Conception

Wak Wak Tree

Humunculus

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Bad Idea

Human Conception as of Today

• Upon ejaculation - 300 to 500 million sperm introduced into vagina

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• Female cervix located at the base of the uterus opens for a few hours to allow sperm to enter the uterus.

• This only occurs for a few hours within a menstrual cycle.

• Only a few thousand spermatocytes will reach the vicinity of the secondary oocyte.

Deterrents

• Cervix

• Acidic environment of uterus

• Bacteria

• Distance

• 2 fallopian tubes

• Timing

• Conception ideally occurs when secondary oocyte is 1/3 distance down the fallopian tube

• Oo is latin for egg

• Cyt is latin for cell

• Oocyte has a short 24 - 36 hour period of viability.

• Spermatocytes can survive roughly 48 hours

• Conception usually occurs within 24 hours of ovulation

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Peristaltic contractions

• Peristaltic contractions (successive muscular contractions) and the action of the cilia transport oocyte and sperm toward each other.

• Contractions only occur when sperm cells are present

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Anatomy of Spermatocyte

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• Acrosome of sperm stores and releases “acrosin” that stimulates the peristaltic contractions.

• Female reproductive tract gives sperm the ability to “conceive”. A 10 hour process called “capacitation” - the removal of the acrosome

Secondary Oocyte

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• Acrosomal membrane dissolves to secrete various enzymes and at appropriate time.

• Acrosin - contractions• Hyaluronidase - dissolves layers of “Corona

radiata” - several layers of cells around oocyte

• Neuraminidase - enzyme that helps sperm cell bind with “Zona pellucida”

Corona Radiata

• Outer layer of cells of oocyte that protects against bacteria and acidic environment

Zona pellucida

• A gelatinous glycoprotein layer inside of corona radiata with special receptor sites for sperm attachment.

• Zona pellucida prevents “polyspermy”

• Electrical changes occur in surface of oocyte which prevents entry of any additional sperm

• Enzymes within oocyte immediately alter receptor sites.

• Sperm enters secondary oocyte and flagellum is shed.

• Nucleus within head of sperm swells - developing into a “male pronucleus”

• Pronucleus is enlarged nucleus with only 23 chromosomes - thus it is “haploid”

• Nucleus within oocyte is the “Female pronucleus”

• Two “pronuclei” fuse into one forming a nucleus with 46 chromosomes - Diploid

• Conception is the fusing of the two pronuclei producing a diploid cell

• Oocyte then completes “meiosis II” thus finally becoming an egg cell (but not really)

• Mitosis begins -rapid cell division producing identical daughter cells

• Cleavage of “egg cell” occurs every few hours.

• NOTE - cell does not grow in size but cell number increases.