The Beginning of Human Development Flashcards
Human Development
Continuous process that begins when an oocyte is fertilized by a sperm. Cell division, migration, apoptosis, differentiation, growth, cell rearrangement transform the fertilized oocyte, a totipotent zygote, into a multicellular human being
Human Embryology
The study of prenatal development
Gestation period
280 days from onset of last menstruation or 266 days from fertilization
Prenatal Periods
Pre-embryonic: fertilization - 2 weeks
Embryonic: 3-8 weeks
Fetal: 9 weeks-birth
Fertilization results in:
- oocyte completing meiosis II
- restoration of diploid chromosome number in zygote
- species variation
- determination of genetic sex
- initiation of cleavage of zygote
Gametogenesis
Process of formation and development of specialized generative cells (gametes)
Spermatogenesis
gamete maturation in males
Oogenesis
gamete maturation in females
Spermatogonium
Stem cell
Antrum
Characteristic of a secondary oocyte
Zona Pellucida
Shell-like structure surrounding an oocyte
- glycoprotein that provides protection
Corona radiata
Follicular cells that spermatid must fight its way through, loses some cytoplasmic material on the way
Mitochondrial sheath
powers that flagellar movement via. ATP synthesis
Ovarian cycle
FSH & LH produce cyclic changes in the ovaries including the growth of follicles, ovulation, and corpus luteum formation
FSH
Follicle stimulating hormone
LH
Luteinizing hormone
HPO
Hypotallamus, pituitary gland, ovaries
- Hypothallamus releases gonadotropin-releasing hormone that acts on pituitary gland, which releases gonadotropic hormones (LH & FSH)
Primary follicle
Activated by FSH, starts to divide rapidly
Theca Folliculi
follicle developed around the secondary oocyte, build-up of fluid inside the theca folliculi results in the release of the oocyte (ovulation)
Corpus Luteum
produces progesterone and estrogen, activated by LH
the theca folliculi transforms to the corpus luteum following ovulation
Estrogen
Released by the corpus luteum, fuses through the plasma membrane and binds to an estrogen receptor. Activated ER transfers transcription factor to the nucleus, results in rapid proliferation
Sperm lytic enzymes
Hylurinidase, acrosin
What occurs upon lack of fertilization
Corpus luteum degenerates, cutting the supply of progesterone and estrogen, resulting in the halting of proliferation. Lining will degenerate, rupturing blood vessels
What occurs upon fertilization
Sperm releases lytic enzymes to make it past the zona pellucida, once past the pellucida becomes impermeable.
First phase
two haploid pronuclei - ootid
Second phase
one diploid nucleus - zygote
When does the first cell division occur
30 hours following fertilization
12 - 34 hours
Zona pellucida is still present, results in the shrinking of cells as they divide. Uterine fluid has digestive enzymes that will slowly degrade the zona pellucida, cells push to one side and surround the zona pellucida and fluid seeps n and creates an inner cavity (embryonic hole)
When does the blastocyst form
4 days following fertilization
What happens 4 days after fertilization
Morula enters the uterus. Fluid-filled space (blastocystic cavity) appears. Fluid passes from the uterine cavity through the zona pellucida to form the cavity. As fluid increases the cavity, it forms 2 parts - tropho and embryoblast
Blast Cells
Cells that have the potential to form something
What happens 6 days after fertilization
Blastocyst attaches to the endometrial epithelium, as soon as it attached the trophoblast proliferates rapidly and differentiates into the cyto and syncitiotrophoblast
Cytotrophoblast
Inner, mono-nuclear layer of the trophoblast
Syncitiotrophoblast
Outer, multi-nucleated photoplasmic mass in which no cell boundaries can be observed
