CONCEPTION,NIDATION AND PLACENTAL DEVELOP0MENT

1
CONCEPTION,NIDATION AND PLACENTAL DEVELOP0MENT
2
CONCEPTION

• FERTILIZATION OR UNION OF THE MALE AND FEMALE
  GAMETES(SPERM AND OVUM)
• SAME AS PREGNANCY

3
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

4
NIDATION
5
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.

6
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.

7
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

8
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.

9
SPERMATOGENSIS AND OOGENESIS
10
STRUCTURE OF SPERM
11
STRUCTURE OF SECONDARY OOCYTE

• 1.OVUM
• 2. ZONA PELLUCIDA
• 3. CORONA RADIATA

12
COMPOSITION OF SEMEN

• FROM THE FOLLOWING ORGANS
• 1.TESTIS
• 2. SEMINAL VESICLE
• 3.PROSTATE
• 4.URETHRAL GLANDS

13
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

14
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

15
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

16
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

17
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.

18
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.

19
FERTILIZATION

• THE ZYGOTE IS CARRIED DOWN THE TUBE BY
  PERISTALSIS AND CILIARY ACTION AND REACHES THE
  UTERINE CAVITY ABOUT 5-6 DAYS AFTER OVULATION.

20
FERTILIZATION
21
IMPLANTATION
22
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.

23

• 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.

24
EARLY DEVELOPMENT
25
DEVELOPMENT OF THE PLACENTA

• FORMS FROM TROPHOBLAST WHICH DIFFERENTIATES TO
• 1.INNER CYTOTROPHOBLAST
• 2.OUTER SYNCYTIOTROPHBLAST

26
FORMATION OF PLACENTAEARLY DEVELOPMENT
27

• 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.

28
FORMATION OF PLACENTALATER DEVELOPMENT
29

• 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, thickness2.5cm at the
  centre.
• Weight500g (the ratio of fetal placental weight
  at term is about 61) It occupies about 30 of
  the uterine wall at term and has two surfaces

30

• 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.

31

• 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.

32

• 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

33

• 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)

34
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

35
PLACENTA