Embryology PPT 1 and 2 Flashcards
1
Q
day 1
A
fertilization
2
Q
day 2-3
A
cleavage
3
Q
day 3
A
compaction
4
Q
blastocyst formation
A
day 4
5
Q
implantation begins
A
day 6
6
Q
how many oocytes at birth
A
2 million
7
Q
how many oocytes at puberty
A
40,000
8
Q
how many oocytes ovulated
A
400
9
Q
__surge causes changes within the ovary and egg for it to rupture
A
LH (luteinizing hormone)
10
Q
Egg is surrounded by the:
A
Zona pelucida: layer of glycoproteins
Corona radiate: granulosa cells that surround the ovary after ovulation
11
Q
Egg is swept into
A
oviduct (uterine tube)
12
Q
Fertilization usually occurs in the
A
ampulla
13
Q
Enters uterus
A
~ day 4
14
Q
Implantation into uterine wall begins
A
~ 6th embryonic day
15
Q
Begins process of cellular division (cleavage)
A
right after fertilization
16
Q
fertilization steps (8)
A
1.Multiple sperm bind to corona radiate
2. Sperm passes through the corona radiata
3. Sperm binds to a ZP protein in the zona pellucida
Causes release of enzmes allowing it to burrow through ZP (acrosome reaction)
4. The cell membrane of 1 sperm fuses with cell membrane of oocyte
5. Initiates calcium influx causing the release of cortical granules (cortical reaction)
Blocks other sperm from fertilizing egg
6. Completion of 2nd meiotic division of the oocyte
7. Male and female pronuclei form fuse
8. Arrangment of the chromososmes for mitotic cell division
17
Q
fertilzation usually occurs
A
ampulla of uterine tubes
18
Q
Zygote is the result of the union of the male and female gametes
A
Restores 46
Maternal and paternal chromosomes are mixed
19
Q
Repeated mitotic cell divisions results in an increase in
A
cell number (not size)
20
Q
A cell formed by cleavage of a fertilized ovum is call a
A
blastomere
21
Q
Blastomeres become __ with division
A
smaller
22
Q
Early blastomeres are
A
totipotent: capable of giving rise to any cell type
23
Q
in the 8 cell stage __ begins
A
compaction
24
Q
Blastomeres tightly align by
A
increased cell adhesion and segregate inside vs. outside
25
Outer cells become
trophoblast – cells that will form placenta
26
Inner cells will form
embryo (inner cell mass)
27
When there are 16-32 blastomeres, the conceptus is referred to
a morula
| inner cells and outer cells
28
morula enters uterus when
about 4 days after fertilization
29
___ are pumped into embryo creating a blastocystic cavity
Sodium and water
30
blastocystic cavity
- Mostly separates the embryoblast and trophoblast
| - Embryo is called a blastocyst
31
blastocyst attaches to endometrium
~ 6 days after fertilization,
32
Prior to implantation, the blastocyst “hatches” from ___
zona pellucida (Enzymatically bores a whole and squeezes out)
33
Early ZP shedding or delayed zygote transport can cause
implantation in the wrong location (ectopic pregnancy)
34
Week 2: days 7-14
- Embryo becomes more deeply embedded within endometrium
- Development of trophoblast into placenta precursor
- Formation of bilaminar embryo, amniotic cavity
- ~ day 10 embyro becomes completely embedded within the endometrium
35
(~day7) Trophoblast proliferates and differentiates into:
cytotrophoblast and syncytiotrophoblast
36
Cytotrophoblast
stem cell population that adds cells to the syncytioblast
37
Syncytiotrophoblast
- Derived from cytotrophoblast proliferation
- Cells lose membranes and form a syncytium
- Located at the embryonic pole (adjacent to embryoblast)
- ~ day 8, begins invading into the endometrium.
- Blastocyst becomes completely embedded ~day 10
38
Synctytiotrophoblast comes into contact with uterine vessels and glands creating a
primitive uteroplacental circulation (lacunae filled with maternal blood)
39
Creates lacunae filled with maternal blood
Synctytiotrophoblast
40
fuse creating a lacunar network
Lacunae
41
Cytotrophoblast form extensions that grow into overlying synctiotrophoblast forming
chorionic villi
42
Villi become penetrated by __ that will eventually form blood vessels
extraembryonic mesoderm (week 2 and 3)
43
Embryoblast differentiate into 2 epithelial layers by
day 8
44
Epiblast:
columnar cells adjacent to amniotic cavity (dorsal side of embryo)
45
hypoblast
small cuboidal cells adjacent to exocoelomic cavity (primitive yolk sac)
46
- Forms into a bilaminar embryonic disc
| - Located between amniotic cavity and the primary umbilical vesicle
embryoblast
47
Amniotic cavity forms within the
epiblast
48
Epiblast cells migrate forming
the amnion which encloses the amniotic cavity
49
Hypoblast migrate and line the blastocystic cavity forming the
exocoelomic membrane
50
Blastocystic cavity referred to as the
primary umbilical vesicle (primary yolk sac)
51
Hypoblast and cytotrophoblast produce
extraembryonic mesoderm
52
Extraembryonic mesoderm proliferates and
- Develops spaces within
| - These spaces fuse to form the extraembryonic coelom (chorionic cavity)
53
precursor to the umbilical cord
Fluid filled cavity that surrounds the umbilical vesicle and amnion
Except at connecting stalk
54
Extraembryonic somatic mesoderm + 2 layers of trophoblast form the
chorion
55
chorion
Outermost fetal membrane
| Contributes to the placenta
56
Week 3 Days (14-21) key events
1. Appearance of primitive streak
2. Development of the notochord and neural induction
3. Differentiation of 3 germ layers (gastrulation)
57
Gastrulation
- Process where the bilaminar embryonic disc is converted into a trilaminar embryonic disc
- Beginning of morphogenesis: the development of the form and structure of organs and parts of the body
58
Gastrulation gives rise to 3 layers
ectoderm
endoderm
mesoderm
59
ectoderm
outside layer, gives rise to skin and nervous tissue
60
mesoderm
middle layer, generates most of the muscle, blood and connective tissue
61
endoderm
epithelial lining and glands of the gut, lung, urogenital tract
62
Gastrulation starts at the beginning of the 3rd week with the
formation of the primitive streak
63
Appearance of primitive streak allow identification of
cranial/caudal, dorsal/ventral, left/right, medial/lateral
64
primative streak appears
caudally in the medial plane on the dorsal aspect of embryonic disc
65
Epiblast proliferate and migrate toward
the median plane of the embryonic disc
66
Epiblast dive within the primitive streak
Push away hypoblast forming definitive endoderm
| Forms mesoderm in between ectoderm and endoderm
67
Remaining epiblast form the
ectoderm
68
the addition of cells to the caudal end
elongates the primitive streak
69
Cell proliferation at the cranial end forms the
primitive node
70
Primitive node functions as
a signaling center
71
Mesoderm is patterned based on where the epiblast pass through the primitive streak
```
Closer to primitive node the more axial in location
Notochord
Paraxial mesoderm
Intermediate mesoderm
Lateral mesoderm
```
72
Notochordal process
Cellular rod that is formed by cell migration cranially from the primitive node/pit
73
Notochordal process formed by when
day 20
74
The notochord: defines
embryo axis and provides support
75
Neurulation:
formation of the neural tube
76
Notochord induces overlying ectoderm to thicken forming the
neural plate
77
Neural plate inviginates to form
neural groove with lateral neural folds
78
week 4 neurulation
Neural folds fuse forming the neural tube
| Neural tube separates from overlying ectoderm
79
folding and clousre of the neural platate first begins in
the cervical region “zips” up toward the head and down toward the tail
80
anterior neuropore closes
day 25
81
posterior neuropore closes
day 28
82
Raschischisis
failure of neural tube folding
83
Anencephaly
failure of anterior neuropore closure
84
Spina bifida:
failure of posterior neuropore closure (other causes
85
Group of cells that arise in the ectoderm at the margins of the neural plate
Neural Crest cells
86
Neural Crest cells
| form a flattened mass on the __ aspect of neural tube
dorsolateral
87
Detach from the neural tube and become migratory
neural crest cells
88
neural crest cells contribute to:
1. Neurons of the spinal ganglia, ANS ganglia, cranial nerve ganglia
2. Pseudounipolar sensory neurons and post synaptic neurons of ANS
3. Enteric ganglia (gut)
4. Melanocytes
5. Schwann cells
6. Adrenal chromaffin cells
7. Pia and arachnoid
8. Parafollicular cells of thyroid gland
9. Also contribute to heart and face development
89
Intraembryonic mesoderm proliferates between the
ectoderm and endoderm
90
3 regions develop from the mesoderm
paraaxial
intermeidate
lateral
91
Paraaxial mesoderm
Head mesenchyme
| Somites
92
Intermediate mesoderm
Urogenital organs
93
Lateral mesoderm
- Split by the formation of the intraembryonic coelom
- Somatic mesoderm (somatopleure): forms the body wall with the ectoderm
- Splanchnic mesoderm(splanchnopleure): form the gut wall with the endoderm
94
Somites
are block-like condensations of paraxial mesoderm that form on the sides of the neural tube
95
Somite pairs begin formation on
day 20, progresses in a cranial to caudal pattern
96
42-44 pairs of somites form, most __disappear leaving 37 pairs
caudal
97
1st 4 pairs contribute to
head
98
8 pairs contribute to the
cervical region
99
12 pairs contribute to the
thoracic region
100
5 pairs contribute to the
lumbar region
101
5 pairs contribute to the
sacral region
102
3 pairs contribute to
coccyx
103
somites subdivide into
sclerotome and dermamyotome
104
Sclerotome
forms meninges, vertebrae and ribs
105
Dermamyotome
Dermis of the neck and back and muscle
106
dermomyotome differentiate into the
dermatome and myotome
107
Myotome splits into:
epimere (dorsal)
| hypomere (ventrally)
108
epimere
Gives rise to epaxial muslces of the back
| Deep back muscles
109
hypomere
Gives rise to hypaxial muscles
Muscles of the abdominal and thoracic wall
Limb muscles
110
Somatic mesoderm:
Lines body wall
111
somatic mesoderm + ectoderm
somatopleure
112
Splanchnic mesoderm:
Covers endoderm
113
splanchnic mesoderm + endoderm
splanchnopleure
114
Coelom
body cavity formed by lateral folding of the embryo
115
Lateral folds fuse at the
ventral midline
116
Lateral folds result in the formation of the
intraembryonic coelom
117
lateral folds eventually divides into the 3 principal body cavities:
pericardial, pleural, peritoneal cavities
118
Craniocaudal and lateral folding draw in the yolk sac (like a purse string) and close off the body wall except at the
umbilicus.
119
flat trilaminar embryonic disc transforms into
cylindrical embryo
120
Ectopia cordis:
failure of the thoracic body wall to close
121
Gastroschisis:
failure of the abdominal body wall to close
122
Vasculogenesis begins
during 3rd week
123
Hemangioblast cells develop in the
extraembryonic splanchnic mesoderm of the yolk sac
124
Hemangioblast cells give rise to
- hematopoietic cell progenitors
- endothelial precursor cells
(Endothelial cells will surround blood cell aggregates forming blood islands)
125
Yolk sac involved in erythropoiesis until about
day 60
126
Differentiating endothelial cells organize into small capillary vessels and fuse to form
channels (vasculogenesis) this process vascularizes the yolk sac,, connecting stalk, and chorionic villi
127
Vessels from ___ go out to placenta and also eventually join with blood vessels in the embryo that have arisen from intraembryonic splanchnic mesoderm to establish circulation.
extraembryonic mesoderm
128
Intraembryonic vessels begin to develop on
day 18
129
Hematogenesis does not begin within the embryo until about
the 4th week
130
2 major phases of hematopoiesis:
- Embryonic (weeks 1-4)
| - Definitive (week 4-term)
131
Embryonic (weeks 1-4) : blood cells arise from
yolk sac extraembryonic mesoderm
132
Definitive (week 4-term):
hematopoietic stem cells that arise from extraembryonic and intraembryonic mesoderm will go on to seed the spleen, liver, and then bone marrow with hematopoietic stem cells.
133
major site of fetal hematopoiesis until bone marrow takes over
liver
134
Vasculogenesis:
blood vessels arise de novo from “hemangioblasts” that develop into blood cells AND vascular tubes
135
Angiogenesis:
growth of new blood vessels from existing ones
136
Foregut
Trachea, esophagus, stomach, duodenum, liver, and pancreas
137
Midgut
Small intestine, ascending colon, proximal 2/3 of transverse colon
138
Hindgut
Distal 1/3 of transverse colon, descending colon, rectum, upper anal canal
139
Weeks 4 – 8
Critical period of many organ systems
140
Organogenetic period:
all main organ systems have begun to develop
141
Major congenital birth defects may result from ___ in weeks 4-8
teratogen exposure
142
Teratogen
an agent that can disturb the development of an embryo (or fetus)
143
Radiation, drugs, infections, chemicals major effects in weeks
4-8
144
What Serves as an important signaling center in the development of the gut, vertebral column and CNS
the notochord
145
The notochord degenerates as the vertebrae form, part persist as ___
the nucleus pulposus
