Embryology: 0-4 weeks Flashcards
At what meiotic stage does ovulation occur? What is the cell’s DNA/chromosome content like at this point?
*Meiosis II metaphase. Haploid in chromosome (1n) and diploid in DNA (2d)
^Starting superficially, what are the three layers of the ovum?
*Corona radiate cells, zona pellucida and the oocyte membrane.
^What cells in the fallopian tube secrete nutrients for the ovum?
*Peg cells
^Where do sperm take swimming lessons?
*Epididymus
^How long is the ovum viable in the female genital tract?
*24 Hours
^What are sperm’s DNA/chromosome content at the time of ejaculation?
*Since they have completed meiosis II, they are haploid in DNA content and in chromosomes.
^What is the main mode of transportation in getting sperm past the cervix and into the fallopian tubes?
*Vaginal contraction and peristalsis
^What happens to the very first sperm to get to the fallopian tube?
*It hides in cilia of fallopian cells, waiting to ambush to ejected egg when it passes.
^What must happen to the sperm before it can fertilize the egg?
*Capacitation (glycocalyx coat degrades around acrosomal head) and acrosome reaction (release of acrosin and trypsin-like enzymes to degrade the zona pellucida)
^How long is sperm viable in the female genital tract?
*24-48 hours.
^How do sperm get through the first barrier to the ovum?
*Hyaluronidase release to digest hyaluronan in corona radiata cells. They tail also starts whipping like a corkscrew.
^What makes up the zona pellucida and what helps the sperm to penetrate it?
*Glycoproteins ZP1,ZP2 and ZP3. ZP3 is a sperm receptor.
^How does the fertilized egg prevent other sperm from entry?
*Release of cortical granules changes the properties of the zona pellucida
^What is released into the ovum cytoplasm when sperm and egg membranes fuse? What survives in the cytoplasm?
*The head (nucleus) and tail (mitochondria) of the sperm enter the cytoplasm. Only the nucleus survives, this is why you inherit mitochondria from your mom.
^What happens to the ovum upon fertilization?
*The ovum finished meiosis II, then both sperm and ovum pronuclei replicate DNA, pronuclei membranes degenerate and mother/father chromosomes line up for first mitotic division.
^What happens during the cleavage stage of conceptus development?
*The fertilized egg undergoes 3 mitotic divisions to form blastomeres that undergo compaction. Compacted blastomeres divide to form a 16-cell morula. At day 3-4 a cavity develops and the blastocyst is formed.
^What will the different compartments of the blastocyst become?
*Inner cell mass will become the embryo proper. The outer cell mass ill become the trophoblast.
^How does the newly fertilized egg compact blastomeres?
*Fluid entry through the zona pellucida.
^What does the blastocyst hatch out of and why?
*The zona pellucida. The zona pellucida is made of stiff glycoproteins that do not allow for expansion and growth.
^What part of the developing embryo allows us to do blood pregnancy tests early on?
*Syncytiotrophoblast. It secretes hCG which prevents the corpus luteum from degenerating.
^What causes the uterus to prepare for implantation?
*Progesterone secretion by the corpus luteum makes the endometrium enter the secretory phase.
^Once the blastocyst has implanted, how the the trophoblast (outer cell mass) differentiate?
*It differentiates into an inner layer, cytotrophoblast and and outer layer syncytiotrophoblast. The syncytiotrophoblast are cells that divided from the inner cytotrophoblast layer and lost their membranes.
^Once the blastocyst has implanted, how does the embryoblast (inner cell mass) differentiate?
*The bilaminar disc forms. Hypoblast layer is adjacent to the blastocyst cavity. Epiblast layer is adjacent to the amniotic cavity.
^What will the different components of the bilaminar disc become?
*The hypoblast will become the yolk sac. The epiblast will become the baby and form the amniotic cavity.
^Where does the amniotic cavity begin forming?
*Within the epiblast.
^What happens to mom’s endometrium around day 9?
*The syncytiotrophoblast cells invade the endometrium and initiate the decidua reaction, the endometrium becomes edematous and begins to secrete glycogen.
^What happens to the yolk sac around day 9?
*The exocoelomic membrane forms within the cytotrophoblast cavity, forming the primitive yolk sac with the hypoblasts.
^How is uteroplacental circulation established?
*First lacunae form in the syncytiotrophoblast, then the cells of the syncytiotrophoblast erode maternal endometrial tissue and maternal blood fills the lacunae to form sinusoids.
^How does the chorionic cavity form?
*The extra-embryonic mesoderm forms between the yolk sac and cytotrophoblast. This develops cavities that eventually push the primary yolk sac inwards to form the chorionic cavity.
^What else does the extra-embryonic mesoderm help form?
*Connecting stalk, extraembryonic somatic mesoderm (lines the cytotrophoblast) and the extaembryonic splanchnic mesoderm (lining the yolk sac)
^Extra-embryonic cavity formation
*
^What is the fate of the primary yolk sac?
*The hypoblast proliferates cells to form the smaller secondary yolk sac. During formation of the secondary yolk sac, large portions of the primary yolk sac are pinched off to for exocoelomic cysts in the chorionic cavity.
^What cascade of development occurs from the bilaminar embryonic disc?
*
^Where does the primitive streak first form?
*Epiblast
^How are the endoderm and mesoderm formed?
*Invagination. Epiblast cells migrate to the primitive streak and dive down.
^How is the ectoderm formed?
*Cells don’t invaginate and stay in the epiblast.
^What is the next structure developed after the primitive streak?
*Oropharyngeal membrane. Cells migrate through the primitive streak in a caudal-cranial direction.
^How does the notochord form?
*Cells invaginate at the primitive streak, migrate forward. Cells from the endoderm detach and form the notochord.
^How does the neural plate form?
*The notochord induces overlying ectoderm cells to thicken.
^How does the neural groove form?
*Proliferation and invagination of the neural ectoderm
^How is the neural tube formed?
*The neural crests come together and the neural groove seals off
^How does lateral embryonic folding occur?
*
^What cavities form as a result of lateral embryonic folding?
*Amniotic cavity and intraembryonic cavity
^How does craniocaudal embryonic folding occur?
*
^What forms as a result of craniocaudal folding?
*Gut tubes, ventral wall fuses and body stalk (eventually the umbilical chords)
^What organs develop from the neuroectoderm?
*CNS, PNS, sensory epithelia of ears, nose and eyes, epidermis (hair and nails), subcutaneous glands, mammary glands, and tooth enamel.
^What organs develop from the surface ectoderm?
*Hair, anal lining, vestibular lining and epidermis
^What develops from the neural crest?
*Ganglia, meninges, schwann and glial cells, thyroid C cells and adrenal medullary cells.
^What develops from the paraxial mesoderm?
*Skeleton, skeletal muscle and dermis
^What develops from the intermediate mesoderm?
* Urinary system and gonadal tissues
^What develops from the parietal mesoderm?
*Muscle, vessels and bone connective tissues
^What develops from the endoderm?
*GI tract, liver, trachea, bronchi and lungs.
