Transcript Fetal Development

Developed by
D. Ann Currie
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Ovary gives rise to oogonial cells.
Cells develop into oocytes.
Meiosis begins and stops before birth.
Cell division resumes at puberty.
Development of Graafian follicle.
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The female gamete are called Ovum.
The ovum are considered fertile for about
12-24 hours after ovulation.
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Production of sperm
First meiotic division:
◦ Primary spermatocyte replicates and divides.
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Second meiotic division:
◦ Secondary spermatocytes replicate and divide.
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Produce four spermatids.
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The male gamete are Sperm.
The sperm can survive in the female
reproductive tract for 48-72 hours.
However they are believed to be healthy and
highly fertile for only 24 hours.
In a single ejaculation the male deposits
approximately 200-500 million sperm in the
vagina. Only hundreds of sperm actually
reach the ampulla. Only one sperm fertilizes
the ovum.
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Fertilization occurs:
when the sperm and ovum unite.
in the ampulla of the fallopian tube.
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Capacitation:
◦ Removal of plasma membrane and glycoprotein
coat
◦ Loss of seminal plasma proteins
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Acrosomal reaction:
◦ Release of enzymes
◦ Allows entry through corona radiata
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Zone pellucida blocks additional sperm from
entering
Secondary oocyte completes second meiotic
division
◦ Forms nucleus of ovum
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Nuclei of ovum and sperm unite
Membranes disappear
Chromosomes pair up
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At the moment of fertilization the sex of the
zygote is determined.
Female have XX (sex chromosomes)
Male have XY ( sex chromosomes)
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Zygote moves through the fallopian tube
towards the cavity of the uterus.
Transportation takes 3 or more days.
Rapid mitotic divisions called cleavage is
occurring.
7-10days after fertilization the blastocyst
implants.
Most frequent site of attachment is the upper
part of the posterior uterine wall.
About 10-14 days after conception
Primary germ layers:
Ectoderm
Mesoderm
Endoderm
Chorionic villi form spaces in decidua basalis
Spaces fill with maternal blood.
Chorionic villi differentiate:
Syncytium: outer layer
Cytotrophoblast: inner layer
Anchoring villi form septa
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Nutrition
Excretion
Fetal respiration
Production of fetal nutrients
Production of hormones
Large molecular compounds can not crossthe
placenta
Other see text
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Body stalk fuses with embryonic portion of
the placenta
Provides circulatory pathway from chorionic
villa to the embryo
Delivers oxygenated blood to the fetus:
One Vein
Returns waste material to maternal
circulation:
Two Arteries
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Amnion:
Encloses the amniotic cavity
The inner membrane that forms about the
2nd week of embryonic development
Forms a fluid-filled sac that surrounds
the embryo and later the fetus.
Chorion:
Is the outer membrane
Becomes vascularized and forms the fetal
portion of the placenta.
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Consists of 800-1200 ml by the end the
pregnancy
Surrounds, cushions, protects, the fetus and
allows for fetal movement.
Maintains body temperature of the fetus.
Contains fetal urine and is a measurement of
fetal kidney function.
The fetus modifies the amniotic fluid through
the processes of swallowing, urinating, and
movement trough respiratory tract.
Other see text.
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First 2 week after conception
Cleavage
Blastomeres form morula
Blastocyst:
- develops into embryonic disc and amnion
Trophoblast:
- develops into chorion
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Beginning at Day 15 through approximately
the 8th week after conception.
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Week 9 after conception to birth
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Beginning development of GI tract
Heart is developing
Somites develop—beginning vertebrae
Heart is beating and circulating blood
Eyes and nose begin to form
Arm and leg buds are present
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Eyelids are closed
Tooth buds appear
Fetal heart tones can be heard
Genitals are well-differentiated
Urine is produced
Spontaneous movement occurs
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Lanugo begins to develop
Blood vessels are clearly developed
Active movements are present
Fetus makes sucking motions
Swallows amniotic fluid
Produces meconium
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Subcutaneous brown fat appears
Quickening is felt by mother
Nipples appear over mammary glands
Fetal heartbeat is heard by fetoscope
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Eyes are structurally complete
Vernix caseosa covers skin
Alveoli are beginning to form
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Rhythmic breathing movements
Ability to partially control temperature
Bones are fully developed but soft and
flexible
Variability seen on FHR monitor
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Increase in subcutaneous fat
Lanugo begins to disappear
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Skin appears polished
Lanugo has disappeared except in upper
arms and shoulders
Hair is now coarse and approximately 1 inch
in length
Fetus is flexed
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Fraternal: two ova and two sperm
Identical: single fertilized ovum
- Originate at different stages
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Umbilical Cord
Fetal Heart Rate-110-160 BPM
Ductus venosus
Ductus arteriosus
Foramen ovale
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