Human development (biology)

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This article is about biological human development. For psychological human development, see Developmental psychology.

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.

1 Biological development
- 1.1 Physical stages
- 1.2 Physical development milestones
2 See also

[edit] Biological development

Development begins with fertilization, the process by which the male gamete, the sperm cell, and the female gamete, the oocyte, fuse to give rise to a diploid cell, the zygote.

In medicine, pregnancy is defined as beginning when a fertilized zygote becomes implanted in a woman's uterus. This occurs when the zygote then becomes embedded into the endometrium (lining of the uterus) where it forms a placenta, for the purpose of receiving essential nutrients through the uterus wall. The umbilical cord in a newborn child signifies the remnants of implantation.

The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of an embryo.

Childbirth is the process in which the baby is born. It is considered by many to be the beginning of a person's life, where age is defined relative to this event in most cultures.

Growth is normally controlled and moderated by the Pituitary Gland, located at the base of the skull in humans.

[edit] Physical stages

Terms for stages of age-related physical development include, with their approximate age ranges:

Zygote, the point of conception, fertilization
Blastocyst the period between conception and embryonic stages
Embryo; the embryonic period starts at three weeks and continues until the end of the 8th week of pregnancy
Fetus; the fetal stage begins at the end of the 8th week and continues until childbirth
Birth

Child
- Neonate (newborn) (0-30 days)
- Infant (baby) (1 month-1 year)
- Toddler (1-4)
- Primary school age (also called prepubescence) (4-12)
  - Elementary school age (also called middle childhood) (4-8)
  - Preadolescence (preteen, or late childhood. The child in this and the previous phase are called schoolchild (schoolboy or schoolgirl), when still of primary school age.) (9-12)
Adolescence and puberty (teenage) (13-19)
Young adult (19-25)
Adult (exact minimum age may vary)
- Early adulthood (20-39)
- Middle age (40-59)
- Advanced adult/Senior citizen/Old age (60+)
Death (occurs at various ages, depending on person)