Human Embryonic Development

From Fertilization to Birth

Every month from the age of 13 or 14 a

females body prepares itself for

fertilization.

Majority of the time fertilization does not

occur leading to menstruation…

The Menstrual Cycle

•The menstrual cycle is controlled by female sex hormones and lasts approximately 28 days, although this can vary.

•The first day of the menstrual cycle occurs on the first day of a period when the blood that has built up on the inside of the uterus flows out of the vagina.

•The bleeding can last from 2 to 7 days.

•After menstruation, hormones (leutenizing hormone) are released in the body that signal the ovary to release another egg. This is known as ovulation.

•Hormones (estrogen) signals the uterus to prepare fresh blood and nutrients that can nurture a new zygote in case the egg is fertilized by a sperm.

The Menstrual Cycle

•If the egg is not fertilized it begins to dissolve

•As the blood is no longer needed, hormones are released that signal to the vessels in the wall of the uterus to constrict and cut off the blood supply.

•The blood is released from the vagina a month from the previous period and the cycle starts again.

Menstruation

http://www.nursingworld.org/mods/archive/mod130/cemha6.htm

Around day 14 of the menstrual cycle when the egg is traveling along the fallopian tube an egg is able to become fertilized if

sperm is present

In order for a couple in a stable loving partnership to enjoy a

sexual relationship without the risk of pregnancy there is a

variety of contraceptives on the market…

Contraception - females

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Chemical contraceptives include the birth control pill. Many work by blocking the surge of the leutenizing hormone and thus prevent ovulation.

Birth control patches release a combination of estrogen and progesterone that also prevents ovulation.

Contraception - females

An IUD (inter uterine device) sits inside the uterus and prevents the fertilized egg from implanting in the uterus

The female condom provides a physical barrier to sperm preventing them from entering the uterus during ejaculation

http://www.pennhealth.com/health_info/Surgery/tuballigation_2.html

http://www.nlm.nih.gov/medlineplus/ency/imagepages/17063.htm

Tubal ligation is an option for women who do not want any more children

Contraception - Male

http://www.mmhc-online.com/articles/vasectomy_reversal.html

A condom provides a physical barrier that prevents the sperm from entering the vagina/uterus when the penis is inside the vagina during ejaculation.

For a male that does not want to have children a vasectomy is a reliable option.

FertilizationWhen the egg is fertilized after ovulation the menstrual blood is used to nurture the zygote and is not lost during a period.

Fertilization

If the sperm is X then:

X(ovum) + X(sperm) = XX (female)

If the sperm is Y then:

X(ovum) + Y(sperm) = XY (male)

When the zygote is formed, the ovum always donates the X chromosome and the sperm can donate either an X or a Y chromosome.

So, at fertilization...

Pregnancy Tests

•When a woman is about two weeks pregnant the levels of the ‘pregnancy hormone’ human chorionic gonadotropin – hCG – can be detected in her urine. The test highly accurate is positive if the stick turn a certain colour.

•Blood tests that can detect the hCG hormone are a little more sensitive and can be given at 6-8 days after fertilization.

From fertilized cell to embryo

4 cell embryo

8 cell embryo

blastocyst

An artists impression

Outside cells become the placenta

Inner circle of cells become the fetus

From fertilized cell to embryo

http://www.nature.com/news/2002/020624/images/embryo_160.jpg

A fetus only a few weeks old without its placenta

The fetus is inside the amniotic sac that is attached to the chorion that will eventually become the placenta

UltrasoundSound waves are used to form an image of the fetus. Major abnormalities and the sex of the child can be identified using the un-invasive procedure

Can you see the babies head and body?

CVS

http://anthro.palomar.edu/abnormal/glossary.htm

•A CVS (chorionic villus sample) is taken during the first trimester (first 13 weeks)

•A CVS has the same genetic material as the fetus and can be used to detect genetic anomalies such as Trisomy 21 (Down syndrome)

Amniocentesis

http://anthro.palomar.edu/abnormal/glossary.htm

•An amniocentesis is a procedure that takes a few mLs of amniotic fluid from around the baby.

•A few of the babies cells can be isolated from the fluid and grown in the laboratory and be tested for the same reasons as a CVS

•Amniocentesis carries a small risk of inducing a miscarriage

Amniocentesis

http://www.leighday.co.uk/doc.asp?doc=299&CAT=972

http://www.nelh.nhs.uk/screening/dssp/procedures.htm

Term Baby

http://www.brandianestesia.it/placenta.html

The Amnotic Sac

Placenta

Amniotic sac

Note: this amniotic sac has been removed from the placenta in order to show it on its own.

The Placenta

The placenta nurtures the growing fetus by providing nutrients and oxygen to every cell. Fetal waste is also removed via the placenta. The mothers blood floods the placenta. Nutrients and oxygen diffuse across the uterus/placenta barrier and are carried to the fetus via the umbilical cord.

http://www.nurseminerva.co.uk/placenta.htm

The PlacentaThe smooth side of the placenta shows the amniotic sac which is next to the fetus. You can see the blood vessels that extract the nutrients from the placenta and lead to the baby via the umbilical cord.

The Birth

This x-ray shows how the skull of the baby fits through the pelvis of its mother during birth.

Umbilical Cord

After the birth of the baby the umbilical cord is cut as the baby is now able to breath and feed independently of its mother.

The Future – Reproductive Technologies

IVF, cloning, ecto-pregnancy, male pill…