UNIT 2 – BIOLOGICAL WORLD 5. Birth


Birth happens in three stages: 1. Labour 2. Delivery of the baby 3. Delivery of the placenta


1. Labour


During labour, the muscles in the uterus wall start contracting. The cervix also widens.


The amniotic sac bursts and the amniotic fluid escapes through the vagina (known as ‘waters breaking’).


2. Delivery of the baby


The contractions push the baby from the uterus, through the cervix and out of the vagina.


The umbilical cord is clamped and cut to close off blood vessels. The stump soon falls off, forming the baby’s belly button.


:Fig. 12.8 Delivery of the baby


11. Ideally, a baby is born headfirst. Why do you think that is? ?


TEST TUBE 3. Delivery of the placenta


After the baby has been delivered, the placenta comes away from the uterus and passes out of the body as the afterbirth.


Contraception


Contraception is the prevention of pregnancy using artificial or natural methods.


Artificial contraception Artificial contraception is the use of mechanical, chemical or surgical methods to prevent pregnancy. The following table outlines a number of artificial contraceptive methods:


Method Mechanical Condom A thin rubber sheath covers the penis to prevent semen entering the vagina.


Intrauterine device (IUD) A plastic and copper device is inserted in the uterus to prevent implantation for 5–10 years.


Chemical Contraceptive pill Implant


Tubal ligation Vasectomy


122 Elements of Science


Tablets containing hormones are taken regularly by a female to prevent ovulation.


A plastic rod is inserted in the upper arm of the female and releases a hormone that prevents ovulation and/or implantation for up to 3 years.


Surgical The fallopian tubes are cut and sealed to prevent fertilisation. The sperm ducts are cut or tied off to prevent the presence of sperm in semen.


:Fig. 12.9 The contraceptive pill How it works


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