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59 Cards in this Set

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What period is Embryology the study of?
1-8 wk
What period is the fetal period?
8-36 wk
Describe the chorion, what important tissues are derived from it? Where is its position in the uterus?
The chorion is a bulky extraembryonic tissue from which the placenta is derived. It is the outermost layer of the developing conceptus.
Describe the amnion. What important tissues are derived from it? What is its position in the uterus
The amnion is an extraembryonic tissue. It is thin and membraneous and makes up the amnionic sac in which the amnionic fluid is stored. It is in contact with the inner somatic mesoderm of the chorion.
Which tissues rupture during water breakage? What purpose does this serve?
Both the amnion and the chorion rupture during water breakage. This serves as a hydrostatic wedge to dialate the cervical canal so that the baby's head doesn't have to. It also serves as a "trigger" in the birth process.
What are the cotyledons? What functional processes do they contain?
The fuctional areas of the placenta that it is divided into. The bumps look like little leaflets. If you break open the cotyledon, there is not much space within it. The material inside is a meshwork of villi (are extraembryonic tissue), this space is called the intervillus space.
What does the intervillus space contain?
Maternal blood.
What do the villi contain? What do they do?
Fetal blood vessels. Exchange waste products, gases, nutrients.
Define conceptus
Everything that arises from fertilization.
Approximately what day is the oocyte relased in the 28 day menstral cycle?
Approximately day 14
What develops in the secondary oocyte after ovulation?
The corpus leuteum.
What does progestrone do to the uterus (endometrium= lining of the uterus)?
Causes the endometrium to shift from a reparitive/proliferative phase to a secretory phase. Now the placenta is receptive to implantation.
Where does fertilization take place?
In the distal portion of the uterine tube.
After what event does mitosis begin in a conceptus?
Fusion of the pronuclei of the egg and sperm.
Why do the cells get smaller during the first few cycles of mitosis after fertilization?
They are still within the zona pellucida. It corrals them. The zona pellucida also helps to time implantation.
When does the zona pellucida break down? Why does it break down at this time? What does it do normally?
About 5 days after fertilization. The conceptus should find itself within the uterine cavity and coming into contact with a receptive endometrium. The zona pellucida serves as a docking site for sperm, prevents polyspermy, helps determine timing of implantation and holds the cells together.
What occurs during the 1st week of development?
Mostly spent moving down the uterine cavity and scouting out the surface of it.
What happens during the 2nd week of development?
Conceptus invades endometrium. At end of the the 2nd week implantation has been completed.
What is menses?
The sluffing off of endometrial tissues.
How does the conceptus signal that it is in the endometrium? Why is this important?
Extraembryonic tissues (corionic mainly) develop and specialize. It signals that it is there via the release of corionic gonadotropin. This causes the corpus leuteum to be mainatianed and causes progesterone levels to be maintained/increased. Therefore menses does not occur.
What do home pregnancy tests test for?
They test for corionic gonadotropin. Also early pregnancy factors can be dectected (very early pregnancy test). These signal the uterus to get ready for the corionic gonadotropin.
What does the corona radiata do?
Makes the oocyte easier for the cilia of the uterus to move.
When does the zona pellucida break down after fertilization?
Four days after fertiliztion.
After how many cells are the mitoses within the zygote dissynchronous?
After 64 cells have been acquired. Prior to that time division went 2->4->8->16 etc.
Describe the morphology of the conceptus once it reaches the uterine cavity.
A ball of cells.
How can you tell that the cells within the zygote have begun to differentiate?
About day 6 a small cavity forms within the ball of cells that makes up the conceptus.
What do the cells on the outsize of the conceptus, inside of the conceptus become eventually? What determines what these cells become?
The cells on the outside become extraembryonic tissue. The cells on the inside become the embryo proper and extraembryonic tissue. This is done soley by position. Therefore orientation is the determinant and differentiation is somewhat is random (the cells are totopotentric/can be anything).
How do the cells know where they are in the conceptus? What is the process called?
They know via cell to cell surface contacts. The process is called compaction.
What does blast- mean?
It means something that is going to form something.
What is a blastula?
Gives rise to a new person.
What is the space within the blastula called?
The blastocystic cavity or blastoceole.
What is the blastula composed of?
Outer and inner set of cells. Inner set of cells are called the embryoblast - give rise to the embryo.
Outer set of cells are called the trophoblast (tropho = nourishing/feeding)- give rise to tissues that support and nourish the inner cell mass.
How many spermatazoa does it take to fertilize the egg?
Some disperse the corona radiata that allow others to get through the zona pellucida in order to fertilize the egg. But technically only one is necessary.
What phase is the conceptus in as it is moving down the uterine cavity? What are the features of this phase.
It is is the blastocyst phase. The zona pellucida has dissolved. It dissolves due to enzymes within it and not due to its postion in the uterine cavity. (4-5 days after fertilization)
How does the blastocyst gain size initially? What does this gain in size immediately follow?
The blastocyst picks up surrounding liquid causing the cells to swell once the zona pellucida dissolves. the cells "hatch".
What cells make contact with the endometium?
The outer cells or trophoblast cells.
Which releases chemicals to communicate, the blastocyst or the endometrium?
Both release chemicals to communicate.
What happens when the trophoblasts come in contact with the endometrium?
The trophoblasts are stimulated to proliferate and fuse together (blend together). Their cell membranes break down. Become a large protoplasmic mass. Thus syncitiotrophblast forms.
What is a syncitiotrophoblast? What does it do?
A large multinucleated nucleated protoplasmic mass. Fused together. Have a common plasmallema. This becomes the DIFFERNTIATED tissue that produces signallying chemicals. It also makes an interface between the conceptus and the maternal tissue. It also taps into maternal blood vessels. (Hopefully small ones)
What is the cytotrophoblast? What does it do?
The cells in the syncitiotrophoblast whose cell membranes do not break down. Retain individual identity. It is a reserve population of cells in order to increase the mass of the syncitiontrophoblast.
What are lacunae? What do they do (collectively)?
Plasmallema bound spaces within syncitiotrophoblast. That coallesce and join with the plasmallema on the outside of the syncitiontrophoblastic mass. This creates an avenue for secretions to reach the inner cell mass. Also maternal blood circulates through them.
Describe the orientation of the syncitiotrophoblast and what the cytotrophoblast does over time.
The syncitiotrophoblast covers the conceptus and the cytotrophoblast grows into the syncitiotrophoblast. This allows more cytotrophoblastic cells to fuse. This also creates the primary villus. (formed from both tissues). These villi go into the lacunar space and become the intravillus space.
Where is extraembryonic mesoderm found?
Within the primary villus. It is now called a secondary villus.
What is a tertiary villus made of?
All the tissues of the secondary villus but also include fetal blood vessels.
Do the embryoblastic tissues need the trophoblast?
Yes but the trophoblast does not need the embryoblast.
Does the syncitiotrophoblast and innervillus space eventually go all the way around the conceptus?
What happens as a result of the chemicals released by the syncitiotrophoblast?
The cells of the endometrium undergo changes. The fibroblasts change size and nature. They release chemicals. This is called the decidual reaction.
What is the altered endometrium called? What does it do?
The deciduam. It downregulates maternal lymphocytes (so they don't attack the fetus) and changes the microenvironment.
What does the lacunar network become?
Intervillus space.
What is the cytotrophoblastic shell?
An area of the cytotrophoblast that has been overshot and where mass can be added externally.
What happens as tertiary villus matures?
They loose cytotrophoblast cells and eventually run out. This allows for fetal blood vessels to come in direct contact with syncitiotrophoblast. This becomes a thin layer that is made of only syncitiotrophoblast.
How selective is the thin syncitiotrophoblast layer? What can move through the layer?
Not very selective, allows for gas, toxins, nutrients, wastes, antibodies, vitamins. (bacteria cannot make it through) However, pathogens that can move on their own can make it through this barrier.
How are cotalydens formed?
They are formed via villus formation where the placenta is pushing up endometrial tissue that will not yield due to insufficient villus formation.
What lines the inner villus space?
What does the villus corion arise from? What does it eventually become?
Deep portions of the corion that does not dissipate due to tension or compression. It is away from the uterine lumen. This is maintained as the placenta.
What is the smooth corion? What does it become?
Part of the corion that has lost its blood vessels due to being stretched. It is towards the uterine lumen. It eventually becomes connective tissue.
What is the decidual basalis? Where is it located?
Part of the endometrium that has undergone the decidual reaction making it invisible to lymphocytes. It is between the conceptus and the myometrium.
Where is the decidual capsularis?
It makes a capsule between the conceptus and the uterine cavity. It ultimately degenerates?
What is the decidual pariatallis?
All the areas of the uterus that have undergone the decidual reaction that are not casularis or basalis.