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PregnancyPregnancy

Passing on your DNAPassing on your DNA

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PregnancyPregnancy

• You have learned what happens in You have learned what happens in the female body if a mature egg is the female body if a mature egg is not fertilized (MENSTRUATION) – now not fertilized (MENSTRUATION) – now it is time to learn what happens if an it is time to learn what happens if an egg IS fertilizedegg IS fertilized

The Egg’s JourneyThe Egg’s Journey

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PregnancyPregnancy

• Once sperm are deposited in the Once sperm are deposited in the vagina, they move through the vagina, they move through the uterus and into the oviducts where uterus and into the oviducts where fertilization occurs – only one sperm fertilization occurs – only one sperm will fertilize the eggwill fertilize the egg

• If the nucleus of a sperm cell fuses If the nucleus of a sperm cell fuses with the nucleus of the egg cell, a with the nucleus of the egg cell, a zygote is created.zygote is created.

The Sperm’s JourneyThe Sperm’s Journey


Pregnancy Pregnancy

• The zygote continues down the oviduct The zygote continues down the oviduct toward the uterus and after 24 to 36 toward the uterus and after 24 to 36 hours, it begins the process of mitosis, hours, it begins the process of mitosis, undergoing a series of rapid cell divisionsundergoing a series of rapid cell divisions

• By the time it reaches the uterus, it has By the time it reaches the uterus, it has become a mass of cells arranged to form become a mass of cells arranged to form an almost hollow ball of cells called a an almost hollow ball of cells called a blastocystblastocyst

BlastocystBlastocyst

• The blastocyst contains a group of The blastocyst contains a group of cells called the inner cell mass which cells called the inner cell mass which forms the embryoforms the embryo

• The outer cells of the blastocyst will The outer cells of the blastocyst will eventually help form the placenta, a eventually help form the placenta, a blood-vessel rich organ that is blood-vessel rich organ that is present only during pregnancy.present only during pregnancy.

ImplantationImplantation

• The embryo now attaches itself to The embryo now attaches itself to the thickened lining of the uterus – the thickened lining of the uterus – this is called implantation and occurs this is called implantation and occurs six to ten days after fertilizationsix to ten days after fertilization

• The attached embryo produces a The attached embryo produces a hormonal signal that prevents the hormonal signal that prevents the woman from menstruating. woman from menstruating.

The First Two WeeksThe First Two Weeks


Embryo DevelopmentEmbryo Development

• During the second week of embryo During the second week of embryo development, cells begin to specialize to development, cells begin to specialize to form a gastrula, in a process called form a gastrula, in a process called gastrulation.gastrulation.

• In gastrulation, the cells of the growing In gastrulation, the cells of the growing embryo become arranged into three distinct embryo become arranged into three distinct layers called germ layers – the endoderm, layers called germ layers – the endoderm, the mesoderm, and the ectodermthe mesoderm, and the ectoderm

Embryo DevelopmentEmbryo Development

• Cells in each layer develop into Cells in each layer develop into different parts of the bodydifferent parts of the body

• The ectoderm for the skin and The ectoderm for the skin and nervous systemnervous system

• The mesoderm forms the kidneys, The mesoderm forms the kidneys, skeleton, muscles, blood vessels, and skeleton, muscles, blood vessels, and gonadsgonads

• The endoderm forms the lungs and The endoderm forms the lungs and lining of the digestive tractlining of the digestive tract

The Embryo Take ShapeThe Embryo Take Shape


Messages in the GenesMessages in the Genes


Supporting TissuesSupporting Tissues

• Between the tenth and fourteenth Between the tenth and fourteenth days of development, the outer days of development, the outer portions of the embryo develop portions of the embryo develop important tissues, the yolk sac, important tissues, the yolk sac, placenta and the amnion.placenta and the amnion.

• The yolk sac supplies nutrients to the The yolk sac supplies nutrients to the embryo for about the first two embryo for about the first two months of developmentmonths of development

Supporting TissuesSupporting Tissues

• The amnion forms a fluid-filled sac around The amnion forms a fluid-filled sac around the embryo which serves as a kind of shock the embryo which serves as a kind of shock absorber to help protect the embryoabsorber to help protect the embryo

• The placenta is the embryo’s supply line for The placenta is the embryo’s supply line for survival inside its enclosed world. It ensures survival inside its enclosed world. It ensures delivery of nutrients and oxygen to the delivery of nutrients and oxygen to the developing organism and makes sure developing organism and makes sure wastes are removed. The embryo is wastes are removed. The embryo is attached to the placenta by the umbilical attached to the placenta by the umbilical cordcord

DifferentiationDifferentiation

• Different cells become specialized to perform Different cells become specialized to perform the different tasks of various tissues and the different tasks of various tissues and organs in the bodyorgans in the body

• By the end of the forth week, the embryo is By the end of the forth week, the embryo is 500 times its original size500 times its original size

• The human gestation period is about 38 The human gestation period is about 38 weeks and can be divided into three block of weeks and can be divided into three block of time based on the formation of different time based on the formation of different tissues and organs. Each block of time tissues and organs. Each block of time (approx. three months in length) is called a (approx. three months in length) is called a trimestertrimester

Feeding the Growing FetusFeeding the Growing Fetus


First Trimester (weeks 1-12)First Trimester (weeks 1-12)

• At four weeks the limbs, eyes, and spine At four weeks the limbs, eyes, and spine begin to formbegin to form

• At eight-nine weeks the embryo forms its At eight-nine weeks the embryo forms its first bone cells – the embryo is now called first bone cells – the embryo is now called a FETUSa FETUS

• By the end of 12 weeks, all the major By the end of 12 weeks, all the major organs have begun their development – organs have begun their development – liver, stomach, brain, and heartliver, stomach, brain, and heart

• The fetus has a length of 100mmThe fetus has a length of 100mm• The sex can be identified using ultrasoundThe sex can be identified using ultrasound

Second Trimester (weeks Second Trimester (weeks 12-24)12-24)• The skeleton begins to form, the The skeleton begins to form, the

brain grows rapidly, and the nervous brain grows rapidly, and the nervous system begins to functionsystem begins to function

• The mother begins to feel movementThe mother begins to feel movement• By 24 weeks the fetus is about By 24 weeks the fetus is about

300mm long300mm long• Most organs are formed but are not Most organs are formed but are not

yet fully developed – little chance of yet fully developed – little chance of survival if born prematurelysurvival if born prematurely

Third Trimester (weeks 24-Third Trimester (weeks 24-38)38)• The fetus rapidly increases in overall size and The fetus rapidly increases in overall size and

begins to move around in its amniotic sac, begins to move around in its amniotic sac, stretching and kicking.stretching and kicking.

• Proper nutritionProper nutrition is more important than is more important than ever before, mainly for the building of vital ever before, mainly for the building of vital brain tissue.brain tissue.

• By the eighth month the fetus opens its eyesBy the eighth month the fetus opens its eyes

• By the end of the third trimester, the fetus By the end of the third trimester, the fetus has grown to an average length of 500mm has grown to an average length of 500mm and an average weight between 2700 and and an average weight between 2700 and 4100 grams4100 grams

Risk FactorsRisk Factors

• Cigarette smoke may constrict the Cigarette smoke may constrict the fetus’s blood vessels, which can prevent fetus’s blood vessels, which can prevent it from getting enough oxygen.it from getting enough oxygen.

• Alcohol can affect the function of the Alcohol can affect the function of the fetus’s brain, central nervous system, fetus’s brain, central nervous system, and physical development. (FAS) and physical development. (FAS) Alcohol can remain in the bloodstream Alcohol can remain in the bloodstream of the fetus for a longer time than in the of the fetus for a longer time than in the mother – liver can’t process the alcoholmother – liver can’t process the alcohol

Risk Factors Cont…Risk Factors Cont…

• Radiation and certain pollutants can Radiation and certain pollutants can lead to cancer or genetic defectslead to cancer or genetic defects

• Certain drugs may cause deformities Certain drugs may cause deformities in new-borns (thalidomide 1950’s)in new-borns (thalidomide 1950’s)

• The risk of genetic disorders The risk of genetic disorders increases with the age of the mother increases with the age of the mother (1 in thousands for young adults – 1 (1 in thousands for young adults – 1 in 20 for women over 45)in 20 for women over 45)

BirthBirth

• During pregnancy, high hormone During pregnancy, high hormone levels help maintain the pregnancy – a levels help maintain the pregnancy – a sharp drop in these hormones cause sharp drop in these hormones cause the muscles of the uterus to begin to the muscles of the uterus to begin to contractcontract

• This process where by the uterus This process where by the uterus contracts and the birth canal opens is contracts and the birth canal opens is called labourcalled labour

Birth – Dilation StageBirth – Dilation Stage

• Uterine contractions cause the cervix Uterine contractions cause the cervix to open, or dilateto open, or dilate

• The amnion breaks and the amniotic The amnion breaks and the amniotic fluid is released through the vaginafluid is released through the vagina

• The dilation stage lasts an average of The dilation stage lasts an average of 2 to 20 hours2 to 20 hours

Birth – Expulsion StageBirth – Expulsion Stage

• Contractions in the uterus become so Contractions in the uterus become so forceful that the baby is pushed forceful that the baby is pushed through the cervix to the birth canal. through the cervix to the birth canal.

• Duration lasts 0.5 to 2 hoursDuration lasts 0.5 to 2 hours

• As the baby move through the canal As the baby move through the canal its head rotates, making it easier for its head rotates, making it easier for its body to pass through the birth its body to pass through the birth canalcanal

Birth – Placental StageBirth – Placental Stage

• The placenta and umbillica cord are The placenta and umbillica cord are expelled from the uterusexpelled from the uterus

• Occurs 10 to 15 minutes after the Occurs 10 to 15 minutes after the baby is bornbaby is born

• The expelled placenta is called the The expelled placenta is called the after birthafter birth

BirthBirth


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Documents

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implantationthe embryo

week of embryo development

mass of cells

group of cells

digestive tractthe embryo

embryothe outer cells

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