Conception to Birth PDF

Human Development ----------------- The study of development begins at the moment of conception. Every human begins with the union of one sperm and one ovum (egg). ### Fertilization: Zygote Formation: Genetic material from each parent fuses to form a zygote. The zygote is the first living cell fo...

Human Development ----------------- The study of development begins at the moment of conception. Every human begins with the union of one sperm and one ovum (egg). ### Fertilization: Zygote Formation: Genetic material from each parent fuses to form a zygote. The zygote is the first living cell formed at conception. Human DNA consists of 23 pairs of chromosomes and 20,000 genes. Genetics: --------- Genotype: The genetic makeup of an organism. Phenotype: The observable physical traits. Single Nucleotide Polymorphism (SNP): A change in a single nucleotide, a type of genetic mutation. These are biomarkers. Independent Assortment: How genes independently separate during the development of reproductive cells. ### Dominant and Recessive Genes: Dominant genes: Always expressed if present. Recessive genes: Only expressed if paired with another recessive gene. Co-dominant genes: Expressed equally (e.g., blood type). ### Sex-Linked Traits: Traits linked to X or Y (sex) chromosomes. Typically recessive and carried on the X chromosome. Examples include color blindness, baldness, hemophilia, and Fragile X syndrome. Developmental Stages: --------------------- ### 1. Germinal Period: First 2 weeks post-fertilization (zygote to implantation). ### 2. Embryonic Period: Weeks 3 to 8 post-conception. Major organs and anatomical structures begin to form. Heartbeat visible at 6 weeks via ultrasound. ### 3. Fetal Period: From week 9 to birth. Rapid growth of organs. ### Neural Tube Formation: Begins at 22 days, eventually forming the central nervous system. ### Week-by-Week Development: 6 Weeks: Embryo is 2.5 cm long. Legs and webbed toes develop. 8 Weeks: Recognizable as human. All major organs present except sex organs. Placenta Formation: ------------------- The placenta develops by the end of the first trimester (12 weeks). Acts as a life-support system, connecting the fetal and maternal circulatory systems via the umbilical cord. Second Trimester (13-26 weeks): ------------------------------- Fetus develops a more distinct human appearance. Quickening: Baby starts to swallow and kick. 20-24 weeks: Hair, lashes, and brows form. Visual and auditory senses become functional. Third Trimester: ---------------- 28 weeks: Eyes open/close and respond to light. Better organized motor skills and sleep-wake cycles. 32 weeks: Brain reaches 25% of adult weight. 36-40 weeks: Brain development slows; fetal body systems prepare for life outside the womb. Prematurity Risks: ------------------ 23 weeks gestation: Considered viable (\~20-35% survival rate). 26 weeks and beyond: Up to 90% survival but with high risks of impairments. ### Short-Term Complications: Breathing: Apnea of prematurity, broncho-pulmonary dysplasia. Heart: Patent ductus arteriosus (PDA), hypotension. Brain: Intraventricular hemorrhage. Immune System: Underdeveloped. ### Long-Term Complications: Cerebral Palsy, Impaired cognitive skills, Vision and hearing problems, Chronic health issues (e.g., SUDI -- sudden unexpected death in infancy). Prenatal Influences on Development: ----------------------------------- Nutrition, Maternal Anxiety, Maternal Health, Teratogens (agents causing birth defects), Health conditions during pregnancy (e.g., anemia, hypertension, depression). ### Examples of Teratogens: Thalidomide: Causes limb malformations. Alcohol: Causes fetal alcohol spectrum disorders (FASD). Screening and Testing: ---------------------- ### Screening Tests: Nuchal Translucency Scan: Ultrasound at 12-13 weeks measuring fluid behind baby's neck. Maternal Serum Screening: Blood analysis for neural tube defects and trisomy 21. ### Diagnostic Testing: Chorionic Villus Sampling (CVS): Performed between 10-12 weeks. Small risk of miscarriage. Amniocentesis: Detects chromosomal abnormalities, performed at 15-16 weeks. APGAR Scoring: -------------- A quick test is performed on a newborn to evaluate physical condition post-birth. Additional Facts: ----------------- Fetuses respond to sounds and light from 25 weeks. 90% of fetal time in the womb is spent asleep. Viability: 23 weeks gestation marks the point where a fetus can potentially survive outside the womb.