Human development (biology)

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Human development is the process of growing to maturity. In biological terms, this entails growth from a one-celled zygote to an adult human being.

Biological development[edit]

General aspects[edit]

Sperm fertilizing an egg

Fertilization occurs when the sperm successfully enters the ovum's membrane. The genetic material of the sperm and egg then combine to form a single cell, called a zygote, and the germinal stage of prenatal development commences.[1] The germinal stage refers to the time from fertilization, through the development of the early embryo, up until implantation. The germinal stage is over at about 10 days of gestation.[2]

The zygote contains a full complement of genetic material and develops into the embryo. Prior to implantation, the embryo remains in a protein shell, the zona pellucida, and undergoes a series of cell divisions. A week after fertilization the embryo still has not grown in size, but hatches from its protein shell and adheres to the lining of the mother's uterus. This induces a decidual reaction, wherein the uterine cells proliferate and surround the embryo thus causing it to become embedded within the uterine tissue. The embryo, meanwhile, proliferates and develops both into embryonic and extra-embryonic tissue, the latter forming the fetal membranes and the placenta. In humans, the embryo is referred to as a fetus in the later stages of prenatal development. The transition from embryo to fetus is arbitrarily defined as occurring 8 weeks after fertilization. In comparison to the embryo, the fetus has more recognizable external features, and a set of progressively developing internal organs. A nearly identical process occurs in other species, especially among Chordates.

Childbirth is the process in which the baby is born. Age is defined relative to this event in most cultures.

Physical stages[edit]

There are no universal definitions for terms of age-related physical development stages, but following are some approximate age ranges:

  • Prenatal (sperm fertilizes egg - birth)
    • Embryo - fertilization - 8 weeks after fertilization)
      • Zygote, the single cell stage which occurs after fertilization
      • Blastocyst, the stage prior to implantation, when the embryo is a hollow sphere
      • Post-implantation embryo, the period 1 – 8 weeks after fertilization (3 to 10 weeks gestation)
    • Fetus, (10th week of pregnancy - birth)
Approximate outline of development periods in child development.

Also sometimes used are terms that specify one's age in numbers, such as:

The Tanner stages can be used to approximately judge a child's age based on physical development.

See also[edit]

Footnotes[edit]

  1. ^ Sherk, Stephanie Dionne. "http://www.healthline.com/galecontent/prenatal-development". Gale Encyclopedia of Children's Health, 2006. Gale. Retrieved 6 October 2013. 
  2. ^ "germinal stage". Mosby's Medical Dictionary, 8th edition. Elsevier. Retrieved 6 October 2013. 
  3. ^ Growth of Asthmatic Children Before Long-Term Treatment with Inhaled Corticosteroids T. Moudiou‌, D. Theophilatou‌, K. Priftis‌ and A. Papadimitriou, M.D. Journal of Asthma. 2003, Vol. 40, No. 6, Pages 667-671.
  4. ^ a b Jaffe-Campanacci Syndrome. A Case Report and Review of the Literature. Mohammad Anwar Hau, MBBS, MMed (Ortho), Edward J. Fox, MD, Justin M. Cates, MD, PhD, Brian E. Brigman, MD and Henry J. Mankin, MD. The Journal of Bone and Joint Surgery (American) 84:634-638 (2002)
  5. ^ [httfp://linkinghub.elsevier.com/retrieve/pii/S0531513106005401 Persistent osteopenia in adolescent idiopathic scoliosis (AIS) – Factors predisposing to generalized osteopenia, a cross-sectional and longitudinal investigation] Warren T.K. Leea, C.S.K. Cheunga, Y.K. Tsec, W.W. Chaua, L. Qina and Jack C.Y. Chenga. doi:10.1016/j.ics.2006.08.003