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Sclera
white, tough outer covering
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Vitreous Humor
Viscous fluid that fills eye
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Cornea
1st lens, transparent, no blood vessels
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Iris
Ring of muscles, colored part of eye, contracts/relaxes in response to light
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Lens
Keeps image in focus
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Retina
converts light into electrical signals through optic nerve, responsible for central and color vision, responsible for peripheral vision
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Optic nerve
contains neurons that connect to the brain
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Eye Development (stages)
- 1. Optic vesicle: close proximity to the non-neural ectoderm to induce lens placode.
- 2. lens placode: invaginates to form the lens vesicle.
- 3. optic vesicle: forms the optic cup and stimulates lens induction.
- 4. cornea develops from ectoderm
- 5. retina differtiation of several layers of cells
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Induction:
cell to cell interaction that determines the fate of a group of cells.
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Zygote:
- Sperm entry point gives the zygote symmetry
- -Anterior/posterior
- -Left/right axes
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Two poles (determines orientation of zygote)
- Animal
- Vegetal
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Cleavage:
Rapid miotic divisions without cell growth (cell stays the same size)
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Mitosis promoting factor
- Increase - mitosis
- Decrease - DNA sythesis
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Blastomeres:
Individual cells
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Morula:
Latin for mulberry
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Development stages: 2 cell, 4 cell, 8 cell, Morula
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Blastula:
Blastomeres move to edges to form a hollow ball
- Blastocoel:
- Fluid inside the blastula
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Gastrula
Invagination: animal pole moves toward vegetal pole
Blastopore: opening
- Archenteron: cavity
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Development stages of gastrula:
- 3 layers:
- Ectoderm: skin, nervous system
- Mesoderm: muscles, circulatory system, cartilage, bone
- Endoderm: internal organs, gut lining
- Deuterostomes (echinoderms, chordates)
- -Blastopore forms the anus
- Protosomes (mollusks, arthropods, annelids)
- -Blastopore forms the mouth
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Yolk Distrubution Isolecithal
- Yolk:
- Evenly distributed
- Sparce
- Holoblastic cleavage
- Complete division of egg into blastomeres
- eg: seastars, mammals
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Yolk Distrubution Mesolecithal:
- Yolk:
- vegetal pole
- moderate pole
- Holoblastic cleavage
- -complete division of egg into blastomeres
- -cells divide slower at vegetal pole (yolk is thicker) ...faster in thinner part
- eg: amphibians
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Yolk distrubution telolecithal
yolk: throughout and dense
- Meroblastic cleavage:
- only a portion of the egg divides into blastomeres (in upper portion by nucleus)
- Discoidal cleavage:
- a type of meroblastic cleavage resulting in a disk of cells at the animal pole
- eg: reptiles, birds
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Chicken gastrulation:
blastodisc: area at animal pole without yolk
ingression: cells of blastoderm migrate and turn in at the primative streak
Cleavage is restricted to blastodisc (telolecithal)
- Primative streak:
- The same as the blastopore in the sea star
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Organogenesis Neurulation:
- 1) nervous system develops from ectoderm
- 2) epidermal cells move centrally
- 3) neural plate folds
- 4) folds elevate and come together
- 5) closing forming neural tube
- 6) neural crest cells migrate to form various structures
- 7) the neural tube then develops into the central nervous system.
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Organogenesis cardiogenesis:
- 1. Heart develops from mesoderm
- 2. paired tubes fuse, blood flows from bottom to top (25-30hrs)
- 3. S-bend (about 33hrs)
- 4. Folds onto self into a loop, atria on the top and ventricles on the bottom (48hrs)
- 5. Divsion into chambers (72hrs)
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Development requires:
- growth
- differentiation - specialization of cells (eg: muscles or nerves)
- organogenesis - organis
- morphogenesis - body begins to take shape
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