Fetal development

Ovum (oocyte)

Female gamete released every 28 days; ovulation

Sperm

Male gamete introduced into vagina during intercourse

Fertilization

Occurs in fallopian tubes; only one sperm unites with ovum

Zygote

Fertilized egg

Morula

Zygote undergoing rapid cell division

Blastula (blastocyst)

Hollow ball of cells formed as blastomeres move outward

Where does early development occur?

In the fallopian tube while traveling to uterus

Implantation

Blastocyst attaches to endometrium (inner uterine lining)

When does implantation occur?

About 2 weeks after fertilization

Placenta

Transfers nutrients and waste between mother and baby; blood does not mix

Embryonic germ layers

Three layers that give rise to all tissues

Ectoderm

Forms brain, spinal cord, nerves, skin, and linings of mouth, nose, and anal canal

Mesoderm

Forms muscles, bones, blood vessels, connective tissues, kidneys, and more

Endoderm

Forms bladder, urethra, and linings of digestive and respiratory tracts

When does embryo become a fetus?

At the beginning of the 3rd lunar month

Fetal circulation

Fetus receives oxygen from mother’s blood, not lungs

Umbilical vein

Becomes ligamentum teres after birth

Ductus venosus

Becomes ligamentum venosum after birth

Foramen ovale

Becomes fossa ovalis after birth

Ductus arteriosus

Becomes ligamentum arteriosum after birth

Umbilical arteries

Become lateral umbilical ligaments after birth

Function of umbilical vein

Carries oxygen and nutrients from the placenta to the baby

Function of ductus venosus

Delivers blood from placenta into inferior vena cava (branches off umbilical vein)

Function of foramen ovale

Opening between left and right atria that bypasses lungs

Function of ductus arteriosus

Connects pulmonary artery to aorta; bypasses fetal lungs

Function of umbilical arteries

Carry fetal blood to placenta to exchange gases and wastes; branch off internal iliac

Umbilical vein after birth

Atrophies and becomes ligamentum teres

Ductus venosus after birth

Atrophies and becomes ligamentum venosum

Foramen ovale after birth

Closes and becomes the fossa ovalis

Ductus arteriosus after birth

Atrophies and becomes ligamentum arteriosum

Umbilical arteries after birth

Atrophy and become lateral umbilical ligaments