Download Physiology of conception

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