Transcript Prenatal Development

Prenatal
Development
Chapter 8
Prenatal Development…
• The process by which a baby-to-be grows
inside the mother
• The process usually takes about 9 months for
a full-term pregnancy
• Or 280 days
• Or 40 weeks
Timeline of Pregnancy
• The timeline of pregnancy can be divided into
3 trimesters
• Trimester3 month time period
First Trimester
• Begins at the moment of Conception
• This is the first 3 months of pregnancy
• The baby-to-be has 3 names during this
period…the zygote, the embryo, the fetus
The Zygote
• A fertilized egg is a single cell, but it soon
begins to divide
• After just a few days, the zygote grows to
about 500 living cells that form a tiny ball
• The zygote travels thru the fallopian tube to
the uterus where it implants itself in the lining
of that organ
The Embryo
• It is an embryo from the time of implantation
into the uterus until the 8th week of pregnancy
• During this time, the cells multiply rapidly
• In a few weeks after implantation, the embryo
is the size of the head of a pin
The Embryo
• As the cells multiply, they begin to take on
different functions…3 layers of cells form that will
eventually develop into all the structures of the
human body
• Ectoderm outer layer of cells…becomes skin,
hair, nails, also forms nervous system, brain,
spinal cord, and nerves
• Mesoderm middle layer…becomes bones,
muscles, blood vessels, some internal organs
• Endoderm internal cell layer…becomes internal
organs such as stomach, liver, and lungs
Embryo
• Midway thru the first trimester, the embryo has grown
to the size of a raisin.
• 2 weeks later it is the size of a grape.
• Then the eyes and inner ears begin to form on the
sides of the embryos head, and the mouth and nostrils
begin as small openings. Next the eyelids begin to
form and the nose, upper lip, and outer ears begin to
take shape. The heart begins to pump blood cells,
although the heartbeat cannot yet be heard. The
digestive and respiratory systems start to form, and
buds that will become arms and legs emerge.
The Fetus
• Fetus name from the beginning of the 9th week until
birth
• At the beginning of the fetal stage, major organs are
present, but still forming
• Heartbeat flutters rapidly and can be heard using a
special instrument
• Bone begin to form taking on a skeletal shape
• Skull and jaws begin to harden
• Muscles begin to develop, as do tissues that connect
muscles to bones
• Arms and legs strengthen
• A very thin skin covers the fetus
The Fetus
• At then end of the 1st trimester, the fetus is about
3 inches long and typically weighs 1 ounce.
• All the fetus’s major organs are growing and
developing
– Intestines move from the umbilical cord to the
abdomen
– Ears and eyes move closer to their final positions
– Liver begins to produce bile
– Kidneys produce urine
– Fetus can open and close its mouth and fists, but
pregnant woman cannot feel these movements
Support System
• As the baby develops, so do structures that will protect
and nourish the developing baby
– Amniotic Fluid fills the sac that surrounds the
developing baby…it cushions the developing baby from
outside pressures
– Placenta tissue, shaped somewhat like a pancake, is
attached to the uterine wall and contains a rich network of
blood vessels
– Umbilical Cord connects the baby to the placenta
– For the Duration of pregnancy, blood will flow from the
mother’s body thru the placenta and umbilical cord,
carrying oxygen and nutrients to the developing baby.
Wastes will pass from the baby thru the umbilical cord and
placenta into the mother’s body for processing and
disposal
– The placenta acts as a filter between the mother’s and
baby’s bodies
2nd Trimester
• 2nd Trimester— 4th, 5th, and 6th months of
pregnancy
• By the end of this period, the fetus will weigh
nearly 2 pounds!
• Eyebrows and lashes appear and Lanugo (aka
fine hair) begins to cover the fetus’s skin
• Fat tissue, which will later keep the newborn
warm, begins to form under the skin
2nd Trimester
• The fetus can move around and kick
• The pregnant woman usually can feel these
movements, a milestone often called, QUICKENING
• Prenatal thumb-sucking begins during the 2nd trimester
• The lungs strengthen and the fetus ‘breathes’ amniotic
fluid in and out
• The fetus swallows amniotic fluid, and nutrients in the
fluid pass thru the digestive system
• The senses—taste, touch, smell, sight, and hearing—
steadily develop
• The eyes now open and close
• The fetus begins to hear sounds including mom’s
heartbeat and other loud noises from outside mom’s
body
3rd Trimester
• 7th, 8th, and 9th months of pregnancy
• Brain and other parts of nervous system continue
to develop
• Brain scans have shown that the fetus sleeps and
may dream
• Heart and circulatory system mature
• Lungs almost fully developed by 9th month
• Fetus steadily grows and gains weight until birth
• Vital fat tissue increases all over the fetus’s body
• Fetus triples its weight
3rd Trimester
• Average birth weight 7.5 lbs.
• Head is largest part of the body, accounting for
¼ of newborn’s weight
• Bones of skull are somewhat soft and pliable
allowing the fetus to pass thru the birth canal
• During 8th month, fetus has less freedom of
movement
• During 8th month, fetus turns head downward in
preparation for a typical birth
• In 9th month, the still growing fetus settles
further down in the woman’s pelvis