Fetal Development

Labor and delivery

Chromosomal abnormalities

After implantation, cells of blastocyst start todifferentiate into three germ layers

Ectoderm- skin and nervous systempituitary gland

Mesoderm- connective tissue and muscleendocrine, cardiovascular, skeletalsystems

Endoderm- digestive, respiratory, urinary,reproductive systems

By blastocyst

By placenta

“Extraembryonic membranes”

Start forming after implantation

Yolk sac- trasnport of nutrients, red bloodcell formation. Role reduced> 6 weeks

Amnion- encloses amniotic cavity. Fluid cushionsdeveloping embryo/fetus

Allantois- forms urinary bladder; umbilical cordChorion- blood vessels help nourish embryo;

develops into placenta

Placenta

Umbilical arteries and veins provide fetalcirculation

Maternal circulation does not actually mixwith fetal blood

Gas and nutrient exchange takes place here

Secretes estrogen and progesterone to maintain endometrium

Four weeks

8 weeks

Labor and childbirth

Laboroxytocin (hypothalamus)prostaglandins

Fetal adrenal gland produces cortisol and anestrogen precursor; makes uterus moresensitive to oxytocin and prostaglandins

CRH secretion by placenta triggers fetaladrenal gland activity

Developmental defects

Aneuploidy (“wrong” number of chromosomes)

Karyotyping- chromosomal analysis

Down syndrome- trisomy 21Edwards syndrome- trisomy 18Patau syndrome- trisomy 13

Triploidy- an extra set of chromosomes

Abnormal number of sex chromosomes

XO- Turner syndrome

XXY- Klinefelter syndrome

XYY syndrome

Arises due to “mistakes” in meiosis

Developmental problems- spontaneous or dueto exposure to harmful substances(teratogens)

Proper fetal development depends on:

Nutrition

Freedom from infection

Avoidance of drugs and alcohol

Avoidance of smokinglowers vitamin levelssubstances in smoke can cross

placental barrier

Development does not stop at birth!

Neonate- rapid growth and neurologicaldevelopment

Puberty- sexual maturation

“Secondary sexual characteristics”

Aging-?

Contraception- prevention of pregnancy

SterilizationAbstinenceHormonal (birth-control pills)

male pill?Anti-implantationBarrier

Infertility

Artificial insemination

Egg donation

Embryo transfer

In vitro fertilization

Intrafallopian transfer

Summary• Progression from gametes to zygote to

multicellular organism• Development, labor and delivery under

hormonal control• Aneuploidy leads to serious

developmental defects• Development does not stop at birth