Human Development Notes

Development involves changes from fertilization onward. It consists of two primary periods: Prenatal (before birth) and Postnatal (after birth).

Prenatal Development:

  1. Pre-embryonic Period (Fertilization to Week 2):
    • Zygote cleavage forms a morula. Identical or conjoined twins may result from split morulas.
  2. Embryonic Period (Weeks 3 to 8):
    • Formation of the blastocyst; implantation occurs, and HCG is secreted.
    • Germ layers form (ectoderm, mesoderm, endoderm) leading to organ development.
  3. Fetal Period (Week 9 to Birth):
    • Significant growth; organs mature.
    • Essential development phases occur, culminating in childbirth.

Childbirth (Parturition):

  • Stages of Labor: Dilation, Expulsion, Placental.
  • Types of Birth: Full-term (≥38 weeks) and Premature (<37 weeks).

Birth Defects:
Affect about 3% of births due to genetic or environmental factors.

Postnatal Development:

  • Stages: Infancy (0-12 months), Childhood (1-13 years), Adolescence (puberty-late teens), Adulthood (remaining years), Aging (organ changes).
  • Growth patterns vary, with significant development during early childhood and adolescence, and gradual decline in mid to late adulthood.