Fertilization, Prenatal Development, and Birth

Comprehensive vocabulary review flashcards covering fertilization, pre-embryonic transit, fetal membranes, placentation, stages of labor, lactation, and the human postnatal life span.

Follicle-Stimulating Hormone (FSH)

The pituitary hormone that drives ovarian follicle growth during the first two weeks of the menstrual cycle.

Luteinizing Hormone (LH) Surge

A sharp hormonal surge occurring around day $14$ of the menstrual cycle that triggers ovulation.

Corpus Luteum

The glandular structure formed from a ruptured ovarian follicle that secretes progesterone to maintain the endometrium.

Secondary Oocyte

The female gamete released at ovulation that travels down the uterine tube and degenerates within roughly $24\text{ hours}$ if unfertilized.

Uterine Tube

The duct (also known as the fallopian tube or oviduct) lined with cilia and smooth muscle where fertilization normally occurs in its outer third.

Conception

The fertilization of an ovum by a sperm cell.

Acrosome

The specialized cap on the head of a sperm cell that releases digestive enzymes to penetrate the outer protective layers of the oocyte.

Second Meiotic Division (Oocyte)

The final meiotic division completed by the oocyte upon sperm binding, resulting in a mature ovum and a tiny polar body.

Polar Body

A tiny nonfunctional cell produced alongside the mature ovum upon completion of the second meiotic division.

Polyspermy Block

Immediate electrical and chemical changes across the egg membrane that harden its outer envelope to permanently prevent additional sperm from entering.

Zygote

A single diploid cell containing $46$ chromosomes ($23$ paternal and $23$ maternal) formed by the fusion of sperm and egg.

Cleavage

A rapid series of mitotic cell divisions without overall growth that begins within $30\text{ hours}$ of fertilization.

Morula

A solid, berry-like cluster of dividing cells formed by day three or four after fertilization as the pre-embryo travels toward the uterus.

Blastocyst

A hollow fluid-filled sphere formed by day five of development, composed of an outer trophoblast layer and an inner cell mass.

Trophoblast

The outer cell layer of the blastocyst that burrows into the uterine lining and contributes to the fetal part of the placenta.

Inner Cell Mass

The compact cluster of cells located within the blastocyst that differentiates into the actual tissues of the embryo.

Implantation

The attachment and burrowing of the blastocyst into the blood-rich endometrium around day $7$ after fertilization via trophoblast enzymes.

Amnion

A thin fetal membrane forming a fluid-filled sac around the embryo that cushions it against physical shocks.

Amniotic Fluid

The protective liquid surrounding the embryo that regulates temperature, prevents tissue adhesion, and acts as a hydraulic shock absorber.

Chorion

The outermost fetal membrane that extends finger-like villi into maternal tissue to construct the placenta.

Yolk Sac

An extraembryonic membrane that produces early blood cells and germ cells prior to the development of the liver, spleen, and bone marrow.

Allantois

An extraembryonic membrane that contributes blood vessels that become the umbilical arteries and umbilical vein in the umbilical cord.

Placenta

A temporary organ composed of maternal uterine tissue and fetal chorionic villi that facilitates nutrient, gas, and waste diffusion without direct blood mixing.

Chorionic Villi

Microscopic, finger-like vascular projections of fetal chorion extending into maternal blood spaces to permit diffusion across capillary walls.

Human Chorionic Gonadotropin (hCG)

A hormone secreted by the trophoblast immediately after implantation that mimics LH to maintain the corpus luteum and progesterone secretion.

Embryonic Period

The developmental phase extending from fertilization through the eighth week ($\text{day } 60$), characterized by organogenesis.

Neural Tube

An embryonic structure formed by the fourth week of development that gives rise to the brain and spinal cord.

Fetus

The developing human from the end of the eighth week ($\text{day } 60$) until birth, marked by rapid growth and functional tissue maturation.

Gestation Period

The full duration of human prenatal development, lasting approximately $266\text{ days}$ (or $38\text{ weeks}$) from fertilization to delivery.

Fraternal Twins (Dizygotic Twins)

Twins that develop when two separate ova are ovulated and fertilized by two distinct sperm cells, sharing genetic similarities of normal siblings.

Identical Twins (Monozygotic Twins)

Twins that develop from a single fertilized ovum (zygote) that splits into two separate cell clusters early in development, sharing identical genetic code.

Conjoined Twins

Identical twins whose early embryonic bodies fail to separate completely during development.

Parturition

The medical term for childbirth, driven by forceful, rhythmic contractions of the uterine wall.

Labor

The rhythmic, forceful contractions of the uterine myometrium that dilate the cervix and expel the infant and placenta.

Oxytocin (in Labor)

A hormone released by the posterior pituitary gland that drives a positive feedback loop with cervical stretching to stimulate and intensify uterine contractions.

First Stage of Labor (Cervical Dilation)

The period of labor from initial regular contractions until the cervix thins, effaces, and dilates to $10\,\text{cm}$, often accompanied by amniotic sac rupture.

Second Stage of Labor (Delivery of the Infant)

The stage of labor extending from full cervical dilation to the birth of the baby through the pelvic canal and vagina.

Third Stage of Labor (Placental Expulsion)

The stage of labor following childbirth where continuing uterine contractions detach and expel the placenta and membranes (afterbirth) while compressing blood vessels.

Lactation

The physiological process following childbirth whereby mammary glands produce and secrete milk.

Colostrum

A yellowish fluid secreted during the initial $2$ to $3\text{ days}$ postpartum, rich in maternal antibodies and proteins to protect the newborn gut.

Prolactin

An anterior pituitary hormone that stimulates milk production (synthesis) within the mammary glands.

Neonatal Period

The first four weeks after birth, during which the newborn (neonate) makes major physiological adjustments to air breathing and thermoregulation.

Infancy

The postnatal period from four weeks of age to $1\text{ year}$, characterized by rapid weight gain, brain growth, tooth eruption, and early motor coordination.

Childhood

The life stage extending from age $1$ until puberty, marked by steady physical growth, cognitive development, language acquisition, and social development.

Adolescence

The life stage beginning at puberty and concluding at physical maturity, marked by reproductive hormonal surges, secondary sex characteristics, and growth spurts.