Human Anatomy (with Fundamentals of Dynamic and Sports Morphology) - Ivanitsky M. F. 2008

Age Morphology
Main stages of ontogenesis, their features and periodization

The human Organism goes through three main developmental stages: evolutionary, stable, and involutionary. Throughout all of them, the body's Cells and Tissues are continuously renewed. As old cells break down and disappear, new ones take their place. This allows the organism to easily adapt to changing environmental conditions and physical activities, including athletic training.

The evolutionary stage is characterized by the predominance of formative structures over those undergoing breakdown, and consequently, by an increase in body mass (specifically, its "active" component excluding the fat fraction). At this stage, the body increases in size until it reaches the proportions typical of an adult organism, known as definitive dimensions. The growth in body mass, an organ, or a tissue area is driven by an increase in the number and size of cells and non-cellular formations, a process termed growth. Thus, growth is the quantitative accumulation of cellular mass. Upon reaching a specific threshold of quantitative changes, one qualitative state of the organism (or its constituent parts) transitions into another, which constitutes development. Development is defined as the irreversible, directed, and systematic age-related transformation of the organism, leading to a new qualitative state. Throughout ontogeny, GROWTH AND DEVELOPMENT constantly Complement each other, illustrating one of the fundamental laws of materialist dialectics—the law of the transition from quantitative to qualitative changes. According to F. Engels, "qualitative changes—in a manner precisely defined for each specific case—can occur solely through the quantitative addition or quantitative subtraction of matter.⁴

⁴ K. Marx and F. Engels, Works, vol. 20, p. 385.

The stable stage of ontogeny is characterized by an equilibrium between Cell Formation and breakdown processes, maintaining relatively constant body mass and dimensions. This stability is quite relative and is perceived as such only when compared to the evolutionary and involutionary stages. The cessation of growth—that is, the accumulation of "active" body mass—signals the onset of maturity. During this period, body mass continues to increase due to the accumulation of adipose tissue, primarily subcutaneously (see p. 348). However, this should not be regarded as a manifestation of growth.

The involutionary stage of ontogeny is distinguished by the predominance of degenerating structures over formative ones, leading to a reduction in body mass and dimensions. It is at this stage that the processes of biological Aging reach their peak. Aging is defined as the cumulative age-related changes occurring in the body's Organs and systems that diminish its adaptive capacity. Aging is a function of time.

Aging is not a disease, yet in many cases it develops against the Background of pathology and may therefore appear premature. At the same time, the view is held that premature aging does not truly exist. Every organism follows its own life cycle. Alongside longevity and slow aging, there is short lifespan and early aging. For any given individual, early aging is timely, as it aligns with the CHARACTERISTICS OF THE organism's genotype.

Aging leads to the disintegration of bodily Functions and increases the probability of mortality. Therefore, genuinely senile changes are considered to be only those that diminish vitality. Alongside these, there are changes that strengthen the organism and enhance the reliability of its organs and systems, known as compensatory-senile changes. The Development of genuinely senile and compensatory-senile changes occurs asynchronously and unevenly, both across different organs within the same system and throughout the body as a whole.

The Nature and causes of aging are currently under intensive study, though they still lack a definitive explanation. There are over two hundred Theories of Aging, and none of them can be considered all-encompassing.

Primary manifestations of aging include alterations in the cellular genetic apparatus. According to the molecular-genetic hypothesis of V. V. Frolkis, age-related Changes in the regulatory Links of the genetic apparatus lead to a decline in the self-renewal of Proteins. Initially, quantitative shifts occur, followed by qualitative changes in Protein METABOLISM. A special place in the age-related restructuring of the organism is occupied by changes in the nervous and circulatory systems. Aging involves the degeneration of Nerve Cells within the Central Nervous system, which weakens its regulatory and trophic influence on the body. Alterations in the Circulatory system exacerbate this process by impairing cerebral Blood flow.

Aging encompasses all organs and systems of the body, manifesting both morphologically and functionally. It involves metabolic shifts, notably a decrease in basal metabolic rate.

GENERAL PATTERNS OF growth and development. The fundamental patterns of growth and development (including aging) include the following.

Endogeneity. The growth and development of an organism are not primarily driven by external influences (although the latter affect The rate of these processes), but rather unfold according to internal laws inherent to the organism and encoded within its hereditary program. Growth and development lead to the attainment of adulthood, making reproduction possible. Any developmental arrest caused by unfavorable environmental conditions during one period of life is reversed by activation when conditions improve in another.

Cyclicity. There are alternating periods of accelerated and decelerated growth. Acceleration is observed before birth, During the first months of life, at ages 6–7 (the mid-growth spurt), and at ages 13–14 (the pubertal growth spurt). Due to the Cyclical Nature of growth processes, The concepts of stretching periods (growth activation) and filling-out periods (growth deceleration accompanied by an increase in body mass) have been proposed. The unevenness of growth is also manifested annually through seasonal acceleration and deceleration. For instance, increases in body length occur predominantly during the summer months, whereas mass accumulation peaks in autumn.

Gradualness. In its development, a human passes through a series of consecutive stages. Under normal conditions, the organism cannot bypass or "skip" any of them. For example, before permanent Teeth erupt, deciduous teeth must appear and subsequently shed after a certain time. Before skeletal growth ceases, bones must attain specific dimensions, and so forth.

Irreversibility. Both growth and aging are characterized by unidirectionality. Once an organism has passed a certain stage of ontogeny, it is no longer capable of reverting to a previous stage. External factors can only delay growth or aging.

Synchronicity. Growth processes, much like aging processes, occur relatively simultaneously across different organs and systems of the body. However, they may proceed at varying rates—a phenomenon known as heterodynamie or rate variation in growth/aging. Furthermore, periods of accelerated or decelerated growth in individual systems may not coincide in time, which is referred to as heterochrony of growth (aging). This synchronicity is severely disrupted during accelerated growth or aging. Consequently, accelerated development (aging) is frequently disharmonious: certain organs and systems outpace others in their rate and the intensity of the process. This disharmony of development is sometimes evident in acceleration.

The concepts of endogeneity, cyclicity, irreversibility, gradualness, and synchronicity in organismal growth, development, and aging are closely linked to the idea of the genetic determinism of ontogeny, resulting from the irreversible and gradual unfolding of the hereditary program.

Age periodization. Within the three main life stages—evolutionary, stable, and involutionary—eleven age periods are distinguished according to the age periodization scheme approved by the USSR Academy of Pedagogical Sciences. Up to age 7 and after age 75, these boundaries show no gender differences. Between these ages, the boundaries for women are shifted to earlier periods compared to men:

Table 2.

When delineating specific age periods, morphological criteria of biological age are taken into account.

A child's biological age is determined by how closely the organism as a whole, as well as its organs and systems, approaches the so-called definitive state achieved upon reaching maturity. An adult's biological age is determined by the extent to which the organism, its organs, and systems are subject to aging processes that alter this definitive state.

Among the morphological indicators of biological age, general (integral) and local features are distinguished. Integral features characterize biological age taking into account body dimensions, skeletal ossification patterns ("bone age"), dental eruption ("dental age"), and secondary sexual characteristics (pubertal age). Local features characterize the biological age of a specific organ system, individual organ, or its component. These vary across different organs and systems of the body.