Placental Development and Gestation Trophoblastic Disease Lecture (Dr. Cole) Flashcards
Fertilization
Must be Preceded by:
1) Sperm Maturation (Epididymus)
2) Sperm Capacitation (Female Reproductive Tract) - Physiological changes necessary to Penetrate the Egg
- Removal of Some Epididymal and Seminal Glycoproteins
- Increase in Membrane Permeability to Ca2+
- Ca2+ Influx maximizes cAMP, Increases Sperm Motility
Sperm Covering
EPIDIDYMAL:
- The Plasma Membrane of Epididymal Spermatozoa contains a Complement of Surface molecules (Proteins and Carbohydrates)
EJACULATED:
- The Surface Molecules in Epididymal Sperm become coated with SEMINAL PLASMA PROTEINS that mask potions of the Membrane Molecules
CAPCITATED:
- When Sperm are exposed to the Female tract Environment, these Seminal Plasma Coatings along with some of the Surface molecules are removed, thus exposing portions of the molecules that can bind to the ZONA PELLUCID of the Oocyte
Three Mian Events in Fertilization
1) Acrosome Reaction
2) Sperm binding to ZP3
3) Sperm Egg Fusion
Acrosome Reaction and Sperm Binding to ZP3
- The outer membrane of the SPERM binds to the ZP3 RECEPTOR and allows for the Acrosome reaction or the release of Enzymes (NEURAMIDASE and ACROSS) from the Acromosal Space of the Sperm to Break Down the Zona Pellucida
Sperm- Egg Fusion
- After the first Sperm fertilizes the Egg, Proteases released form the Cortical Granules present in the Egg remove OLIGOSACCHARIDES from ZP3 and partially cleave ZP2!!!!!!!!!
- This process, called Cortical Reaction, prevents POLYSPERMY, an egg to be fertilized by more than one Sperm. POLYSPERMY results in NONVIABLE ZYGOTES
Immunoglobulin superfamily protein IZUMO is required for Sperm to FUSE with eggs as is PROTEIN CD9 (Egg)
- A mutation in IZUMO creates the INABILITY for the Sperm to Fuse to the Egg and undergo this Acrosome Reaction
Cortical Reaction
FAST COMPONENT: Change in RESTING POTENTIAL of Oocyte Plasma Membrane prevents further binding of Sperm
SLOW COMPONENT: Release of Cortical Granules containing Enzymes (into PVS) that Destroy Sperm Receptors
Development of Blastocysts
- Zygote undergoes Cleavage
- Develops into MORULA, once it has attained a 8 cell number
- Differentiates into BLASTOCYST, with outer Trophoblast, Inner Cell Mass and surrounding the BLASTOCYST Cavity
- The Blastocyst hatches from its ZONA PELLUCID at 6 to 7 days
Implantation of the Balstocyst
- Hatch from ZP
- APPOSITION: Adhesion to Endometrium
- Trophoblastic and Endometrial Cells express ADHESION Molecules (Integrins)
- Implantation mediated by PENETRATION TROPHOBLASTIC Cells
Uterine Receptivity and Decimal Reaction
- Corresponds to days 20 to 24 of a regular 28 day cycle
- Optimal State of Endometrial Maturation for the Implantation
- Consists in Vascular and Edematous Endometrial Strome, Secretory Endometrial Glands, and Apical Microprosesses, the PINOPODES, on the APICAL Domain of the Luminal Endometrial Lining Cells
- Cell enlarge, become PALE Staining and STORE LIPIDS and GLYCOGEN under the Influence of PROGESTERONE!!!!
Day 6 to 7: Blastocyst Implantation
1) Differentiated SYNCYTIOTROPHOBLASTIC CELLS invade part of the Myometrium (Interstitial Invasion)
2) Reduction in Number of DESMOSOMES facilitates Embryo Penetration
***PINOPODES are Apical Epithelial Cellular Protrusion of the Endometrium
Interstitial Invasion
- Invasion of the ENDOMETRIUM and the Inner THIRD of the MYOMETRIUM
- Determined by the action of Secretory Proteolytic Enzymes released by the SYNCYTIOTROPHOBLAST
- Proteases erode the branches of the SPIRAL UTERINE ARTERIS to form spaces or LACUNAE of Maternal Blood within the SYNCYTIOTROPHOBLAST Mass
Endovascular Invasion
- Initiates the PRIMITIVE UTEROPLACENTAL Circulation and represents the Starting Point of the FUTURE INTERVILLOUS SPACE!!!!
***TROPHOBLAST Infiltration —> LACUNAE!!!
Uteroplacental Circulation
- Established when Trophoblastic Cells are in DIRECT CONTACT with Maternal Blood
hCG
- The SYNCYTIOTROPHOBLAST begins the Secretion of HUMAN CHORIONIC GONADOPTROPIN (hCG) into he MATERNAL LACUNAE
- Secretion fo ESTROGEN and PROGESTERONE by the SORPUS LUTEUM is now under the control of hCG!!!!!!