11

ACCESS HEACCESS HE

Human Biology.Human Biology.

Reproduction.Reproduction.

Fertilisation.Fertilisation.

22

Fertilisation.Fertilisation.

• The ‘three day window’.– Sperm are capable of fertilising an ovum for

approximately 24 hours once inside the female genital tract.

– Ovum is ‘fertilisable’ for approximately 8 hours after ovulation.

33

Fertilisation.Fertilisation.

• Several million sperm may have been deposited inside the vagina.

• Several hundred sperm swim through the uterus and into the Fallopian tubes looking for an ovum.

• Only one sperm is required to fertilise an ovum.

• The lucky sperm penetrates the membrane of the ovum and enters inside.

44

Fertilisation.Fertilisation.

• The ovum has been fertilised within the Fallopian tube.

• Tail of the sperm breaks down, its task accomplished.

• The head (nucleus) grows.• The nucleus of the sperm and the nucleus of the

ovum fuse together thus forming one single nucleus.– Male chromosomes (23) and female chromosomes

(23) join together to make one complete cell. – This is the very first cell of a new baby and it is

called a zygote.

55

Mitosis (Cell Division).Mitosis (Cell Division).

• The zygote divides into 2, then 4, then 8, then 16 and so on.

• This process is called mitosis.

• (Gametes are produced by meiosis).

• Most cells reproduce by the process of mitosis.

• Each daughter cell has exactly the same genetic material as the parent cell.

66

Zygote – Morula – Blastocyte.Zygote – Morula – Blastocyte.

• The zygote becomes a little ball of cells.• The little ball of cells is called a morula.• After 5 days the morula becomes a multicellular

structure.• The multicellular structure is called a blastocyst.• On the 7th day after fertilisation the blastocyst

implants itself into the endometrium of the uterus.

• This process is called implantation.

77

The Embryo.The Embryo.

• By day 24 the blastocyst has formed a fluid sac.• The fluid sac is called the amniotic cavity.• The amniotic sac contains an embryo.• The embryo at this stage looks a bit like a

seahorse!• The developing baby is called an embryo until

the 8th week of pregnancy.• The endometrium and part of the blastocyst knit

together and this develops into the placenta.

88

The Placenta.The Placenta.

• The placenta is the baby’s support system.

– Nutrients and oxygen diffuse into the foetal blood from maternal blood at the placenta.

– Carbon dioxide and waste products diffuse from foetal blood into maternal blood at the placenta.

99

1010

The foetus.The foetus.

• The developing baby is called a foetus from 8weeks until birth.

• The foetus develops in the amniotic cavity.

• The fluid protects the baby from shocks and pressure.

• The fluid allows the foetus to grow independantly.

1111

1212

The Birth.The Birth.

• Giving birth is called parturition (Latin for labour).• Cervical plug of mucus protects uterine contents.• The first sign of labour is usually the ‘show’.• The ‘show’ is when the mucus plug is expelled. • When birth is imminent the membrane of the amniotic

cavity breaks down.• The anniotic fluid is released by the vagina.• ‘Breaking of the waters’ is how we refer to the release of

the amniotic fluid.• Cervix becomes dilated.• Birth usually occurs within the 40th week after fertilisation.

1313

1414

The Placenta.The Placenta.

• The placenta functions as the alimentary tract, kidneys and lungs for the foetus.

• Progesterone is necessary for the development of the placenta.

• Progesterone is essential for maintenance of the pregnancy.

• There is no direct contact between maternal and foetal bloods although they are very close.

• Diffusion is the method by which materials interchange between mother and foetus.

1515

Placenta – protective Barrier.Placenta – protective Barrier.

• The placenta is a protective barrier.

• Most micro-organisms cannot cross it.

• Unfortunately some can pass through.– Viruses such as AIDS, chicken pox,

encephalitis (inflammation of the brain), measles, poliomyelitis, and rubella.

– Alcohol and drugs pass straight through the placenta barrier.

1616

Chorion.Chorion.

• Chorion: The embryonic part of the placenta. It is a membrane that totally surrounds the embryo from implantation.

• The chorion produces chorionic gonadatrophin hormone throughout pregnancy.

• Chorion villus: Chorionic villus are finger like projections of chorion that contain the foetal blood vessels.

1717

Foetal Blood Circulation (Liver).Foetal Blood Circulation (Liver).

• The placenta acts as the alimentary tract for the foetus therefore foetal circulation bi-passes the kidneys and liver.

• Ductus Venosus: The blood vessel that bi-passes the foetal liver.

• Blood is sent straight through the liver to the inferior vena cava.

1818

Foetal Blood (Lungs).Foetal Blood (Lungs).

• The placenta acts as the lungs for the foetus therefore foetal circulation bi-passes the lungs.

• Blood flows directly from the right atrium of the heart to the left atrium through a hole in the septum called the foramen ovale (oval window).

• Blood going from the right ventricle into the pulmonary artery is diverted into the descending aorta by the ductus arteriosus thus the lungs are bi-passed.

1919

Baby’s First Breath.Baby’s First Breath.

• As soon as a baby is born the first breath causes the foramen foramen ovale and the ductus arteriosus to close.

• All blood now flows through the lungs to become oxygenated.

• All products of digestion are now taken to the liver to be processed.

2020

Conclusion.Conclusion.

• We only have three days in which to become fertilised: The ‘three day window’.

• The ovum becomes fertilised in the Fallopian tubes.• The fertilised ovum is called a zygote.• Zygote divides by mitosis. • Meiosis (reduction division) forms gametes.• Zygote becomes a morula (little ball of cells).• Morula becomes a blastocyst after 5 days.• Blasocyst implants into endometrium on 7th day.• Blastocyst forms amniotic sac containing embryo.• The developing baby is called an embryo until the 8th week of

pregnancy.• Endometrium and part of blasocyst knit together to form placenta.• Placenta is baby’s support system.

2121

Conclusion.Conclusion.

• First sign of going into labour is usually the ‘show’; expelling of cervical mucus plug.

• Then the ‘breaking of the waters’; release of amniotic fluid.• Cervix becomes dilated.• Birth usually takes place within the 40th week after fertilisation.• Placenta is the alimentary tract, kidneys and lungs for the foetus.• Placenta is a protective barrier for foetus.• Some micro-organisms, alcohol and drugs can pass.• Progesterone is essential for pregnancy.• Chorion: membrane completely surrounding foetus.• Chorionic villus: Contain foetal blood vessels.• Foetal lungs, liver and kidneys are bi-passed.• As soon as baby is born, the first breath causes the bi-pass

structures to close so that all organs should be able to function.• Isn’t it all absolutely wonderful?