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FIRST TRIMESTER
BY: Heather, Maria, & Ibelise
STAGE ONE :
one day post ovulation
• Fertilization begins when a sperm penetrates an oocyte (an
egg) and it ends with the creation of the zygote. The
fertilization process takes about 24 hours.
• Within 11 hours following fertilization, the oocyte has extruded
a polar body with its excess chromosomes. The fusion of the
oocyte and sperm nuclei marks the creation of the zygote and
the end of fertilization.
• It takes only one sperm to fertilize the egg
• Penetration of the zona pellucida takes about twenty minutes
STAGE TWO :
1.5-3 days post ovulation
• The cells divide into two smaller sets called
blastomeres
• Each cell division occurs every twenty hours
becoming smaller with every division
• When cell division generates about sixteen cells, the
zygote becomes a morula. It leaves the fallopian tube
and enters the uterus three to four days after
fertilization
• The blasocele then forms in the morula and creates
the blastocyte, which forms two more cells
STAGE 4-5
7-12 days post ovulation
The uterus is therefore swollen with new blood
capillaries and the circulation between
mother and blastocyst begins, a process
needed for the continuation of pregnancy
Trophoblast cells destroy cells of the uterus
and make blood pools that eventually form
the placenta.
The blastocyst forms into two layers
1) The epiblast – the embryo and the ambiotic
fluid
2) The hypoblast- the yolk sac
STAGE 6-9
13 -21 days post ovulation
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Villi forms & embryo attaches to the uterus
Fetus is attached by an umbilical cord
Gastrulation occurs & embryonic disc forms
The layers of the embryonic disc are the
ectoderm the mesoderm and the endoderm
Eventually the ectoderm changes from two
layers to three layers
The egg is now shaped like a pear
Blood cells are already developed
Endocardial cells fuse to form embryo’s two
heart tubes
DEVELOPMENT
STAGE 10-13
21-30 days post ovulation
• Neural crests contribute to the skull and face formation
• Heart tube takes on a s shape and cardiac muscle contraction
begins
• Fluids begin to get pumped through the body
• Central nervous system is most developed
• Embryo curves into a C shape and arches that are the neck and
face show under the forebrain
• Brain and Spinal cord are largest most compact tissue of
embryo
• Blood system continues to develop
• Somite form sclerotome which becomes cartilage
• Back muscle is formed along with the ribs
• The digestive epithelium layer begins to differentiate into the
future locations of the liver, lung, stomach and pancreas
Weeks 4 -10
STAGES 14-16
31-42 days post ovulation
• Brain and head grow rapidly and the mandibular and
hyoid arches are noticeable
• Spinal cord wall contains three zones : ventricular the
mantle and the marginal.
• The adenohypophyseal pouch develops into the anterior
pituitary
• Brain has increased in size
• Thorax appears more and the esophagus lengthens
• Brain has cerebral hemispheres and the hind brain is
responsible for heart regulation breathing and muscle
movements
• Retina pigment is visible and lens pit has grown into a d
shape.
Medical Tests
STAGE 17 – 20
44-55 days post ovulation
• Jaw and facial muscle are now developing & teeth beds begin
to form.
• Nasofrontal groove becomes distinct and sense of smell forms
in brain
• Heart separate into 4 chambers and nipples form
• Eye pigments develop and scalp gets nerves
• Kidney produces urine, body is cubed shaped & ossification of
skeleton begins
• Head is more erect inner ear forms the canals
• Gonads and limbs form
• Toenails bone cartilage and muscle forms
• Brain is connected to tiny muscles and nerves
• Testes & ovaries are distinguishable
• Upper limps are longer and toes are formed.
STAGE 21-23
56- 60 days post ovulation
• Eyes are still on the side of the embryos head
• Fingers lengthen and features are still in a web
shape
• The have and head become more humanly shaped
• Heart development slows down the clitoris and penis
begin to form
• Taste buds form & primary teeth are at cap stage
• Intestine begin to migrate to the body
• Limbs are well formed
• Tail is gone and surface layer skin appears
DISORDERS :
ectopic pregnancy
ECTOPIC PREGNANCY
ECTOPIC PREGNANCY
• If a fertilized egg implants outside the uterus, it's called an
ectopic pregnancy. One in 50 pregnancies ends this way.
• Here's how it happens: After conception, the fertilized egg
travels down your fallopian tube on its way to your uterus.
• If the tube is damaged or blocked and fails to move the egg
toward your womb, the egg may become implanted in the
tube and continue to develop there.
• Because almost all ectopic pregnancies occur in one of the
fallopian tubes, they're often called "tubal" pregnancies
• The only way to handle this is to abort the pregnancy
• Failure to get the pregnancy aborted can result in fallopian
tubes bursting which causes internal bleeding and could
eventually lead to death