Exam 3 - Fertilization, Implantation, Embryonic Development Flashcards
Where does fertililzation occur?
Fallopian tube
- Two haploid cells (23 chromosomes each) come together to form a diploid zygote (46 chromosomes)
What happens four days after fertilization? What is the progression of the zygote?
Four days (72 hours) after fertilization the morula (ball of 12-16 cells) increases in size –> central cavity formed –> blastocyst –> enters endometrium and selects area for implantation
Components of a blastocyst
- Zona pellucida - holds cell together
- Syncytiotrophoblast - endometrial covering of embryonic placental villi, invades wall of uterus to establish circulation between mother and embryo
- Cytotrophoblast - inner layer of trophoblast
Blastocyst germ layers
- Endoderm - forms inner lining of organs
- Mesoderm - develops organs
- Ectoderm - forms exoskeleton
Undergo transformation after 3 weeks
What two tissue types develop during implantation?
- Syncytiotrophoblast - burrows into endometrium and becomes primary source of hCG (causes implantation bleeding)
- Cytotrophoblast - forms columns of cells that anchor villi of placenta (point of contact between maternal and fetal tissue)
- After 12-20 weeks, cytotrophoblast extends deep into endometrial tissue
What happens if cytotrophoblast invasion into decidual tissue is late?
Maternal spinal arteries remain small –> nutritional needs of fetus not met by the small placenta due to limited maternal blood flow
What is thought to be the beginning of preeclampsia?
Late invasion of the cytotrophoblast into decidual tissue
- Associated with fetal growth restriction, PROM, preterm delivery, preterm labor
What is morphogenesis?
Genetically controlled cell groups become organized and specialized stem cells that develop into specific cell types
What is the consequence of early morphogenesis?
Incomplete organogenesis
- Referred to as anencephaly or lack of brain development
When are all major organs formed?
By beginning of fetal period
- 10 weeks - growth accomplished by hyperplasia (increasing cell numbers) and hypertrophy (increase cell size)
- 32 weeks - hypertrophy is dominant
At what week does limb development begin?
Week 3
When are face and hand movements first noted?
12-13 weeks
When are limb, head, and torso movements noted?
12-16 weeks
When do fetuses begin to suck their thumb?
15 weeks
When are respiratory movements noted?
24 weeks
