Pregnancy: From Fertilization to Birth BC Science Probe 9 Section 4.3 Pages

Pregnancy So females produce eggs and males produce sperm… but how does the rest happen?

Fertilization During sexual intercourse, millions of sperm are released into the vagina. – Most will die on the way – Only about 100 will actually make it to the oviduct where they can try to penetrate the egg.

Fertilization To prevent more than one sperm getting in, the egg releases a special protein the prevents the others as soon as one gets through. Then the single sperm’s nucleus fuses with the egg’s nucleus to produce a zygote. This is the beginning of a (approximately) 9- month pregnancy.

First Trimester Fertilization – end of month 3. The zygote begins dividing in the oviduct and is called an embryo when it implants in the uterus but the end of week 1. Hormones are secreted that prevent menstruation from happening.

First Trimester After implantation, a sac forms around the embryo and is filled with amniotic fluid. – Supports – Protects – Keeps warm

First Trimester By week 4 – The brain and nervous system are developing. – The heart is beating – The embryo is now 500 times bigger than the zygote (it’s now about 5mm long)

First Trimester Week 5 – Eyes nose and ears start to show up. – Limb buds and tail are visible. The tail will reduce by the time the baby is born and all that will be left is the tail bone.

First Trimester Week 8 – The embryo has the beginnings of all the organs and is now called a fetus. – It looks human, but is about the size of a lima bean.

First Trimester The fetus gets its nutrition from the mother through the placenta. – It has blood vessels from both the mother and the baby – Nutrients and oxygen are brought to the baby from the mother. – Wastes are taken away from the baby. – The placenta is connected to the fetus by the umbilical cord.

First Trimester Month 3 – Muscles and bones forming – Fetus can flex and may hiccup – Heart is beating – Sex organs are forming – About 12 cm long and 50 g

First Trimester Signs of pregnancy in the first trimester: – No menstruation – Enlarged breasts – Nausea – Hormones in a blood test – Very little weight gain

Second Trimester The fetus will be about 30 cm long by the end of the 6 th month. It grows a lot during the second trimester The fetus will be able to kick

Second Trimester Week 24 – The fetus looks like a baby, but still tiny – Fingers and toes can be seen – Eyelashes have developed – The fetus is covered in fine hair

Third Trimester Most of the mass gets put on in the last three months. Organ systems are functioning. The fetus sleeps and wakes and reacts to the outside world.

Third Trimester Brain is developing rapidly. Bones are developed but still soft. Eyelids are open. Fetal hair will disappear in the last month.

Third Trimester By 37 weeks, the fetus is considered full-term and ready to be born.

Birth Controlled by hormones, the muscles in the mother’s uterus contract regularly (labour) to get ready to push the baby out. This happens approximately 9 months after fertilization.

Birth The cervix begins to dilate. The membrane surrounding the baby is forced into the vagina (now called the birth canal).

Birth The amniotic membrane breaks and amniotic fluid lubricates the canal. The is called “water breaking”.

Birth Once the cervix has widened to 10 cm, uterine contractions push the baby’s head into the birth canal. The baby’s head is followed by the rest of the body.

Birth When the head and shoulders are free, the rest of the baby slips out and the baby is born! A while later that placenta is pushed out also. Once the baby is breathing on her own, the umbilical cord is cut and tied. (Your belly button is your umbilical cord scar.)

Stem Cells and Differentiation The DNA in the zygote has all of the instructions to make all of the specialized cells in a body. – This is called differentiation when unspecialized cells become specialized.

Stem Cells and Differentiation Stem cells are unspecialized cells that can reproduce themselves. When these cells undergo cell division, the daughter cells either remain stem cells, or begin differentiating.

Stem Cells and Differentiation As the fetus grows and develops, the stem cells lose their ability to differentiate into all types of tissues. Only certain tissues keep making stem cells and even then, they can only form into different types of that tissue. – For example: the stem cells found in bone marrow can differentiate into different types of blood cells.

Stem Cells and Differentiation Stem cells are continually being researched to develop new technologies. As a source for stem cells for research, the blood from the umbilical cord of a newborn can be used.

Twins Fraternal Twins – Two eggs get released at the same time. Usually one from each ovary. – Both eggs get fertilized. – Each zygote develops its own placenta. – They have the same birthday, but are as similar or different as any brothers or sisters.

Twins Identical Twins – Come from one fertilized egg. – The egg splits at the zygote or early embryo stage. – They share the same placenta. – These twins have the same DNA because they came from the same egg and sperm.