Pregnancy

Passing on your DNA ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

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

The Egg’s Journey ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

Pregnancy Once sperm are deposited in the vagina, they move through the uterus and into the oviducts where fertilization occurs – only one sperm will fertilize the egg Once sperm are deposited in the vagina, they move through the uterus and into the oviducts where fertilization occurs – only one sperm will fertilize the egg If the nucleus of a sperm cell fuses with the nucleus of the egg cell, a zygote is created. If the nucleus of a sperm cell fuses with the nucleus of the egg cell, a zygote is created.

The Sperm’s Journey ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

Pregnancy The zygote continues down the oviduct toward the uterus and after 24 to 36 hours, it begins the process of mitosis, undergoing a series of rapid cell divisions The zygote continues down the oviduct toward the uterus and after 24 to 36 hours, it begins the process of mitosis, undergoing a series of rapid cell divisions By the time it reaches the uterus, it has become a mass of cells arranged to form an almost hollow ball of cells called a blastocyst By the time it reaches the uterus, it has become a mass of cells arranged to form an almost hollow ball of cells called a blastocyst

Blastocyst The blastocyst contains a group of cells called the inner cell mass which forms the embryo The blastocyst contains a group of cells called the inner cell mass which forms the embryo The outer cells of the blastocyst will eventually help form the placenta, a blood-vessel rich organ that is present only during pregnancy. The outer cells of the blastocyst will eventually help form the placenta, a blood-vessel rich organ that is present only during pregnancy.

Implantation The embryo now attaches itself to the thickened lining of the uterus – this is called implantation and occurs six to ten days after fertilization The embryo now attaches itself to the thickened lining of the uterus – this is called implantation and occurs six to ten days after fertilization The attached embryo produces a hormonal signal that prevents the woman from menstruating. The attached embryo produces a hormonal signal that prevents the woman from menstruating.

The First Two Weeks ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

Embryo Development During the second week of embryo development, cells begin to specialize to form a gastrula, in a process called gastrulation. During the second week of embryo development, cells begin to specialize to form a gastrula, in a process called gastrulation. In gastrulation, the cells of the growing embryo become arranged into three distinct layers called germ layers – the endoderm, the mesoderm, and the ectoderm In gastrulation, the cells of the growing embryo become arranged into three distinct layers called germ layers – the endoderm, the mesoderm, and the ectoderm

Embryo Development Cells in each layer develop into different parts of the body Cells in each layer develop into different parts of the body The ectoderm for the skin and nervous system The ectoderm for the skin and nervous system The mesoderm forms the kidneys, skeleton, muscles, blood vessels, and gonads The mesoderm forms the kidneys, skeleton, muscles, blood vessels, and gonads The endoderm forms the lungs and lining of the digestive tract The endoderm forms the lungs and lining of the digestive tract

The Embryo Take Shape ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

Messages in the Genes ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

Supporting Tissues Between the tenth and fourteenth days of development, the outer portions of the embryo develop important tissues, the yolk sac, placenta and the amnion. Between the tenth and fourteenth days of development, the outer portions of the embryo develop important tissues, the yolk sac, placenta and the amnion. The yolk sac supplies nutrients to the embryo for about the first two months of development The yolk sac supplies nutrients to the embryo for about the first two months of development

Supporting Tissues The amnion forms a fluid-filled sac around the embryo which serves as a kind of shock absorber to help protect the embryo The amnion forms a fluid-filled sac around the embryo which serves as a kind of shock absorber to help protect the embryo The placenta is the embryo’s supply line for survival inside its enclosed world. It ensures delivery of nutrients and oxygen to the developing organism and makes sure wastes are removed. The embryo is attached to the placenta by the umbilical cord The placenta is the embryo’s supply line for survival inside its enclosed world. It ensures delivery of nutrients and oxygen to the developing organism and makes sure wastes are removed. The embryo is attached to the placenta by the umbilical cord

Differentiation Different cells become specialized to perform the different tasks of various tissues and organs in the body Different cells become specialized to perform the different tasks of various tissues and organs in the body By the end of the forth week, the embryo is 500 times its original size By the end of the forth week, the embryo is 500 times its original size The human gestation period is about 38 weeks and can be divided into three block of time based on the formation of different tissues and organs. Each block of time (approx. three months in length) is called a trimester The human gestation period is about 38 weeks and can be divided into three block of time based on the formation of different tissues and organs. Each block of time (approx. three months in length) is called a trimester

Feeding the Growing Fetus ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#

First Trimester (weeks 1-12) At four weeks the limbs, eyes, and spine begin to form At four weeks the limbs, eyes, and spine begin to form At eight-nine weeks the embryo forms its first bone cells – the embryo is now called a FETUS At eight-nine weeks the embryo forms its first bone cells – the embryo is now called a FETUS By the end of 12 weeks, all the major organs have begun their development – liver, stomach, brain, and heart By the end of 12 weeks, all the major organs have begun their development – liver, stomach, brain, and heart The fetus has a length of 100mm The fetus has a length of 100mm The sex can be identified using ultrasound The sex can be identified using ultrasound

Second Trimester (weeks 12-24) The skeleton begins to form, the brain grows rapidly, and the nervous system begins to function The skeleton begins to form, the brain grows rapidly, and the nervous system begins to function The mother begins to feel movement The mother begins to feel movement By 24 weeks the fetus is about 300mm long By 24 weeks the fetus is about 300mm long Most organs are formed but are not yet fully developed – little chance of survival if born prematurely Most organs are formed but are not yet fully developed – little chance of survival if born prematurely

Third Trimester (weeks 24-38) The fetus rapidly increases in overall size and begins to move around in its amniotic sac, stretching and kicking. The fetus rapidly increases in overall size and begins to move around in its amniotic sac, stretching and kicking. Proper nutrition is more important than ever before, mainly for the building of vital brain tissue. Proper nutrition is more important than ever before, mainly for the building of vital brain tissue. By the eighth month the fetus opens its eyes By the eighth month the fetus opens its eyes By the end of the third trimester, the fetus has grown to an average length of 500mm and an average weight between 2700 and 4100 grams By the end of the third trimester, the fetus has grown to an average length of 500mm and an average weight between 2700 and 4100 grams

Risk Factors Cigarette smoke may constrict the fetus’s blood vessels, which can prevent it from getting enough oxygen. Cigarette smoke may constrict the fetus’s blood vessels, which can prevent it from getting enough oxygen. Alcohol can affect the function of the fetus’s brain, central nervous system, and physical development. (FAS) Alcohol can remain in the bloodstream of the fetus for a longer time than in the mother – liver can’t process the alcohol Alcohol can affect the function of the fetus’s brain, central nervous system, and physical development. (FAS) Alcohol can remain in the bloodstream of the fetus for a longer time than in the mother – liver can’t process the alcohol

Risk Factors Cont… Radiation and certain pollutants can lead to cancer or genetic defects Radiation and certain pollutants can lead to cancer or genetic defects Certain drugs may cause deformities in new-borns (thalidomide 1950’s) Certain drugs may cause deformities in new-borns (thalidomide 1950’s) The risk of genetic disorders increases with the age of the mother (1 in thousands for young adults – 1 in 20 for women over 45) The risk of genetic disorders increases with the age of the mother (1 in thousands for young adults – 1 in 20 for women over 45)

Birth During pregnancy, high hormone levels help maintain the pregnancy – a sharp drop in these hormones cause the muscles of the uterus to begin to contract During pregnancy, high hormone levels help maintain the pregnancy – a sharp drop in these hormones cause the muscles of the uterus to begin to contract This process where by the uterus contracts and the birth canal opens is called labour This process where by the uterus contracts and the birth canal opens is called labour

Birth – Dilation Stage Uterine contractions cause the cervix to open, or dilate Uterine contractions cause the cervix to open, or dilate The amnion breaks and the amniotic fluid is released through the vagina The amnion breaks and the amniotic fluid is released through the vagina The dilation stage lasts an average of 2 to 20 hours The dilation stage lasts an average of 2 to 20 hours

Birth – Expulsion Stage Contractions in the uterus become so forceful that the baby is pushed through the cervix to the birth canal. Contractions in the uterus become so forceful that the baby is pushed through the cervix to the birth canal. Duration lasts 0.5 to 2 hours Duration lasts 0.5 to 2 hours As the baby move through the canal its head rotates, making it easier for its body to pass through the birth canal As the baby move through the canal its head rotates, making it easier for its body to pass through the birth canal

Birth – Placental Stage The placenta and umbillica cord are expelled from the uterus The placenta and umbillica cord are expelled from the uterus Occurs 10 to 15 minutes after the baby is born Occurs 10 to 15 minutes after the baby is born The expelled placenta is called the after birth The expelled placenta is called the after birth

Birth ogram_adv.html# ogram_adv.html# ogram_adv.html# ogram_adv.html#