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Physiology of Conception • FERTILISATION IS THE FUSION OF SPERMATOZOON WITH THE OVUM • FERTILISATION OCCURS IN THE AMPULLARY END OF THE TUBE • OVUM IS RELEASED FROM THE STIGMA • PICKED UP BY THE FIMBRIAL END OF THE TUBE WHICH OVERLIES THE OVARY AT THE TIME OF OVULATION • OVARY NOURISHED BY CORONA MOVES TO THE AMPULLARY END OF THE TUBE TO FUSE WITH THE CAPACITATED SPERM • OUT OF MILLIONS OF SPERM DEPOSITED INTO THE VAGINA ONLY 1 % REACHES THE CERVIX • A FEW THOUSAND CAPACITATED SPERM REACH THE TUBE BY THEIR SWIMMING ACTION • ONLY 300-500 SPERM REACH THE OVUM • CHANGES IN THE SPERM BEFORE FERTILISATION: CAPACITATION: RECONDITIONING OF SPERM MAKES IT MORE SUITABLE FOR PENETRATION OF OVUM GLYCOPROTEIN COAT AND SEMINAL PLASMA ARE REMOVED FROM THE AREA OVERLYING THE ACROSOME MAKING PENETRATION EASIER • ACROSOMAL: OCCURS AFTER THE SPERM BINDS TO THE ZONA PELLUCIDA AND RESULTS IN THE RELEASE OF ENZYMES REQUIRED TO PENETRATE ZONA LIKE ACROSOME AND TRYPSINASE • • • • FERTILISATION: PENETRATION OF CORONA RADIATA PENETRATION OF ZONA PELLUCIDA FUSION OF OOCYTE AND SPERM CELL MEMBRANES • POST FERTILISATION EVENTS: • ZYGOTE IN 2 CELLED STAGE REACHES THE AMPULLA TRAVERSES THE TUBE AND FALLS INTO THE UTERINE CAVITY • INTIALLY LOOSELY ARRANGED UNTIL 8 CELL STAGE • MORULA: CLEAVAGE RESULTS IN COMPACTION WITH CELLS BOUND TOGETHER BY CELL JUNCTIONS 3DAYS AFTER FERTILISATION IT FORMS A 16 CELLED STAGE CALLED MORULA THE INNER CELLS OF MORULA FORM INNER CELL MASS WHICH LATER FORMS THE PLACENTA • BLASTOCYST: MORULA ENTERS THE UTERINE CAVITY AND FLUID BEGINS TO PENETRATED THE ZONA INTO THE INTERCELLULAR SPACES OF INNER CELL MASS THE SPACES EVENTUALLY COALESCE TO FORM THE BLASTOCOELE AND EMBRYO IS CALLED THE BLASTOCYST • CELLS OF THE INNER CELL MASS FORM THE EMBRYOBLAST • CELLS OF THE OUTER CELL MASS FORM THE TROPHOBLAST • ZONA PELLUCIDA DISAPPEARS TO ALLOW IMPLANTATION • IMPLANTATION: • IS THE PROCESS BY WHICH BLASTOCYST PENETRATES THE UTERINE MUCOSA, FIRST THE EPITHELIUM AND THEN THE CIRCULATORY SYSTEM OF THE MOTHER • OCCURS 5-7 DAYS AFTER FERTILISATION IN THE UPPER POSTERIOR WALL OF THE UTERUS • TROPHOBLASTIC CELLS OVERLYING THE EMBRYOBLAST BEGIN TO PENETRATE THE UTERINE MUCOSA IN THE SECRETORY PHASE, BETWEEN THE GLAND OPENINGS • IT INVOLVES THE FINE INTERACTION BETWEEN THE TROPHOBLAST AND ENDOMTERIUM • INVOLVING INTEGRINS, LAMININ AND FIBRINONECTIN. • BLASTOCYST BURROWS INTO THE COMPACT LAYER OF ENDOMETRIUM WHICH IS RENDERED VASCULAR DUE TO THE SECRETORY CHANGES INDUCED BY PROGESTERONE FROM CORPUS LUTEUM • BY 8TH DAY TROPHOBLAST OVERLYING THE EMBRYOBLAST STILL BURROWS INTO THE MATERNAL TISSUES AND CAN BE DIFFERENTIATED INTO 2 LAYERS • INNER CYTOTROPHOBLAST AND OUTER SYNCYTIOTROPHOBLAST • INNER CELL MASS DIFFERENTIATES INTO HYPOBLAST AND EPIBLAST • 9th DAY: • BLASTOCYST HAS COMPLETELY EMBEDDED INTO THE ENDOMETRIUM • AT THE EMBRYONIC END SYNCYTIOTROPHOBLAST BECOMES A SYNCITIUM WITH LACUNA FORMING WITHIN • EVENTUALLY THE CELLS PENETRATED DEEPLY AND ERODE THE ENDOTHELIAL LINING OF THE MATERNAL CAPILLARIES • SYNCITIAL LACUNA BECOMES CONTINUOUS WITH MATERNAL SINUSOIDS AND MATERNAL BLOOD WASHES THE TROPHOBLAST ESTABLISHING UTEROPLACENTAL CIRCULATION • THE SYNCITIAL LINING IS REPLACED BY NITABUCH MEMBRANE • THIS LIMITS THE PENETRATION OF TROPHOBLAST INTO THE MYOMETRIUM • CELLS FROM THE HYPOBLAST FORMS AN HEUSER’S MEMBRANE THAT LINES THE INNER PART OF HYPOBLAST FORMING PRIMITIVE YOLK SAC • 11-12 DAY: • CELLS APPEAR BETWEEN INNER CYTOTROPHOBLAST AND OUTER SURFACE OF PRIMITIVE YOLK SAC • THE CELLS LIE LOOSELY- EXTRA EMBRYONIC MESODERM • CAVITY IS CHORIONIC CAVITY HUMANS OOGENESIS: THE PROCESS INVOLVED IN THE DEVELOPMENT OF THE MATURE OVUM PRIMITIVE GERM CELLS TAKE THEIR ORIGIN FROM YOLK SAC AT THE END OF 3RD WEEK AND THIR MIGRATION TO THE DEVELOPMENTAL RIDGE IS COMPLETED AT THE END OF 4TH WEEK • GERM CELLS UNDERGO MEIOTIC DIVISION AND DIFFERENTIATE TO OOGONIA • REACHES MAXIMUM AT 20TH WEEK • THEY FURTHER DIVIDE, SOME ENTER THE PROPHASE OF 1ST MEIOTIC DIVISION CALLED PRIMARY OOCYTE • AT CELLS SURROUND IT CALLED PRIMODIAL FOLLICLES- OVER THE CORTEX OF OVARY • AT BIRTH NO MITOTIC DIVISION –ALL ARE REPLACED BY PRIMARY OOCYTE • AT PUBERTY 400000 PRIMARY OOCYTES ARE LEFT BEHIND HUMANS • SPERMATOGENESIS: • THE DEVELOPMENT OF SPERMATIDS FROM PRIMODIAL MALE GERM CELLS AND THEIR DIFFERENTIATION TOSPERMATOZOA IS SPERMATOGENESIS • TIME FOR DEVELOPING A MATURE SPERMATOZOON FROM SPERMATOGONIUM IS 61 DAYS • Thank you