Fertilization and Development
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Transcript Fertilization and Development
Fertilization and Development
Fertilization
Fertilization of the Ovum occurs in the
oviduct
– Only one sperm allowed
• Electrical block
• Surface of ovum altered
• Binding sites for sperm
altered
Development
Nuclei of sperm and ovum fuse to form the
zygote
– 1st division (mitosis) Occurs in oviduct 30 hrs
after fertilization
Development
Cell division continues as mass moves
through the oviduct to the uterus
– a central hollow forms and fills with fluid
– Now called a blastocyst
• Cells on inside develop into embryo
• Outer cells develop into
supportive cells
– Identical Twins
Implantation
On 6th day blastocyst breaks free of zona
Implantation blastocyst in uterine wall on
day 7- 8
Implantation
Implantation
Endometrium is maintained
– Human corionic gonadotropic hormone (HCG)
sectreted by outer cells (Chorion) of blastocyst to
maintain corpus luteum
• LH levels remain high
• HCG used in pregnancy tests
– Corpus luteum maintains
levels of estrogen and
progesterone to maintain
endometrium
The Embryo
During implantation, the outer layer of
cells of the blastocyst produces two
membranes that surround, protect, and
nourish the embryo
– Chorion forms the placenta
– Amnion forms amniotic sac
Development
Considered an embryo after implantation is
complete
– Approx. 2 weeks from fertilization
Chorion
Amnion
Forms a fluid filled sac that insulates the
embryo and fetus that protects from
–
–
–
–
Infection
Dehydration
Impact
Temperature changes
Umbilical cord
Contains one vein and two arteries
– vein carries nutrient and oxygen rich blood
to the fetus.
– two arteries return blood containing waste
from fetal circulation back to the placenta.
• It takes about 30 seconds for a blood cell to
make the round trip through the cord
– cord can be as long as 4 feet at birth.
Prenatal Development
The in’s and then outs
Prenatal development
Pregnancy usually last for approximately nine
months
Divided into three trimesters
First Trimester
– Fertilization to the end of the 3rd month
– by second week – germ layers form
• Ectoderm, endoderm, and mesoderm
– At one month – size is only 7mm
Prenatal development
First Trimester (Cont.)
– Heart and brain have formed
• heart rate can be heard at 10 weeks with a special
instrument called a Doppler
–
–
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–
Limb buds with fingers and toes present
Placenta begins developing
Considered fetus after 8th week
Movement occurs around 9th week
• Sucking reflex
st
1
Trimester
4 wks
8 wks
12 wks
nd
2
Trimester
Fetus is 57 mm – 350 mm long
recognizable body form
– Arms, hands, fingers, legs, feet and toes are
fully formed
• Bone begins to replace cartilage
most of organs and tissues developed
– Eyes are almost fully developed
nd
2
Trimester
16 wks
20 wks
nd
2
Trimester
At the end of 16 wks:
– Fetus is developing reflexes such as sucking and
swallowing
– Sex is identifiable
– Skin is bright pink, transparent and covered with soft,
downy hair
At the end of 20 wks:
– Mother begins to feel fetal movement
– Internal organs are maturing
– Eyebrows, eyelids and eyelashes appear
nd
2
Trimester
At the end of 24 weeks:
– Eyelids begin to part and eyes open
occasionally for short periods of time
– Skin is covered with protective coating called
vernix
– Fetus is able to hiccup
rd
3
Trimester
Rapid growth
– Fetus is 350 mm – 530 mm long
– Body mass increases from 0.68 kg to 3.4 kg
– Organs are maturing
rd
3
Trimester
At the end of 7 months:
– If born at this time, he/she will be considered a
premature baby and require special care
– Taste buds have developed
– Fat layers are forming
– Skin is still wrinkled and red
rd
3
Trimester
rd
3
Trimester
At the end of 8 months:
– Tremendous brain growth occurs at this time
– Most body organs are now developed with the
exception of the lungs
• Movements or "kicks" are strong enough to be
visible from the outside
• Kidneys are mature
• Skin is less wrinkled
• Fingernails now extend beyond fingertips
rd
3
Trimester
At the end of 9 months:
– The lungs are mature
– Baby is now fully developed and can survive
outside the mother's body
• Skin is pink and smooth
• Baby settles down lower in the abdomen in
preparation for birth and may seem less active
Parturition (Birth)
Uterine contractions signal beginning of labor
– Cervix thins and begins to dilate (max. 10 cm)
– Labor starts when contractions are 10-15 min
Amniotic membrane is forced into birth canal
– Often bursts and amniotic fluid lubricates the canal
(water breaking)
– Usually ruptures during delivery but may occur before
Contractions start moving baby through birth
canal
Parturition
Hormones involved in birth
Relaxin
– Produced by placenta causes ligaments in
pelvis to loosen
Oxytocin
– positive feedback loop enhances strength of
contractions
– Prostaglandins also involved
Hormones involved in birth
Milk Production
– Prolactin
• Levels increase dramatically after birth occurs
• estrogen & progesterone levels drop
• Stimulates glands in the breasts to produce fluids 1.5 L/day
– Oxytocin
• Stimulates contractions that move milk into ducts
• Also causes contractions of sm. Muscle in uterus to return to
normal size