Descriptive Embryology Flashcards
(40 cards)
Fertilization- Recognition
Oocyte has glycoprotein coat on PM (vitelline/zona pellucida in humans)
Sperm secretes protein which binds to receptors on the coat so fertilization only occurs between egg and sperm of same species
Zona pellucida binds sperm, acrosome reaction creates fast charge based block of
polyspermy
Fertilization- Penetration
PM of sperm and oocyte fuse togeher
Nucleus of sperm enters egg
Vetelline layer forms membrane to prevent other sperm from entering
Fertilization- Meiosis and completion of fertilization
Meiosis 2 completes
In humans, sperm penetrates egg, meiosis 2 is triggered in oocyte
Produces egg adn polar body
2 nuclei fused to form zygote
Chromosomes replicated
Cleavage
Zygote undergoes division but remains the same size- newly divided cells are blastomeres
Blastomeres
Each smaller than the previous
Poles
Dense areas within zygote are naturally separated from the less dense
Forms animal pole and vegetal pole (yolk/food)
Early cleavages are polar (contain both poles) and later divisions become parallel with the equator
Indeterminate Cleavage
Cleavage is indeterminate if it produces blastomeres that if seperated, can individually complete normal development
Do not have a pre set fate- have equal potential to produce fully functional embryos
Also known as regulative cleavage
Determinate Cleavage
Blastomeres that cannot develop into a complete embryo if seperated from other blastomeres
If cleaves, resulting embryos will be incomplete and dysfuntional
Have a decided fate
Also known as mosaic cleavage
Morula
After multiple divisions, resulting ball of cells is a morula
Blastocyst
Cell divisions continue, liquid fills the morula between trophoblast and embryoblast
Entire structure= blastocyst
In other animals, called blastula or blastophere
Gastrula
Gastrulation (forming gastrula) occurs when group of cells invaginate into blastula
Has 3 germ layers (ectoderm, mesoderm, endoderm)
Archenteron
Cavity resulting from invagination into blastula
Blastopore
Opening into archenteron
Extraembryonic Membrane Development
Only develops in birds, reptiles, and humans (amniotes)
Consists of chorion, allantois, amnion, yolk sac
Chorion
Outer membrane of extraembryonic membrane
In birds and reptiles, for gas exchange
In mammals, implants into endometrium and later forms placenta (nutrient, gas, water exchange between embryo and mother)
Placenta
Made up of chorion and endometrium
Allantois
Sack that branches off archenteron
eventually encircles the embryo and forms a layer beneath the chorion
In birds/reptiles- waster storage for uric acid, later fuses with chorion
In mammals- transports wastes to placenta, eventually forming umbilical cord (transportation between embryo and placenta)
Amnion
Encloses amniotic cavity
Aminiotic cavity is filled with fluid (cushion for embryo)
Yolk Sac
Used for nutrients in birds and reptiles
In humans, first site of RBC synthesis
Protostomes
Spiral Cleavage
Early cleavage occurs at a slight angle (misaligned cells)
Opening of archenteron (blastopore) becomes mouth
Coelom (cushion) forms by mesoderm splittig
Deuterostomes
Radial Cleavage
Early cleavage is straight (cells aligned in a vertical axis)
Opening of archenteron (blastopore) becomes anus
Coelom (cushion) forms by outpouching in wall of archenteron
Organogenesis
After gastrulation, cells begin to differentiate from one another
Allows formation of different tissues and organs
Notochord
Cells on the upper/dorsal mesoderm
Provides support
Neural Tube
Neural plate—.> neural groove—> neural tube
Develops into CNS
More cells roll off the top of the neural tube, which become the teeth. bones, skull, pigment, cells, and nerves
