Descriptive Embryology Flashcards
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
Polyspermy
Multiple sperms fertilize and egg
Results in inviable zygote
Cortical Reaction
Slow Block to polyspermy
When sperm comes into contact with egg, non-penetrable fertilization membrane created
Enzymes (cortical granules) in egg released and eat away at zona pellucida as well- specifically the glycoproteins that allow sperm to bind (so other sperm can’t bind)
Occurs due to calcium oscillations inside the oocyte
Sperm Binding
Outside of sperm binds to zona pellucida
Acrosomal Reaction
Acrosomal tip released from sperm, releasing enzymes and digest zona pellucida
Fast Block
Sperm binds to egg
Na channels on egg opens, Na moves down concentration gradient (into egg), causing depolarization
Prevents sperm from binding
Trophoblast
Outer layer of blastocyst
Becomes placenta
Embryoblast
Inner layer of blastula
Embryonic stem cells (more plastic than somatic stem cells)
Also called inner cell mass
Blastocoel
Fluid pushes embryoblast outward to form a circular cavity
Endoderm Becomes
Digestive system
Liver
Pancreas
Inner layers of lungs
Mesoderm Becomes
Notochord
Circulatory system
Epithelial layers of lungs
Skeletal system
Muscular system
Ectoderm Becomes
Hair
Nails
Skin
Nervous System
Parthenogenesis
An animal’s ability to develop from an egg that has not been fertilized
Form of asexual reproduction
Parthenocarpy
Parthenogenesis except for the creation of fruit in plants
Neoteny
Adults retain their young counterpart’s morphological characteristics
Amphimixis
Another name for fertilization resulting in a zygote
Epimorphosis
Full differentiated cells re-obtain stem cell like features
