Fertilization, Pregnancy, & Birth

What is fertilization?

The fusion of male and female gametes in the female reproductive tract to form a zygote.

Where must the oocyte be located for fertilization to occur?

In the fallopian tube.

What must occur before a sperm can fertilize the oocyte?

Capacitation.

What is capacitation?

Effects on the sperm flagellum that increase motility and removal/destabilization of proteins around the acrosomal region to enhance penetration ability.

What happens to sperm-binding receptors during capacitation?

They are redistributed in the female reproductive tract.

What is the first step of fertilization?

The sperm burrows through the corona radiata to reach the zona pellucida.

What triggers the acrosomal reaction?

Binding of the sperm to the zona pellucida.

What is the acrosomal reaction?

The release of hydrolytic enzymes from the acrosome.

How do acrosomal enzymes aid fertilization?

They digest a tunnel through the zona pellucida, allowing sperm to reach the ovum.

What causes the sperm to traverse the zona pellucida?

The digestive enzymes plus the propulsive force of the flagellum.

What happens after the sperm reaches the ovum's surface?

The plasma membranes of the sperm and egg fuse.

What does membrane fusion trigger in the oocyte?

Oocyte activation and completion of meiosis.

What enters the ovum after membrane fusion?

The sperm's pronucleus (n).

What forms when the sperm and egg pronuclei join?

The zygote nucleus (2n).

What event prevents polyspermy?

Release of cortical granules after sperm-egg membrane fusion.

How do cortical granules prevent polyspermy?

They modify the zona pellucida to make it refractory to additional sperm penetration.

What is the germinal stage?

The stage beginning at conception and lasting through blastocyst development.

What is the embryonic stage?

The stage when the blastocyst develops distinct human characteristics and becomes an embryo.

What is the fetal stage?

The stage that begins around 9 weeks and lasts until birth.

What happens on day 0 after fertilization?

First cleavage occurs.

What is the embryo at the 2-cell stage called?

Blastomeres.

What occurs on day 2 of development?

The 4-cell stage forms.

What is formed on day 3 of development?

The early morula.

What occurs on day 4 of development?

The advanced morula forms, still inside the zona pellucida.

What forms by day 6 of development?

The blastocyst.

What is gestation?

The period from fertilization to birth.

What is pregnancy?

The period after implantation has been completed.

Why is gestation different from pregnancy?

Because early pre-implantation embryonic loss is common.

What do trophoblasts develop into?

The fetal portion of the placenta.

What is the inner cell mass?

The part of the blastocyst that becomes the embryo.

When is a woman considered not pregnant, even though the "pregnancy clock" starts?

During the first two weeks after the last menstrual period.

What forms during early first-trimester fetal development?

The amniotic sac, umbilical cord, and placenta.

What is the function of the amniotic sac?

A fluid-filled sac that protects the embryo, regulates temperature, and initially contains maternal plasma.

What is the function of the umbilical cord?

Connects the fetus to the placenta.

What is the placenta?

A temporary organ that delivers oxygen and nutrients to the fetus and removes waste.

When are all major body organs and systems forming?

During the first trimester.

When is the fetus most vulnerable to teratogens like alcohol, drugs, medications, and illnesses?

During the first trimester.

When do all major organs and systems finish forming in the fetus?

During the 2nd trimester.

What fetal movements develop in the 2nd trimester?

Kicking, general movement, and reflexes like swallowing and suckling.

What sensory abilities begin in the 2nd trimester?

The fetus can respond to stimuli, hear sounds, and eyelids begin to open.

What physical growth occurs in the 2nd trimester?

Rapid growth and fat accumulation.

When may a fetus survive with intensive care?

At the end of 24 weeks.

What occurs in the 3rd trimester regarding fetal size?

The fetus continues to grow in size and weight.

Which organs continue maturing during the 3rd trimester?

The lungs, kidneys, and brain.

Why do skull bones remain soft before birth?

To allow easier passage through the birth canal.

What position does the fetus move into during the 3rd trimester?

Head-down position.

What is vernix caseosa?

A creamy, protective coating covering the fetus's skin.

What is unique about the placenta as an organ?

It is transient—it grows during pregnancy then is expelled after birth.

What is placentophagy?

The eating of the placenta after birth; common in mammals but rarely practiced by humans and camels.

What major functions does the placenta perform?

Endocrine functions, gas exchange (like lungs), detoxification (like liver), water balance (like kidneys), and hematopoiesis (produces RBCs).

Are maternal and fetal blood ever in direct contact?

No, they are never in direct contact.

Where does exchange of nutrients, oxygen, and waste occur between mother and fetus?

In the placenta.

Why does fetal hemoglobin have a higher affinity for oxygen?

To pull oxygen off maternal hemoglobin.

What do the umbilical arteries carry?

Deoxygenated blood from the fetus to the placenta.

What does the umbilical vein carry?

Oxygenated blood back to the fetus.

What hormone does the placenta produce that maintains the corpus luteum?

Human chorionic gonadotropin (hCG).

What symptoms can hCG contribute to?

Extreme fatigue and nausea.

What does human placental lactogen (hPL) do to maternal glucose metabolism?

It dulls the maternal insulin response, increasing glucose availability for the fetus.

What maternal condition can hPL increase the risk of?

Gestational diabetes.

What is the role of relaxin during pregnancy?

It increases laxity of cartilage and ligaments to aid delivery, making the mother more vulnerable to falls.

What are the effects of placental estrogens?

They promote endometrial growth, support breast tissue development for lactation, and make the mother hypercoagulable.

What does progesterone do during pregnancy?

It maintains endometrial growth and relaxes smooth muscle, affecting digestion and bladder function.

What respiratory changes occur during pregnancy?

The growing fetus pushes against the lungs.

What cardiovascular changes occur during pregnancy?

Blood volume increases.

How do the breasts change during pregnancy?

They enlarge and become tender.

Why do heartburn and constipation occur during pregnancy?

Relaxation of smooth muscles in the gastrointestinal tract.

Why does frequent urination occur during pregnancy?

Increased pressure on the bladder.

What causes darkening of the skin (areola, linea nigra) during pregnancy?

Increased melanocyte-stimulating hormone (MSH).

Why do joints loosen during pregnancy?

Relaxin causes loosening of joints and postural changes.

What metabolic impacts occur during pregnancy?

Weight gain and decreased insulin sensitivity due to hPL.

What endocrine changes occur during pregnancy?

Changes in levels of hCG, hPL, estrogen, progesterone, oxytocin, and other hormones.

What is parturition?

The process of delivering a fully developed baby from the womb.

Is the exact trigger for labor known?

No, it is still unclear.

What does oxytocin (OXT) do during labor?

It prompts uterine contractions and cervical stretching increases oxytocin in a positive feedback loop.

What is the role of prolactin (PRL)?

It stimulates milk production.

What role does oxytocin play in breastfeeding?

It is necessary for the milk ejection ("let-down") reflex.