PHYS - Pregnancy, Parturition, Lactation Flashcards
Where does fertilization occur?
Ampulla of the Uterine Tube
Where does implantation occur?
Fundus of the uterus
What are the 2 steps of fertilization
Capacitation
Acrosomal Reaction
What is capacitation?
Uterine and fallopian tube wash away inhibiting factors on sperm
Makes the sperm membran more permeable to Ca2+
Activates sperm
What is the acrosome reaction
Reaction necessary fro sperm to break through barriers blocking its access to the egg
Acrosome: contains Hyaluronidase and proteolytic enzymes
1) Hyaluronidase helps break through the corona radiata
2) Zona Pellucida
- ZP1 (crosslinks ZP2 and ZP3)
- ZP2 - blocks polyspermy
- ZP3 - activates acrosome reaction (SPERM HAVE ZP3 RECEPTORS; requires capacitation for receptor to function). Once sperm binds ZP3 to receptor, acrosome releases enzymes breaking through zona pellucida
ZP3 receptor falls off sperm, and it is then able to bind to ZP2, which tells ovum to not allow any more sperm to enter (blocks polyspermy)
3) Sperm and DNA enter ovum
Where is the sperm resevoir and what is it for?
Sperm resevoir in Ithmus of uteirine tube
Holds on to sperm if ovum has not been released yet from ovary
What are the steps of the cortical reaction?
1) Hardening of the Zona Pellucida
- Once ZP2 in the Zona Pellucida binds to the removed Sperm ZP3 receptor, ZP2 becomes ZPf
ZPf hardens the Zona Pellucida preventing anymore sperm from appraoching the egg
2) Release of Ca2+ stimualtes the completion of Meiosis II (ovum is arrested in Metaphase II until fertilization)
3) Egg activation
- Once meiosis is completed, egg is activated and the sperm pronucleus and egg pronucelus fuse, initiating the 1 st embryonic cleavage
What are the 2 steps of the first week of embyronic development?
1) Compaction and Blastocele Development
- Morulla (16 cell mass) is formed after 3 days
- Formation of tight junctions and desmosomes allows the formation of a blastocyst at day 4. Blastocyst is composed of an outer layer of Trophoblast cells, a fluid filled space called the blastocoele, and an Inner cell mass
- Inner cell mass becomes the developing embryo; trophoblast cells become extraembryonic structures (placenta)
2) Blastocyst hatching
- Hardened zona pellucida at day 5 is still surrounding the developing Blastocyst
- Implantation cannot occur while the zona pellucida is surrounding the blastocyst
- Blastocyst hatches from the zona pellucida at day 5 before it implants
What is differentiation potential of the morulla vs the blastocyst inner cell mass?
Morulla cells are totipotent (can become any cell)
Inner cell mass cells are Pleuripotent (can be come endoderm, mesoderm, or ectoderm, but cannot become any extraembryonic structures)
What are some cmplications with Blastocyst hatching?
If balstocyst fails to hatch from the zon pellucida, implantation cannot occur, resutling in infertility
If blastocyst hatches from the Zona Pellucida too early, you can have an ectopic pregnancy, where the blastocyst implants into the uterine tube instead of the uterus
What are the Cytotrophoblasts?
Trophoblast cells of Blastocyst differentiate into either Cytotrophoblasts or Syncytiotrophoblasts
Cytotrophoblasts are cells that support the Syncytiotrophoblasts
What are Syncytiotrophoblasts?
Trophoblast cells of the blastocyst differentiate into either Ctyotrophoblasts or Syncytiotrophoblasts
Syncytiotrophoblasts are cells that:
- Increase invasion of the Extracellular Matrix of the Endometrium (allowing implantation to occur)
- Secretes hCG
- Becomes steroidogenic at 10 weeks, taking over for the corpus luteum
- Acts as a medium for gas exchange, waste/nutrietn excahnge, etc
WHat is hCG?
Pregnancy is maintained via secretions of Estrogen and Progesterone
Placenta (Syncytiotrophoblasts) is not able to sustain adequate steroid synthesis to maintain the pregnancy until Week 10
So instead, Syncytiotrophoblast cells synthesize and secrete hCG, which maintains the corpus luteum, which secretes enough Estrogen and Progesterone to maintain the pregnancy
hCG secretion stops at week 10 when placent makes its own steroids
What are the steps of Implantation?
1) Apposition
- Blastocyst makes contact with endometrium
- Inner Cells Mass rotates so that its facing the endometrium
2) Attachment
- Trophoblast cells adhere to the epithelial cells of the endometrium
- Intiates changes in the endometrial stroma (decidualizaton)
3) Invasion
- Trophoblasts differentiate into Syncytiotrophoblasts and cytotroophoblasts
- Blstocyst degrades endometrial epithelial cells, invading the endometrium, and fuses to the endometrium
What is decidualization?
It is the maternal response to implantation
- Endometrial stroma becomes filled with enlarged, glycogen-rich decidual cells
- Endometrial stroma, becomes known as the Decidua
- Participates in active exchange of gases, nutrients, and waste
- Protects pregnancy from mothers immune system
- Decidual cells allow proper depth of implantation, preventing the blastocyst from invading through the uterus and entering the perineum
