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

Constitutional Morphology and Sexual Dimorphism
Sexual Dimorphism

Sexual dimorphism (from an anatomical perspective) refers to differences in the size and shape of Organs and body parts between men and women. It is important for physical education teachers and coaches to understand these characteristics, given that women currently account for over half the population in most industrialized nations worldwide. Consequently, the potential for women's sports is substantial. Furthermore, due to their specific biological Functions, women ensure the reproduction of the population, making it crucial to understand how sports participation might impact these functions.

The male and female organisms make distinct contributions to the evolutionary process. The female body performs a vital biological function as the custodian of hereditary information. Male representatives serve merely as an evolutionary “testing ground,” where natural “experiments” determine the value or harmfulness of newly formed traits arising from Gene Mutations. If these traits prove beneficial in the course of evolution, they are consolidated in the offspring; if they prove detrimental, the male individuals carrying these traits perish. This has no impact on The Fate of the species, because, as noted earlier, female individuals are the guardians of the species' genetic core. Through the Genetic information it preserves, the female Organism determines human hereditary continuity by safeguarding its genetic heartland.

Sexual differences are associated with belonging to a specific sex. However, the very concept of “sex” is far richer and more complex than is sometimes assumed.

Manifestations of Sex

Several characteristics of sex are distinguished: genetic, hypothalamic, gonadal, genital, somatic, psychodynamic, and psychological. In every individual, these sex characteristics exist in highly complex interrelations.

The various characteristics of sex emerge in a specific sequence during ontogenesis. First and foremost, genetic sex is determined at the moment a female egg is fertilized by a male sperm Cell. A genetically normal male has one X and one Y sex chromosome in his somatic Cells, whereas a genetically normal female has two X Chromosomes. Germ Cells contain a single sex chromosome: female cells carry an X chromosome, while male cells carry either an X or a Y chromosome. The genetic sex of the embryo is determined by the specific sex chromosome carried by the fertilizing sperm. If the sperm bears an X chromosome, a girl is born with an XX set of sex chromosomes; if it carries a Y chromosome, a boy is born with an XY set.

Disorders in the embryonic sex chromosome Complement can manifest as either a decrease or an increase in chromosome number. An example of the former is found in females with an XO chromosome complement, meaning one of the X chromosomes is missing. Such women exhibit a characteristic appearance (short stature, stocky build) and are incapable of bearing children.

An example of the latter case (albeit quite rare) is found in males with an extra Y chromosome, resulting in an XYY sex chromosome set. These men are tall, physically well-developed, and show no abnormalities in body Structure.

Genetic sex triggers the restructuring of The Cell nuclei in the hypothalamic region of the Brain along male or female lines, thereby determining hypothalamic sex. At the next stage of development, neural influences associated with the Hypothalamus prompt the restructuring of the previously indifferent gonad into a male or female pattern, establishing Gonadal Sex. The restructuring of Gonads into the male pattern occurs very early, and the newly formed Testis initiates its endocrine activity. The formation of the Ovary and, most importantly, its functional activation occur much later. This is because the male gonad must counteract the action of Female Sex Hormones supplied via the Placenta from the mother's body to the embryo and fetus. To protect itself, the male organism must ramp up testicular activity in utero and saturate the body with Male Sex Hormones. This situation does not arise in the developing female body, as maternal sex hormones successfully perform all necessary functions within it.

The next sex characteristic is genital sex, which is defined by The Development of external and internal genitalia along male or female lines. The formation of these organs is linked to the organism's saturation with male or female sex hormones. If the levels of male and female sex hormones in the body are balanced—that is, if during prenatal development a boy's body has a higher concentration of male sex hormones and a girl's body has more female sex hormones—the Development of the internal and external genitalia will proceed naturally. However, if testicular function proves insufficiently high and maternal female sex hormones dominate, features of female genital sex may emerge against the backdrop of a male gonadal sex, or Male reproductive organs may remain underdeveloped. Discrepancies between gonadal and genital sex are termed Hermaphroditism, which can be true or pseudohermaphroditism. True hermaphroditism is rarer and involves the presence of both female and male gonads in the body. Pseudohermaphroditism is relatively more common and is characterized by the presence of secondary sexual characteristics of both sexes, while possessing gonads of only one sex.

From the moment of birth and throughout the neonatal stage, signs of somatic sex begin to emerge. Early childhood features a so-called sex-neutral stage of development, during which the gonads are not yet functioning very actively. Characteristics of somatic sex—related to growth processes, body proportions, and secondary sex characteristics—begin to manifest vividly at the beginning and middle of the second decade of life. Male or female body proportion types are formed in accordance with levels of male and female sex hormones. The male somatic sex is characterized by broader shoulders and a narrower pelvis compared to the female somatic sex. Clear indicators of somatic sex include secondary sexual characteristics (see p. 430). The subsequent sex characteristics are psychodynamic sex and psychological sex; however, these fall under the purview of another discipline, namely psychology. Morphological differences between men and women

Traits dependent on sex include the size of the body, its individual parts, and its organs. These differences are established at the organismal, systemic, organ, and all other levels of living matter, right down to the subcellular level, given that sex chromosomes (XX in women and XY in men) are identifiable at the subcellular level. Consequently, men and women differ both qualitatively and quantitatively, with quantitative differences predominating across all levels of living matter, although these features have not always been thoroughly studied.

Body size. On average, body length is 165.1 cm for men and 153.5 cm for women. These are group-average data characteristic of our country's population. The tallest men and women in our country reside in the Baltic republics, while the shortest and lightest are representatives of small indigenous peoples of the North and the Far East. A gradient of decreasing body length and weight is observed from the northwest to the southeast of our country.

Men and women also differ in the proportions of their body mass components. The Skeleton (bone mass) accounts for an average of 16% of body weight in women and 18% in men (14% in newborns). The muscular component accounts for 36% of body weight in women and 42% in men (sometimes reaching up to 50% in male athletes). The adipose component accounts for 18% of body weight in women and 12% in men.

Male and female organisms also differ in the development of individual parts of The Musculoskeletal System. The most pronounced differences appear in Skeletal structure, which is driven by several factors. On the one hand, musculature is more developed in men than in women. The formative influence of mechanical loads associated with muscular activity on the skeleton is well documented (see p. 50); consequently, Muscle Development inevitably impacts skeletal architecture. On the other hand, skeletal development is closely tied to endocrine organs and the body's hormonal status. For instance, V.V. Bunak, who studied crests on monkey skulls, was the first to explain the formation of these elevations not only through mechanical stresses associated with temporalis muscle traction, but also through unique hormonal conditions. Sexual dimorphism is most clearly expressed in The structure of The Skull and pelvis.

The male skull. It is characterized by larger dimensions (compared to the female skull), prominent superciliary arches, and larger sizes of the Mandible and cranial sites for muscle attachment (the coronoid process of the mandible as the attachment site for the temporalis muscle, the masseteric tuberosity at the angle of the mandible for the masseter muscle, the mastoid process for the sternocleidomastoid muscle, and the external occipital protuberance).

The female skull. It is characterized by smaller dimensions compared to the male skull. However, this is correlated with the smaller overall size of the body and its skeletal framework, making the difference in absolute values entirely natural. Of greater interest are qualitative distinctions: a more vertical forehead and smoother bone contours lacking prominent projections or roughness at muscle attachment sites.

Sexual differences are especially pronounced in the STRUCTURE OF THE pelvis. A woman carries a child within her pelvic cavity for nine months, right up until childbirth. Naturally, this reproductive function leaves a mark on the Structural Features of the female pelvis, which exceeds the male pelvis in both transverse and anteroposterior dimensions. This specific pelvic architecture, in turn, influences the structure and curvature of the spinal Column.

The female body also differs from the male body in the structure of other organs, with absolute and relative differences frequently displaying opposing patterns.

Morphological differences in ontogenesis

These differences manifest in the dynamics of growth, development, and Aging in male and female organisms. Age-related periodization, which accounts for biological age indicators in children and adolescents, initially features identical timelines for boys and girls in early postnatal life. However, starting from the end of the first decade, a distinct chronological asynchrony emerges. Specifically, each developmental stage (second childhood, adolescence, youth) concludes on average one year earlier in girls and young women than in boys and young men. As a result of this earlier cessation of growth in females—particularly spinal elongation—Internal Organs occupy a skeletotopically higher position in women than in men (for example, the origins and terminations of the Larynx, Pharynx, and Esophagus are situated one vertebra or half a vertebra higher in women than in men). Thus, the skeletotopy of internal organs in women more closely resembles their juvenile positioning. At the same time, due to weaker musculature in women (particularly abdominal wall musculature in multiparous women) and laxity of the ligamentous apparatus supporting certain internal organs, a downward displacement of internal organs occurs during aging. This affects the Kidneys, Liver, reproductive organs, and others. Age-related displacement of internal organs also occurs in men, but to a significantly lesser degree. Because growth processes initially position women's internal organs relatively higher, while aging causes them to descend more intensively, the skeletotopical differences in organ placement between men and women tend to level out with advancing age.

Thus, the morphological features of sexual dimorphism are highly multifaceted. They are closely intertwined with the functional manifestations of dimorphism, differences in health status between men and women, women's longer average life expectancy, and numerous other factors.

The female organism is biologically more resilient to external stressors. However, certain workloads that are easily tolerated by men prove overwhelming for women.