Flashcards in Chapter 3 - Embryogenesis Deck (45)
When can the acrosomal apparatus of the sperm enter the oocyte?
After meiosis II has come to completion.
What is the cortical reaction?
Occurs after penetration of the sperm through the membrane (through the coronal radiata and the zone pellucida).
It releases calcium ions to depolarize the membrane:
1. To prevent fertilization by more than one sperm
2. To increase metabolic rate of newly formed diploid zygote.
(The result is he FERTILIZATION MEMBRANE)
What is cleavage?
When the zygote undergoes rapid mitotic cell divisions.
-the first: creates the embryo (no longer a zygote since it is multicellular now)
-continues to multiply without growing in size: increases surface area for exchange of gas and nutrients.
Indeterminate versus determinate cleavage:
Indeterminate cleavage: the cells can still develop into complete organisms.
Determinate: committed to differentiating into a certain type of cell
What is a morula?
After many cell divisions of "cleavage", the embryo is a MORULA.
What is the ampulla?
The widest part of the Fallopian tube, where fertilization of the secondary oocyte generally occurs.
What is blastulation?
Process through which the morula becomes the BASTULA, which is a hollow ball of cells with a fluid-filled inner cavity (called the blastocoel)
Is mammalian blastula is called a BLASTOCYST
What is a blastocyst?
A mammalian blastula.
A hollow ball of cells with a fluid-filled interior.
Blastocoel - fluid interior
Trophoblast - surround cells. Give rise to the chorion (eventually the placenta)
Inner cell mass - protrudes inwards and gives rise to the organism itself.
What is the chorion?
Extraembryonic membrane that develops into the placenta.
The trophoblast a form chorionic villi, which penetrate the endometrium.
Chorionic villi then develop into the placenta and support maternal-feats gas exchange.
***the chorion also forms a membrane around the amnion, adding protection.
The umbilical cord:
What is it made up of?
What does it do?
Made of 2 Arteries and 1 Vein (work the reverse: the vein carries oxygenated blood) encased in a gelatinous substance.
These carry blood/waste to and from the placenta for exchange.
What is the yolk sac?
The site of early blood cell development.
Supports the embryo until the placenta is functional
What is the allantois?
Involved in early fluid exchange between embryo and yolk sac.
(The allantois + yolk sac will eventually form the umbilical cord)
What is the Amnion?
Surrounds the allantois and embryo. Filled with amniotic fluid. This fluid serves as "shock absorber" during pregnancy.
What is gastrulation?
The generation of three distinct cell layers (primary germ layers):
The result of gastrulation is called a Gastrula.
What is the archenteron?
What is the blastopore?
The invagination of the membrane into the blastocoel (the inside "hollow" fluid-filled portion)
*this develops into the gut
The blastopore is the opening of the archenteron.
What anatomical feature does the blastopore become?
In deuterostomes (humans) = the anus
In protostomes = the mouth
What does the ECTODERM give rise to?
Nervous system (and adrenal medulla)
Epidermis / integument
Lens of the eye, tooth enamel
Lining of the mouth, anus, sweat glands, hair and nails
What does the MESODERM give rise to?
Most of the excretory system
Muscular and CT layers of digestive system, respiratory system, and adrenal cortex
What does the ENDODERM give rise to?
Epithelial lining of digestive and respiratory systems (incl lungs)
Organs such as the pancreas, thyroid, bladder, parts of the liver and distal urinary tracts.
What is selective transcription (of the genome)?
The process by which only genes needed for a particular cell type are transcribed.
Ie only genes to produce certain hormones are turned on in certain hormone-producing cells.
Results in different cell types with highly specialized function, despite all having the same genes and coming from the same exact cell.
What is induction?
The ability for one group of cells to determine the fate of other nearby cells.
Involves chemicals called INDUCERS, which diffuse from the organizing cells to the responsive cells. It ensures proximity of cells that work together within an organ.
What is the process?
The development of the nervous system
1. Mesodermal cells form the NOTOCHORD
2. Overlying ectodermal cells form NEURAL FOLDS which surround a neural groove
3. Neural folds grow toward each other until they fuse to make the NEURAL TUBE (gives rise to central nervous system)
4. Neural crest cells at the tip if each neural fold give rise to the peripheral nervous system
What are the stages of early development?
(Happens at about 3 weeks)
What is spina bifida?
Failure of the neural tube to close.
Some of the spinal cord becomes exposure to the outside world (to varying degrees)
Folic acid can prevent this complication
What is anencephaly?
Failure of the neural tube to close.
Some of the brain fails to develop and the skull is left open - this is UNIVERSALLY FATAL.
Folic acid can prevent this complication.
What is a teratogen?
What are some examples?
A teratogen is a substance that interferes with development.
Vary based on route of exposure, length of exposure, rate of transmission, identity of the teratogen.
Examples include alcohol, prescription drugs, viruses, bacteria, environmental chemicals (such as polycyclic aromatic hydrocarbons).
What is potency of stem cells?
What are the 3 levels of potency?
It's ability to differentiate into any type of cell.
TOTIPOTENT: can differentiate into any cell type (most potent) - cells of the embryo, up until it differentiates into the 3 germ layers.
PLURIPOTENT: can differentiate into any cell type EXCEPT those in placental structures.
MULTIPOTENT: can differentiate into multiple types of cells within a particular group.
How can cell-cell communication occur?
(Ie what are types of inducers)
AUTOCRINE: act on the same cell that produced the signal
PARACRINE: act on cells in the local area
JUXTACRINE: not via diffusion, but by directly stimulating receptors on an adjacent cell
ENDICRINE: involves secreted hormones via the bloodstream, reaches distant target tissues.
What are growth factors?
Inducers; peptides that promote differentiation and mitosis in certain tissues.