Human Fetal Development

Female Reproductive Organs

Conception Every 28 days, an ovum, lasts 24 hours Millions of sperm, viable for up to 6 days Conception in the fallopian tube Tubal pregnancy Conceptions most likely: on day of ovulation or the two days preceding ovulation

Conception Chromosomes join & form zygote Sperm attaches & penetrates ovum

Progress Before Birth: Prenatal Development 3 phases germinal stage = first 2 weeks conception, implantation, formation of placenta embryonic stage = 2 weeks – 2 months Period of rapid growth and differentiation, organogenesis formation of vital organs and systems fetal stage = 2 months – birth bodily growth continues, movement capability begins, brain cells multiply age of viability Prenatal development begins with the germinal stage, lasting from conception to about 2 weeks. During this stage, rapid cell division occurs, and the mass of cells migrates to the uterus and beings to implant into the uterine wall, forming a placenta during the implantation process. The placenta is a structure that allows oxygen and nutrients to pass into the fetus from the mother’s bloodstream and bodily wastes to pass out to the mother. The embryonic stage lasts from 2 weeks to 2 months and is the period when most of the vital organs and bodily systems such as the heart, spine, and brain emerge. The embryonic period is a time of great vulnerability; if anything interferes with development during this time period, effects can be devastating. The fetal period lasts from 2 months to birth. During the early parts of this stage, the muscles and bones begin to form. The body continues to grow and function, with sex organs developing in the 3rd month and brain cells multiplying during the final 3 months. Somewhere between 22 and 26 weeks, the age of viability is reached…when the baby could survive if born prematurely. At 22 or 23 weeks, chances for survival are slim, but by 26-28 weeks chances improve to a survival rate of about 85%.

Gametes and Zygote Sperm Sperm Ovum Gametes (reproductive cells) Fertilization Zygote

The Period of the Zygote or the Germinal Stage First Two weeks following conception From fallopian tubes to attachment to the uterine wall Blastocyst, 60-70 cells, 4th day Embryonic disk (organism) Outer Ring (umbilical cord & placenta) Implantation between days 7 & 9

Blastocyst has an outer layer of cells called the trophoblast, an inner cell mass, and a fluid filled cavity called the blastocele. The trophoblast and part of the inner cell mass will form the membranes of the fetal portion of the placenta, the rest of the inner mass forms the embryo. Blastocele Trophoblast Blastocyst

Zygote Period Continued Amnion Membrane, amniotic fluid Yolk sack produces blood cells Chorion Membrane Placenta - Food, oxygen, waste Umbilical cord 30% of zygotes do NOT survive

The Period of the Embryo 5.5 Weeks 9 Weeks From 2nd week through 2nd month Very rapid prenatal development Embryonic disk folds into three layers Ectoderm - Nervous system (fast develop.) & skin Mesoderm - skeleton, muscles, circulation Endoderm - Digestion, lungs, urinary tract

Endodermal Differentiation

Embryonic Period Cont. Many body parts develop the 2nd month Fingers, toes, facial features, nervous system cells fire, teeth buds have formed Embryo’s posture becomes upright The embryo can move The embryo responds to touch (mouth & feet)

11 Week Fetus

The Period of the Fetus Growth and finishing Third month Organs, muscles & nervous system organize and connect External genitals – visible with ultrasound End of first trimester

Second Trimester 13-24 weeks - first movement felt Vernix covers fetus, prevents chapping Lanugo hold vernix to skin Trillions of brain neurons produced Stimulated by sound and light

Third Trimester Age of viability - 22 to 26 weeks Cerebral cortex enlarges Responsive to external stimulation Fat layer develops for temp. reg. Moves to the upside-down position Fetus moves less

Ready for birth.

Figure 11.1 Overview of fetal development

What can go wrong? Two basic kinds of problems: Genetic: Improper cell division: e.g., Trisomy 21 Gene defects: Single gene defects Recessive gene defects Environmental: teratogens Teratogen = monster maker Any environmental agent that produces birth defects

Influence of Teratogens Larger doses, over time, more negative Genetics can help or hinder teratogens Several negative factors increase impact Sensitive periods especially important Embryonic period most susceptible Physical and psychological effects

Drugs Thalidomide – sedative - 1960’s Aspirin - low birth weight, infant death Poor motor develop., lower IQ Heavy caffeine use - miscarriage Premature births, irritability

Illegal Drugs Cocaine, heroin, methadone Prematurity, low birth weight Physical defects, breathing problems, Drug addiction & death Cocaine - lasting difficulties Genital, urinary tract, kidney, heart deformities Brain seizures

Crack babies Lowest birth weight Central nervous system damage Fathers on cocaine may pass it on Multiple harmful effects of more than one drug

Tobacco use Low birth weight and premature births Impaired breathing Miscarriage & infant death Placenta doesn’t work correctly Greater concentration of carbon monoxide Passive smoking also injurious

Alcohol Fetal alcohol syndrome (FAS) Large amounts of alcohol, whole pregnancy Mental retardation Slow physical growth Facial abnormalities Alcohol interferes with cell duplication Especially neural cells Draws oxygen away from organism

Fetal Alcohol Syndrome

Hormones Diethylstilbestrol (DES), 1945-70 Vaginal cancer Malformation of the uterus Miscarriage, low birth weight In males, genital abnormalities, cancer

Radiation Hiroshima & Nagasaki X-Rays - avoid during pregnancy Miscarriage, slow physical growth Underdeveloped brains Malformation of skeleton & eyes X-Rays - avoid during pregnancy

Environmental Pollutants 100,000 in common use Mercury Mental retardation, speech problems Difficulty chewing & swallowing Uncoordinated movements Polychlorinated Biphenyl (PCB) Lower birth weight, smaller heads Poor memory, lower verbal IQ

Maternal Disease Viruses - Most not harmful Rubella HIV & AIDS Heart defects, cataracts, deafness Genital, urinary & intestinal problems HIV & AIDS 20-30% Mothers pass to infants Fast growth in infants Most survive 5 to 8 months

Maternal Disease Cont. Herpes viruses Bacterial & Parasitic Diseases Babies infected during pregnancy or at birth Bacterial & Parasitic Diseases Toxoplasmosis from meat or cats 40% transmission Eye & brain damage

Positive Health Activities Moderate, low impact exercise Healthy diet - vitamin supplements Malnutrition causes problems WIC Program Low stress Intense anxiety >> miscarriage, premature birth, low birth weight, respiratory illness, Cleft palate & Pyloric stenosis

Domestic Violence 7-8% pregnant women are beaten Twice the miscarriage rates

Rh Factor Mother Rh -, father Rh+, Child Rh+ Antibodies against foreign Rh protein RhoGam within 72 hours

Prenatal Health Care Every month of pregnancy visit MD 2X/Month for the last two months

Watch For . . . Diabetes complications Toxemia Get vaccinations before becoming pregnant

Watch This Video http://www.youtube.com/watch?v=hRZe1Af5NQk

The Developing Baby: Conception to Birth Fertilization: the sperm and egg join in the fallopian tube to form a unique human being. 46 chromosomes combine, 23 from each parent, which pre-determine all of a person's physical characteristics and even some personality characteristics. Fertilized egg: This picture is of a fertilized egg, only thirty hours after conception. Magnified here, it is no larger than the head of a pin. Still rapidly dividing, the developing embryo is called a zygote at this stage. The embryo floats down from the fallopian tube and towards the uterus, where it attaches at approximately day 4 to 5 post-conception.

5 weeks – Embryo is the size of a raisin 5 weeks – Embryo is the size of a raisin. By day twenty-one, the embryo's tiny heart has begun beating. The neural tube enlarges into three parts, soon to become a very complex brain. The placenta begins functioning. The spine and spinal cord grows faster than the rest of the body at this stage and give the appearance of a tail. This disappears as the child continues to grow. Embryo at about 6 weeks: Notice the large neural tube and the formation of the heart and other internal organs. Embryo at approximately 7 weeks: Eyes, fingers, toes and most internal organs have formed, but are not yet fully functional.

7 weeks – Facial features are visible, including a mouth and tongue 7 weeks – Facial features are visible, including a mouth and tongue. The eyes have a retina and lens. The major muscle system is developed and the unborn child moves as if practicing. The child has its own blood type, distinct from the mother's. These blood cells are produced by the liver now instead of the yolk sac. Embryo in Amniotic sac Embryo at 8 weeks Amniotic Sac Placenta 8 weeks – The unborn child, called a fetus at this stage, is about half an inch long. The tiny baby is protected by the amniotic sac, filled with fluid. Inside, the child swims and moves gracefully. The arms and legs have lengthened, and fingers can be seen. The toes will develop in the next few days. Brain waves can now be measured.

10 weeks – The heart is almost completely developed and very much resembles that of a newborn baby. An opening the atrium of the heart and the presence of a bypass valve divert much of the blood away from the lungs, as the child's blood is oxygenated through the placenta. Twenty tiny baby teeth are forming in the gums; some babies are even born with teeth emerging from the gums. The baby at 12 weeks: notice the webbing on the fingers, with the digits still fused Fetus at 12 weeks Vocal chords are complete, and the child can and does sometimes cry silently. The brain is fully formed, and the child can feel pain. The fetus may even suck his thumb. The eyelids now cover the eyes, and will remain shut until the seventh month to protect the delicate optical nerve fibers. Notice head size and chest size in comparison to an adult.

14 weeks – Muscles lengthen and become organized 14 weeks – Muscles lengthen and become organized. The mother will soon start feeling the first flutters of the unborn child kicking and moving within. 15 weeks – The fetus has an adult's taste buds and may be able to savor the mother's meals. Foods the mother eats can affect movement of the baby Fetus at 4 months or about 16 weeks Face is fully developed and A downy hair covers the skin. Face is fully formed. Eyes are fully formed but not yet functional. 16 weeks – Five and a half inches tall and only six to 1- ounces in weight Eyebrows, eyelashes and fine hair appear. The child can grasp with his hands, suck her thumb, kick, or even somersault.

20 weeks – The child can hear and recognize her mother's voice 20 weeks – The child can hear and recognize her mother's voice. Though still small and fragile, the baby is growing rapidly and could possibly survive if born at this stage. Fingernails and fingerprints appear. Sex organs are visible. Using an ultrasound device, the doctor can tell if the child is a girl or a boy. This is a a baby girl. 5 months old Beginning to form hair on all body parts Definite sleep/awake cycles now. REM sleep occurs. Again at 5 months Approximately 8-10 inches long and 1 to 2 pounds Body position is often still “head up” Baby is viable at this point with at least a 50/50 chance of survival outside the womb. 24 weeks – Seen here at six months, the unborn child is covered with a fine, downy hair called lanugo. Its tender skin is protected by a waxy substance called vernix. Some of this substance may still be on the child's skin at birth at which time it will be quickly absorbed. The child practices breathing by inhaling amnionic fluid into developing lungs.

30 weeks – For several months, the umbilical cord has been the baby's lifeline to the mother. Nourishment is transferred from the mother's blood, through the placenta, and into the umbilical cord to the fetus. If the mother ingests any toxic substances, such as drugs or alcohol, the baby receives these as well. 7 months. Room is getting tight at this point. The baby is less able to move, squirms and pushes more than flutters and kicks. Most babies begins to get into a head down position getting ready for birth. 32 weeks – The fetus sleeps 90-95% of the day with REM sleep dominating the sleep cycle, an indication of dreaming. The baby is very viable at this point, with a 75% or higher chance of survival. If the baby is born, the concerns are with adequate lung development. Final lung development does not occur until about 37 weeks.

Birth at 38-42 weeks 40 weeks is normal gestation The baby weighs on average 7 lbs. and is 20 inches long. At birth the baby can see, hear, move and recognizes the voices of her parents or others who have been near the mother. A healthy newborn arrives in the world She is immediately checked over, given an Apgar score and then presented to her parents. Often the father or other important family member is asked to cut the umbilical cord. A new child is welcomed into the world