Human Reproduction - Weebly

Human ReproductionPregnancy and Birth

Junior Science

Lesson Objectives• Understand the following in relation to

human reproduction:– know the stages of a human pregnancy

– Give the function of the placenta, amniotic fluid and umbilical cord.

– List three things that happen before, during and after birth.

Fertilisation• Fertilisation usually happens in the fallopian tube• A fertilised egg – zygote – undergoes cell division to

form the embryo and moves down into the uterus.

• Implantation is the attachment of the embryo to the lining of the uterus.

Pregnancy

• The fertilised embryo attaches to the wall of the uterus and develops within the womb into a Foetus.

• The foetus becomes surrounded by a membrane called Amnion, which fills with a fluid.

• The foetus develops inside this protective sac filled with Amniotic Fluid

• It receives food and oxygen via a blood supply in the Placenta.

Amnion and Amniotic Fluid

• Amnion– Membrane surrounding baby

– Contains amniotic fluid

– Breaks just before birth = “water broke”

• Amniotic Fluid– The “water” – surrounding baby

– Buoyant cradle for baby• Protection

• Free movement

The Placenta

The Umbilical cord attached

to the baby’s navel is connected to the placenta.

The Placenta allows food and

oxygen to pass from the

mother’s blood to the baby’s

blood, and waste products (CO2, salts, urea) to leave the baby’s

blood.Mother and baby’s blood do not circulate together, materials pass using diffusion.

Labour and BirthA full term pregnancy is 40 weeks, when the baby is fully developed, the following happens:

1. Around 30 weeks the baby flips upside down so its head is at the cervix

2. 1-2 days before birth the brain releases a chemical which causes the muscles of the uterus to begin to contract, this also opens the cervix

3. A few hours before birth - The sac of protective fluid breaks open.

4. The muscles of the uterus / womb contract very strongly to push the baby out

5. After the baby is born, the placenta is also pushed out of the womb

6. The umbilical cord between baby and placenta is cut.

Breastfeeding

• This is the most nutritious option for baby– Milk changes as baby grows

• Antibodies from mom create immunity for baby

• Studies have shown correlation between breastfeeding and higher intelligence in baby.

• Bond w/baby is stronger

Twins/Multiple Births

• Two types

– Monozygotic

• From one egg

• Identical

– Dizygotic

• From two eggs

• Fraternal

• Not identical

Identical twins• One zygote

• Splits in 2

• No one knows why!

• Completely random = does NOT run in families

• Same exact DNA

• Nature’s clones

Fraternal Twins

• 2 separate eggs get fertilized with 2 different sperm cells

• More than one egg got released during ovulation

• Siblings– Can be sisters

– Brothers

– Brother and sister

• Tends to run in families

Conjoined Twins• Used to be called “Siamese” twins

• First well known case was in Siam

• Identical twins that never completely separated during development

• Sometimes can be separated, depending on what is shared.