1.3 embryology - zygote to primitive epithelia Flashcards
1
Q
embryonic stage of development
A
fertilization - week 8 (day 56) when all major structures are present
2
Q
fetal stage of development
A
day 57 - birth
period of growth and differentiation of tissues and organs formed in embryonic period
3
Q
fertilization - beginning and end
A
sperm/oocyte contact to mixing chromosomes
4
Q
cleavage divisions
A
mitotic divisions of zygote resulting in collection of blastomeres
5
Q
blastomere
A
cell produced by zygotic cleavage. collection forms 12 cell morula
6
Q
morula enters uterus, develops fluid filled cavity, becomes this
A
blastocyst
7
Q
embryoblast
A
inner cell mass of blastocyst gives rise to embryo
8
Q
trophoblast
A
outer cell mass of blastocyst gives rise to placenta
9
Q
endometrium
A
luminal layer of uterus, simple columnar epithelium with connective tissue stroma
10
Q
stroma
A
connective tissue framework
11
Q
2 layers of endometrium
A
functionalis
basalis
12
Q
decidua
A
functionalis becomes the decidua during pregnancy
13
Q
cytotrophoblast
A
thin, mitotically active layer that develops from the trophoblast after implantation
14
Q
what happens to the trophoblast after implantation?
A
proliferates rapidly and becomes the cytotrophoblast and the syncytiotrophoblast
15
Q
trophoblast turns develops into what 2 layers after implantation?
A
cytotrophoblast
syncytiotrophoblast
16
Q
syncytiotrophoblast
A
outer mass of the trophoblast consisting of a multinucleated mass with no cell boundaries
17
Q
what is the chorion formed by?
A
extraembryonic mesoderm, syncytiotrophoblast, and cytotrophoblast
18
Q
what does the chorion do?
A
contributes to fetal portion of placenta
19
Q
ectopic pregnancy
A
implantation of blastocyst outside of uterus, usually in ampulla of oviduct
20
Q
bilaminar disc - what does it arise from and when?
A
arises from changes in the embryoblast in the second week of development
21
Q
epiblast
A
thick, dorsal aspect of the bilaminar disc consisting of high columnar cells related to the amniotic cavity
22
Q
hypoblast
A
ventral layer of the bilaminar disc located below the epiblast, consisting of small cuboidal cells related to yolk sac formation and extraembryonic mesoderm
23
Q
what is another name for the hypoblast?
A
primitive endoderm
24
Q
does the hypoblast contribute to the tissues of the embryo?
A
no
25
yolk sac
ventral structure lined by hypoblast cells, below hypoblast layer
26
function of the yolk sac?
- origin of primordial germ cells
- early blood cell development
- regulation of nutrients to embryo
27
how is the amnion formed?
from cells that separate from the epiblast
28
what does the amnion do?
encloses the amnionic cavity
29
amnionic cavity
surrounds embryo and fetus with amnionic fluid - critical to health of embryo
30
primitive streak
thickened band of epiblast cells appearing at the beginning of week 3 in the caudal, dorsal aspect of the bilaminar disc. epiblast cells migrate down through streak to form endoderm and mesoderm during gastrulation
31
where does the primitive streak first appear?
caudal, dorsal aspect of the bilaminar disc
-aka-
caudal aspect of the epiblast
32
when does the primitive streak first appear?
beginning of week 3
33
epiblast cells migrate through the primitive streak to form what 2 layers during gastrulation?
endoderm
| mesoderm
34
gastrulation
period of epiblast proliferation, migration, and differentiation through which the 3 germ layers form
35
what are the 3 germ layers formed during gastrulation?
ectoderm
mesoderm
endoderm
36
what do the ectoderm, endoderm, and mesoderm give rise to?
All cells, tissues, and structures of the embryo
37
brain growth, tooth development, secondary sex characteristics, and ossification of bones are all examples of development that occurs
postnatally
38
what are the two phases of prenatal development?
embryonic period
| fetal period
39
4 significant developmental processes of the embryonic stage include:
cellular proliferation, migration, differentiation, formation of all major internal and external structures
40
what is another name for the embryonic period?
the period of organogenesis
41
what does the "period of organogenesis" refer to?
the embryonic period, in which all the major events of organ formation occur
42
why is the embryonic period also called the period of organogenesis?
all major events of organ formation occur
43
time frame of the embryonic period
fertilization to day 56 (week 8)
44
time frame of fetal period
day 57 (9th week) to birth
45
what is the fetal period significant for?
growth and maturation of the organ systems developed in the embryonic period
46
how many chromosomes are typical of a human somatic cell?
46
47
daughter cells of zygotic cleavage divisions are called
blastomeres
48
the 12-32 blastomere stage is called the
morula
49
how many cells in the morula
12-32 cells
50
the morula turns into the ___ by ____
the morula turns into the blastocyst by absorbing fluid and forming a large central cavity -- the blastocyst cavity
51
what are 3 components of the blastocyst
embryoblast
trophoblast
blastocyst cavity
52
cells that migrate to the interior of the blastocyst become the
embryoblast (inner cell mass)
53
cells that migrate to the periphery of the blastocyst become the
trophoblast
54
why does the zona pellucida degenerate?
to allow for implantation and growth
55
when does implantation occur?
~day 6
56
what causes the endometrial layer to to increase in thickness and and provide nourishment for the embryo?
hormonal control
57
when does the trophoblast begin to proliferate and divide into two layers?
as it contacts the endometrium
58
teratogen
environmental agents that cause congenital abnormalities (i.e. alcohol, drugs, radiation)
59
name 3 teratogens
alcohol, drugs, radiation
60
what is the critical period of susceptibility to teratogens? why?
the embryonic period between weeks 2 and 8. critical period of tissue and organ system development
61
when in the embyronic period is the embryo apparently not as susceptible to teratogens? why?
first 2 weeks. because death of the embryo (spontaneous abortion) is more likely to occur
62
when do embryonic cells apparently transition from totipotent to pluripotent?
when the morula becomes the blastocyst
63
fertilization age vs gestational age
age from fertilization vs age since last normal menstrual period (LNMP)
64
typical menstrual cycle length
28 days
65
typical time of fertilization
day 14-15 of menstrual cycle
66
approximate difference between gestational and fertilization age
14 days (2 weeks)
67
another name for fertilization age
conception age
68
which is older, gestational age or fertilization age? by how much?
gestational age is 14 days older
69
normal gestational age at birth (days)
280 days
70
normal fertilization age at birth (days)
266 days
71
how do you calculate estimated due date from date of last menstrual period?
subtract 3 months, add 7 days
-or-
add 9 months and 7 days (280 days)
72
mom's last period was Sept 5th, what is the estimated due date (EDD) of her baby?
June 12th
73
what region of the blastocyst gives rise to only extraembryonic cells?
trophoblast - outer cell mass
74
what region of blastocyst gives rise to intraembryonic cells?
embryoblast - inner cell mass
75
what is the function of extraembryonic tissues?
allow embryo to survive in female uterus
76
implantation induces the trophoblast to do what?
divide into 2 layers: cytotrophoblast and syncytiotrophoblast
77
of the two layers of the former trophoblast, which is inner and which is outer?
inner - cytotrophoblast
| outer - syncytiotrophoblast
78
of the two layers of the former trophoblast, which produces hCG?
syncytiotrophoblast
79
the syncytiotrophoblast produces what hormone?
human chorionic gonadotropin, hCG
80
what hormone can be used to detect pregnancy?
human chorionic gonadotropin, hCG
81
how many days after implantation can hCG be detected by an early pregnancy detection kit?
6-12 days after implantation
82
how many days after fertilization can hCG be detected by an early pregnancy detection kit?
12-18 days after fertilization
83
"ectopic" =
"out of place"
84
are ectopic pregnancies potentially life threatening? why?
Yes. Internal bleeding.
85
decidua
the pregnant endometrium
86
decidua reaction
stromal cells of the decidua become large rounded cells filled with glycogen and lipids
87
____ penetrates deeper into the stroma of the decidua and erodes the cells and walls of blood vessels
syncytiotrophoblast
88
what is the role of hCG?
induces the ovary to produce estrogen and progesterone to maintain the pregnancy
89
hCG is secreted by ___
| in order to ___
the uterus-syncytiotrophoblast
| induce the ovary to produce estrogen and progesterone to maintain the pregnancy
90
in what week does the bilaminar disk form?
week 2
91
which layer of the bilaminar disk encloses the amnonic cavity?
the epiblast
92
what kind of tissue forms all glands of the body?
epithelial tissue
93
what kind of tissue covers the body surface and lines cavities?
epithelial tissue
94
all ____ cells contact a basal lamina
epithelial
95
what are the two cavities formed in week 2?
amniotic cavity
| yolk sac
96
cells from which part of the bilaminar disc form the amnion that lines the amnionic cavity?
cells from the epiblast
97
cells from which part of the bilaminar disc form the membrane of the yolk sac?
cells from the hypoblast
98
early networks that form in the uterine lining to supply blood to the embryo are called
lacunar networks
99
trophoblastic lacunae and enlarged blood vessels of the uterus meet to form the
primordial uteroplacental circulation
100
cells of the epiblast surrounding the amniotic cavity are called
amnioblasts
101
the migration of cells from the hypoblast over the inner surface of the cytotrophoblast form
the primary yolk sac
102
the secondary (definitive) yolk sac replaces the primary yolk sac through
a second migration of primordial endodermal cells from the hypoblast
103
2 important functions of the yolk sac
hematopoiesis, primordial germ cells... formation? migration? unclear...
104
hematopoiesis
blood cell formation
105
the yolk sac is important during what time period
the first 4 weeks of development, then it regresses and typically vanishes by birth
106
primordial germ cells are first recognized where
on the wall of the yolk sac prior to migration to gonads
107
the development of the three layered embryo from the bilaminar disc is called
gastrulation
108
the primitive streak moves from
caudal to rostral (cranial)
109
the primitive pit is found on the __ end of the primitive groove
cranial
110
T/F the primitive streak establishes major body axes
True
111
4 body axes established by the primitive streak include:
caudal / cranial
medial / lateral
right / left
dorsal / ventral
112
this structure appears to arise from the cranial end of the primitive streak, inserts into the endoderm, forms a thickening, contributes to the oropharyngeal membrane, forms an important signaling center involved in formation of the forebrain of the central nervous system, and contributes connective tissue to the head region
the prechordal plate
113
what cells form the primitive endoderm?
hypoblast cells before the primitive streak develops and replaces with the definitive endoderm
114
summarize the formation of the endoderm during gastrulation
early epiblast cells slip through the basal lamina in the primitive streak and displace the primitive endoderm (hypoblast cells) with the definitive endoderm
115
summarize the formation of the mesoderm during gastrulation
later epiblast cells migrating through the primitive streak and past the endoderm form the mesoderm
116
summarize the formation of the ectoderm during gastrulation
cells remaining in the epiblast layer (not migrating through the primitive streak) form the ectoderm
117
this structure replaces the primitive pit
the notochord
118
the notochord extends cranially to the
prechordal plate
119
what is the fate of the hypoblast after gastrulation?
unclear. apparently estraembryonic structures and the cloacal membrane
120
cloacal membrane
membrane over anus that breaks down early in development
121
oropharyngeal membrane
membrane over the mouth that breaks down early in development
122
the notochord is considered a derivative of which germ layer?
the mesoderm
123
3 layers of the chorion
- extraembryonic somatic mesoderm (and splanchnic mesoderm?) (line amnion & yolk sac)
- cytotrophoblast layer
- syncytiotrophoblast layer
124
the chorionic cavity divides the extraembryonic mesoderm into the...
-extraembryonic somatic mesoderm (lines trophoblast and amnion)
-extraembryonic splanchnic
mesoderm- lines the yolk sac
125
the fetal and maternal contributions to the placenta are
chorion (fetal)
| decidua (maternal)
126
can drugs, viruses, or alcohol cross the placental membrane?
Yes.
127
draw the amnionic cavity, the secondary yolk sac, the chorionic cavity, and the remnant of the primitive yolk sac
draw it
128
3rd week most significant for
conversion of bilaminar disc to trilaminar disc through gastrulation
129
what day does the primitive streak appear?
15-16 days post fert
130
in the bilaminar disc, high columnar cells form the __
epiblast
131
function of the syncytiotrophoblast
secrete hCG along with the uterus
132
in week 2 when the yolk sac forms, does the yolk sac contain yolk? what nourishes the embyro?
the yolk sac contains no yolk. the embryo is nourished by the lacunar networks
133
in week 2, what new layer of cells forms between the yolk sac and the cytotrophoblast?
the extraembryonic mesoderm
134
cavities form in the extramebryonic mesoderm and form a new space, the...
chorionic cavity
135
the chorionic cavity divides the extraembryonic mesoderm into these 3 layers...
- extraembryonic somatic mesoderm -- lining trophoblast and amnion
- extraembryonic splanchnic mesoderm -- lines the yolk sac
- chorion, lines the chorionic cavity
136
does the extraembryonic splanchnic mesoderm line the primary or secondary (definitive) yolk sac?
the definitive yolk sac -- the primary yolk sac is pinched off and regressing
137
when the primary yolk sac is pinched off it becomes the....
exocoelemic cyst
138
in what layer of embryonic cells are the lacunar networks formed?
syncytiotrophoblast
139
when does the decidua reaction begin? how long does it last?
Amusingly, the decidual reaction in humans begins with ovulation. This doesn't make too much intellectual sense, though, so I'll forgive you if you want to believe it begins with implantation, as is true in many other animals. A major purpose of decidualization is to prepare the uterine mucosa for a "burrowing" conceptus. The decidualized cells limit the ability of the trophoblast to enzymatically dissolve the mucosa. (You want the conceptus to become encapsulated within the mucosa, but you don't want it to reach the muscularis layer.) The mucosa remains decidualized for the duration of the pregnancy. (During a normal cycle, the decidualization is relatively insignificant, and any decidualized cells are lost at menstruation.)
