REPRODUCTIVE SYSTEM - 2 LECTURE 19

Female Reproductive Organs

Oogenesis

Over 300 million sperm enter the female at ejaculation. Only about 100 of these live to enter the fallopian tube. In order to fertilize the ovum, a sperm must become capacitated. This takes at least 7 hours after ejaculation. pH increases Hyperactivation of the flagellum Capacitated sperm are guided to the oocyte by chemotaxis and thermotaxis

Sperm Sperm Oocyte Sperm (b) Sperm surround the oocyte, attacking its defensive barriers. Oocyte Sperm

When the sperm enters the oocyte, Ca2+ is released from the endoplasmic reticulum. A calcium wave travels through the oocyte to the opposite side from the entry of the sperm The Ca2+ has several effects: Prevents other sperm from entering the oocyte (polyspermy) Activates the oocyte to finish meiosis to become a haploid ovum

Implantation

Ectoderm – epidermis and neural tissue 16 DAYS Ectoderm – epidermis and neural tissue Mesoderm – connective tissue and muscle Endoderm – epithelium of lungs and gut

A Comparison of bird with human sacs

Placenta and Amniotic Sac Formation As the blastocyst develops, the endometrium also changes to form the decidua basalis. This joins with the chorion frondosum to form the placenta.

Molecule exchange across the placenta Umbilical arteries deliver fetal blood to placental vessels. This blood circulates within the placenta and returns to the fetus via the umbilical vein. Maternal blood is also delivered to/from the placenta. In this way, maternal and fetal blood do not mix, but are separated by only two cell layers. Molecules diffuse across tissues of the placenta for exchange.

Amniocentesis Samples from the amniotic fluid can help diagnose genetic abnormalities such as Down syndrome. Samples are taken at week 16

Pregnancy Averages 38 weeks from fertilization Takes 2 weeks for blastocyst to form Weeks 3 to 8: embryonic period Weeks 9 to birth: fetal period

LABOR AND PARTURITION