Ch. 28 Pregnancy And Human Development

cortical reaction The cortical reaction occurs upon sperm penetration of the oocyte. This prevents polyspermy.

cleavage, morula, blastocyst, gastrula The product of initial cleavage is the morula, which eventually becomes the blastocyst. The blastocyst implants and becomes the gastrula.

yolk sac: provides nutrients to developing embryo The yolk sac is the site of early blood cell formation.

ectoderm The ectoderm is the most superficial of the three primary germ layers and becomes the and CNS.

embryo Embryonic development occurs post implantation until about week 8, when the human body plan exists.

hCG Human chorionic gonadotropin (hCG) secreted by the placenta is required to maintain the corpus luteum and prevent menstruation.

the cardiovascular system The cardiovascular system has to increase its transport capabilities in order to supply the fetus with nutrients during development.

ligamentum arteriosum The ductus arteriosus becomes the ligamentum arteriosum which connects the aorta and pulmonary trunk.

heart The heart develops from the splanchnic mesoderm.

decidua basalis and chorionic villi The decidua basalis and chorionic villi form the placenta.

Sperm

female reproductive tract

approach; corona radiata

The acrosomal enzymes released from many sperm digest holes through the zona pellucida. After penetrating the corona radiata, sperm bind to ZP3 (zona protein 3) glycoprotein receptors found within the zona pellucida to trigger the acrosomal reaction. The acrosomal reaction involves release of acrosomal enzymes from the sperm to digest holes in the zona pellucida. Hundreds of sperm must release acrosomal enzymes that digest the zona pellucida and clear a path that enables the fertilizing sperm to reach the oocyte plasma membrane receptors.

They allow the contents of the sperm to enter the oocyte cytoplasm. The sperm's membrane binds to the oocyte's sperm-binding receptors. This binding causes the sperm and oocyte plasma membranes to fuse together, allowing the contents of the sperm to enter the oocyte cytoplasm.

Ca2+ levels

cortical reaction

multiple

cytoplasm

zona pellucida; sperm receptors

block of polyspermy

Capacitated sperm stream toward secondary oocyte Approach Acrosomal reaction Binding Fusion Cortical reaction Block of polyspermy Completion of meiosis II and fertilization

surfactant; alveolar collapse

a gestation period The gestation period is the 40 week period of time that includes oocyte maturation, ovulation, fertilization, and embryonic and fetal development.

conceptus (embryo, zygote, fetus) Conceptus is a general term. It covers a broader spectrum than just a single-celled fertilized egg; it includes later stages as well.

blastocyst The blastocyst implants after about seven days. It consists of a hollow ball of cells with a smaller, inner cell mass pressed to the inside wall.

placenta The decidua basalis (formed from part of the endometrium) and the chorionic villi (from the chorion) become the placenta.

amnion The amniotic fluid, found in the amnion and intimate with the embryo, protects the embryo from physical trauma and maintains a constant homeostatic temperature.

foramen ovale The foramen ovale is a direct passage through the interatrial septum, so blood may bypass the nonfunctional lungs. It closes at birth.

umbilical vein The umbilical vein takes oxygenated blood to the liver from the placenta, while the two umbilical arteries transport blood from the fetus to the placenta.

pulmonary bypass shunts, which serve to bypass the lungs The most oxygenated blood enters the right side of the heart. Normally blood from the right side of the heart is supplied to the lungs for oxygenation. Because this does not need to happen, this oxygenated blood is shunted to the left atrium or directly to the aorta.

Oxytocin stimulates the uterus to contract. Oxytocin from fetal cells, and eventually the posterior pituitary, stimulates the uterus to contract both directly and through the release of prostaglandins.

prostaglandins Prostaglandin release from the placenta in response to oxytocin serves as the trigger to begin the vigorous, rhythmic contractions of true labor.

dilation stage The dilation stage often lasts the longest, up to 12 hours or more.

-derm-

embry-

lact(i)-

sclero-

lactation

ectoderm

embryoblast

sclerotome

Although a single sperm fertilizes the egg, many others prepare the egg for its entry. Although only one sperm actually fertilizes the oocyte, hundreds of sperm must contribute the enzymes from their acrosomes to digest the holes in the egg that allow one sperm to penetrate and fertilize it.

A tightening of pelvic ligaments to help bear the extra weight of the growing fetus The hormone relaxin relaxes pelvic ligaments and the pubic symphysis, allowing the pelvis to widen in preparation for birth.

oxygen The umbilical cord is comprised of the umbilical vein and two umbilical arteries. Lending to knowledge from the cardiovascular system and a comparison of veins and arteries: Arteries take blood away from the heart and veins return blood back to the heart. Here, the umbilical vessels are in relationship to the fetus; therefore, the umbilical vein transports oxygenated and nutrient-rich blood to the fetus, and the umbilical arteries carry deoxygenated, nutrient-poor blood from the fetus to the placenta.

vascular shunt The concept of a vascular shunt is one that routes materials from one point to another, bypassing a particular area. In this case, the ductus venosus, foramen ovale, and ductus arteriosus function to bypass blood from the developing fetal liver and lungs.

ligamentum arteriosum

median umbilical ligaments

ligamentum venosum

fossa ovalis

ligamentum teres.