Ch. 3 Fetal Development

Mitosis

Division and multiplication of body cells.

spermatogenesis

Process of mitosis for sperm

oogenesis

Process of mitosis for ovum

Meiosis

makes unique sex cells (sperm and egg) for sexual reproduction. The new cell contains 23 chromosomes from the sperm and 23 chromosomes from the ova

Occurs when a sperm penetrates an ovum and they unite = zygote

Fertilization

Site of Fertilization

Takes place in the outer third of the fallopian tube, near the ovary

survival time of sperm ejaculated into the area of the cervix

7 days

Trisomy 18

severe genetic disorder caused by an extra copy of chromosome 18. many infants do not survive beyond the first month due to health problems (5-10% living last their first birthday

Site of implantation

After fertilization, the zygote travels to the uterus for implantation.

Chorion

Outermost extraembryonic membrane: Develops into the fetal part of the placenta

Placenta

Fetal–maternal exchange of gases, nutrients, and wastes.

Amnion

•Second thin membrane that envelops and protects embryo

Amniotic Sac

•chorion and amnion form an amniotic sac filled with fluid (bag of waters)

Volume of amniotic sac throughout pregnancy

~30 mL at 10 weeks

350 mL at 20 weeks;

700-1000 mL at 37 weeks

Functions of Amniotic

Fluid

Regulates temperature, prevents adhesion, protects from infection/injury, and allows fetal movement

Yolk Sac

Forms around day 9; produces early RBCs until the fetal liver takes over (~6 weeks), then degenerates.

Age of viability

22 weeks of gestation but requires NICU care to survive

Three Stages of Prenatal Development

•Zygote: cell formed by union of sperm and ovum

•Embryo: second to eighth week of development

•Fetus: ninth week until birth

Four hormones produced by the Placenta

•Progesterone

•Estrogen

•Human chorionic gonadotropin (hCG)

Human placental lactogen (hPL)

Role of Progesterone in pregnancy

Maintains uterine lining, reduces contractions, supports breast development, increases maternal metabolism, and stimulates fetal testosterone production.

Role of estrogen in pregnancy

Promotes uterine growth, uterine blood flow, and breast gland development.

Role of Human Chorionic Gonadotropin (hCG) during pregnancy

Keeps the corpus luteum producing estrogen and progesteroneto maintain pregnancy; detectable early and used in pregnancy tests.

Human Placental Lactogen

 (hPL)

Decreases maternal insulin sensitivity, making more glucose available to the fetus for growth.

Wharton’s jelly

Covers and cushions umbilical cord vessels

•Normal length of the umbilical cord

•55 cm (22 inches)

AVA

An easy way to remember the number and type of umbilical cord vessels is the name “AVA,” which stands for “Artery-Vein-Artery”

Fetal Circulatory Shunts

•Ductus venosus: bypasses the liver. closes functionally when cord is cut (permanently in about 1 week)

•Foramen ovale:bypasses the lungs (right atrium-left atrium). closes within 2 hours after birth (permanently by age 3 months)

Ductus arteriosus: bypasses the lungs (pulmonary artery-aorta) closes within 15 hours (permanently in about 3 weeks)

Monozygotic twins

from a single fertilized ovum (identical)

Dizygotic twins

•from two separate fertilized ovum (fraternal)

How many vessels in the umbilical cord and what do they do?

AVA

1. Umbilical vein → carries oxygen-rich, nutrient-rich blood from the placenta TO the fetus.

2. Umbilical arteries → carry oxygen-poor blood and waste products from AWAY from the fetus the placenta.

Vein = TO baby

Arteries = AWAY from baby

Explain fetal circulation pathway

polyhydramnios

a pregnancy condition defined by an excessive accumulation of amniotic fluid surrounding the baby +1000ml