Human Development and Developmental Stages

Introduction

• Discussion on human anatomy and physiology.
• Focus on the development of the human body from a single cell to trillions of cells.

Viewing the Fetus

• Examination of a real human fetus.
• Observation of limb anatomy, digits, male genital structures, and umbilical cord.

Developmental Stages

Ovulation and Fertilization

• Ovary releases one egg during ovulation (approx. 28-day cycle).
• Hyper ovulation leads to phenomena like fraternal twins.
• Ovum lifespan: ~24 hours.
• Sperm cells can survive 3-5 days in the female reproductive tract.
• Sperm and ovum are haploid cells with 23 chromosomes each.
• Fertilization forms a zygote, a diploid cell with 46 chromosomes.

Cellular Development

• One cell (zygote) contains all information to develop into a human.
• Differentiation into various tissues: nervous tissue, bones, muscles, organs.

Organ Development Timelines

• Day 18-19: Heart begins to develop.
• End of the third week: Heart starts to beat.
• 7th-8th week: Formation of all four heart chambers.
• 26-30 weeks along: Fetus has a mostly formed heart, entering the third trimester.

Trimester Breakdown

First Trimester

• Critical stage of development, formation of major organ systems.
• Vulnerable to drugs, radiation, microbes, infections.

Second Trimester

• Nearly complete development of organ systems.
• Development of distinctive human characteristics.

Third Trimester

• Rapid fetal growth, doubling in weight.
• Organ systems become fully functional.

Terminology in Human Development

• Embryonic Period: Weeks 1-8, developing human is an embryo.
• Fetal Period: Weeks 9-38, developing human is a fetus.
• Post-birth: Termed neonate/newborn, and other stages like infant, toddler, etc.

Final Thoughts

• Appreciation for human development and those donating bodies to science.
• Brief mention and endorsement of Brilliant.org as an educational tool.