Fertilization to Birth

Learning outcomes

• Define fertilization• Know the three stages of pregnancy• Explain what happens in each stage• Know what stem cells are and where they

come from

Fertilization (Post Coitus)

• Out of millions, only about 100 sperm make it as far as the oviduct

• They surround the egg and try to penetrate the egg’s outer coating

• As soon as one sperm penetrates the egg the egg releases a protein that prevents other sperm from penetrating

• The sperm’s nucleus fuses with the egg’s nucleus to produce the zygote.

The nine months of pregnancy are divided into three trimesters (three-month periods) for convenience.

The first ‘trimester’

• The zygote begins dividing in the oviduct and is called an embryo when it implants into the uterus by the end of the first week. • Hormones are secreted that prevent

menstruation from happening.

The first ‘trimester’

• A sac forms around the embryo and is filled with amniotic fluid, which supports, protects, and maintains a warm environment for the embryo until birth. When a mother’s water breaks during birth, it is this amniotic fluid that is released.

The first ‘trimester’

• By the fourth week, the brain and nervous system are developing, and the heart is beating.• The beginnings of eyes, ears, and

nose are noticeable at the end of week five.

The first trimester…

• Week 8 the embryo is the size of a bean and has the beginnings of all the organs and is called a fetus.

The Placenta

• The fetus receives nutrition from the mother through the placenta.

• The placenta contains blood vessels from the mother and blood vessels from the fetus. Nutrients and oxygen diffuse from the mother’s blood into the fetus’s blood. Wastes from the fetus diffuse into the mother’s blood.

The first trimester con’t

• Month 3 muscles and bones are forming. The fetus can flex arm and leg muscles, and may hiccup. The heart is beating and blood is circulating. Sex organs are forming, and gender can be determined.

The first trimester

• Signs of pregnancy: no menstruation, enlarged breasts, and sometimes nausea

• The fetus is most susceptible to birth defects during the first trimester.

The second trimester

• time of intense growth for the fetus. • Movement of the fetus can be felt by the

mother.• At 24 weeks, the fetus resembles a tiny infant.

Fingers and toes have elongated. Facial features are more developed, and eyelashes are visible.

The third trimester

• The fetus puts on most of its mass • All organ systems are ‘online’• The fetus has sleeping and waking patterns

and reacts to external stimuli• The brain is developing rapidly

3rd Trimester

• Bones are developed but still soft• Lungs continue to mature right up to birth• The fetus turns so that the head is pointing

down in preparation for birth

Labour

• Begins when the uterus has regular contractions

Stem cells and differentiation

• Differentiation = the process of growing from unspecialized cells into many different specialized cells

• Stem cells are unspecialized cells that have the ability to reproduce themselves.

• When stem cells undergo cell division, the daughter cells will either remain stem cells or begin differentiating into one of many different types of specialized cells.

Using stem cells for medicine

• stem cells can be used to grow new new tissue in isolation… For example, to grow new heart muscle cells to replace cells that have been damaged in heart attacks.

• In order to do research, however, scientists need a source of stem cells.

• Stem cells can be found in…– bone marrow– in the blood in the umbilical cord of a newborn– extra embryos produced after in vitro fertilization.