Human Reproductive Biology

Semen Content and Composition

• Semen content: citric acid, free amino acids, fructose, enzymes, prostaglandin, potassium, and zinc
• 45-60% of the fluid is from seminal vesicles
• 13-33% is from the prostate gland
• 5% is from the testicles and epididymis

Follicle Maturation and Ovulation

• Oocytes: ~2 million at birth, ~40,000 at puberty, and ~400 ovulated over a lifetime
• Leutinizing Hormone surge from the pituitary gland causes changes in tissues
• Follicle maturation: swelling within the follicle due to increased hyaluronan
• Matrix metalloproteinases degrade surrounding tissue, leading to follicle rupture

Egg Release and Fertilization

• Egg and surrounding cells (corona radiata) are ejected into the peritoneum
• Corona radiata provides bulk to facilitate capture of the egg
• Acrosome reaction: sperm bind to ZP proteins in the zona pellucida, initiating the release of enzymes
• Enzymes from the sperm allow it to burrow through the zona pellucida
• Cortical reaction: prevents other sperm from fertilizing the egg (polyspermy)

Fertilization and Meiosis II

• Fertilization: fusion of male and female gametes
• Meiosis II complete: formation of male and female pronuclei
• Decondensation of male chromosomes
• Fusion of pronuclei: zygote formation

Week 1 Embryonic Development

• Day 1: fertilization
• Day 2-3: cleavage
• Day 3: compaction
• Day 4: formation of blastocyst
• Day 6: implantation

Cleavage and Blastocyst Formation

• Cleavage: cell division without growth, resulting in multiple smaller cells
• Goals: grow zygote to multicellular embryo
• Formation of the blastocyst: sodium channels appear on the surface of the outer trophoblast cells, pumping sodium and water into the forming blastocoele

Implantation

• Ectopic implantation: implantation in a location other than the upper portion of the uterus
• Implantation "rupture" can lead to life-threatening hemorrhage