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