Human Development – Chapter 29 Review

Question-and-Answer flashcards covering fertilization, embryonic development, implantation, placentation, fetal circulation, maternal changes, labor, neonatal transition, and lactation for Chapter 29.

What is fertilization?

The fusion of chromosomes from one sperm and one secondary oocyte to form a diploid zygote.

Why must fertilization occur within a narrow time window after ovulation?

Because the secondary oocyte remains viable and receptive to sperm penetration for only a few hours.

How many chromosomes does the zygote contain?

46 chromosomes (diploid), 23 from the sperm and 23 from the oocyte.

What is sperm capacitation?

Biochemical changes in the sperm membrane (especially the acrosome) that enable it to penetrate the corona radiata and zona pellucida.

Which sperm structure releases enzymes to digest the zona pellucida?

The acrosome.

What cellular layer immediately surrounds the ovulated secondary oocyte?

The corona radiata.

Name the glycoprotein layer just outside the oocyte plasma membrane.

Zona pellucida.

What prevents polyspermy after one sperm enters the oocyte?

Oocyte membrane depolarization and cortical reactions that harden the zona pellucida and remove sperm receptors.

Define male and female pronuclei.

Separate nuclei that contain the haploid chromosomes of the sperm and oocyte prior to their fusion.

When is fertilization considered complete?

When the male and female pronuclei merge to form one diploid nucleus.

What is aneuploidy?

Any abnormal number of chromosomes (e.g., monosomy, trisomy).

Give an example of a trisomy disorder.

Trisomy 21 (Down syndrome).

Embryonic period timeframe

From fertilization to the end of week 8.

What is a morula?

A solid ball of ~16+ cells formed about 3 days after fertilization.

Define blastocyst.

A hollowed-out structure with an inner cell mass and a fluid-filled cavity that enters the uterus around day 4–5.

Role of the trophoblast

Forms the outer wall of the blastocyst and later gives rise to the placenta.

What does the inner cell mass become?

It forms all three embryonic germ layers (ectoderm, mesoderm, endoderm).

Which hormone is secreted by the trophoblast soon after implantation?

Human chorionic gonadotropin (hCG).

Why is hCG clinically important?

It maintains the corpus luteum (thus progesterone and estrogen) and is detected by pregnancy tests.

Name the two layers derived from the trophoblast during implantation.

Cytotrophoblast and syncytiotrophoblast.

What is the amniotic cavity?

Fluid-filled space between the amnion and the embryo that cushions and protects the developing fetus.

Primary function of the yolk sac in humans

Forms the first blood cells and part of the future gut.

What structure forms the umbilical cord?

The allantois, an outpouching of the yolk sac.

List the three primary germ layers.

Ectoderm, mesoderm, endoderm.

Major derivatives of ectoderm

Nervous system and epidermis (plus some epithelial linings).

Major derivatives of mesoderm

Muscle, connective tissue, and most of the cardiovascular and skeletal systems.

Major derivatives of endoderm

Epithelia of the digestive, respiratory, and urogenital tracts and associated organs.

Define organogenesis.

Process during which the three germ layers differentiate into the body’s organs (weeks 3–8).

Foramen ovale function in fetal circulation

Shunts blood from the right atrium to the left atrium, bypassing fetal lungs.

Postnatal remnant of the foramen ovale

Fossa ovalis.

Ductus arteriosus purpose

Connects pulmonary trunk to the aorta, further diverting blood from non-functional fetal lungs.

Adult remnant of ductus arteriosus

Ligamentum arteriosum.

What is the ductus venosus?

Fetal vessel that bypasses the liver by shunting blood from the umbilical vein to the inferior vena cava.

Postnatal remnant of ductus venosus

Ligamentum venosum of the liver.

Umbilical arteries: direction and oxygen content

Carry low-oxygen blood away from the fetus to the placenta (two vessels).

Umbilical vein: direction and oxygen content

Carries oxygen-rich blood from the placenta toward the fetus (single vessel).

Why are there two umbilical arteries but one umbilical vein?

To ensure efficient removal of fetal wastes while a single, wider vein suffices to deliver oxygenated blood.

Define gastrulation.

Formation of ectoderm, mesoderm, and endoderm from the inner cell mass.

What is full-term pregnancy?

Approximately 38 weeks from fertilization (40 weeks from last menstrual period).

Braxton Hicks contractions

Irregular ‘practice’ uterine contractions that may occur before true labor.

Three stages of true labor

Dilation, expulsion, placental (afterbirth).

Hormone that stimulates uterine contractions during labor

Oxytocin.

Role of prostaglandins in labor

Soften (efface) and dilate the cervix; enhance myometrial contractions.

Define effacement.

Thinning of the cervix during the dilation stage of labor.

Average cervical dilation for delivery

Approximately 10 cm.

Why must the placenta be expelled completely?

Retained fragments can cause postpartum hemorrhage.

Primary maternal respiratory change during late pregnancy

Decreased diaphragmatic excursion leads to shallower, more frequent breaths.

Reason pregnant women often experience heartburn

Enlarged uterus displaces the stomach upward, weakening the gastro-esophageal sphincter.

Approximate healthy weight gain in pregnancy

About 11–13 kg (25–28 lb).

What is the Apgar score?

Rapid newborn assessment (color, heart rate, reflexes, muscle tone, respiration) taken at 1 and 5 minutes after birth.

Why is the first neonatal breath difficult?

High surface tension in collapsed alveoli is overcome using surfactant produced late in fetal life.

Which pituitary hormone stimulates milk production?

Prolactin (anterior pituitary).

Which hormone causes milk ejection (let-down)?

Oxytocin (posterior pituitary).

Explain positive feedback in breastfeeding.

Infant suckling → increased oxytocin & prolactin → more milk ejection & production → continued suckling.

What is colostrum?

Early, yellowish, protein-rich milk produced for the first 2–3 days; high in maternal antibodies.

When does ‘true milk’ typically come in?

Around day 3–4 postpartum, with higher water, fat, and lactose content.

Main immunological benefit of breastfeeding

Passive transfer of maternal antibodies (especially IgA) to the infant.

How does breastfeeding aid uterine involution?

Oxytocin released during nursing stimulates mild uterine contractions that shrink the uterus.

Define placenta.

Temporary organ derived from fetal trophoblast and maternal endometrium for nutrient/gas exchange and hormone secretion.

Which fetal membrane forms the chorionic villi?

Chorion (derived from trophoblast).

First fetal organ to function

The heart (begins beating around week 3–4).

What is organogenesis completion marked by?

End of week 8; embryo officially termed a fetus thereafter.

Why is folic acid important in early pregnancy?

Prevents neural tube defects by supporting ectodermal derivatives.

What metabolic change causes frequent urination in late pregnancy?

Enlarged uterus compresses the urinary bladder.

Which fetal vessels become the medial umbilical ligaments after birth?

Umbilical arteries.

What adult structure arises from the umbilical vein?

The round ligament (ligamentum teres) of the liver.