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THE PROCESS OF CONCEPTION
OVAReleased from the Graafian
FollicleWill be surrounded by a ring
of mucopolysaccharide fluid (Zona pellucida) and a circle of cells (Corona radiata)◦ Zona pellucida and Corona
Radiata protects the ova by serving as a buffer against injury
Moves from the ovary to the fallopian tube through the cilia and peristaltic movement of fallopian tube
SPERMPer ejaculation, 2.5ml semen
containing 50-200M spermatozoa is released (ave 400M sperm/ejaculation)
Moves through the cervix, uterus, fallopian tube because of their flagella and uterine contractions
Undergoes CAPACITATION (changes in the plasma membrane of the sperm head to reveal sperm binding receptor sites) before penetrating into the corona radiata
Sperm clusters around coronal cells
Will release HYALURONIDASE (proteolytic enzyme) to dissolve the corona radiata
Sperm penetrates the cell; cell membrane of ova changes composition to become impenetrable to other sperm
Sperm and ova fuse carrying 23 pairs of chromosomes each◦If sperm carries X sex chromosome paired
with the ovum X chromosome = female zygote
◦If sperm carries Y sex chromosome paired with the ovum X chromosome = male zygote
IMPLANTATIONZygote move from fallopian
tube to uterusIt will undergo series of
mitotic divisions resulting to a cleavage formation, 1 in every 22 hour, with the cleavage division happening 24 hours after fertilization
Once it reaches the uterus, zygote is now composed of 32 -50 ball of cell termed as a MORULA
Another 3-4 days, morula becomes a BLASTOCYST consisting of:
◦An inner cell mass which will become the future embryo
◦Trophoblast which will become the placenta and membranes
At approx 8-10 days after fertilization, blastocyst attaches to the endometrium◦ Sheds off last residues of
corona radiata and zona pellucida
◦ Brushes against endometrium (apposition) and settles down
A slight vaginal bleeding is experienced during implantation stage because capillaries are ruptured by the implanting trophoblast cells
EMBRYONIC & FETAL STRUCTURES
DECIDUA – uterus that has grown thick and vascular
3 areasDecidua basalis – lies directly
under the embryo (portion where the trophoblast establish communication with maternal blood vessel)
Decidua capsularis – portion that stretches or encapsulates the surface of the trophoblast
Decidua vera – the remaining portion of the uterine lining
CHORIONIC VILLIMiniature villi
similar to probing fingers that appear on the 11th or 12th day
They begin the formation of the placenta
Consists of a central core of connective tissue and fetal capillaries
Consists of 2 layers of trophoblast cells:◦Syncytiotrophoblast (syncitial layer) –
produces HCG, somatomammotropin (human placental lactogen), estrogen and progesterone
◦Cytotrophoblast (middle or Langhan’s layer) – functions in early pregnancy to protect the growing embryo and fetus from infection (eg syphilis)
PLACENTA15-20CM IN
DIAMETER, 2-3 CM DEEP, 400-600g at full term
Has 25-30 cotyledons (placental compartments that lie on the maternal side)
Has 2 sidesMaternal – dirty
roughFetal – shiny smooth
FUNCTIONS:Serves to conduct oxygen and nutrients for
the fetusSecretes endocrine hormones (syncytial cells)
hCG – 1st placental hormone - enusures corpus luteum to
continuously produce progesterone and estrogen
- supresses maternal immunologic reaction so that placental tissue is not detected and rejected as a foreign substance
- if fetus is male, stimulates the testes to begin producing testoterone
- at 8 week, begins progesterone production, as a result, CL disintegrates and hCG production decreases
ESTROGEN (estriol) – “hormone of women”
- contributes to mammary gland development of mother in preparation for lactation
- stimulates uterine growth to accommodate growing fetus
PROGESTERONE - “Hormone for Mothers” - necessary to maintain endometrial
lining of the uterus during pregnancy - reduces contractility of uterus
during pregnancy preventing preterm labor
HUMAN PLACENTAL LACTOGEN (human chorionic somatomammotropin)
- with both growth promoting and lactogenic (milk producing) properties
- promotes mammary gland (breast) growth in preparation for lactation
- regulates maternal glucose, protein and fat levels so that adequate amounts of these are always available to the fetus
AMNIOTIC FLUID800-1200mlSlightly alkaline pH 7.2Fetal urine adds to its volume
Functions:Shields fetus against pressure or blow
to the mother’s abdomenProtects fetus from temperature
changeAids in muscular development because
it allows fetus’ freedom to moveProtects the umbilical cord from
pressure protecting fetal oxygen supply
Hydramnios – excessive amniotic fluid - more than 2000ml or
pockets of fluid larger than 8cm on UTZ
Oligohydramnios – reduction in the amount of amniotic fluid
- less than 300ml or no pockets of fluid larger than 1 cm on UTZ
AMNIOTIC MEMBRANESChorionic membrane – the outermost fetal
membrane; purpose is to form a sac that contains the amniotic fluid
Amniotic membrane – 2nd membrane lining the chorionic membrane; forms beneath the chorion
- produces amniotic fluid - produces phospholipid that initiates
the formation of prostaglandins which can cause uterine contractions and may be the trigger that initiates labor
UMBILICAL CORDFormed from the amnion and chorion53cm (21 in) length; 2 cm thickWharton’s jelly – a gelatinous
mucopolysaccharide that forms the bulk of the umbilical cord giving it its body; prevents pressure on the veins and arteries
Outer surface is covered with amniotic membrane
Composed of 1 vein (carrying blood from placental villi to the fetus) and 2 arteries (blood from fetus back to palcental villi)
Blood flow is 350ml/min at term
Walls are with smooth muscles, no nerve supply
Function:Transports oxygen and
nutrients to the fetus from placenta and return waste products from fetus to placenta