1. Development

2. 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

5. Sperm fertilizing egg

6. 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

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

8. Cleavage

10. 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

13. 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.

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

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

18. 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.

20. Cross section of embryo

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

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

27. 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.

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

31. Growth
Second and third trimesters are primarily growth stages

32. 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

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

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

39. 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.

45. Gestation
= pregnancy
9 full months; three trimesters

46. 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)

49. 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

50. Note the positive feedback cycle

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

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