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Linear growth is a complex process regulated by the growth hormone (GH) – insulin-like growth factor-1 axis, the thyroxine/triiodothyronine axis, androgens, estrogens, vitamin D, glucocorticoids and possibly leptin. [25] GH is secreted by the anterior pituitary gland in response to hypothalamic, pituitary and circulating factors.
In biological terms, the development of the human body entails growth from a one-celled zygote to an adult human being. Fertilization occurs when the sperm cell successfully enters and fuses with an egg cell (ovum). The genetic material of the sperm and egg then combine to form the single cell zygote and the germinal stage of development commences.
While the adult human skull is about one seventh of the total body length, the newborn's is about 1 ⁄ 4. Normal head circumference for a full-term infant is 33–36 cm at birth. [ 6 ] At birth, many regions of the newborn's skull have not yet been converted to bone, leaving "soft spots" known as fontanels .
Adult development encompasses the changes that occur in biological and psychological domains of human life from the end of adolescence until the end of one's life. Changes occur at the cellular level and are partially explained by biological theories of adult development and aging. [1]
Tissue growth is the process by which a tissue increases its size. In animals, tissue growth occurs during embryonic development, post-natal growth, and tissue regeneration. The fundamental cellular basis for tissue growth is the process of cell proliferation, which involves both cell growth and cell division occurring in parallel. [1] [2] [3] [4]
Early childhood development is the period of rapid physical, psychological and social growth and change that begins before birth and extends into early childhood. [1] While early childhood is not well defined, one source asserts that the early years begin in utero and last until 3 years of age.
Human biology also encompasses all those organisms that live on or in the human body. Such organisms range from parasitic insects such as fleas and ticks, parasitic helminths such as liver flukes through to bacterial and viral pathogens. Many of the organisms associated with human biology are the specialised biome in the large intestine and the ...
Body shape has effects on body posture [29] and gait, and has a major role in physical attraction. This is because a body's shape implies an individual's hormone levels during puberty, which implies fertility, and it also indicates current levels of sex hormones. [1] A pleasing shape also implies good health and fitness of the body. Posture ...