergo periodic fluctuations throughout the day. For example, body Temperature varies rhythmically over the course of the day: it is elevated during the day (peaking at 6 p.m.) and decreases at night. The lowest level occurs between 1 a.m. and 5 a.m., with an amplitude of fluctuation of 0.6–1.3°C. Body temperature depends on The rate of biochemical processes. During the daytime, METABOLISM is more intense, which dictates higher human physical activity. Heart rate is maximal at 3–4 p.m., respiratory rate at 1–3 p.m., systolic Blood pressure at 3–6 p.m., red blood Cell count at 11 a.m.–12 p.m., and leukocyte count at 9–11 p.m. In pathology, the disruption of many rhythms is observed. For instance, in hypertensive patients, blood pressure does not drop at night, but rather increases.

People are generally categorized into morning and evening chronotypes. The former ("larks") fall asleep early in the evening and wake up early in the morning. Conversely, the latter ("owls") fall asleep late and, accordingly, wake up later. Individuals of these different types differ in their performance levels during morning and evening hours. There are also groups of people who do not fit into either of these types ("pigeons").

The body's biorhythms become severely misaligned with the environmental daily cycle when a person crosses into a different time zone. This disrupts the coordination of certain biorhythms, triggering a distinct pathological state known as desynchronosis (jet lag). Consequently, human performance and productivity decline.

When experiencing a 12-hour time zone shift, the body adapts to the new conditions within 10–15 days. A 2-hour shift has a minimal negative impact.

Lunar biological rhythms (28 days) are driven by the Moon's rotation around the Earth. They are most pronounced in marine organisms (tidal rhythms). In humans, the female Menstrual cycle is governed by this rhythm, and Pregnancy duration in obstetrics is measured in lunar months. Seasonal fluctuations are also observed in animals and humans, associated with increased daylight in spring and its reduction in autumn and winter. The bioelectrical activity of the Brain and Muscular System is higher in spring and summer, and lower in winter. Seasonal dynamics in the exacerbation of certain diseases—such as tuberculosis, Hypertension, and rheumatism—have also been documented.

Living organisms are influenced by rhythmic changes in solar activity, which repeat on average every 11.1 years. When the number of sunspots (active regions) on the Sun increases, powerful streams of radiation reach the Earth, affecting its magnetic field and ionosphere. Some researchers have obtained data indicating that the number of admissions to psychiatric clinics rises sharply during days of heightened solar activity. The frequency of cardiovascular Diseases and complications also increases.

In the late 19th century, Czech psychologist H. Swoboda and German physician W. Fliess put forward a hypothesis that every individual, from birth, possesses three cycles associated with physiological (23 days), emotional (28 days), and intellectual (33 days) activity. At the midpoint of each cycle lies a critical, or zero, day. The first half of the cycle (leading up to the critical day) is considered a positive period (a peak in performance, physical, emotional, and intellectual states). The second half is a negative period during which conditions deteriorate. Observations suggest that accidents occur more frequently on the zero days of the physical cycle, emotional breakdowns on those of the emotional cycle, and a decline in cognitive performance on those of the intellectual cycle. The coincidence of all critical days occurs once a year. The hypothesis regarding the existence of these specific biorhythms has not found universal scientific acceptance.

It should be noted that social factors and work schedules (social time cues) exert a profound influence on human biological rhythms. The restructuring of rhythms associated with changes in work and rest routines has been observed during prolonged stays in isolated environments (such as anechoic chambers / sensory deprivation chambers).

Chronobiology (from Greek *chronos* - time) is a branch of biology that studies biorhythms. The medical significance of chronobiology includes: 1) determining the optimal time for medication administration and surgical Procedures; 2) establishing the optimal human activity regime (for instance, night work structured as a "12-hour shift followed by 24 hours of rest" is less favorable than multi-week night shifts aligned with the circadian rhythm); 3) scheduling seasonal courses of preventive Treatment for PEPTIC ULCER DISEASE, rheumatism, and tonsillitis; 4) forecasting and preventing the exacerbation of certain diseases and accidents; 5) timing athletic training. It is considered more rational to recommend rest and rehabilitation for convalescing patients (particularly those with cardiovascular pathologies) in sanatoriums located within their native region. This is explained by the fact that a person arriving from another time zone experiences desynchronosis for the first few days, and the same applies upon returning home, as biorhythms must readjust in reverse.