Flashcards in Week 6 Fertilization/ Early Development- Holy Deck (22):
glycoprotein and lipid content changes in sperm plasma membrane during passage through female reproductive tract
Where does fertilization occur?
ampulla of the oviduct
Describe the acrosomal reaction
-swimming action of sperm penetrates follicle layer
-sperm plasma membrane proteins bind ZP-3 (zone pellucida glycoprotein)
-Binding activates sperm Na+/H+ and Ca+ transporters.
-increase sperm cytoplasmic pH
-Ca+ influx triggers exocytosis of acrosomal vesicle
-Hydrolytic enzymes of the acrosome digest the zona and allow sperm to contact the egg plasma membrane
Important of Ca+ in sperm-egg binding and fusion?
Sperm phospholipase C produces IP3 from phosphotidylinositols, opening calcium channels in egg ER.
-cortical granule exoctosis
-allows meiosis II to be completed by activating APC
-Initiation of developmental program of the egg
What are two blocks to polyspermy?
Fast block- fusion of sperm and egg plasma membrane cause a rapid membrane change that is immediately inhibitory to further fusion with sperm
Slow block- release of cortical granules modify zona, destroying the sperm-binding capability of ZP3
What are two important stages of the Morula?
-Formation of inner and outer cells (inner cells make body of the embryo, outer/trophoblast makes extraembryonic tissues)
-compaction: change in the was blastomeres interact with each other, from tight/gap junctions and flatten together to form tight ball. Cells become polarized
6/7 days after fertilization
hydrolytic enzymes from embryo are relased to degrade the zona pullcida that envelopes embryo
-blastocyst "hatches" out of zone
-Zona prior to hatching helps prevent ectopic implantation
implantation at a site other than the posterior wall of the uterine cavity, usually ampulla of the oviduct, ovary, or abdominal cavity
implantation close to the mouth of the cervix and placenta partially covers the cervical canal
What does the trophoblast form into?
-Some form syncytiotrophoblast which fuse to the hormonally prepared endometrium. Secretes HCG to tell mom to keep secreting estrogen and progesterone
-cells that do not fuse are call cytotrophoblast cells (which replicated via mitosis and then fuse with syncytiotrophoblast to keep it growing)
What is delamination?
isolates the inner cell mass a seperate entity from the trophoblast.
inner cell mass flattens to from circular disc composed of two cell layers
closet to amniotic cavity is the epiblast (tall columnar)
closet to the primary yolk sac are the hypoblast (cuboidal)
What do the epiblast and hypoblast form?
Epiblast will make the embryo, hypoblast will only make extraembryonic structures
mass migration of cells which end up forming the three germ layers of they body (all germ layers originate from the epiblast)
thickening of epilast in middle due to migration of epiblast cells toward the midline of the embryonic disc. Streak turns into a groove through which other epiblast cells migrate to form the mesoderm and endoderm. (cells remaining in the epiblast become the ectoderm)
Notochord formation and functions
Mesoderm cells migrate to form the notochord.
-lends longitudinal mechanical support to the embryo
-serves as POWERFUL inductive force on the subsequent differentiation of many cell types.
Neural tube formation
Epiblast (ectoderm) cells directly overlaying the notochord are induced by the notochord to proliferate and to form a thickening called the neural plate. Plate makes folds, folds curve around to make neural tube.
cells that have detached from the fold migrate within the embryo and eventually give rise to ganaglia, schwann cells, meninges, adrenal medulla and melanocytes.
Embryonic mesoderm forms three series of swelling
Paraxial mesoderm gives rise to what structure?
SOMITES! Periodic thickenings that occur along the length of the paraxial mesoderm, form in pairs, one on each side of the notochord --> give rise to most of the axial skeleton, associate musculature and adjacent dermis of skin
intermediate mesoderm gives rise to what?
formation of urogenital system
lateral mesoderm gives rise to what?
serous membranes of pleura, pericardium, peritoneum, connective tissue, and muscle of viscera, heart, blood cells