Conception, Implantation and fertelisation

Pre-implantation changes to the zygote include development of the embryonic disc, tissues, membranes, and the process and result of embryonic disc folding.

Implantation involves attachment and invasion, and the prolongation of the corpus luteum.

Normal sites include the upper posterior wall of the uterus, while abnormal sites include the uterine tube, rectouterine pouch, intestinal mesenteries, ovary, and cervical internal os.

The placenta is formed by both fetal and maternal tissues and involves the placental membrane between maternal and fetal blood.

The mature placenta functions in gaseous exchange, nutrient transport, excretion, hormone and protein synthesis, and has a limited lifespan.

The three main decidual layers are the decidua basalis, decidua capsularis, and decidua parietalis.

The fetal membranes include the amnion, chorion, yolk sac, and allantois, originating from the trophoblast and extra-embryonic mesoderm.

In dizygotic twins, each has its own placenta and fetal membranes. In monozygotic twins, the arrangements depend on when the embryo separated.

Capacitation is the process where glycoproteins are removed from the sperm's plasma membrane, increasing cytoplasmic pH and calcium permeability, which enhances motility.

The acrosomal reaction involves chemical changes in the acrosome of the spermatozoa when it contacts the zona pellucida of the oocyte, aiding in penetration.

The cortical reaction is the release of cortical vesicles from the oocyte plasma membrane after fusion, preventing polyspermy by making the zona pellucida impermeable to additional sperm.

The head and tail of the sperm enter the oocyte's cytoplasm, the oocyte completes meiosis, and the male and female pronuclei form, leading to the formation of the zygote.

The zona pellucida is a glycoprotein shell surrounding the oocyte that facilitates sperm binding and the acrosomal reaction.

The primitive streak appears in the midline at the caudal end of the epiblast, establishing the left and right sides of the embryo and initiating gastrulation.

The primary germ layers are the endoderm, mesoderm, and ectoderm, formed by the migration and differentiation of epiblast cells.

The syncytiotrophoblast is a multinucleated, invasive cell mass that secretes hormones like hCG and progesterone, and releases enzymes to digest the endometrium during implantation.

The cytotrophoblast forms the syncytiotrophoblast and chorionic villi, which are important for early placental development.

Abnormal implantation sites can lead to ectopic pregnancies, placenta praevia, and other complications that may result in haemorrhage or other risks during pregnancy.

The zona pellucida is a glycoprotein shell surrounding the oocyte that facilitates sperm binding and the acrosomal reaction.

The fimbriae sweep the ovulated ovum into the uterine tube.

The epithelial cells are highly ciliated, aiding in the transport of the ovum.

Spermatozoa become immotile and temporarily bind to epithelial cells, waiting for the oocyte.

The release of a chemoattractant by the oocyte triggers the reactivation of spermatozoa.