36.2 Human Development Before Birth: Bio 30 Nwrc

36.2 Human Development Before Birth Bio 30 NWRC

Fertilization (video) Implantation in the uterus

Ovulation Fertilization (occurs in the oviduct)

Fertilization • Only 1 sperm fertilizes the egg but 100s are needed to bombard and break down the egg’s plasma membrane – once the egg’s membrane is weakened and a sperm penetrates it – the egg forms a barrier which does not allow any other sperm to enter.

Early Development

Morula

From One Cell to Blastula to Blastocyst

ExtraEmbryonic Membranes

ExtraEmbryonic Membranes

Amnion:A thin, tough, membranous sac that encloses the embryo. It is filled with a fluid in which the embryo is suspended. Chlorion:The outer membrane enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta. Yolk Sac: Functions as the circulatory system of the human embryo before internal circulation begins. Allantois:It is important in the formation of the umbilical cord and placenta in mammals.

The Placenta The placenta is partially of fetal origin and partly of maternal origin The fetal portion is composed of highly specialized cells from the outermost embryonic membrane, which form projections that contain the fetal blood vessels. These projections are called chorionic villi. The maternal portion is formed by a modification of the lining of the uterus, and the fetal villi grow into the uterine lining

The umbilical cord inserts into the fetal surface. Note the vessels radiating out from the cord over the fetal surface in this normal term placenta.

The Placenta • Basically, the placenta is made up of a combination of cells from the mother and the growing baby • The mother and the fetus both have their own circulatory systems

3 Trimesters of Development • FIRST TRIMESTER At the end of 8 weeks the embryo is called a fetus. All the organ systems have begun to form by the end of the 1st trimester the fetus can move and has fingerprints.

This little boy is at 9 weeks gestational age of embryonic life. Note the thin amnionic cavity surrounding the embryo.

First Trimester

3 Trimesters of Development • Second TRIMESTER The fetus has now developed all its organs and systems and will now focus on growing in size and weight.

3 Trimesters of Development • Third TRIMESTER During the third trimester, the fetus continues to grow in size and weight. The lungs are still maturing and the fetus begins to position itself headdown.

Diagnosis in the Fetus • Ultrasound A sonogram provides images of the infant in the womb. It can be used to • Judge gestation • Measure fetal growth • Evaluate abnormalities • Reveal the sex of fetus

Diagnosis in the Fetus • Amniocentesis: A sample of amniotic fluid can be withdrawn and analyzed (fluid contains fetal cells). It is useful for • Diagnosing sex linked disorders • Chromosomal defects • Sex can also be determined

Diagnosis in the Fetus • Chorionic Villus Sampling (CVS) • Tissue is taken from membrane surrounding the fetus. Can test for: • (1) Chromosomal abnormalities. • (2) Some inherited disorders. Dominant, Recessive and X-linked patterns of inheritance. • End of 35-2

Assessment • 1. The zygote divides by mitosis and becomes a morula (solid ball of cells) The morula hollows out and becomes a blastocyst….

Assessment • 2. The barrier surrounding the egg could not be penetrated and fertilization would not occur

Assessment • 3. refer to notesthere is too much information to summarize on a slide.

Assessment • 4. During pregnancy progesterone and estrogen levels remain high preventing another menstrual period. During a menstrual period levels of progesterone and estrogen drop near the end of the cycle.