Early Embryology Week 3 Flashcards
What is ovulation and when does it occur?
1 mature oocytes is released from the ovary and swept into the oviduct. This occurs 2 weeks into the ovulation cycle.
What are synonyms for oviduct?
Fallopian tube, uterine tube
Where in the fallopian tube does fertilization take place? Describe its location.
The Ampulla is the location where fertilization takes place and it is the wide distal portion of the oviduct.
The oocyte is now in the ampulla of the fallopian tube. Sperm will travel from the _______ to the _______. It takes ______ to ________ for the sperm to travel.
cervix to the fallopian tube , 30 minutes-6 days. If the egg hasn’t been released into the oviduct, the sperm can stay in the ampulla for up to 6 days.
From exterior to interior, describe the three linings of the uterus. Which one is the thickest during ovulation?
Perimetrium, Myometrium, Endometrium. The endometrium is the thickest.
What is myometrium made of?
Smooth muscle
What is the coat on the outside of the egg called? When does it exist?
The Zone of Pellicuda is a sperm barrier that is bypassed only during fertilization. It will disintegrate when the blastocyst reaches the uterus.
When the male and female pronuclei come together, what are they called? What is the number of chromosomes in the gamete and in the ______?
Zygote. Gametes have n and Zygotes have 2n.
What does fertilization result in?
Diploid chromosomes, Gender Determination and cleavage is initiated
What is XX?
Female
What is XY?
Male
Within what time period does the sperm have to meet the egg in order for fertilization to occur once the egg is swept into the ______?
24 hours, ampulla
What happens to the zygote after fertilization? Zygotes are ___- cell stage.
The zygote rapidly divides via mitosis.
What are the 3 stages of zygote division and how many cells are in each stage?
- Zygote- 2 cell
- 4-Cell
- Morula-16 cell
When does the advanced morula enter the uterine cabin?
4 days after fertilization
What happens to the morula after it enters the uterine cabin? What is the name of the structure? How long does it take to form.
Cells continue to replicate and the “ball” of cells forms a fluid filled center surrounded by the cells. This is called a blastocyst and forms 5 days after fertilization. (About 1 day after morula enters the uterine cabin)
What happens to the blastocyst? What 3 structures are apparent at this stage?
Some cells of the blastocyst congregrate into an inner cell mass called the EMBRYOBLAST.
Other cells form a ring around the blastocyst called TROPHOBLASTS that provide nutrition for the embryo.
A BLASTOCOELE , a fluid filled cavity, forms.
What does trophoblast layer eventually turn into?
Placenta
What is implantation and when does it occur?
The morula/blastocyst is pushed along the fallopian tube until it enters the uterus about 6-7 days after fertilization.
Abnormal implantation can occur. Which location of implantation can cause placenta previa?
Implantation in the cervix, inferior to the uterine cavity can cause placenta previa because placenta is blocking the cervical opening preventing vaginal birth.
Now the blastocyst is in the uterus. What happens to the trophoblasts? When does this happen?
The trophoblasts differentiate into TWO layers. The cytotrophoblast and the syncytiotrophoblast. This happens during week 2.
What do cytotrophoblasts do? Are there distinct cell borders?
They serve as stem cells for syncytiotrophoblasts. Yes, there are distinct cell borders.
What do synctiotrophoblasts do? Do they have distinct cell borders?
It turns into the placenta. There are no distinct cell borders.
What does pregnancy testing measure?
Pregnancy tests rely on the fact that the synctiotrophoblasts will produce hCG when present indicating pregnancy.
The blastocyst is in the uterus. What happens to the embryoblast?
The embryoblast divides into two layers called the hypoblast and the epiblast.
What two cavities are formed once the embryoblasts differentiates?
Amniotic cavity and Exocoelomic cavity
What does the amniotic cavity develop into?
It will expand and surround the embryo.
What happens to the primitive yolk sac in humans?
It will regress. The placenta will replace the function of the yolk sack.
Describe amniocentesis.
A needle is guided ultrasonically to pull amniotic fluid out. The things cells have sloughed off in the amniotic fluid can be key in determining conditions.
Along with the primitive yolk sack cavity and the amniotic fluid, what other structures are formed?
Extraembryonic Somatic mesoderm
Extraembryonic Splanchic Mesoderm
Chorionic Cavity with fluid filled sack.
What does the extraembryonic somatic mesoderm form?
The out body wall
What does the extraembryonic splachnic mesoderm form?
The inner area where organs will be.
When does the amniotic cavity completely replace the yolk sac?
3 months
What two structures disappear by the third month?
Chorionic cavity and yolk sac
What are trophoblastic lacunae?
Trophoblastic lacunae are large pools of blood in the uterine wall that can leak during time period (week 2). It may be mistaken for a period.
What is gastrulation and when does it happen?
Gastrulation occurs during Week 3 when the bilaminar embryo turns into a trilaminar embryo.
What are the three germ layers produced by gastrulation?
Ectoderm
Mesoderm
Endoderm
What does the ectoderm produce?
Neural system, skin, appendeges
What does the mesoderm produce?
Musculoskeletal tissue, membrane that lines cavities
What does the endoderm produce?
Foregut, midgut and hindgut
The epiblast is ________ and the hypoblast is __________. (Describe location)
Ventral, Dorsal
What two structures are important at the gastrulation stage?
Oropharyngeal membrane and primitive streak
What is the oropharyngeal membrane?
Indicated the head end as it will be the future oral cavity.
What is the primitive streak? What does it represent in the body?
The primitive streak is where the epiblast cells will migrate to to replace it with the three germ layers. It is the midline.
What cells migrate into the primitive streak and in which direction do they migrate?
Epiblasts migrate from the primitive streak towards the oropharyngeal membrane.
How are the ecto, endo and mesoderm formed?
The first batch of epiblasts to migrate replace the hypoblast and become the ectoderm. The second batch and third batch become mesoderm and endoderm respectively.
What is the future anus?
Cloacal membrane
What is Teratogenesis?
Agent responsible for birth defects
What is holoprosencephaly? What is another name for it?
Injury to anterior midline of germ disk causing injury in cranial end. The forebrain isn’t separated into left and right hemispheres. May be due to genetics or high alcohol usage. Cyclopia
What is caudal dysgenesis ? What is another name for this?
Any injury to the caudal/cloacal aspect of germ disk. Can be caused due to genetics and environmental insults.
Sirenomelia
What are sacrococcygeal tumor?
These are teratogenesis associated with the remnant of the primitive streak which forms the lowest part of the vertebrae column. Cells become unregularted.
What can result in conjoined twins?
Splitting of the primitive node
