Fetal Development (PDF)

Fetal Development Fundamental information Average human pregnancy is 40 weeks from the first day of the LMP (last menstrual period). 1st trimester: 0-13 weeks gestation ○ Primary focus: Development of the foundation of all major body syste...

Fetal Development Fundamental information Average human pregnancy is 40 weeks from the first day of the LMP (last menstrual period). 1st trimester: 0-13 weeks gestation ○ Primary focus: Development of the foundation of all major body system 2nd trimester: 14-26 weeks gestation ○ Primary focus: Growth of the major body systems & further maturation 3rd trimester: 27 - 40 weeks gestation ○ Primary focus: Weight gain Term: 37-42 weeks gestations Pre-term: < 37 weeks gestation Post-term: > 42 weeks gestation EGA: estimated gestation age Stages of Fetal Development: *Do not focus heavily on anatomy & physiology! Need to have a general idea of what is developing during which stage of development* Stage 1: Preembryonic stage (0-2 weeks) Stage begins with fertilization and ends at 2 weeks after conception Fertilization occurs when the ovum and the sperm join = Zygote cell (46 chromosomes) The zygote cell will undergo further division via mitosis as it travels into the uterine cavity from the site of fertilization (fallopian tube). Zygote enters the uterine cavity 72 hours after fertilization. Implantation occurs 7-10 days after fertilization. ○ Implantation typically occurs at the fundus of the uterus. The rich blood supply & thick tissue layer is needed for the placenta. Pregnancy has not occurred until implantation Cellular differentiation: ○ Ectoderm: CNS, special senses, skin, and glands ○ Mesoderm: MSK, urinary, circulatory, and reproductive ○ Endoderm: respiratory, liver, pancreas, and digestive system Stage 2: Embryonic stage (2-8 weeks) The stage develops the umbilical cord and placenta. Umbilical cord Purpose: regarded as the lifeline from the mother to fetus One large vein and 2 small arteries! ○ Vein: Oxygenated blood from mom to fetus ○ Arteries: deoxygenated blood from fetus to mother Umbilical cord surrounded by Wharton's jelly to prevent compression and trauma to the cord in the intrauterine environment Amniotic fluid Purpose: ○ Cushioning against impacts to the maternal abdomen ○ Maintaining a stable temperature - 1 degree higher than mother ○ Promoting prenatal development by the following actions: ○ Allowing symmetric development as the major body surfaces fold toward the midline ○ Preventing the membranes from adhering to developing fetal parts ○ Allowing room and buoyancy for fetal movement Oligohydramnios is associated with ○ Deficient levels of amniotic fluid  ○ Poor placental blood flow ○ Preterm rupture of the membranes ○ Failure of fetal kidney development ○ Blocked urinary excretion ○ Poor fetal lung development (pulmonary hypoplasia) ○ Malformations such as skeletal abnormalities from compression of fetal parts Hydramnios : Also called (Polyhydramnios) excess levels of amniotic fluid Placenta: Primary purpose: ○ Filter between the mother and fetus ○ Waste elimination ○ Delivery of hormones, nutrients, & oxygen “lungs of the fetus” Damage to the placenta will greatly affect fetal oxygenation ○ Antibody Transfer Many in the immunoglobulin G (IgG) class of antibodies are passed from mother to fetus through the placenta Protection from immune attacks Rh factor Teratogens: substance that interferes with normal embryonic or fetal development that will have postnatal effects physically or functionally ○ Ex. Syphilis, Cytomegalovirus (CMV), Herpes, Varicella, Rubella, Toxoplasmosis, radiation, lead, mercury, or drugs Endocrine Functions ○ Produces several hormones ○ Human Chorionic Gonadotropin (hCG) Promotes normal nutrition and growth of the fetus as well as maternal breast development for lactation Basis for early pregnancy tests. The release of hCG to maintain the corpus luteum to release progesterone after fertilization until the placenta can take over in hormone production. It can be found in maternal blood & urine. Peak production occurs for the first 6 to 8 weeks or 60-70 days post fertilization Doubles every 48-72 hours hCG levels are associated with “morning sickness” ○ Estrogen Causes enlargement of the uterus Enlargement of the breasts, Growth of the ductal system of the breasts Enlargement of the external genitalia ○ Progesterone “Hormone of pregnancy” Essential for normal continuation of the pregnancy. Supports the endometrium during pregnancy to provide an environment to facilitate fetal survival. ○ hPL (Human Prolactin Lactogen) -Antagonist of insulin! Decreases maternal metabolism of glucose & increases free fatty acids. Glucose is diverted to the fetus to facilitate growth. Alters maternal metabolism of carbs, fats, and proteins from utilizing glucose. Breast development for lactation ○ Relaxin Synergistic with progesterone to maintain pregnancy! Dilates the cervix, softens the pubic symphysis during L&D to slightly increase pelvic size, and may delay labor contractions by suppressing oxytocin. 3rd stage: Fetal development (9-40 weeks)  Further growth & development of of fetal body systems Very important for mothers to be on prenatal supplements like folic acid in order to avoid any neural tube defects. Primary development events (Table 5.2 pg80) *Do no get too specific into the anatomy & physiology but just have a general idea of the major developments* Highly recommend looking at the textbook chart Week 3 -All body systems begin to form - Neural tube is still open at each end. Week 4 -Regular heart rhythm is detectable -Neural tube is closed at each end. Week 6 -Brain waves detectable -Lungs begins to development -Circulation established -CNS forms Week 8 -Heart is fully formed, Heartbeat detectable with ultrasound -Placenta function takes over corpus luteum -Fetus begins to resemble human Week 9-12 -Genitals can be recognized as male/female (12 weeks gestation) -All organs are present but not fully functional and need further maturation Week -Lanugo begins to develop (fine hair) 13-16 -Fetal movement may begin Week -Quickening (fast & rapid fluttering sensation d/t fetal movement) (17-20 weeks) 17-20 -Rapid brain growth -Fetal heart tones clearly detectable with stethoscope auscultation -Vernix forms (white greasy film covering fetus) -Brown fat production complete Week -Alveoli begins formation in the lungs 21-24 -Surfactant production begins -Fetus is active, Fetal movements become progressively noticeable Week -Fetus assumes the head down position 25-28 -CNS begins to control some function Week -Lungs are still maturing 29-32 -Rhythmic breathing movements occur -Body fat is rapidly increasing Week -Head is in the tilt down position 33-38 -Fetus takes up nearly all intrauterine space -Lanugo disappears -Mother supplies fetus with antibodies -Term at 37 weeks gestations -Well developed ability to exchange gas Fetal Circulation How does the placenta act as the fetal lungs? *Baby gets all oxygenated blood from placenta* “Placenta is the lungs for the baby until birth” Blood NEVER MIXES (between mom and fetus) One umbilical Vein (O2) and TWO umbilical arteries (CO2) The Umbilical cord is the lifeline between the fetus and the placenta Shunts: Three Shunts which allow blood with the highest oxygen content to be sent to the fetal heart and brain Pushing/Pulling blood away from the lungs!! (*know the names & location & blood flow) Ductus venosus: ○ Located: liver! ○ Purpose: umbilical vein enters at umbilicus, head toward liver, d/t ductus venosus (shunted to inferior vena cava) It will then enter the right atrium and encounter Foramen Ovale Foramen Ovale: ○ Located: right and left atrium! ○ Purpose: prevents majority of blood that enters right atrium from enter into pulmonary circuit Most blood enters into left atrium (for system circuit) Ductus Arteriosus: Location: pulmonary artery connects to descending aorta Purpose: shunts blood away from lungs!! ○ Deoxygenated blood from the superior vena cava = enters right atrium = right ventricle = pulmonary arteries ○ Causes blood to become mixed!!! (CO2 and O2) ○ BUT ductus arteriosus shunts blood away from lungs and to system flow How is blood shunted away from lungs? d/t pressure differences* Blood moves from High to low pressure Lungs = extremely high pressure Right side = still high but not as high as lungs Left side = less pressure How does fetal circulation change during transition to neonatal circulation? Cutting umbilical cord - stopping transfer ○ Ductus venosus decays Lungs: open and fluid inside releases ○ Decreases high pressure in lungs ○ Decrease pressure in right side heart Helps foramen ovale closes! PFO: patent foramen ovale (sometimes it doesn't close) Placenta removal =causes ductus arteriosus to close ○ D/t senstiviity of prostaglandins & placenta removal drops levels