Download UNIT 2: PRENATAL DEVELOPMENT

UNIT 2: PRENATAL DEVELOPMENT
CH. 4: PREGNANCY
Pregnancy is a process through which a new human prepares to enter the world.
CONCEPTION
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A cell is the smallest unit of life that is able to reproduce itself.
• Life begins with the joining of two separate cells-one from the male and one
from the female
• These cells involved in reproduction are called germ cells
§ Male germ cell: Sperm
§ Female germ cell: Ovum, or egg
•
Joining of the two germ cells is called conception, which is when the ovum and
sperm combine to form a single cell called a zygote, also called a fertilized egg.
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How do these two types of germ cells form and unite to create a new life?
• Ovum are produced and stored by the women’s ovaries
• During the menstrual cycle, ovulation occurs
• This is when an ovary releases an ovum
• When the egg (ovum) us released, it travels towards the fallopian tube
• These are two hollow tubes that extend from either side of the uterus,
which is the organ in which the baby develops and is protected until birth
• Once inside the fallopian tube, the ovum moves very slowly through the
tube. Here, the ovum is ready and available to be joined by sperm.
• Conception usually happens when the ovum is less than one-third of the
way down the fallopian tube. After this point, conception is less likely
because the ovum typically lives 24 hours after ovulation.
• When a sperm successfully enters the ovum, this is called fertilization
§ Conception has occurred and the zygote begins to form
GENETIC FACTORS AND THE UNBORN BABY
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Genetic factors are the traits passed through the genes
• Parents genes combine to make a blueprint for the unborn child’s growth and
development
• This is also called a genome and guides growth and development as the
baby changes from a zygote to a baby
• Heredity
• The genetic code is stored in DNA. This is found in chromosomes, or
threadlike structures that carry genes in living cells.
• Chromosomes and Genes
• Each human baby receives a total of 46 chromosomes, which form 23 pairs.
Half of these are from the mother, half are from the father.
• Each chromosome contains 20,000 genes, which determine a person’s
individual traits.
GENETIC FACTORS AND THE UNBORN BABY
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Dominant and Recessive Traits
• The genes from each parent work together to determine the appearance of each trait in a child
• Dominant traits are those that always show in a person even if only one gene of the pair is
inherited for that trait
• Recessive traits typically do not show in a person unless both genes for the trait are inherited
from each parent. Most often, it takes to recessive genes for a recessive trait to show.
• A person who inherits only one recessive gene for a trait becomes a carrier of that trait,
which makes it possible to show up in later generations.
• Sex Chromosomes
• Of the 23 pairs of chromosomes, 22 of them are alike in both males and females. The 23rd
pair is different.
• This pair is called the sex chromosomes
• FEMALES have a chromosome pair called XX
MALES have a chromosome pair called XY
• All mother’s eggs (ovum) carry the X chromosome
• All males sperm cell will carry either an X or Y chromosome.
• The Sperm determines the sex of the child.
MULTIPLE PREGNANCY
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Sometimes, two or more babies develop in the same pregnancy, called a multiple
pregnancy
• These are far less common than single pregnancies
MULTIPLE PREGNANCY
•
Fraternal births
• The most common multiple pregnancy is caused when multiple babies develop from two
or more ovum, each fertilized by different sperm which means each child has a different
genetic makeup
• Children born in these multiple births are called fraternal children
• These children may or may not be the same gender
• Each child in a fraternal birth develops in their own chorion, which is a membrane
that surrounds the baby in the uterus.
• Identical births
• In identical births, children develop from a single ovum that was fertilized by a single
sperm
• Chances for an identical birth is much less than a fraternal birth
• In the first few days of pregnancy, the ovum splits to produce 2 or more children and it
is unknown as to why this happens.
• Babies from identical births have the same genetic makeup
• Identical children are always the same gender and share chorion
STAGES IN PRENATAL DEVELOPMENT
Many changes happen between conception and birth. The development that takes place during this time
is called prenatal development
• First Stage: The Germinal stage
• This stage lasts about two weeks after conception
• The fertilized egg (zygote) remains a single cell for about 30 hours before it starts to divide
• On the third day, it has formed into a hollow ball of 32 cells
• About 10 days after conception, the ball of cells begins to embed in the wall of the uterus and
continue to divide.
• The chorion and amnion, or amniotic sac, begins to form
• This is a fluid filled sac that surrounds the baby in the uterus.
• The placenta, an organ filled with blood vessels that nourish the baby in the uterus, begins to
develop.
• The umbilical cord, or the cord that connects the baby to the placenta, grows from the
developing child at the site of the future navel (belly button) and connects with the placenta.
STAGES IN PRENATAL DEVELOPMENT
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Second Stage: The Embryonic Stage
• The most critical stage of pregnancy because almost all body systems develop during
this stage
• This stage lasts about 6 weeks, and during this stage the baby is called an embryo
• By the end of this stage, the embryo has tiny arms, legs, fingers, toes, and a face as well
as all of the major organs such as the heart, brain, and lungs.
• Embryo does not yet have solid bones, but is supported by cartilage, which is a soft,
elastic, flexible tissue that provides structure for the body.
• Baby now receives both good and harmful substances from the mothers placenta through
the umbilical cord.
• Because the baby’s body parts are developing so quickly, passing harmful substances
to the baby can have lifelong effects.
• Mom should eat healthful foods so her baby receives needed nutrients.
• Mom should AVOID substances like alcohol, drugs, caffeine, tobacco, and X-rays that
may harm the baby
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STAGES IN PRENATAL DEVELOPMENT
Third Stage: The Fetal Stage
• When bone cells start to replace cartilage, the baby enters the fetal stage of development,
which begins about 9 weeks after conception until birth
• During this stage, the baby is known as a fetus
• By the 4th month, the fetus has usually grown enough to give the mother a pregnant look
• MILESTONES:
• In the 3rd month, parents-to-be may be able to hear their baby’s heartbeat.
• Between the 4th and 5th month a mother will begin to feel her baby move.
• The baby can also turn, swallow, and even suck its thumb.
• When the mother feels movements of the fetus, this is called quickening. This is caused by
the fetus moving its head and pushing with the hands, feet, and limbs.
• When the fetus is 7 months (or 28 weeks), most babies could survive if they were born
at this time. This is known as the age of viability.
• By this time, the baby’s brain has more control over the body systems than before.
However, most babies would still need some intensive care in the hospital.
• A baby’s chance of survival improves with each week closer to 9 months
• In most cases, the baby turns to a head down position in the 9th month to prepare for birth