Human Development & Aging

Fertilization

The union of sperm and egg forming a zygote

Zygote

A single-cell organism resulting from fertilization

Cleavage

Series of rapid cell divisions without growth after fertilization

Morula

Solid ball of cells resulting from cleavage

Blastocyst

Hollow structure formed after morula, implants into uterine wall

Implantation

Attachment of blastocyst to endometrium around day 6

Trophoblast

Outer layer of blastocyst that helps form placenta

Embryo

Term used from implantation until the 8th week of development

Fetus

Term used from 8 weeks of development until birth

Placenta

Organ that exchanges nutrients, gases, and wastes between mother and fetus

Umbilical cord

Connects fetus to placenta; contains 2 arteries and 1 vein

Amniotic sac

Fluid-filled sac surrounding and protecting the fetus

Amniotic fluid

Cushions fetus and maintains stable temperature

hCG (human chorionic gonadotropin)

Hormone secreted by trophoblast to maintain corpus luteum

Corpus luteum (in pregnancy)

Continues secreting progesterone until placenta takes over

Placental hormones

Include estrogen, progesterone, and hPL to maintain pregnancy

Organogenesis

Formation of organs during first 8 weeks of development

Neural tube

Forms the brain and spinal cord; closes by day 28

Teratogen

Substance that can cause birth defects during development

Quickening

First fetal movements felt by mother, usually around week 16

Viability

Ability of fetus to survive outside uterus, usually after 24 weeks

Labor

Series of uterine contractions leading to childbirth

Dilation stage

Cervix opens from 0 to 10 cm

Expulsion stage

Baby moves through birth canal

Placental stage

Delivery of placenta after birth

Lactation

Milk production by mammary glands after birth

Prolactin

Hormone from anterior pituitary that stimulates milk production

Oxytocin

Hormone that triggers milk ejection and uterine contractions

Colostrum

First milk produced; rich in antibodies

Neonatal period

First 4 weeks after birth; rapid physiological changes occur

Postpartum

Period following childbirth when the mother’s body returns to pre-pregnancy state