Human Development Notes
Human Development Stages After Fertilization
- Fertilization: Fusion of ovum and sperm (Day 1)
- Morula: Solid ball of cells (Day 3)
- Blastocyst: Hollow ball of cells (Day 5)
- Trophoblast: Forms embryo, fetal membranes, placenta (Days 5-7)
- Embryo: From fertilization to the 8th week
- Fetus: From the 9th week to birth (~40 weeks)
- Neonate: From birth to 28 days old
- Infant: Less than 1 year old
Three Phases of Human Development
- Pre-embryonic phase: Weeks 1-3
- Embryonic phase: Weeks 4-8
- Fetal phase: Week 9 to birth
Morula
- A solid ball of cells that forms about three days after fertilization.
Blastocyst
- A hollow ball of cells that forms around five days after fertilization.
Three Types of Embryonic Germinal Tissues
Major Structures and Tissues Developed from Each Germinal Layer
- Ectoderm: Skin, nervous system (brain, spinal cord)
- Mesoderm: Muscles, bones, cardiovascular system
- Endoderm: Lining of the digestive and respiratory tracts, liver, pancreas
Hormone Used in Pregnancy Tests
- Chorionic Gonadotropin Hormone (CGH), also referred to as hCG
Major Events During the Three Phases of Development
Pre-Embryonic Phase (Weeks 1-3):
- Fertilization -> Zygote -> Morula -> Blastocyst
- Implantation into the uterus
- Development of placenta
- Differentiation into germ layers
- Neural tube begins forming
- Secretion of CGH/hCG
Embryonic Phase (Weeks 4-8):
- Development of brain regions
- Heart starts beating
- Limb formation, eye/ear/nose development
- Bones begin calcifying
- Formation of primary teeth
Fetal Phase (Week 9 to Birth):
- Organs continue to grow and mature
- Sex determination (around 3rd month)
- Eyelids, nails form; kidneys produce urine
- Movement felt (around 5th month)
- Lungs (alveoli) begin to develop
- Fat deposition, testes descend (7th month)
- Baby prepares for birth (8th-9th months)