CAS BI 105 Lecture Notes - Lecture 16: Umbilical Vein, Umbilical Cord, Blastocoel
30 Apr 2018
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Steps of Development
1. Fertilization - gametes meet and produce a zygote (a one-celled diploid organism resulting from
mitosis)
2. Cleavage - cell division & mitosis (not meiosis because cells are identical)
3. Gastrulation - cells go to the stomach
4. Neurulation - cells go to the nervous system
5. Organogenesis - organs are formed and the gut is formed
6. Metamorphosis
Fertilization
•1. Acrosomal Reaction
•Sperm enzymes break through a portion of the egg wall
•2. Sperm fuses to the egg wall
•Sperm releases nucleus into the egg
•3. Fast Block to Polyspermy
•Ions are sent out to deionize and prevent other sperm from binding to the egg wall
•4. Cortical Reaction (how sperm release their nucleus into the egg)
•Sperm’s endoplasmic reticulum releases calcium allowing vesicles to be released inside the egg
•4a. Slow Block to Polyspermy
•Enzymes in the sperm pull the Zona Pellucida away from the egg to be hardened and used as a
nuclear envelope
•Zona Pellucida - entrances to the egg
•When the Zona Pellucida is pulled off, the excess sperm that did not bind is also pulled off
•5. Calcium triggers the egg to start mitosis and cellular respiration
Cleavage
•Cell Division without cell growth
•Resulting cell ball stays the same size
•Cells rotate between mitosis and s-phase (DNA replication)
•*no rest = no G1 or G2 phase
•After cell division, the resulting cell ball is called a blastula
•The inside of the blastula is filled with water
•This water is known as the blastocoel
•A small portion of the blastocoel eventually turns into a yolk (like a nucleus)
•For Mammal Embryos
•1. Compaction
•Condensing the blastula
•2. Change in Name
•Happens when the blastocoel expands
•When the blastocoel expands, the cells that form the wall become thinner, allowing the water to
expand and take up more room
•cell ball = blastula —> blastocyst
•egg = embryo —> morula
•3. Cleavage Stops
•This happens when the cells surrounding the blastula are normal
•*normal = have an even cytoplasm:nucleus ratio
•Single cell surrounding the blastula - blastomere
•4. Cleavage & Implantation
•Cleavage occurs in the fallopian tubes
•Ovaries are both a reproductive organ and an endocrine gland
•Endocrine Gland - a gland that releases hormones (ex: estrogen)
•The egg develops in a follicle within the ovary
•Follicle - protective shell around the egg that releases hormones
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Document Summary
Acrosomal reaction: sperm enzymes break through a portion of the egg wall, 2. Sperm fuses to the egg wall: sperm releases nucleus into the egg, 3. Fast block to polyspermy: ions are sent out to deionize and prevent other sperm from binding to the egg wall, 4. Cortical reaction (how sperm release their nucleus into the egg: sperm"s endoplasmic reticulum releases calcium allowing vesicles to be released inside the egg, 4a. Calcium triggers the egg to start mitosis and cellular respiration. Cleavage stops: this happens when the cells surrounding the blastula are normal, *normal = have an even cytoplasm:nucleus ratio, single cell surrounding the blastula - blastomere, 4. Change in name: cell ball = blastocyst = trophoblast, implantation occurs when the trophoblast adheres to the uterus wall, 4b. Uterus wall envelops the trophoblast to protect it: trophoblast begins to invade and reproduce itself within the envelope, the envelope made by the uterus wall turns into the placate, 5.
