Development

Fertilization The haploid sperm joins with the haploid egg to make a diploid zygote or embryo Fertilization occurs in the oviduct Sex of baby is determined at the time of fertilization

Sperm fertilizing egg

Fertilization Fraternal twins are the result of 2 different eggs fertilized by 2 different sperm Identical twins are the result of a single egg/sperm that subsequently splits into twins. These twins are genetically identical. Ectopic pregnancy is a pregnancy in an abnormal site, usually when the fertilized egg gets stuck in the oviduct

Cleavage Day 1-4 pregnancy Mitosis division that occurs in oviduct as embryo moves towards the uterus

Cleavage

Blastocyst Day 5 In uterus Rearrangement of cells into outer cells destined to become the placenta Inner mass of cells destined to become the baby

Blastocyst Implantation occurs on day 7-8 Blastocyst burrows its way into mom’s endometrium for nourishment & protection Embryo secretes HCG, Human Chorionic Gonadotropin, that serves to keep the corpus luteum making estrogen and progesterone.

HCG HCG is the basis for the do-it-at-home pregnancy test Urine test Highly accurate

Gastrulation Week 2 pregnancy Germ layers form, which are layers of cells destined to become certain organs depending on their position

Gastrulation Germ Layers Ectoderm is outer layer destined to become nervous tissue and skin. Mesoderm is middle layer destined to become skeleton, muscles, heart, blood, vessels…. Endoderm is inner layer destined to become lungs and digestive structures.

Cross section of embryo

Neurulation 3 weeks Embryo is 2mm long Neural tube forms resulting in brain and spinal cord

Organogenesis Week 4 All major organs, arm/leg buds, have begun their formation

First Trimester Most organ development occurs during the first trimester (3 months) of pregnancy This is the time when the embryo is most susceptible to damage.

Embryo vs. Fetus By the end of the second month, the embryo looks distinctly human, and is now called a fetus

Growth Second and third trimesters are primarily growth stages

Placenta Begins development at 4 weeks and becomes fully functional by 12 weeks Provides nourishment and oxygen for fetus, removes fetal waste and makes estrogen and progesterone

Placenta Comprised of maternal tissue – the endometrium Comprised of fetal tissue – the chorion

Placenta Umbilicus is comprised of arteries/vein that link the fetus to the placenta

Fetal Amnion Sac surrounding fetus Filled with amniotic fluid that provides protection, facilitates movement, and keeps a warm temperature An amniocentesis is a sampling of this fluid checking for chromosomal and genetic abnormalities.

Gestation = pregnancy 9 full months; three trimesters

Childbirth Labor occurs when contractions are regular and occurring about every 30 min. As contractions get stronger, amnion is ruptured and amniotic fluid is released (“water” breaking)

Childbirth Estrogen causes minor contractions forcing the baby’s head against mom’s cervix Stretching of the cervix causes the release of OXYTOCIN which causes large contractions Oxytocin is made in the hypothalamus but released from the pituitary

Note the positive feedback cycle

Childbirth Relaxin, made by the placenta, relaxes cervix and birth canal

Childbirth As the contractions occur even after the baby is delivered, the afterbirth (placenta) is passed.