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CONCEPTION,NIDATION AND
PLACENTAL DEVELOP0MENT
CONCEPTION
FERTILIZATION OR UNION OF THE
MALE AND FEMALE GAMETES(SPERM
AND OVUM)
SAME AS PREGNANCY
NIDATION
IMPLANTATION OR EMBEDDING OF
THE PRODUCT OF FERTILIZATION
OR ZYGOTE INTO THE UTERINE
CAVITY
A NIDUS IS A CAVITY IN WHICH
PLANT SPORES DEVELOP
NIDATION
SPERMATOGENESIS
STAGES OF DEVELOPMENT OF THE
SPERM OCCURING IN THE TESTIS.
THE PROCESS STARTS AT PUBERTY
IT TAKES ABOUT 72 DAYS FROM
SPERMATOGONIUM TO MATURE
SPERM.
OOGENESIS
STARTS DURING INTRAUTERINE
LIFE.
ALL THE PRIMARY OOCYTES ARE
FORMED BEFORE BIRTH.
THE PRIMARY OOCYTE BEGINS THE
FIRST MEIOTIC DIVISION JUST
BEFORE BIRTH.
COMPLETION OF THE PROPHASE
OCCURS JUST BEFORE PUBERTY.
OOGENESIS
BEFORE PUBERTY, THE PRIMARY
OOCYTE INCREASES IN SIZE AND
ZONA PELLUCIDA FORMS AROUND
IT.
BEFORE OVULATION, PRIMARY
OOCYTE COMPLETES FIRST MEIOTIC
DIVISION ,RESULTING IN
SECONDARY OOCYTE AND FIRST
POLAR BODY
OOGENESIS
WITH THE ONSET OF OVULATION,THE
NUCLEUS OF THE SECONDARY OOCYTE
ENTERS THE SECOND MEIOTIC DIVISION
AND PROCEEDS TO METAPHASE UNTIL
FERTILIZATION.
THE SECONDARY OOCYTE RELEASED AT
OVULATION IS CALLED OVUM.
IT IS SURROUNDED BY ZONA PELLUCIDA
AND CORONA RADIATA.
SECOND POLAR BODY IS FORMED AFTER
FERTILIZATION AND IS EXPELLED.
SPERMATOGENSIS AND
OOGENESIS
STRUCTURE OF SPERM
STRUCTURE OF SECONDARY
OOCYTE
1.OVUM
2. ZONA PELLUCIDA
3. CORONA RADIATA
COMPOSITION OF SEMEN
FROM THE FOLLOWING ORGANS
1.TESTIS
2. SEMINAL VESICLE
3.PROSTATE
4.URETHRAL GLANDS
TRANSPORT OF SEMEN
ALKALINE SEMEN DEPOSITED IN THE
VAGINA AFTER SEXUAL INTERCOURSE
COAGULATES THEN LIQUIFIES.
AFTER 30MINS IN THE VAGINA WHICH IS
ACID THEY LOOSE MOTILITY AND UNABLE
TO PENETRATE THE CERVICAL MUCUS
AND DIE.
SPERMS CAN SURVIVE FOR 1-3 DAYS IN
THE CERVICAL MUCUS AND FURTHER 2
DAYS IN THE FALLOPIAN TUBE
TRANSPORT OF SPERM
BY PERISTALSIS ASSISTED BY
TUBAL FLUID ,CILIA AND MUSCULAR
CONTRATION.
DURING THE JOURNEY TO THE TUBE
THE SPERMS GAIN ABILITY TO
FERTILIZE THE OVUM BY
PROCESSES OF CAPACITATION AND
ACROSOMAL REACTION
CAPACITATION AND
ACROSOMAL REACTION
CAPACITATION-THE PROCESS WHICH
REMOVES THE SPERM MEMBRANES.
ACROSOMAL REACTION IS THE PROCESS
WHEREBY THE CAPACITATED SPERM
LOOSES ITS ACROSOMAL MEMBRANES
RELEASING THE ENZYMES WHICH HELPS
THE PENETRATION OF THE ZONA
PELLUCIDA
OVUM
AT OVULATION, THE FIMBRIAL END OF
THE TUBE COMES VERY CLOSE TO THE
OVARY.
WHEN THE OVUM IS RELEASED, IT IS
CARRIED BY PERITONEAL FLUID INTO
THE TUBE BY CILIARY ACTION OF
EPITHELIAL CELLS AND MUSCULAR
CONTRACTIONS.
THE FERTILE LIFE OF THE OVUM IS
ABOUT 24 HRS
FERTILIZATION
NORMALLY OCCURS AT THE
AMPULLA OF THE FALLOPIAN TUBE
INVOLVES FUSION OF OVUM AND
SPERM.
ONLY ONE SPERM FERTILIZES THE
OVUM
SPERM IS ATTRACTED TO OVUM BY
CHEMOTAXIS.
FERTILIZATION
MANY SPERMS ENTER THE ZONA
PELLUCIDA BUT AS SOON AS ONE
SPERM GETS INTO THE CYTOPLASM,
THE OVUM SEPERATES FROM THE
ZONA.
THE HEAD OF THE SPERM WHICH IS
THE NUCLEUS FUSES WITH THE
NUCLEUS OF THE OVUM TO FORM
THE ZYGOTE.
FERTILIZATION
THE ZYGOTE IS CARRIED DOWN THE
TUBE BY PERISTALSIS AND CILIARY
ACTION AND REACHES THE UTERINE
CAVITY ABOUT 5-6 DAYS AFTER
OVULATION.
FERTILIZATION
IMPLANTATION
EARLY DEVELOPMENT AND
EMBEDDING OF BLASTOCYST
ZYGOTE UNDERGOES MITOTIC
DIVISION FORMING TWO DAUGHTER
CELLS CALLED BLASTOMERES
WITHIN 30 HRS AFTER
FERTILIZATION
LATER DIVISION OCCURS ABOUT
EVERY 24HRS UNTIL A MORULA
FORMS WHICH IS ABOUT 16
BLASTOMERES.
CAVITY APPEARS IN THE MORULA AND IS
NOW CALLED BLASTOCYST.
THE BLASTOCYST CONSISTS OF 1.OUTER
LAYER CALLED TROPHOBLAST
2.INNER CELL MASS WHICH GIVES RISE
TO THE EMBRYO
THE TROPHOBLAST ERODES AND DIGEST
THE ENDOMETRIUM NOW CALLED
DECIDUA.
EARLY DEVELOPMENT
DEVELOPMENT OF THE
PLACENTA
FORMS FROM TROPHOBLAST WHICH
DIFFERENTIATES TO
1.INNER CYTOTROPHOBLAST
2.OUTER SYNCYTIOTROPHBLAST
FORMATION OF PLACENTA
EARLY DEVELOPMENT
TROPHOBLAST PENETRATES THE
ENDOMETRIUM NOW CALLED DECIDUA.
DECIDUA BASALIS IS UNDERNEATH THE
CONCEPTUS AND IS INVOLVED IN THE
MATERNAL SIDE OF THE PLACENTA.
CYTOTROPHOBLAST PROLIFERATES AND
FORM CLUMPS THAT EXTENDS TO THE
SYNCYTIOTROPHOBLAST TO FORM THE
PRIMARY VILLI.
FORMATION OF PLACENTA
LATER DEVELOPMENT
Placenta: Later development
Placental growth continues to term
Until week 16 the placenta grows both thickness and
circumference due to the growth of the chorionic villi with
accompanying expansion of the intervillous space.
After 16 weeks growth occurs mainly circumferentially.
The placenta at term
Circular, diameter 15-20, thickness~2.5cm at the centre.
Weight~500g (the ratio of fetal: placental weight at term is
about 6:1) It occupies about 30% of the uterine wall at
term and has two surfaces:
Fetal surface
Covered by a smooth, glistening amnion with the
umbilical cord usually attached at or near its
centre.
The branches of the umbilical blood vessels are
visible beneath the amnion as they radiate from
the insertion of the cord.
The amnion can be peeled off from the underlying
chorion except at the insertion of the cord.
Maternal surface
 Has a rough and spongy appearance and is
divided into several velvety bumps called the
cotyledons (15-20) by septa arising from the
maternal tissues.
 Each cotyledon may be supplies by its own spiral
artery.
 Numerous small greyish spots may be visible on
the maternal surface representing calcium
deposition in degenerated areas.
Umbilical cord
Vascular cable that connect the fetus to the placenta.
Varies from 30 to 90cm long , covered by amniotic
epithelium.
Contains two umbilical arteries and one umbilical vein
embedded into the Wharton's jell.
The arteries carry deoxygenated blood from the fetus to the
placenta and the oxygenated blood return to the fetus via
the umbilical vein.
In a full-term fetus, the blood flow in the cord is
approximately 350ml\min
PRIMARY VILLI BRANCHES
EXTENSIVELY INTO SECONDARY
AND TERTIARY VILLI AND FINALLY
CHORION FRONDOSUM.(fetal portion
of the placenta)
MORE INVASION OF THE DECIDUA
BASALIS TAKES PLACE,WITH THE
FORMATION OF THE
COTYLEDON(15-20)
PLACENTAL FUNCTION
1. LUNG FUNCTION-GASEOUS EXCHANGE
2.KIDNEY FUCTION-EXCRETION OF
HYDROGEN IONS AND BREAKDOWN
PRODUCTS OF OTHER SUBSTANCES
3. GI. FUNTION-NUTRIENT FUNCTION
4.HORMONE PRODUCTION
5.IMMUNE FUNCTION-TRANSFER OF
IMMUNOGLOBULINS TO THE FETUS
6.LIVER FUNCTION-DETOXIFICATION OF
DRUGS
PLACENTA