Embriology - week 1 Flashcards
1
Q
Prenatal is how many weeks?
A
38 from conception, 40 from gestational
2
Q
prenatal is 40 weeks from what?
A
LMP -
3
Q
Embryonic period is how many weeks?
A
First 8 - all major organs formed, sensitive to harmful factors
4
Q
Fetal period is how many weeks
A
30 weeks - organs grow and become more complex
5
Q
What is organogenesis?
A
The embryonic 8 week period
6
Q
Early embryology states focus on what characteristics?
A
Morphologic
7
Q
State 1 of Embryology is what?
A
Fertilization -
8
Q
Embryonic development ends at what state?
A
Stage 23 (day 56)
9
Q
At 3 weeks, what occurs?
A
Gastrulation, notochord, and beginning of nerual tube
10
Q
At week 4 what occurs?
A
Neural tube closes, heart beats, arm buds form, tail and gill grooves form
11
Q
At week 5, what occurs
A
Eye parts form, leg buds, brain enlarges
12
Q
At week 6, what occurs?
A
6 - webbed fingers , external ears, pigment in retina, tales and gills disappear
13
Q
At week 7, what occurs?
A
Webbed toes form, bones begin to harden, back straightens, eyelids
14
Q
At week 8, what occurs?
A
Upper limbs bend at elbows, gentialia begins, fingers distinct
15
Q
At week 9, what occurs?
A
toes separate, major brain parts are present
16
Q
At week 10, what occurs?
A
chin grows, nostrils separate, face appears human, genitalia appear male or female
17
Q
At week 11 and 12, what occurs?
A
Defined neck, genitalia complete, sucking reflex.
18
Q
What is cell differentiation?
A
During development, cells specify moving from multipotent stem cell.
19
Q
What cells are formed in the Ectoderm?
A
Skin, Neuron of brain, Pigment.
20
Q
What cells are formed in the Mesoderm?
A
Muscles, Tubule cell of Kidney, RBC
21
Q
What cells are formed in the Endoderm?
A
Pancreatic, Thyroid, Lung
22
Q
What are germ cells?
A
Sperm and Egg.
23
Q
What is gastrula?
A
An embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells.
24
Q
What is Morphogenesis?
A
Formation of shape during development.
25
Can cells change the way in which they adhere to each other, and migrate to other locations?
Yes, during morphogenesis.
26
What is dysmorphogenesis?
Abnormal development of body structures - may occur because of malformation or deformation.
27
What is malformation in a fetus?
When the processes required to normally form a structure fail to occur.
28
Cell Signaling - what is it?
When one group of cells influence the development of another adjacent, nearby or distant group of cells.
29
How do cells know what to do?
Signaling an array of different protein groups allows cells to gain information about their current and future tasks: migration, proliferation, differentiation, etc
30
What is paracrine signaling?
Activates directly or by blocking the activity of an inhibitor - signal transdution pathways
31
Paracrine signaling - what are the four groups of signal proteins?
Wnt, Hedgehog, Fibroblast growth factor (FGF), and Trasnforming growth factor beta (TGF-beta)
32
What is Wnt?
One of four groups of paracrine signaling proteins - fruit flies w/o wings, bind to Frizzled transmembrane cell surface receptors (G protein-coupled - involved in body patterning, cell fate, proliferation and migration.
33
If Wnt fails - what happens?
Limb, eye, genitourinary and bond development disorders; soluable forms of Frizzled (sFrps) bind Wnt proteins and inhibit Wnt signalling.
34
What are Hedgehogs?
One of four paracrine signalling proteins - work like a skeleton key - their effect depneds upon cell type, dosage, and how differentiated the cell is.
35
Mutations of the Hedgehog gene cause what?
First identified in Drosophila - early mutations cause naturally occurring spiky denticles to occur in a solid region rather than a strip, made embryo shorter, giving hedgehog appearance.
36
Hedgehog family in human - include what?
Sonic hedgehog homologue (SHH), Indian HH (IHH), and Desert HH (DHH).
37
Sonic hedgehog has a key role in what body parts?
Neural, bone, limb and kidney development; muscle patterning; and lung branching.
38
Are Hedgehogs involved in the development of special sense organs?
Yes. It binds to a cell surface transmembrane receptor called Patched.
39
How many varieties of FGGs are there, and what are their functions?
22, key players in range of processes - limb and neural development, angiogenesis, very early patterning and induction of mesoderm development.
40
What do FGF's vind?
FGF receptors (FGFRs) and heparan sulphate proteoglycans - are all part of the signal transduction process.
41
What is TGF-Beta?
Part of a superfamily of signaling factors, includes the bone morphogenetic proteins BMPs. Originally associated with tumor development.
42
How many types of TGF-Beta and BMPs have been discovered?
Three forms of TGF-Beta and 15 BMPs. TGF-Beta ligans bind to a type II TGF-Beta receptor that recruits a type 1 receptor - triggering a SMAD cascade, changing DNA transcription
43
Juxtacrine Signaling - what is it?
Does not involve diffusible factors; can occur between adjacent cells or between a cell and the Extracellular matrix. affect include the neural system and heart.
44
What is a Notch gene?
Great importance in cell differentiation and inducing specific cell clusters that lead to neurone, endothelial, cardiocyte, and T cell development. - Helps maintain stem cell populations.
45
What happens if signals are interrupted during key periods of development?
Congenital abnormalities. Teratogens may have significant effects.
46
What are Teratogens?
Classes of teratogens include radiation, maternal infections, chemicals, and drugs.
47
What does the drug thalidomide do if taken during early limb development?
Phocomelia (hands and feet attached to abnormally shortened limbs)
48
What actions occur in the first week of fertilzation?
Ovulation (hypothalmus - leutin, estrogen); Fertilization in Ampulla - Zygote forms; Cleavage (16 cell); Morula converts to Blastocyst (Blastolation); (Inner and Outer Cell Mass); Inner converts to Embryoblast, Outer Tryphoblast; Embryoblast converts to Bilaminar disc, Tryphoblast converts to cyto and ssstobtropblasts (make placenta) - then goes to bilaminar to trilaminar ...
49
What is the neural crest?
Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia.
50
What is gastrulation?
Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a multilayered structure known as the gastrula
51
Name the three germ layers.
ectoderm, mesoderm, and endoderm
52
Where and when is the Primitive Streak formed?
The primitive streak is formed at the beginning of gastrulation and is found at the junction between the extraembryonic tissue and the epiblast on the posterior side of the embryo and the site of ingression.
53
What forms bilateral symmetry?
The primitive streak.
54
What is a Terotegen?
Any agent that can disturb the development of an embryo or fetus... radiation, maternal infections, chemicals, and drugs.
55
What is a fibroblast?
A cell in connective tissue which produces collagen and other fibers.
56
What is transcription?
Transcription is the process in which a gene's DNA sequence is copied (transcribed) to make an RNA molecule
57
What is gametogenesis?
Special cells are created: Spermatogenesis and Oogenesis. These are two gametes. If they blend together they become a Zygote.
58
Mitosis vs. Meiosis?
Mitosis - one cell becomes two - genetically identical - 46 chromosomes; Meiosis: cells divide to become gametes - two step process - Meiosis 1 and 2 - to become a haploid cell - 23 chromosomes
59
What is an aneuploid embryos?
An gamete with an incorrect number of chromosomes (20% oocytes) (2 -3% of sperm).; majority do not come to term, more frequent as ovum age.
60
What is Turner's Syndrome?
Aneuploid oocyte - gamete has no genetic material - so ovum is X (from male) and 0 (from female. XO. If MALE is formed under this circumstance, it is inviable and missing way too many things (lots come from female).
61
What is Kleinfeller's Syndrome?
Aneuploid oocyte gives ovum 2 XX, plus the Y - XXY., for females this is a XXX.
62
What is trisomy and monosomy?
Too many or not enough chromosomes respectively.
63
What is trisome 21?
Down syndrome.
64
What is Monosomy X?
Turner's syndrome.
65
What is nondisjunction?
Abnormal gametes - Incorrect division of chromosomes - Turnes, Kleinfellers, etc
66
Spermatogonia - what is it?
The most primitive cell.
67
Phases of Spermatogenesis?
Spermatocyte - secondary spermatocyte - spermatid - sperm (released into lumen)
68
What are Sertoli Cells?
Support cells in spermatogenesis. Stretching from the lumen to the endge of the tubule?
69
What do Sertoli Cells do?
Nourish the developing sperm and form blood-testis barrier to control spermatogenesis; and inhibit spermatogenesis before puberty and stimulate process during puberty.
70
Where do sperm develop?
In the Seminiferous tubules in the testes. The testes are divided into many lobules, and each lobule contains many tiny seminiferous tubules.
71
How do sperm mature in the seminiferous tubules?
They start to mature on the outside and move inward toward the lumen.
72
What is the epididimus and the Ductus deferens?
epididmus comes from testes and then turns into the Ductus deferens.
73
What is a protamines?
A protein that stabilizes the nucleus during spermiogenesis when the nucleus condenses
74
Is excess cytoplasm generated during spermiogenesis?
Yes. Is pinches off as a residual body as the sperm becomes sleek.
75
How many days does spermiogenesis take?
64 - 50 to 150 million / day
76
What is the acrosomal vesicle?
In the head of the sperm a vesicle containing an enzyme helps to pierce the zona pelucida.
77
What happens if one or both Ductus defernes (or vas deferens) is blocked?
sperm doesn't get into ejaculate - lower sperm count or no sperm count - Ductus deferens is a tiny muscular tube.
78
What is the function of the epididmus?
Stores the sperm - connects testes to Ductus defernes (or as deferens)
79
Oogenesis - what is it?
Maturing of germ cell in female to produce gamete.
80
Are females born w/ all of their eggs?
Yes - and the maturation process begins ithe utero and is completed after puberty. - 2 Mil at birth, 40K at puberty - ~480 over lifetime (12/year)
81
When does Oogenesis end?
Menopause.
82
What is the prenatal maturation process of Oocytes?
During early fetal life, oogonia proliferate via mitosis and enlarge to form primary oocytes before birth.
83
What are primary (primodial) follicles?
The primary role of the follicle is oocyte support. From birth, the ovaries of the human female contain a number of immature, primordial follicles. These follicles each contain a similarly immature primary oocyte.
84
How many stages of the primordial follicle are there during the creation of primary oocytes?
The primary follicle develops into a secondary follicle. The secondary follicles look very similar to primary follicles, except that they are larger, there are more follicular cells, and there are small accumulations of fluid in the intracellular spaces called follicular fluid (nutritive fluid for the oocyte).
85
What is the corpus luteum?
A corpus luteum is a mass of cells that forms in an ovary and is responsible for the production of the hormone progesterone during early pregnancy. The role of the corpus luteum depends on whether or not fertilization occurs.
86
What is the zona pelucida?
Surrounds the oocyle, pierced by a sperm cell, giving rise to corona radiata (no other sperm may pass!)
87
Does a corpus luteum form each month? Where? Why?
The menstrual cycle has two phases, the follicular phase and the postovulatory, or luteal, phase. The luteal phase lasts for approximately two weeks. During this time, a corpus luteum forms in the ovary. ... The corpus luteum is essential for conception to occur and for pregnancy to last. corpus Luteum creates progesterone.
88
is the corpus luteum involved in creating the menstral cycle or developing the fetus?
Both -it generates progesterone - needed for both processes.
89
Does the postnatal oocyte further develop?
Yes. After puberty - it increases in size, and before ovulation completes first meiotic division giving rise to the secondary oocyte and the first polar body.
90
What is an interesting fact about the Secondary oocyte?
When fertilized it completes Meiosis II, giving rise to the Ootid and second polar body.
91
What is an Ootid?
Haploid gamete post fertilization, giving rise to ovum
92
What happens to the polar bodies?
Polar bodies form because the egg cell (oocyte) does not divide evenly. The resulting cells have the same DNA, but one is much smaller, called a polar body. ... This is the type of cell division that results in haploid cells. The cell with more cytoplasm becomes a mature ovum while the polar body usually dissolves.
93
What is the difference between an oogonia and an oocyte?
In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis, forming oogonia. During oogenesis, the oogonia become primary oocytes.
94
Where do female follicles reside in the reproductive system?
In the ovaries of the female reproductive system, an ovarian follicle is a fluid-filled sac that contains an immature egg, or oocyte. These follicles are found in the ovaries. During ovulation, a mature egg is released from a follicle.
95
What is the histology of follicles in the reproductive system?
Histologically these cysts are thin walled and filled with pale acidophilic residue or blood; they may contain cell debris, degenerating oocytes, or foamy, vacuolated, or pigment-laden macrophages. These follicles are lined by one to four layers of cuboidal granulosa cells, and there is no luteinization.
96
What is a corpus luteum?
A yellowish mass of progesterone-secreting endocrine tissue that forms immediately after ovulation from the ruptured graafian follicle in the mammalian ovary
97
What happens to a corpus luteum if pregnancy occurs?
The corpus luteum secretes estrogens and progesterone. The latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. If the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.
98
From a primary spermatocyte, how many useable sperm are formed?
4. Start with 1 -> Secondary spermatocyte 2 (meiotic division 1) -> 4 spermatids (Meiotic division II) -> Differentiation -> 4 spermatozoa.
99
From a primary oocyte, how many useable ootids are formed?
1 + 3 polar bodies.
100
What is the function of the cortical granulaes?
Prevents entry of other sperm once one enters into the zona pelucida.
101
What is the cortical reaction?
The cortical reaction is a process initiated during fertilization by the release of cortical granules from the egg, which prevents polyspermy, the fusion of multiple sperm with one egg.
102
What is the zona pelucida?
The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. ... It is secreted by both the oocyte and the ovarian follicles. The zona pellucida is surrounded by the corona radiata.
103
What is the corona radiata made of?
Corona radiata is a layer of granulosa cells. It's formed in Graafian follicle, where the granulosa cells surrounding the secondary oocyte are termed as corona radiata. When the ovum is released from the ovary (ovulation), the corona radiata also comes along.
104
What is more important, the egg or the sperm?
Since it is so much bigger than sperm, the egg is the source of cytosol and organelles,particularly mitochondria, for the future zygote
105
Can multiple sperm bind to the corona radiata?
Yes. Multiple sperm bind to the corona radiata, but only a single sperm usually fertilizes the egg
106
What is the acrosome reaction?
Sperm bind to ZP proteins in the zona pellucida; this initiates the release of enzymes from the sperm allowing it to burrow through the zona pellucida.
107
What is the zona reaction?
The corona reaction. Cortical granule enzymes digest ZP proteins so other sperm can no longer bind.
Hyaluronic acid and other proteoglycans are also released that become hydrated and swell, thus pushing the other sperm away.
108
What is a male pronuclei?
A pronucleus (plural: pronuclei) is the nucleus of a sperm or an egg cell during the process of fertilization. The sperm cell becomes a pronucleus after the sperm enters the ovum, but before the genetic material of the sperm and egg fuse.
109
What is a female pronuclei?
Contrary to the sperm cell, the egg cell has a pronucleus once it becomes haploid, and not when the sperm cell arrives.
110
What happens when the male pronucli and oocyte merge?
Fertilization. A zygote is formed.
111
Does the zona pelucida disappear during fertilization?
No, it hardens after the sperm is allowed in and forms the outside of where the cleavage and creation of blastomeres occur.
112
What phase do chromosomes decondense?
Telophase and Cytokinesis
Mitosis ends with telophase, or the stage at which the chromosomes reach the poles. The nuclear membrane then reforms, and the chromosomes begin to decondense into their interphase conformations. Telophase is followed by cytokinesis, or the division of the cytoplasm into two daughter cells.
113
States of embryonic development - day 1, day 2 -3, day 3, day 4, day 6?
Fertilzation, cleavage, compaction, formation of blastocyst, Implantation.
114
What is the trophoblast?
Late blastocyst - forms the ring with the embryoblast on one side. It becomes much of the placenta.
115
What is a morula?
Cleaved zygote with 16 - 32 cells, not yet implanted.
116
What is a blastomere?
A cell created by cleavage.
117
Are blastomeres totipotent?
Yes.
118
What is the inner cellular mass in reproduction?
After cleavage and compaction, the inner cellular mass forms along a side of the trophoblast, and becomes the embryo.
119
How is a blastocyst formed, and what is it?
During cavitation of the human embryo, sodium channels appear on the surface of the outer trophoblast cells; sodium and water are pumped into the forming blastocoele
120
What is blastocoele?
The fluid lake formed after compaction.
121
What is a blastocyst?
The outside is the zona pelucida, on the inside is the ring of trophocytes, the blastocoele, and the inner cell mass.
122
When does the blastocyst "hatch" and how?
It escapes out of the zona pelucida just prior to implantation. Inability to hatch or premature hatching can result in infertility or and abnormal implantation in the uterine tube.
123
What is an Ectopic pregnancy?
Implantation of the blastocyst somewhere other than the upper portion of the uterus - rupture can lead to life-threatening hemorrhage.
124
Where does fertilization normally occur?
The ampulla.
125
What connects the ovaries to the fallopian tubes?
Fimbriae. The fimbriae of the uterine tube, also known as fimbriae tubae, are small, fingerlike projections at the end of the fallopian tubes, through which eggs move from the ovaries to the uterus. The fimbriae are connected to the ovary
126
What are fsh and lh in the reproduction cycle?
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are called gonadotropins because stimulate the gonads - in males, the testes, and in females, the ovaries. They are not necessary for life, but are essential for reproduction
127
Where do the fsh and lh in the reproduction cycle come from?
FSH stimulates the growth and maturation of immature oocytes into mature (Graafian) follicles before ovulation. Luteinizing Hormone (LH) is a gonadotropin synthesized and secreted by the anterior pituitary gland in response to GnRH.
128
Where is fsh and lh produced?
Anterior pituitary gland. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland, and regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and luteinizing hormone (LH) work together in the reproductive system.
129
What causes the hypothalmus to release GnRH?
GnRH is a hormone produced in the hypothalamus region of the brain. GnRH moves through the bloodstream to the pituitary gland. There, it binds to certain receptors. Those receptors signal the pituitary gland to create two more hormones: LH and follicle-stimulating hormone (FSH)
130
What can trauma to the hypothalmus do?
Any trauma or damage to the hypothalamus can also cause a loss of gonadotrophin-releasing hormone secretion, which will stop the normal production of follicle stimulating hormone and luteinising hormone, causing loss of menstrual cycles (amenorrhoea) in women, loss of sperm production in men, and loss of production of hormones from the testes and ovaries.
131
How many layers of the endometrium are there in the female reproductive system?
Basal layer (own blood supply, not sloughed off); compact and spongy layers = functional layer - which disintegrate during menstruation and after childbirth.
132
What is the infundibulum in the female reproductive system?
The infundibulum catches and channels the released eggs; it is the wide distal (outermost) portion of each fallopian tube. The endings of the fimbriae extend over the ovary; they contract close to the ovary's surface during ovulation in order to guide the free egg
133
What structure is between the external and interior os
The cervical canal.
134
What is the mature follicle called?
The mature follicle is often called the Graafian follicle. ... The secondary oocyte together with the polar body and some surrounding follicle cells are released when the follicle ruptures at the surface of the ovary; this is called ovulation
135
What is the corpus albicans?
The corpus albicans is the regressed form of the corpus luteum. As the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans.
136
What are the 2 layers of the endometrium?
The stratum functionalis is a thick superficial layer that is sloughed off during menstruation and grows anew during each cycle. It is therefore a temporary tissue with an "unfinished" appearance -- not quite as tidily organized as the mucosal tissues in most other organs.
137
Does the endrometrius change shape?
Yes. Endometrial thickens during the follicular phase of the menstrual cycle, peak prior to ovulation, plateau during the early luteal phase and then decline prior to menstruation
138
Describe the zona reaction?
Cortical granule enzymes digest ZP proteins so other sperm can no longer bind.
Hyaluronic acid and other proteoglycans are also released that become hydrated and swell, thus pushing the other sperm away.
139
What happens during Week 2 embryonic development?
- Implanted embryo becomes more deeply embedded in endometrium
- Further development of trophoblast into placenta
- Development of a bi-laminar embryo, amniotic cavity, and yolk sac.
140
Days 8 - 12
- Trophoblast further differentiates and invades maternal tissues
- -Cytotrophoblast: stem cell population
- -Syncytiotrophoblast: invasive fused cells (syncytium) derived from cytotrophoblast
- -Breaks maternal capillaries, trophoblastic lacunae fill with maternal blood
- Inner cell mass divides into epiblast and hypoblast:
- -Epiblast contributes to forming the overlying amniotic membrane and amniotic cavity
- -Hypoblast contributes to forming the underlying yolk sac.
141
What is the role of the egg sac in embryonic development?
The yolk sac is the extraembryonic membrane that surrounds the egg yolk. The yolk sac has a well-developed vascular system that transports nutrients from the egg yolk to the developing embryo
142
What is the Syncytiotrophoblast ?
Syncytiotrophoblast is the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother
143
What is Heuser's Membrane?
Heuser's membrane (or the exocoelomic membrane) is a short lived combination of hypoblast cells and extracellular matrix. At day 9-10 of embryonic development, cells from the hypoblast begin to migrate to the embryonic pole, forming a layer of cells just beneath the cytotrophoblast, called Heuser's Membrane.
144
What is the epiblast?
The outermost layer of an embryo before it differentiates into ectoderm and mesoderm.
145
What is the cytotrophoblast?
The (or layer of Langhans) is the inner layer of the trophoblast. It is interior to the syncytiotrophoblast and external to the wall of the blastocyst in a developing embryo. ... Cytotrophoblastic cells play an important role in the implantation of an embryo in the uterus.
146
When can you first observe the amniotic cavity?
t the beginning of the second week, a cavity appears within the inner cell mass and when it enlarges it becomes the amniotic cavity. ... These cells are also derived from epiblast which is transformed into ectoderm. The amniotic cavity is surrounded by a membrane, called the amnion.
147
What is the hypoblast?
The hypoblast is a tissue type that forms from the inner cell mass during early embryonic development. It lies beneath the epiblast and consists of small cuboidal cells. The hypoblast gives rise to the yolk sac, which in turn gives rise to the chorion
148
What is the trophoblastic lacunae?
One of the spaces in the early syncytiotrophoblastic layer of the chorion before the formation of villi; in human embryos maternal blood enters these spaces by the 10th day; with the differentiation of the chorionic villi they become intervillous spaces, sometimes called intervillous lacunae.
149
What is the function of the fibrum coagulum?
DAY 9: blastocyst embeds deeper into endometrium, and a fibrin coagulum "plug" (blood clot and cellular debris) closes the penetration defect in uterine epithelial surface - interstitial implantation. Trophoblast progresses in development, especially at the embryonic pole, and vacuoles appear in the syncytium.
150
What is the function of the extraembryonic cavity?
"The coelomic cavity is part of the extraembryonic mesoderm, surrounding amniotic cavity, embryo, and yolk sac in the early gestation. It is now believed to represent an important transfer interface and a reservoir of nutrients for the embryo
151
What is the exocoelomic membrane?
It surrounds the exocoelomic cavity (primitive yolk sac), i.e. it lines the inner surface of the cytotrophoblast. At this point, the exocoelomic cavity replaces the blastocyst cavity.
152
What is the function of the extraembryonic mesoderm?
The extraembryonic mesoderm supports the epithelium of the amnion and yolk sac as well as the villi, which arise from the trophoblastic tissue. It also is involved in the development of the fetal blood.
153
What's the difference between the extraembryonic somatic mesoderm and splanchnic mesoderm?
The mesoderm of the amnion and chorion is referred to as extraembryonic somatic mesoderm because it is associated with the ectoderm and is avascular. The mesoderm of the yolk sac and allantois is called the extraembryonic splanchnic mesoderm because it is associated with the endoderm and is heavily vascularized.
154
What is the exocoelomic cyst?
The exocoelomic cysts are the remnants of the transient primary yolk sac structure, often found at the abembryonic pole of the extraembryonic coelom. Exocoelomic Vesicles.
155
What does the connecting stalk become?
The connecting stalk, which is the precursor of the umbilical cord, is formed by mesenchymal cells, and it connects the amnion cavity and the extracoelomic cavity.
156
What is the purpose of the secondary yolk sac?
The secondary or sonographic yolk sac has essential functions in embryonic development, including: 1. provision of nutrients to the developing embryo and other functions.
157
What can inhibit implantation of the blastocyst?
Large doses of progestins and/or estrogen (morning after pills); IUD
158
What is placenta previa?
Implantation of a blastocyst in the inferior segment of the uterus near the internal os partially or completely covering the os (cervix). Depending upon location there will may be different outcomes.
159
Is placenta accreta life threatening?
Placenta accreta is a condition in which part of or the entire placenta attaches to the uterine wall. ... All types of placenta accreta are dangerous and the most significant risk is life-threatening hemorrhage. In fact, up to 90 percent of women with the condition will need a blood transfusion.
160
Where should the placenta attach?
The placenta attaches to the wall of your uterus, and your baby's umbilical cord arises from it. The organ is usually attached to the top, side, front or back of the uterus. In rare cases, the placenta might attach in the lower area of the uterus.
161
Facts about spontaneous abortions?
- Frequency of 10% to 20%
- Most spontaneous abortions of embryos occur during the first 3 weeks
- Sporadic and recurrent spontaneous abortions are two of the most common gynecologic problems
- Frequency of early spontaneous abortions is difficult to establish
- A spontaneous abortion occurring several days after the first missed period is very likely to be mistaken for a delayed menstruation
162
Process of neurolation?
As cells of the epiblast pass through the primitive streak during gastrulation, some of those cells are destined to form a distinct collection of cells in the midline of the developing embryo.
The primitive node extends as a tube of mesenchymal cells running in the midline of the embryo between the ectoderm and endoderm. This is the notochordal process. It grows and extends in a cranial direction developing a lumen.
Around day 20 the notochordal process fuses with the endoderm beneath it, forming the notochordal plate.
A couple of days later the cells of the notochordal plate lift from the endoderm and form a solid rod, again running almost the full length of the midline of the embryo. This is the notochord
