Human Reproduction

Conception/Fertilization

Conception/Fertilization Ejaculation Release of 300-500 million sperm Egg needs to be in oviduct Sperm to egg, not an easy task Go wrong direction 2 paths – only 1 leads to an egg Get distracted or confused Get attacked by female’s white blood cells Acidic environment Current

Once egg is located… Dissolve protective goo surrounding egg One gets through – enters egg Instant biochemical change in zygote No more sperm allowed in

Zygote begins development

Implants in uterine lining Endometrium= outer lining of uterus Becomes placenta Embryo supported via umbilical cord Uses mother’s nutrients Continues development Once pregnant, progesterone levels stay high in mom

Fetal Development Anmion Amniotic Fluid Membrane surrounding baby Contains amniotic fluid Breaks just before birth Amniotic Fluid The “water” surrounding baby Buoyant cradle for baby Protection Free movement\ To reduce temperature fluctuation To lubricate the vagina during birth

Fetal Development Umbilical Cord Placenta Blood vessels from placenta to baby Mom’s & baby’s blood do not circulate together! Can have 2 different blood types Diffusion Placenta As a place of exchange of materials between mother and the fetus For secreting hormones

The Placenta Finger-like villi increases the surface area for efficient diffusion Maternal blood and fetal blood flows in opposite direction to speed up diffusion of materials between them Maternal blood capillaries and fetal blood capillaries are separated by thin membrane to shorten the distance of diffusion of materials to prevent high pressure of maternal blood from breaking the delicate fetal blood vessels to prevent clotting of maternal and fetal blood if their blood groups are incompatible

6 weeks Heart has already formed Neural tube has formed and nervous system continues to develop 1/5 – ¼ of an inch long Folds at anterior end will become jaws, cheeks and chin Ear canals have begun Kidneys, liver and lungs are forming

9 weeks Is now called a fetus 1” long Spleen and gal bladder are forming Beginning of external ears Spontaneous movements – can’t be felt by mom yet Heartbeat can be heard

12 weeks Most systems are fully formed 2 ½” long and ½ ounce Tripled in size in the last three weeks!! Pituitary gland has begun producing hormones Bone marrow is making white blood cells Mom may barely “show”

2nd Trimester Mostly growth Looks more like a baby Some preemies survive at this stage

15 weeks 4 ½” long and 2 ounces Ears are on the side of the head (they started out on the neck!) Eyes are moving to the front of the face form the side of the head Baby is practicing breathing, sucking, moving, and swallowing Mom now has a “bump”

18 weeks 5 ½” long and 5 ounces Rolls, kicks, and punches can now be felt by mom Myelin now covers the nerves Sensory areas of the brain are specializing Baby gets the hiccups

20 weeks – half way there!! 6 ½” long and 10 ounces A boy or a girl?? External genitalia can be seen at this point Testicles are starting to descend, vagina is forming Can control movements Taste buds begin to develop

24 weeks 8 ½” long and more than a pound Packing on the fat Organs are growing Has hair now Skin is thin and transparent

3rd Trimester More growth Kicking, rolling, stretching Eyes open – Week 32 Lungs mature Rotates to head-down position

Birth Labor – muscles used to open cervix Baby flips upside down Head first! Feet first = Breech (bad) Cesarian Section (“C-section”) surgical removal of baby After baby is born mom delivers placenta (“afterbirth”) that detaches from uterus

Breastfeeding Most nutritious option for baby Milk changes as baby grows Antibodies from mom create immunity for baby Studies have shown correlation between breastfeeding and higher intelligence in baby. Bond w/baby is stronger

Twins/Multiple Births Two types Monozygotic From one egg Identical Dizygotic From two eggs Fraternal Not identical

Identical twins One zygote Splits in 2 No one knows why! Completely random = does NOT run in families Same exact DNA Nature’s clones

Fraternal Twins 2 separate eggs get fertilized with 2 different sperm cells More than one egg got released during ovulation Siblings Can be sisters Brothers Brother and sister Tends to run in families

Conjoined Twins Used to be called “Siamese” twins First well known case was in Siam Identical twins that never completely separated during development Sometimes can be separated, depending on what is shared.