Lab 16: Embryonic Devo Flashcards
From Sperm gets to egg till haploid
- Sperm Penetrates Egg: Acrosomal enzymes and strong flagellar movements help the sperm penetrate the cells of the corona radiata and contact the zona pellucida
- Sperm move inside: Enzymes digest a path through the zona pellucida until the sperm contacts the oocyte.
- The egg completes meiosis II and produces a second polar body.
- Sperm and egg nuclei swell and become pronuclei.
- Pronuclei rupture and the chromosomes mix (produce diploid zygote)
From Zygoat to blastocyte
- rapid mitotic divisions occur (referred to as cleavage)
- fourth day post-fertilization, the zygote is a solid sphere of cells
- Called morula now
- passes into the uterus.
- morula divides, develops a hollow cavity and accumulates fluid.
- zona pellucida disintegrates.
- Called blastocyst now
- process of differentiation of cells begins (inner cell mass forms embryo, outer mass [trophoblast] forms placenta)
- Day 6/7: begins implantation. (blastocyst adheres to the uterus endometrium)
outer cell mass (trophoblast)
- trophoblast develop into two layers(inner cellular trophoblast; outer syncytial trophoblast.)
- syncytial trophoblast secrete enzymes to allow uterine wall penetration (also secretes Human chorionic gonadotropin (HCG) that detects preggo)
- HCG stimulates the corpus luteum to secrete estrogen and progesterone (HCG is what’s detected in pregnnacy testS)
inner cell mass
- organizes into embryonic disc, 2 layers (epiblast [top], hypoblast)
- space in epiblast enlarges into amniotic cavity, fills with fluid.
amniotic fluid function
cushions and protects the embryo from trauma and extreme temperatures, and keeps the fetal tissues moist
what’s Amniocentesis?
Amniocentesis - drawing amniotic fluid to examine fetal cells
What is Water broke during pregnancy
amnion may rupture, releasing the fluid when “one’s water breaks”
Yolk Sac
- Fomed by cells migrating from edge of the hypoblast to cover inner blastocyst cavity
- Function: provides nourishment to the embryo while the placenta is being established
14 Days post fertilizatin
14 Days post fertilizatin
• blastocyst covered by endometrium
• Extraembryonic mesoderm cells (from yolk sac) form layer around amnion/yolk sac
• large cavity develops
• extraembryonic mesoderm + trophoblast = chorion (encases embryo)
• chorion develops chorionic villi
• Blood vessels form in the chorionic villi for diffusion of gas/nutirents in embryo
Week 3 post fertilization
- gastrulation occurs: epiblast and hypoblast cell layers into primary germ layers
- epiblast becomes ectoderm, hypoblast is endoderm, and the cells proliferating in between form mesoderm
- Epiblast –> ectoderm
- Hypoblast –>endoderm
- cells proliferating in between –> mesoderm
Cell Layers Give Rise to:
- Ectoderm: epidermis, glands and nervous tissue.
- Endoderm: epithelial lining and glands of the digestive and respiratory systems.
- Mesoderm: muscle, blood, bones, the heart and kidneys
• Allantois: develops from the endoderm and mesoderm, forms part of the urinary bladder/umbilical chord
Weeek 4 post fertilization
- heart is beating, precursors of skeletal muscles appear, elements of the nervous system are developing, buds are present for arms and legs and small discs for the eyes and ears.
- organ system arise from prim germ layers
- Placentation is the process of forming the placenta
- chorionic villi in the endometrium compress and degenerate
- chorionic villi below embryo form placenta
- placenta produces human chorionic gonadotropin to help maintain pregnancy
- placenta acts as a barrier to most micoorganisms but does allow viruses such as measles, chicken pox, encephalitis, and poliomyelitis to cross, as well as many drugs and alcohol.
End of month 2
- Caledd fetus, 3 cm long.
- fetus grows, uterus expands, materal abdominal organs displaced
- cellular differentiation of Fetal organs
- Bones calcify, sensory organs complete formation, and fetal movements are detectable.
Ovulation:
primary follicues –> Graafian follicle
- under the influence of LH and FSH
- primary follicles increase in size
- follicular cells proliferate form a ring of granulosa cells around ovum.
- Only one follicle will typically reach the maturity needed for ovulation.
- primary–> secondary follicle (larger oocyte and more layers of follicular cells)
- connective tissue condenses and differentiates as thecal layers –> called Graafian follicle
Follicle is known as a Graafian follicle, or mature follicle
• When the follicle is mature, the theca interna cells begin to secrete the hormone estrogen
ovulation:
Graafian follicle–> zygoate
- primary oocyte undergoes meiosis I: produce the haploid secondary oocyte + polar body (which degenerates).
- Ovulation: Graafian follicle ruptures and releases secondary oocyte (stimulated via Pituitary hormones)
- Pituitary hormones stimulate ovulation
- secondary oocyte enters uterine tube; transported to uterus
- Penetration of the oocyte by a sperm
- produce haploid ovum + second polar body (which degenerates)
- ovum (n) + sperm (n) fuse into zygote (2n)
After ovulation
• ruptured follicle forms corpus luteum (secretes progesterone and estrogen)
- progesterone: important for development of the placenta + suppression of follicle maturation during pregnancy
• Loose connective tissue fills former follicular cavity
• No pregnancy: corpus luteum degenerates into corpus albicans (scar tissue)
