Fertilization Flashcards
How long is the female reproductive cycle?
about 28 days
Days 1-14 of female reproductive cycle
FSH –> Estrogen –> Proliferative
Days 15 - 28 of female reproductive cycle
LH –> Progesterone –> Secretory
- increase in vascular supply to endometrium
What disrupts the female reproductive cycle?
- pregnancy = causes hormones to keep going, endo stays, increase progesterone
What causes women to feel sick when pregnant?
progesterone
Gametogenesis
- meiosis (splitting in half)
- sperm/oocyte become haploid
What happens on Day 14?
- ovulation
- increasing progesterone
What happens on Days 15-16?
- fertiliization
- happens in ampulla of tube
- sperm penetrates zona pellucida
What does the zona pellucida do?
allows only 1 sperm to fertilize egg
Once fertilization occurs, what does the ovum become?
- a zygote
- restores # of chromosomes to diploid (now 23 pairs)
Basic embryology after fertilization
- fertilization = unicellular embryo
- repeated mitotic divisions occur (cleavage)
- shape of blastomeres change & interact differently
- networks of blood vessels suck the sperm into the egg
What is the result of repeated mitotic divisions (cleavage)?
- rapid increase in # of cells (blastomeres): 2, 4, 8, 16, 32
- occurs w/in fallopian tubes
What happens when the blastomeres change shape?
- 16 blastomeres = morula
- usually time for it to enter the uterus
Process of fertilization
- 2-cell stage
- 4-cell stage
- 8-cell stage
- Morula
- Early blastocyst
- Later blastocyst
- Rearrangement of cells creates and inner cell mass called Blastocyst
2-cell stage
polar body, zon pellucida, blastomere
4-cell stage
4 blastomeres
8-cell stage
has zona pellucida
Morula
has zona pellucida
Early blastocyst
- inner cell mass
- degenerating zona pellucida
- blastocyst cavity
- trophoblast
Later blastocyst
- inner cell mass
- blastocyst cavity
- trophoblast
Creation of blastocyst
- fluid filled space separates the outer layer (trophoblast) & central blastomeres (inner cell mass)
- zona pellucida is shed
- trophoblasts attach to endo, proliferate into 2 layers
2 layers of trophoblasts
- cytotrophoblasts (inner)
- syncytiotrophoblasts (outer)
Structures of a blastocyst
- polar body
- inner cell mass
- blastocyst cavity
- trophoblast
- remnant of zona pellucida
Does a pregnancy stay in the blastocyst cavity?
No, it surrounds itself w/ endometrium
How do syncytiotrophoblasts work?
implant into the endometrium by ‘burrowing’
How do trophoblasts contribute to pregnancy?
- become the membranes surrounding the pregnancy (Chorion)
- inner cell mass becomes the embryo (baby)
Embryology Timeline (Days)
- Day 15: fertilization
- Day 16: mitosis-cleavage, morula
- Days 19-21: blastocyst, zona pellucida shed
- Days 21-28: human chorionic gonadotrophin released, implantation
What percentage of pregnancies fail?
75% (most don’t know they are pregnant)
Hormones levels during fertilization/morula/blastocyst stage
- LH & FSH declining
- progesterone increasing
Hormone levels during implantation stage
- trophoblasts produce hCG
- progesterone continues increasing
- blastocyst must ‘burrow’ into endometrium
Are menstrual & gestational the same? Why or why not?
- yes
- duration of pregnancy based on menstrual cycle & the physiology of the components of gestation
What is the embryological age?
the age since fertilization only (some books say ovulation)
What is the gestational age?
- pregnancy is clinically evaluated in terms of ‘weeks’
- 40 weeks or 10 lunar months (28 day cycles) is considered term
Summary of fertilization
- physiological extension of the female reproductive cycle
- zygote formation & early embryology
- pregnancy detection
