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In which cell divisions are the centromeres pulled apart?
Meiosis II and Mitosis
In which cell divisions are hapliods and diploid cells made?
- Meiosis I, II = haploid
- Mitosis = diploid
In which cell divisions are synapsis, crossing-over, and independent assortment unique?
Meiosis II does or does not have S-phase?
Male meiosis characteristics?
Equal cytokinesis, continuous source of sperm, occurs in waves. Primary spermatocyte -MeioI-> secondary spermatocyte -MeioII-> spermatid
Female meiosis characteristics?
- Oocyte hogs most of cytoplasm (unequal cytokinesis)
- Meiosis I begins before birth and arrests by 5th month of fetal life at synapsis...
- Meiosis I finishes at ovulation
- Meiosis II arrests at metaphase, then finishes at fertilization
- No replenishment of oogonia
- Primary oocyte -MeioI-> Sec. oocyte+polar body -MeioII-> Mature oocyte + 3 polar bodies
Which autosomal trisomies allow birth?
Trisomy 13,18,21 (13 and 18 usually die soon after birth)
Which aneuploidies of sex chromosomes allow life?
XO (only survivable monosomy), XXY, XYY
What characteristic enables women to be very susceptible to nondisjunction?
advancing maternal age
What are the 5 reasons for non-disjunction (or aneuploidy) to occur?
- 1. Defects in crossing-over (chiasmata region)
- 2. Premature degradation of cohesins (hold sister chromatids together)
- 3. limited region of homology that supports synapsis of X and Y
- 4. spindle assembly "checkpoints" function poorly
- 5. mosaicism (some cells have normal chromosome # and others are aneuploid) from early mitotic divisions in zygote
What are the characteristics of a sperm that differentiated from a spermatid?
- 1. growth of flagellum
- 2. conversion of golgi into acrosome
- 3. condensation of nucleus
- 4. excess cytoplasm discarded
Sex chromosome or autosome aneuploidies occur:
A. at the same rate in men and women
B. over 80% in men
C. over 80% in women
Sex chromosome aneuploidy (same rate for gametes derived from men and women)
Autosomeal aneuploidy (over 80% occur in eggs rather than sperm)
What is importance of acrosome of sperm?
Explain characteristics of nucleus and tail?
- Acrosome - sac of digestive enzymes needed to bore through Zona Pellucida
- Nucleus - tightly condensed DNA
- Tail - mitochrondrial sheath to provide energy for flagellum
Describes changes in sperm that occur upon exposure to female reproductive tract, receptors on ZP, and inducing rapid motility
Zona Pellucida (ZP)?
- thich matrix around ooctye which allows:
- - sperm binding, triggers acrosome reaction
- - block polyspermy
- - prevents premature/ectopic implanation
** oocyte offers nutrients for embryonic life for several days
Examples of sperm capacitation in female reproductive tract?
- -Expose receptors for corona cells and ZP
- -greatly increase motility
- -chemotaxis toward egg-cumulus complex
How do Copper IUDs work
- -They prevent capacitation by making both sperm and egg unwell.
- -99.5% effective
- -Cause inflammation in uterus to discourage sperm from fertilization
Two blocking mechanism of the oocyte against polyspermy?
- 1. Cortical Reaction: release of cortical granules that cross-link the ZP
- 2. Depolarization of egg membrane upon sperm fusion
3 days after fertilization, zygote looks like a grape-like cluster of cells
When the zygote forms a smooth ball of cells ~3 days after fertilization
Blastocyst layers and what they will become?
- Inner cell mass = Hypoblast (lining of epiblast)+ Epiblast
- Trophoblast = outside lining
- Epiblast = embryo proper and amniotic sac
- Hypobast = extraembryonic endoderm that forms yolk sac
- Trophoblast = fetal chorion, or placenta
Fraternal (Dizygotic) twins are? Share what?
Two eggs ovulated and sep. fertilized. They share same uterus but not any membranes.
3 Types of Monozygotic Twins? What do each share?
- ~25% splitting of zygote first few cleavages (share nothing but uterus; dichorionic diamnionic)
- ~75% complete splitting of inner cell mass (share uterus, placenta; monochorionic diamnionic)
- Conjoined Twins: incomplete splitting of inner cell mass (share chorion/placenta, amniotic sac; monochorionic monoamnionic)
What is placenta previa?
If implantation occurs too close to cervix, but within uterus (prevents safe vaginal delivery)
- Cytotrophoblast - single layer of cells that arises from trohphoblast during implantation
- Synctiotrophoblast - multi-nucleated cells that branch out
Enzymes secreted from synctiotrophoblast that degrade uterine wall and pull entire blastocyst into wall
What are decidual cells (i.e. decidual reaction)?
Production of glycogen and lipids of stromal cells in uterus to nourish embryo
The formation of new blood vessels
Risk factors for extopic pregnancies?
- - Pelvic Inflammatory Disease
- - Cigaretta Smoking (affects smooth muscle perstalsis/cilia that move egg)
- - In vitro fertilization
- - Maternal age greater than 24
Bilaminar embryonic disk consists of?
Epiblast and hypoblast
Which is ventral and which is dorsal? (Epiblast, hypoblast)
- Epi = dorsal
- Hypo = ventral
Formed within inner cell mass by fluid secretion (it is dorsal to epiblast). It acts as a shock-buffer for embryo.
Extraembryonic mesoderm forms from ___ cells and forms the ____ and _____.
Extraembryonic mesoderm forms from epiblast cells and forms the chorionic cavity and blood vessels of the chorion, definitive yolk, and connecting stalk.
Definitive (secondary) yolk sac is initially dervied by _____-derived endoderm and then ____-dervied endoderm?
Chorion consists of what cell types/layers?
The chorion is formed by the two trophoblast layers (cytotrophoblast/synctiotrophoblast) and extraembryonic mesoderm.
Primitive Uteroplacental circulation?
The lacunae fill with materal blood around the synctiotrophoblast. The early embryo gets nutrients via this method until primary chorionic villi form.
Primary chorionic villi?
Outgrowths form the cytotrophoblasts into the synctiotrophoblast that become blood-filled lacunar network
Cranial end of the primitive streak is the ___?
Primitive groove is? First cells to migrate (ingress) are: endoderm, ectoderm, mesoderm?
- - the depression of the middle of the primitive streak
- - endoderm
What happens to a cell's fate after compaction?
Cell fate becomes restricted...they become determined.
Epiblast is dorsal; Hypoblast is ventral
Cranial part of primitive streak is also known as ______
Caudal part of primitive streak is also known as ______
- Epiblast is dorsal; Hypoblast is ventral
- Cranial part of primitive streak is also known as anterior
- Caudal part of primitive streak is also known as posterior
Cell fates in gasturlation are determined based on their ____ along the streak and ____ from the node.
position along the streak and distance from the node
FGF + BMP4 dorsalize or ventralize mesoderm?
FGF + BMP4 antagonist dorsalize or ventralize mesoderm?
FGF+ BMP4 = ventralize mesoderm into intermediate and lateral plate mesoderm
FGF + BMP4 antagonist (form primitive node) = dorsalize mesoderm to form notochord and somitic mesoderm
Formation of the neural tube?
- Dorsal ectoderm's lateral edges fold to form neural tube
Where is the fusion of the neural plate?
Fifth somite (i.e. mid-region) then is zipped up and down simultaneously
Why do neural tube defects arise?
Incomplete fusion of the neuropores (ends of the neural tubes are being "zip-tied")
What signals the end/completion of neuralation?
What is the function of the notochord? What germ layer does it belong to?
Defines body axis, signaling center; MESODERM!
What defines ventral/dorsal fates of the neural tube?
Notochord (directly below NT) induces floor plate (i.e. ventral) by expressing sonic hedgehog (SHH).
- The ectoderm expresses BMPs that cause dorsal NT fates
Dorsal-most side of the neural tube gives rise to?
Which cells undergo epithelial-to-mesenchymal transformation?
The mesenchymal neuro crest migrate through mesoderm to form?
A wide variety of tissues/organs
What are the 4 neural crest cell regions?
- 1. Cranial neural crest
- 2. Cardiac neural crest
- 3. Vagal/sacral neural crest - parasympathetic ganglia of gut
- 4. Trunk neural crest -
- consisting of dorsolateral migrating trunk neural crest giving rise to melanocytes and ventromedial migrating neural crest cells forming dorsal root ganglia/nerves
Neural crest is part of which germ layer?
What are the four regions of mesoderm and what do they give rise to?
1. axial (chordamesoder) = notochord
2. paraxial mesoderm = head, myotome = skeletal muscle (myotome), dermatome (dermis), sclerotome (cartilage)
3. intermediate mesoderm = kidney (nephrotomes, nephrogenic chord), gonads (urogenital structures)
4. lateral mesoderm = parietal mesoderm (somatic) = body walls & thin serous membrane around body cavities, visceral mesoderm (splanchnic) = gut wall, & thin serous membranes around each organ
Derivatives of endoderms?
GI tract, liver, gall blader, pancreas
Anterior forgut (cranial region) and posterior hindgut (caudal) are connected by midgut and attached to vitelline duct which is attached to yolk sac
What does the notochord eventually develop into?
Nucleus Polposus (jelly-like susbtance in the middle of spinal chord)
Importance of folate (folic acid) in formation of neural tubes?
Folate is used to synthesize DNA (purin synthesis) therefore it is important for reducing Neural Tube Defects.
Flowchart of embryology stuff.