Sperm & Ovum Anatomy, Fertilization, and Prenatal Development

Flashcards covering prenatal development, from sperm and ovum anatomy to the stages of labor and lactation.

Acrosome

A cap on the head of the sperm containing digestive enzymes that help the sperm penetrate the ovum.

Sperm Mid Piece

The part of the sperm cell that contains energy-producing mitochondria.

Flagellum

The tail of the sperm used for swimming movements.

Gestation

The period ranging from conception until birth, lasting approximately $266$ days.

First trimester

The first phase of pregnancy, occurring from week $1$ through week $12$.

Second trimester

The phase of pregnancy consisting of week $13$ through week $24$.

Third trimester

The phase of pregnancy from week $25$ until birth.

Zona pellucida

A layer surrounding the plasma membrane of the ovum that acts as a strict gatekeeper, allowing only one sperm to enter.

Corona radiata

The outermost layer of the ovum that provides vital protein and is the first layer a sperm needs to penetrate.

Zygote

The cell formed when the genetic material of the ovum and sperm unite, containing $46$ chromosomes.

Pre-embryonic stage

The stage of prenatal development from fertilization through week $2$.

Embryonic stage

The stage of prenatal development from week $3$ through week $8$.

Fetal stage

The stage of prenatal development from week $9$ until birth.

Blastomeres

Two daughter cells formed by mitosis within $24$ to $36$ hours of fertilization.

Morula

A cluster of $16$ cells with a blackberry appearance resulting from mitotic division or cleavage.

Blastocyst

A fluid-filled pre-embryonic structure consisting of the trophoblast and inner cell mass.

Trophoblast

The outer layer of the blastocyst that eventually forms the placenta.

Inner cell mass

The part of the blastocyst that eventually becomes the embryo.

Ampulla

The site of fertilization within the fallopian tube.

Implantation

The process where the blastocyst attaches to the endometrium $6$ days after ovulation.

Fertilization Membrane

The thickened layer created when cortical granules release enzymes once a sperm penetrates the zona pellucida to prevent more sperm from entering.

Dizygotic twins

Also known as fraternal twins, they develop from two distinct egg-sperm combinations.

Monozygotic twins

Also known as identical twins, they form when one embryo splits into two or more separate embryos during early development.

Yolk sac

A structure that produces red blood cells until the sixth week and contributes to the formation of the digestive tract.

Embryonic disc

A flattened structure formed from the inner cell mass that gives rise to the ectoderm, mesoderm, and endoderm.

Ectoderm

The outermost germ layer that forms the epidermis, nervous system, sensory organs, and mammary glands.

Mesoderm

The middle germ layer that forms muscles, bones, the circulatory system, the lymphatic system, and the urogenital system.

Endoderm

The innermost germ layer that forms the epithelial linings of the digestive and respiratory tracts, as well as the liver and pancreas.

Amnion

A transparent sac that envelops the embryo and is filled with fluid to protect against trauma and temperature changes.

Chorion

The membrane that surrounds other membranes and eventually forms the fetal side of the placenta.

Allantois

A structure serving as the foundation for the umbilical cord that eventually becomes the urinary bladder.

Placenta

The lifeline that acts as the fetus's lungs and digestive system, forming approximately $11$ days after conception.

Umbilical Cord

The connection between the fetus and placenta containing $2$ arteries and $1$ vein.

Umbilical vein

The vessel that carries oxygenated, nutrient-rich blood from the placenta to the fetus.

Ductus venosus

A special shunt that allows blood to bypass the liver and go directly to the inferior vena cava.

Foramen ovale

An opening in the atrial septum that allows blood to go directly from the right atrium to the left atrium, bypassing the lungs.

Ductus arteriosus

A shunt that connects the pulmonary artery to the descending aorta to bypass the non-functional fetal lungs.

Umbilical arteries

The vessels that exit the fetal body to carry deoxygenated blood and waste products to the placenta.

Chorionic villi

Fingerlike projections of the chorion that penetrate the uterus to link the embryo to the placenta.

Lacunae

Sinuses in the endometrium where maternal blood pools around the chorionic villi.

HCG (Human Chorionic Gonadotropin)

A hormone secreted by the placenta that should double every day during a normal pregnancy.

Lanugo

Fine hair that covers the body of a fetus, appearing around week $20$.

Vernix caseosa

A white cheese-like substance that covers the fetal body.

Surfactant

A substance that the fetal lungs begins to produce around week $24$.

Dilation stage

The longest stage of labor involving cervical effacement and widening of the cervix.

Cervical effacement

The progressive thinning of the cervical walls during labor.

Expulsion stage

The stage of labor that begins with full dilation and ends when the baby is born.

Placental stage

The final stage of labor involving the delivery of the afterbirth.

Afterbirth

The delivered placenta, amnion, and other fetal membranes.

Prolactin

The hormone responsible for the production of milk.

Oxytocin

The hormone responsible for the secretion of milk and stimulation of uterine contractions.

Acini

Structures in the breast whose development is stimulated by progesterone.

Estrogen (Lactation role)

The hormone that stimulates the growth of ducts within the mammary glands.

Day 22

The approximate time during development when the heart begins to beat.

Fetal visibility at 8 weeks

At this point, brain waves are detectable, bone calcification begins, and arms and legs are recognizable.

Fetal status at 12 weeks

The face is well formed, gender is distinguishable, and eyes are developed but lids are fused shut.

Fetal status at 28 weeks

Eyes open and close, and the respiratory system is capable of gas exchange.

Fetal status at 32 weeks

Amount of body fat increases rapidly and rhythmic breathing movements begin.

Full term

A period defined as a $2$ week window starting at $39$ weeks gestation.

Sperm Ejaculation Volume

Approximately $300 \times 10^6$ sperm are released into the female vagina during ejaculation.