Human Life Cycle and Puberty

Human Life Cycle

• Fertilization and meiosis alternate during the entire life cycle.
• Gametes act as vehicles to deliver and combine parental DNA.
• The chromosome number is restored in the zygote after fertilization.
• The zygote develops into an embryo, which then develops into an adult.

Human Life Stages

• Various physical, physiological, and behavioral changes during puberty prepare humans for adulthood.

Male Physical Changes During Puberty

• Development of facial hair and hair under the arms.
• Skin becomes oilier.
• Shoulders get wider.
• Pubic hair grows.
• Neck, chest, and leg muscles grow bigger and stronger.
• The penis becomes longer and wider.
• Testes get larger.

Female Physical Changes During Puberty

• Shoulders get wider.
• Skin becomes oilier.
• Breasts start to develop.
• Hair grows under the arms.
• Hip bones widen.
• Pubic hair grows.
• Weight gain occurs on hips.
• Leg muscles grow bigger and stronger.
• The whole body becomes curvier.

Life Stages

• Infancy occurs from ages 0-2, marked by continuous physical development.
• Childhood occurs from ages 2-12, marked by locomotor and cognitive skill development.
• Adolescence occurs from ages 13-19, marked by undergoing various changes related to puberty.
• Adulthood occurs from age 20 onwards, marked by sexual maturity (physically and behaviorally).

Male Reproductive Anatomy

• The seminal vesicle contributes alkaline fluid to nourish and protect sperm cells.
• The prostate gland contributes fluid that neutralizes semen and vaginal fluid.
• The bulbourethral gland contributes fluid that functions for lubrication.
• The penis is the copulatory organ that conveys sperm to the female reproductive tract.

Female Reproductive Anatomy

• The ovaries produce and nourish egg cells (female gonads).
• The fallopian tubes facilitate fertilization and lead to the uterus.
• The fimbriae are appendages of the fallopian tubes that catch eggs during ovulation.
• The uterus is a highly vascularized sac that nourishes the developing embryo.
• The vagina allows further entry of foreign materials.
• The external genitalia are accessory structures of the female reproductive system.

Gametogenesis: Spermatogenesis

• Spermatogenesis occurs in the seminiferous tubules of the male testis.
• Nourishing Sertoli cells are included.
• This process starts during puberty and continues throughout life.
• Egg cells with enough nutrients are produced.
• Spermatogonia undergo minimal growth, dividing to become primary spermatocytes.
• Meiosis I of a primary spermatocyte produces two secondary spermatocytes.
• Each spermatid differentiates to become a functional and motile spermatozoon.