Conception

Wak Wak Tree

Humunculus

Bad Idea

Human Conception as of Today Upon ejaculation to 500 million sperm introduced into vagina

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 hour period of viability. Spermatocytes can survive roughly 48 hours Conception usually occurs within 24 hours of ovulation

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

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

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.