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Fertilization. Growth and maturation of oocyte. Growth of the oocyte Essential for successful fertilization and embryonic development Before the ovulation. Immature oocyte surrounded by cumulus cells. Oocyte. Blastocyst stage embryo. Oocyte growth. Primordial. Primary. Secondary. - PowerPoint PPT Presentation
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Fertilization
Growth and maturation of oocyte
• Growth of the oocyte– Essential for successful
fertilization and embryonic development
• Before the ovulation
Immature oocyte surroundedby cumulus cells
Blastocyst stage embryo
Oocyte
Growth and maturation of oocyte
• Growth of oocytes
– Primordial follicles • Commitment for
development and differentiationPrimordial Primary Secondary Antral
Oocyte growth
Cumulus-oocyte complex
Oocyte
Cumuluscells
Growth and maturation of oocyte• Specialized granulosa
cells that surround the oocyte– Cumulus cells
• Assist growth of the oocyte
• Produce growth factors and hormones that are essential for normal oocyte growth and development
• Combined structure of the oocyte and cumulus cells – Cumulus-oocyte complex
(COC)
Primordial Primary Secondary Antral
Oocyte growth
Cumulus-oocyte complex
Oocyte
Cumuluscells
Growth and maturation of oocyte
• The oocyte increases its size and volume during its growth phase– No mitosis– The maximal number of oocytes present on the
ovaries • Set before birth • numbers decrease throughout fetal and adult life
– Undergo meiosis • ultimately results in reduction of number of chromosomes by
half (46 to 23)– Haploid cells
Growth and maturation of oocyte
• Process of meiosis
– Begins before primordial follicles are formed– Arrested during oocyte growth
• Growth of the oocyte– Almost completed by the time the follicle reaches the
antral stage
• Meiosis – Arrested until LH surge
• Granulosa cells produce factors that inhibit premature resumption of meiosis
Growth and maturation of oocyte
• Oocyte after LH surge
– Formation of a polar body
• a small, round structure in the space between the cytoplasm (inside of the cell) and the clear outer membrane of the oocyte (zona pellucida)
• Contains a portion of maternal chromosomes
• Expelled as a part of meiosis in order to reduce number of chromosomes present in the oocyte
Polar body
Zonapellucida
Oocyte
Growth and maturation of oocyte
• Resumption of meiosis– Changes in the function of cumulus cells
• Loss of contact with each other and with the granulosa cells, • Essential for the oocyte to be released from the preovulatory
follicle• Production of “sticky” mucus
– Necessary for the COC to be picked up by fimbriae after being released from the preovulatory follicle
Release of the oocyte
• The COC – Expelled to the outer
surface of the ovary after the ovulatory follicle ruptures
– Covered with “sticky” mucus
– Remains on the site of ovulation unless being picked up by the fimbriae of the oviduct
Oocyte in the oviduct
• The pickup of COC – The structural design
of the fimbriae– Close proximity of
the ovary to the oviduct
– Coordinated contraction of ligaments surrounding the ovaries and uterus
Fimbriae
Infundibulum
Ampulla
Isthmus
Ampullary-Isthmic Junction
Uterotubal Junction
Ovary
Site of ovulationAdapted from Hafez, 1993
Oocyte in the oviduct
• Lifespan of oocyte – 20 to 24 hours after being released from the
ovulatory follicle
Infundibulum
AmpullaIsthmus
Fimbriae
Ampullary-isthmic Junction
Uterotubal Junction
Oocyte in the oviduct
• Time to reach uterus from the infundibulum of the oviduct– Approximately 90 hours in cows – Approximately 48 to 72 hours in women
• Oocyte must be fertilized at appropriate time to ensure survival of the embryo when it enters the uterus
Infundibulum
AmpullaIsthmus
Fimbriae
Ampullary-isthmic Junction
Uterotubal Junction