MSCT Week 3: Embryology Basic Body Plan Flashcards
1
Q
First Trimester AKA
A
Embryonic Period
2
Q
2nd and 3rd Trimesters AKA
A
Fetal Period
3
Q
Embryonic Period Timeline
A
Fertilization to 8 weeks
4
Q
Organogenesis is?
A
Formation of Organs
5
Q
The basic body plan is set up during _______________.
A
Weeks 1-3 of the embryonic period
6
Q
Fetal Period Timeline
A
9 weeks until birth (38-weeks post-fertilization)
7
Q
Clinicians describe pregnancy by trimesters, three-month periods starting with the date of the onset of? and ending with?
A
Onset of the last menstrual period and ending with birth
8
Q
landmark events during the first week
4 listed
A
- Fertilization
- Cleavage
- Blastocyst formation
- Implantation
9
Q
describe how oocytes are selected
4 steps
A
- with each ovarian cycle, 5-15 ovarian follicles with surrounding epithelial cells begin to grow
- only one reaches maturity (called an Ovum)
- ovum is ovulated (released) from the follicle in response to a surge in luteinizing hormone from the pituitary gland
- The fimbrae, (fingerlike projections of the uterine or oviduct sweep the ovum into the uterine tube or oviduct
10
Q
Ovum are ovulated in response to?
A
A Surge of luteinizing hormone (LH) from the pituitary gland
11
Q
Fimbrae are?
A
Finger-like projections of the uterine tube or oviduct that sweep the ovum into the uterine tube
12
Q
uterine tube AKA
A
Oviduct
13
Q
Oviduct AKA
A
Uterine Tube
14
Q
How does fertilization occur?
4 steps
A
- when sperm swim through the uterus and oviduct to meet the ovum in a wide part of the oviduct called the ampulla
- As soon as a sperm enters the ovum, the ovum completes the second meiotic division and the female pronucleus forms
- The head of the sperm swells and becomes the male pronucleus
- This diploid cell is now called a zygote
15
Q
Zygote is?
A
Diploid cell that is the progenitor of the embryo
16
Q
Cleavage is characterized by?
A
Mitotic divisions without growth
17
Q
Cleavage begins…
A
as the one-celled zygote moves through the oviduct toward the uterus
18
Q
The cells of the cleaving embryo are called?
A
Blastomeres
19
Q
Blastomere potency
A
Blastomeres are totipotent until the 4-8 cell stage
20
Q
Blastomeres give rise to…
A
The embryo and the fetal part of the placenta
21
Q
When an embryo has 16 cells it is called a…
A
Morula (mulberry)
22
Q
Morula means?
A
Mulberry
23
Q
As the cells of the morula divide, they _________ and ______________.
A
As the cells of the morula divide, they compact (move closer together) and secrete fluid to form a cavity (cavitate)
24
Q
After the morula divides and cavitates it is now a?
A
Blastocyst
25
The blastocyst arrives in the uterine cavity by
4-5 days after fertilization
26
4-5 days after fertilization?
The blastocyst arrives in the uterine cavity
27
When does the blastocyst attach to the uterine wall (implant)?
By day 6
28
By day 6, the blastocyst...
begins to invade the uterine wall (Implantation)
29
Implantation in the uterus timeline
day 6 - first 2 weeks
30
Identify
+
What time in development is pictured?
Week 1 of embryonic development
31
blastomere cell types
blastomeres of the 6-day embryo segregate into two distinct cell types
Inner cell mass (embryoblast)
Outer Cell Mass (Trophoblast)
32
Inner cell mass AKA
Embryoblast
33
Outer Cell Mass AKA
Trophoblast
34
Identify
35
Embryoblast gives rise to?
these cells form the embryo and are pluripotent stem cells
36
The Trophoblast gives rise to?
These cells surround the embryoblast and blastocyst cavity and will form the fetal part of the placenta
37
During week 2, the embryoblast and trophoblast each differentiate into?
2 layers and 2 cavities form giving rise to the bilaminar embryo
38
Bilaminar Embryo is?
embryoblast with 2 layers and 2 cavities formed by the embryoblast and trophoblast
39
Name the layers of the embryoblast
* Epiblast
* Hypoblast
40
The trophoblast differentiates into the?
* Syncytiotrophoblast
* Cytotrophoblast
41
The Epiblast is?
Columnar cells that secrete fluid to form the amniotic cavity above them
42
The Hypoblast is?
Cuboidal cells below the epiblast that migrate to line the blastocyst cavity converting it to the primitive yolk sac
43
Identify
44
Syncytiotrophoblast
* Outer layer
* one cytoplasm with many nuclei; a syncytium
45
Cytotrophoblast
* Inner Layer
* Actively proliferating cells
46
describe embryoblast development
47
By 12 days, the blastocyst is?
Completely embedded in the uterine wall
48
Lacunae means
Lakes
49
spaces in the syncytiotrophoblast called Lacunae serve what function?
Connect to capillaries in the uterine wall to establish the placental blood supply
50
The hypoblast cells lining the primitive yolk sac proliferate to form?
Loose connective tissue called extraembryonic mesoderm
51
Extraembryonic mesoderm arises from
The hypoblast cells lining the primitive yolk sac
52
How is the chorionic cavity formed?
spaces appear in the extraembryonic mesoderm and coalesce to form the chorionic cavity by 13 days
53
The connecting stalk function
suspends the bilaminar embryo within the chorionic cavity
54
The connecting stalk is composed of?
Extraembryonic mesoderm
55
The secondary or definitive yolk sac is characterized by?
The suspension of the bilaminar embryo in the chorionic cavity by the connecting stalk
56
Identify
+
what is this called?
Primary Yolk Sac 12 days
57
Identify
+
What is this called?
+
When does this occur?
13 days Secondary Yolk Sac
58
Explain the primary to secondary yolk sac transition
59
Dizygotic or Fraternal Twins arise from?
+
Dizogitic twins represent what percentage of twins?
* Two oocytes fertilized by two sperm and represent
* 70% of all twins
60
The zygotes in dizygotic twins are genetically?
Distinct
61
Implantation of dizygotic twins?
Implant separately
62
Dizygotic twins fetal structures
Have separate
* fetal membranes
* placentas
* amnions
* chorions
63
% of twins that are monozygotic?
30% of twins
64
Monozygotic twins develop from?
One oocyte fertilized by one sperm
65
Monozygotic twins mechanism
the zygote splitting at different stages of development so the twins are genetically identical
66
Monozygotic twins are genetically?
Identical
67
Fetal structures of monozygotic twins
Depending on when the splitting occurs, the placentas, amnions and chorions can be separate or shared
68
If the zygote splits at the two-cell stage...
The embryos implant separately and develop similarly to dizygotic twins, each with its own placenta, amnion and chorion
69
If the inner cell mass splits at the early blastocyst stage...
The embryos occupy the same chorion, but have separate amnions and one placenta
70
If splitting occurs in the bilaminar embryo...
The embryos share an amnion, chorion and placenta
71
Conjoined twins result from?
Very rarely when the embryos do not separate fully
72
Describe monozygotic and dizygotic twinning and structures shared, splitting stages...
73
Hydatidiform mole properties and prevalence
* In 0.1% to 0.5% of pregnancies the fetal part of the placenta forms but the embryo does not.
* This is called a molar pregnancy or hydatidiform mole
* Hydatidiform moles can be complete or partial
74
Hydatidiform mole means
* Greek
* hydatidos meaning water
* mole means spot
75
A complete mole characterization
* complete lack of an embryo
* the placental or chorionic villi become swollen as fluid is taken up from the maternal circulation and has nowhere to go and become swollen and resemble bunches of grapes or drops of water
76
Do Complete moles abort?
Yes, usually early
77
Clinical signs of a complete mole
5 listed
* preeclampsia (maternal high-blood pressure) during the 1st trimester
* vaginal bleeding
* elevated chorionic gonadotropin (hCG)
* High hCG secreted by the trophoblast result in excessive nausea and vomiting
* 3-5% of complete moles develop into malingnat disease called gestational trophoblastic neoplasia, a malignant tumor of the trophoblast (one histologic type is carcinoma)
78
Gestational Trophoblastic Neoplasia
* A malignant tumor of the trophoblast (one histologic type is choriocarcinoma)
* 3-5% of complete moles develop into gestational trophoblastic neoplasia
79
High levels of hCG result in?
Excessive Nausea and vomiting
80
Preeclampsia during the first trimester, vaginal bleeding and elevated human chorionic gonadotropin indicate what?
Complete mole
81
Diagnosis method of a complete molar pregnancy
Cytogenetic analysis
82
A cytogenetic analysis of a complete molar pregnancy will show?
normal diploid karyotype but all chromosomes are parentally derived
83
Possible karyotypes of a complete molar pregnancy
3 listed
* 46 XX
* 46 XY
* 46 YY
84
Dispermic fertilization mechanism and possible karyotypes
two sperm fertilizing an oocyte that lacks or loses its own nucleus with a karyotype of...
* 46 XX
* 46 XY
85
Monospermic Fertilization mechanism and possible karyotypes
One sperm that fertilizes an oocyte lacking a nucleus, the sperm undergoes mitosis without cytokinesis, doubling its DNA with a karyotype of...
46 XX
86
46 YY Zygote
doesn't develop as it lacks X chromosome genes essential for development
87
Partial moles result from?
dispermic fertilization of a normal oocyte or fertilization by a single abnormal diploid sperm
88
PArtial moles result in?
fetal tissue is present and spontaneous abortion usually occurs in the second trimester
89
Possible karyotypes of partial moles
Usually triploid
* 69, XXX
* 69, XXY
* 69, XYY
90
Week 3 of development
The major event of the third week is converting the 2-layer embryo into a 3-layer embryo (trilaminar embryo)
91
blastomeres are totipotent until the?
4-8 cell stage
92
Trilaminar Embryo AKA
3-layer embryo
93
Gastrulation establishes
the 3 layers that will give rise to all adult tissues and organs
94
When is the primitive streak developed?
15 days
95
Where is the primitive groove?
In the center of the primitive streak
96
Where is the primitive node?
along the cranial end of the primitive groove
97
Where is the primitive pit?
In the center of the primitive node
98
What defines the major body axes?
Formation of the primitive streak (cranial-caudal, medial-lateral) (primitive streak is the median or midline
99
During gastrulation, TGFβ and Wnt signaling causes?
FGF8 production
100
FGF8 stimulates
epiblast cell migration (epithelial to mesenchymal transition)
101
During gastrulation, epiblast cells migrate where?
Toward the center of the bilaminar disc-shaped embryo forming the primitive streak and dive down or invaginate through the primitive groove to replace hypoblast cells beneath them
102
When the hypoblast is replaced by epiblast cells this layer is now called?
Endoderm (inside layer)
103
Epiblast cells then migrate between the newly formed endoderm and epiblast layers form the?
Intra-embryonic mesoderm (middle layer)
104
The remaining epiblast cells that did not migrate from the upper layer become the?
Ectoderm (outside layer)
105
Identify structures and stage
Trilaminar Embryo
106
Cells migrate which direction first in gastrulation?
Cranially first and then caudally last so that cranial or head mesoderm forms first
107
Ectoderm forms?
* Central and Peripheral Nervous Systems
* Some head skeletal and connective tissue
* Epidermis, hair, nails
* Sensory epithelium of nose, ear and eye
108
Mesoderm forms?
* Skeletal, smooth, and cardiac muscle
* cartilage, bone, connective tissue, blood
* components of the kidneys and gonads (urogenital system)
109
Endoderm forms?
* Epithelium of gut and its derivatives (live, gallbladder, pancreas)
* Epithelium of the respiratory system
110
gastrulation 17-22 days
111
Tube-within-a-tube body plan
The neural tube is not considered one of the tubes because it is not formed by body folding
112
Caudal Regression Syndrome AKA
Caudal Dysplasia
113
Caudal Regression Syndrome is?
* A disorder that impairs the development of the lower (caudal) half of the body
* this can include the lower limbs, lower back, and the lower gastrointestinal (gut) and urogenital (urinary and genital) tracts
114
The underlying mechanism of Caudal Regression Syndrome
* abnormal growth and migration during gastrulation resulting in abnormal development of the caudal mesoderm
* Which is the last mesoderm to form
115
The last mesoderm to form is?
Caudal Mesoderm
116
Caudal Dysplasia Risk Factors
Multiple genetic and environmental factors are implicated in caudal dysplasia including:
* maternal diabetes
* Wnt gene defects
* Vascular Abnormalities
* Teratogens
117
Sirenomelia AKA
Mermaid Syndrome
118
Sirenomelia is?
an extreme and rare form of caudal dysplasia but it may be a distinct disorder
119
Sirenomelia example
120
Embryonic Induction
* the stimulation of a specific developmental pathway in one group of cells (the responding tissue) by a closely approximated second group of cells (the inducing tissue).
* It is also referred to as instructive interactions
* In other words, a signal passes from the inducing to responding tissue, changing the fate of the responding tissue
121
Embryonic Induction AKA
Instructive Interactions
122
Embryonic Induction mechanisms
3 listed
* Diffusion of the inducing molecule from one cell to another
* Contact between the extracellular matrix of one cell to another
* Direct contact between the inducing and responding cells
123
Examples of embryonic Induction
4 listed
124
Primitive Streak Formation Embryonic induction
125
Mesoderm Formation Embryonic induction
126
Neural Induction Embryonic induction
127
Lens Induction Embryonic induction
128
Ectopic Induction
129
The period of susceptibility AKA
period of maximal sensitivity
130
The period of susceptibility
* is when the embryo is especially vulnerable to environmental factors causing abnormal development
* this occurs during weeks 4-8 of the embryonic period when organs are forming during organogenesis
* Insults during the first 3 weeks generally result in death of the embryo and spontaneous abortion
131
Congenital Anomaly
* something that is different or unusual at birth
* AKA birth defect
*
132
Congenital anomalies account for more than _____ of infant deaths
20%
133
Etiology of congenital anomailes
* 50% of etiology of congenital anomalies is unknown
* the other 50% is due to environmental factors, chromosomal defects, mutant genes, or are multifactorial
134
135
Possible mechanisms of congenital anomalies
4 listed
* Faulty embryonic induction (mutant signaling molecule genes)
* defects in apoptosis
* defects in migration
* developmental arrest
136
Period of susceptibility timeline
137
Causes of Congenital Anomalies
5 listed
138
Anomaly definition
means a marked deviation from normal
139
Association definition
nonrandom appearance of 2 or more anomalies together; cause is not known
140
Congenital definition
Present at birth
141
142
Deformations definition
result from mechanical forces that mold a part of the fetus over a prolonged period
143
Malformation definition
a structural defect in the body due to abnormal embryonic or fetal development
144
Syndrome Definition
Is a group of anomalies occurring together that have a common cause
145
Sequence Definition
is when a primary anomaly itself determines additional defects
146
Teratogen Definition
Is any agent or factor that can disturb the development of an embryo
