Where does fertilization occur
In the ampulla of the fallopian tube
- upper third of the fallopian tube
How long does it take for the egg to
... [Show More] travel from the place of fertilization to the uterus for implantation?
7 days
Capacitation
Once in the female reproductive tract, the protective coat on sperm head is removed
- It allows the head to penetrate the zona pellucida
- Capacitation allows the acrosomal enzymes to be released later
Acrosome
The end of the head of sperm
Components of the zona pellucida
3 glycoprotein layers
- ZP1(outer), ZP2, ZP3(inner)
Acrosomal Reaction
1) Receptors on the sperm head bind to ZP3
2) A rise in Ca2+ inside the sperm will trigger the release of the acrosomal contents into the oocyte
8 Steps in fertilization
1) Sperm head attaches ti zona pellucida
- Receptors on the PM of the sperm bind to ZP3, triggering acrosomal reaction
2) Acrosomal reaction occurs
- Increase in Ca2+ causes acrosomal contents to be expelled into oocyte
3) Hydrolyzing enzymes in the acrosomal cap facilitate the sperm to penetrate the zona pellucida
4) Cell membranes of sperm and oocyte fuse
- IP3 is formed, causing Ca2+ release from internal stores
5) Increase in Ca2+ triggers oocytes 2nd meiotic division and cortical reaction
- Granules exocytose and cause the zona pellucida to harden
6) 2nd meiotic division finishes and nucleus decondenses = female pronucleus (1N)
- Oocyte divides into mature oocyte and 2nd polar body
7) Sperm nucleus deondenses into the male pronucleus (1N)
8) Male and female pronuclei fuse, forming a zygote
- Zygote (2N) = 46 chromosomes
Cortical Reaction
1) A rise in Ca2+ in the oocyte triggers reaction
2) Electron dense granules in the oocyte exocytose
3) Exocytosis of the granules releases enzymes that act on glycoproteins in the zona pellucida, causing them to harden, preventing any more sperm from entering
Overview of oogenesis and arresting points
Fetal oogenesis
- Primary oocyte begins 1st meiotic division and is arrested in prophase
Puberty oogenesis
- Primary oocyte finishes 1st meiotic division
- 2nd meiotic division begins and is arrested in metaphase
Fertilization
- Fertilization triggers completion of the 2nd meiotic division into a mature oocyte
Morula Stage
Fertilized ovum resides in fallopian tube and continues to divide (12 or more cells)
- receive nourishment from fallopian tube secretions
Morula will move through isthmus to uterus by beating cilia and contractions
Blastocyst
Ball like structure w fluid-filled inner cavity
- Transforms from morula to blastocyst in the uterine cavity
- It freely floats for about 72 hours before it implants to the uterus
7 Days after ovulation
Progesterone from corpus luteum vascularize the endometrium to prepare for pregnancy
Predecidulization
9-10 days after ovulation
- Stromal cells transform into rounded decidual cells
- Decidual cells spread across superficial layer of endometrium making it more compact (zona compact), separating it from deep spongy later (Sona spongiosa)
Decidualization
The predecidual changes are sustained and extended
What does the corpus luteum secrete
Progesterone
- Maintains endometrium
What does the uterine glandular epithelium secrete?
Steroid dependent proteins for nourishment, growth and implantation
What does the Endometrium Secrete?
- Cholesterol
- Steroid
- Other nutrients
Maternal Cellular Immune system
may recognize the blastocyst as a enemy and kill it
Immunosupressive Agents
Blastocyst secretes hCG that has immunosupressive characteristics
- This depresses the mothers immune system so she doesn't reject the blastocyst
Some women have hypersensitive immune systems, and will still reject the blastocyst
hCG
Human Chorionic Gonadotropin
- Sustains corpus luteum after maternal LH levels fall
- Has growth promoting ability
- Acts as an autocrine growth factor that promotes trophoblasts (outer layer of blastocyst that implants into endometrium)
Blastocyst during implantation
embeds in uterine lining
- adheres to epithelial cells
- Breaks through basement membrane
- invades stroma
In vitro fertilization-embryo transfer (IVF-ET)
Oocytes are removed from women, fertilized in vitro, then the embryos are implanted back into women
Steps to IVF-ET (5)
1) Ovarian Stimulation
2) Cycle Monitoring
3) Oocyte retrieval
4) Insemination
5) Embryo transfer
1) Ovarian Stimulation
Females only develop 1 dominant follicate each cycle, but success rate isn't high so more are needed
- GnRH analogues are given to gonadotropins to down-regulate hypothalamic-pituitary axis (prevents premature LH surge and ovulation)
- Give high dose of external gonadotropin(LH, FSH) to trigger the release of many dominant follicles
2) Cycle Monitoring
- follicular growth is monitored by sonographic imaging and estradiol levels
- When folliculogenesis is indicated, LH surge is stimulated by injecting hCG
- LH surge will complete maturation of multiple follicles and oocytes
- Oocytes must be removed after maturation, but before ovulation (34-36 hours) [Show Less]