Cleavage Flashcards
Cleavage forms from_____ to _____
Day 1-5
Patterns of cleavage
1.) Poles
2.) Cleavage pattern divisions (1-5)
3.) Cleavage patterns yolk
4.) Timing of cleavage pattern
Cleavage humans
1.) Recap
2.) At 8-cell stage (morula)
3.) Morula by day 4
4.) Blastocyst by day 5
Principles of cleavage
1.) Now 1 cell: initial phase of cell division after fertilization (within 24 hours)
2.) New established combination of DNA, complete set of genetic information
3.) Rapid series of mitotic cell divisions and cells form daughter blastomeres
4.) Cell is “cleaved” or “cut up” into smaller cells (within Zona Pellucida)
5.) Cleavage produces cells of a geometric progression
6.) Morula (solid ball)
Cell is “cleaved” into smaller cells within the ________
Zona pellucida
Nucleocytoplasmic reaction (“cleaved”)
- specific ratio of nucleus to cytoplasm
- SAME overall size but the cell divides
Cleavage geometric progression
- 2 cells
- 4 cells
- 8 cells
- 16 cells
- 32 cells
(hard to follow 32 cells)
Morula
- solid, ball-like structure
- up to 32 cells “raspberry”
- same size as original egg
Morula (16-32 cells) is also known as_______
“raspberry”
Timeline
- Time 0: sperm + egg (zygote)
- 24 hours: 2 cells
- 40 hours: 4 cells
- 3 days: 6-12 cells
- 4 days: 16-32 cells (morula)
egg + sperm –> fertilization –> zygote
true
1st mitotic divisions are called_______ and results in _____ daughter cells
cleavage; 2 (2n)
Blastomeres
smaller than original cell, daughter cells
Morula
embryo at 16-32 cell stage
– blast
immature cell (actively making something)
– cyte
mature cell
– cyst
sac full of fluid
ESC
Embryonic Stem Cells from inner cell mass (ICM) of blastocyst
Pluripotent
ESC that can become any one of the 3 germ line cells
Differentiate
Cell than can alter into another specific cell
Embryo
After zygote and into 1st cell divisions, from implantation through 8th week pregnancy
Fetus
after 9 weeks of fertilization 11 weeks gestation
Holo
entire or complete
Mero
part
Meso
middle
Gestation age has a _______ lag time to fertilization time
2 week
3 “D” roles of cleavage
1.) Divison
2.) Distribution
3.) Differentiation
Divison
to pass on many identical copies of the genome to each cell (mitotic process to create diploid somatic cells)
Distribution
To produce a large number of cells that can relocate to one another and build a structure of the organism
“Blastomeres as bricks!”
Differentiation
To give themselves a molecular DNA determination, identify via touch
Cell division
1.) The nucleus divides by mitosis
2.) The cytoplasm divides by cytokinesis
Nucleus (mitosis)
- Chromosomes are condensed, copied and pulled apart in the various stages of mitosis to create two genetically identical cells
-*the KEY organelles of mitosis of the mitotic spindle’s specialize microtubules, organized by pair of centrioles
Stages of mitosis
1.) Interphase
2.) Prophase
3.) Metaphase
4.) Anaphase
5.) Telophase
Cytoplasm (cytokinesis)
-*The KEY organelle and cytokinesis is a contract tile ring of ACTIN in MYOSIN filaments
- closing contractile ring create a CLEAVAGE FURROW that pinches through the cytoplasm
Cytokinesis
Creation of the cytoplasm into two new daughter cells (pinch into 2 new daughter cells)
Cytokinesis and Mitosis are Separately regulated events
True
- complete mitosis before cytokinesis
_______ signals often directed the first few cleavages
Maternal
Walther Flemming
- drawing of chromosomes during mitosis, circa 1880
- “Cell substance, nucleus, and cell division”
- Flemming repeatedly observed the different forms of chromosomes leading up to and during cytokinesis, the ultimate division of one cell into two during the last stage of mitosis
Poles
- Animal pole
- Vegetal pole
Animal pole
area of egg that has little or no Yolk
Vegetal pole
concentration of Yolk
Bilateral symmetry result of_______ ______
cytoplasmic segregation
1st cleavage
(2) from animal to vegetal pole
2nd cleavage
(4) occurs at right angle to the 1st again from animal to vegetal pole
3rd cleavage
(8) HORIZONTAL cleavage, BETWEEN animal and vegetal poles
4th cleavage
(16) from animal to vegetal pole DOUBLE cleavage plane
5th cleavage
(32) HORIZONTAL cleavage, BETWEEN animal and vegetal poles DOUBLE plane II to cleavage III
Morula
16 blastomere in animal pole + 16 blastomeres in vegetal pole
Cleavage pattern is affected by____
Yolk
- how much and where is it located?
Alecithal (humans)
- negligible or no Yolk (all placentals)
Microlecithal
- small yolk (urchins)
Mesolecithal
- 1/2 yolk (amphibians)
Macrolecithal
- Max yolk (insects, fish, reptiles, birds, monotremes)
Lecithal
having yolk
Isolecithal (humans)
eggs have yolk evenly distributed in the cytoplasm (sea urchins, mammals)
Telolecithal
eggs have yolk concentrated at one end (amphibians and birds)
- polarity
Centrolecithal
eggs have the yolk in the center, surrounded by “skin of cytoplasm” (drosophila)
- ex. insect
Holoblastic (humans)
if yolk is sparse and evenly distributed, there is complete cytokinesis
Meroblastic
if yolk is dense and unevenly distributed, division is partial or incomplete
The more yolk, the _____ divisions
harder
What cell pattern of motion do humans have?
Rotational
Timing of cleavage pattern
- synchronous (same time division)
- asynchronous (NOT same time division)
We have a __________ timing of cleavage pattern
asynchronous
Cleavage pattern in humans
- Microlecithal relies on maternal body for nutrients
- holoblastic (has complete cytokinesis)
- Cleavage rate is slower (divisions every 24 hours)
- rotational divisions
- asynchronous cell divisions
- Days 1 thru 3, fertilization –> cleavage 2, 4, 6, 8 cells
Day 4: At 8 cell stage to Morula (16-32 cells)
- cell divisions continue
- up to 16-32 cells is called morula
- compact ball of cells
- next phase: becoming Blastocyst
Opening
antrum
Morula will give rise to
- embryo proper
- extraembryonic membranes
- contribute to placenta
Day 4 morula (16-32) then Day 5___________
Blastocyst (100-200 cells)
Day 5: Cells tightly adhere=
compaction
Day 5: Cells begin to______
flatten
Day 5: Cells-to-cell
contact
Day 5: Blastocyst
- compaction
- flatten
- contact
- outer cell surface Convex
- Inner cell surface Concave
- Some cells migrate to surface and others migrate to center
- Oviduct
- 30 or so cells
- absorbs fluid
- Trophoblast becomes epithelium with Tight Junctions
- Blastocoel forms within morula
- ICM form a compact mass at one side of the cavity
- Now called a BLASTOCYST (after 7-8 rounds of cell divisions)
Outer Cell Mass (OCM)
Some cells migrate to surface
- Trophoblast (placenta)
Inner Cell Mass (ICM)
Some cells migrate to center
- Embryo
Blastocyst will give rise to
- embryo proper
- extraembryonic membranes
- contribute to placenta
Trophoblast Tight Junctions
- E-cadherin (within membrane)
- gap junctions (channel)
- adherens junctions (“velcro”)
- desmosomes (embedding membranes together)
Blastocoel
Blastocyst cavity forms within morula
Inner cell mass also known as________
embryoblasts (form a compact mass at one side of the cavity)
Timeline
Pronuclear
- Day 0
Cleavage stage
- Day 1
- Day 2
- Day 3
Morula
- Day 4
Blastocyst
- Day 5+
Tight junction
interlocking junctional proteins
Anchoring/Adhering junctions
protein filaments
Desmosome junction
linker protein (ex. Cadherin)
Gap junctions
Channel between cells formed by connexons
- allows for communication between cells
Blastocyst (by Day 5)
- arriving at uterus
- enzymatically bores a hole in Zona Pellucida and hatches out
- Naked and can interact with endometrium and binds
- Endometrium and uterine wall responds– more vascularization
- Trophoblast produces hCG
- By week 11-12, the placenta takes over Progesterone production and corpus luteum becomes corpus albicans
- TWINS
Trophoblast produces hCG
- Human Chorionic Gonadotropin
- supports Corpus Luteum which continues to supply PROGESTERONE to maintain pregnancy and grow lining
Placenta
Progesterone production in pregnancy
