Gastrulation Flashcards
1
Q
thick layer of glycoproteins surrounding the oocyte that supports the oocyte in development
A
zona pellucida
2
Q
Describe the different types of granulosa cells (responsible for follicle development):
A
- cumulus oophorus: anchor oocyte to follicle wall
- mural granulose cells: line the wall of the follicle
- corona radiata: firmly anchored to the zona pellucida
3
Q
Describe the process of fertilization:
A
(sperm contact the plasma membrane of the oocyte)
- acrosome reaction: sperm head releases enzymes allowing for its passage through corona radiate and zona pellucide
(a single sperm enters the oocyte)
- zona reaction: changes in the zona pellucide renders it impermeable to other sperm
- fusion of egg and sperm cell membranes
- sperm head and tail enter the secondary oocyte
- formation of male and female pronuclei: nucleus of the oocyte is now the female pronucleus; sperm head enlarges, forming the male pronucleus while the sperm tail diffuses
- pronuclei fuse forming the zygote (n=46)
- metabolic activation/initiation of cleavage, chromosomes of the zygote are arranged on a cleavage spindle
4
Q
Describe the process of cleavage and when it occurs:
A
- begins ~30 hours after fertilization
- repeated mitotic divisions of the zygote
- cells in this stage are named, blastomeres
- at 9-cell stage, undergo compaction
- at 12-32 cells, the developing human is named morula (means mullberry)
*cell growth is limited because of the zona pellucida, thus the cells start compacting and become smaller in size*
5
Q
Describe blastogenesis and when this occurs:
A
- morula enters the uterus ~day 4
- blastocystic cavity appears ~day 5 (create from fluid called uterine milk)
- developing human is now termed blastocyst: embryo and its membranes (trophoblast and embryoblast)
- after ~2 days, the zona pellucida degenerates and that blastocyst “hatches”
(zona pellucida degrades from enzymes released by blastocyst, forming the late blastocyst which is ready to implant in the uterine wall)
6
Q
Diagram of fertilization:
(good study tool)
A
7
Q
- many zygotes, morulae, and blastocysts are lost early on in development, at a rate of ~45%
- causes: inadequate production of progesterone/estrogen from corpus luteum; chromosomal abnormalities, including abnormal segregation, duplication, deletions, dispermy (69 chromosomes), etc.
- may require dilation and curettage (D&C)
A
spontaneous abortion
8
Q
Describe implantation and trophoblast differentiation, and when they occur:
A
- late blastocyst attaches to endometrium in the uterus, with the embryoblast (inner cell mass) being adjacent to the uterine wall, occurs ~6-8 days
- trophoblast (inner layer of cells within blastocyst) differentiates into cytotrophoblast and syncytiotrophoblast
- syncytiotrophoblast invades the endometrium via enzymatic digestion
- blastocyst “burrows” into the endometrium and becomes superficially implanted
9
Q
Describe the embryoblast, trophoblast, cytotrophoblast, and syncytiotrophoblast:
A
- embryoblast: inner mass of cells that gives rise to the human body
- trophoblast: inner lining of cells that plays a role in inplantation and placenta formation; gives rise to cytotrophoblast and syncytiotrophoblast
- cytotrophoblast: remains as boundary of the inner lining of blastocyst
- syncytiotrophoblast: lack cell membranes, produces syncytium which is a single cell or cytoplasmic mass containing several nuclei, plays a role in blastocyst implantation
10
Q
Describe the process of bilaminar embryonic disc formation and when it occurs:
A
- embryoblast differentiates during implantation ~7 days, into the epiblast and hypoblast
- hypoblast creates the exocoelomic membrane ~9-10 days (these cells are an inner layer to the cytotrophoblast), which eventually gives rise to the chorion
- epiblast remains as a mass of cells; an amniotic cavity forms and cells separate from epiblast, forming the amnion (encloses the embryo and houses amniotic fluid)
11
Q
Describe the process of primary umbilical formation:
A
- primary umbilical vesicle = hypoblast + lining of the exocoelomic membrane
- gives rise to the extraembryonic mesoderm, a layer of tissue that surrounds amnion and umbilical vesicle, will develop spaces that join and fuse to create the extraembryonic coelom
*primary umbilical vesicle is equivalent to the yolk sac present in other animals*
12
Q
Describe the process of the formation of the secondary umbilical vesicle:
A
- extraembryonic coelom forces primary umbilical vesicle to decrease in size
- majority of the primary umbilical vesicle pinches off and is eventually lost
- secondary umbilical vesicle forms from hypoblast cells (these cells migrate inside of the primary umbilical vesicle, site of origin of primordial germ cells)
13
Q
At the same time as the formation of secondary umbilical vesicle, the chorionic sac is formed, describe this process:
A
- extraembryonic coelom separates the extraembryonic mesoderm into: extraembryonic somatic mesoderm (lines trophoblast and amnion) and the extraembryonic splanchnic mesoderm (surrounds umbilical vesicle)
- the chorionic sac is thus formed, which is the extraembryonic somatic mesoderm + trophoblast; the chorion is the fetal component of the placenta
14
Q
- when the implantation of the blastocyst occurs outside of the uterine cavity
- 2% of all pregnancies
- typically occur in the oviduct (95-98%)
- sx: abdominal pain, amenorrhea, vaginal bleeding, profuse bleeding and rupture of the oviduct wall
A
ectopic pregnancy
15
Q
- process by which cells from the epiblast migrate to form the primary germ layers
- establishes basic body plan: a tube within a tube
- begins during week 3 of development, w/ formation of the primitive streak (thin depression on the surface of the epiblast)
- once all germ layers are present, the trilaminar embryonic disc is established
- defines all body axes: cranial-caudal, dorsal-ventral, medial-lateral, left-right
A
gastrulation
17
Q
- rod of cells that defines longitudinal axis of the embryo
- cells migrate cranially from the primitive node and pit, forming this structure
- extends to prechordal plate, site of future mouth
- gives rise to the notochord
A
notochordal process
18
Q
Descibe the process of formation of notochordal process and when this occurs
A
- formation begins w/ cranial extension from primitive node
- forms a hollow tube, the notochordal process
- grows cranially between ectoderm and endoderm until it reaches the prechordal plate
- hollows out, forming a canal
- by day 20, the formation of notochordal process is complete
19
Q
- solid mesodermal rod derived from the primitive node
- extends from the oropharyngeal membrane to the primitive node
- functions as the primary inductor (signaling center) in the early embryo
- induces the formation of the neural plate from the embryonic ectoderm and provides signaling for development of axial musculoskeleton
- will degenerate as the vertebral bodies form and give rise to the nucleus pulposus (intervertebral discs)
A
notochord
20
Q
Describe the process of notochord formation:
A
- floor of the notochordal process fuses w/ the underlying embryonic endoderm
- fused layers will degenerate, allowing contact between the notochordal canal into the umbilical vesicle
- floor of the notochordal canal disappears and the notochordal process forms the notochordal plate (flattened, grooved plate of cells in contact laterally w/ the embryonic endoderm)
- cranially, notochordal plate cells proliferate and undergo infolding, forming the notochord
- notochord pinches off from the endoderm and the umbilical vesicle
- separates the germ layers (endoderm and mesoderm)
22
Q
- primary germ layer
- epidermis of the skin and epidermal derivatives
- central and peripheral nervous systems
- neural crest cells, eyes, and internal ears
A
ectoderm
*epithelia comes from all germ layers*
23
Q
- primary germ layer
- all skeletal muscle
- visceral smooth muscular coats, serosal linings of all body cavities, urogenital ducts and organs
- most of the cardiovascular system, blood cells, lining of vasculature
- cartilage, bones, tendons, ligaments, dermis, and stroma of internal organs in the trunk
A
mesoderm
*epithelia comes from all germ layers*
24
Q
- primary germ layer
- epithelial linings of the respiratory and digestive tracts
- glands opening into the GI tract
- glandular cells of accessory GI organs (liver and pancreas)
A
endoderm
*epithelia comes from all germ layers*
