Conception Wak Tree Humunculus Bad Idea Human Conception

Conception

Wak Tree

Humunculus

Bad Idea

Human Conception as of Today • Upon ejaculation - 300 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 24 - 36 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

Let’s go to the video

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.