Cardiac Embryology (Part 1): Topic 5 Flashcards
1
Q
Where does fertilization occur?
A
Ampullary region of the fallopian tube
2
Q
What forms a zygote?
A
Sperm + Oocyte
3
Q
What undergoes cell divisions?
A
Zygote
4
Q
When does the embryo reach the 2 cell stage?
A
30 hours post fertilization
5
Q
When does the embryo reach the 4 cell stage?
A
40 hours post fertilization
6
Q
When does the embryo reach the 12-16 cell stage?
A
72 hours (3 days) post fertilization
7
Q
Describe the series of mitotic division that occurs.
A
Cells increase in number
Become smaller with each division
8
Q
What are the cells called after cleavage of the zygote during mitotic cell divisions?
A
Blastomeres
9
Q
Cells are loosely arranged until what stage?
A
8 cell stage
10
Q
After which cleavage do cells have maximized contact with each other?
A
After the 3rd cleavage
11
Q
What is compaction?
A
Cells separate into inner and outer cells
12
Q
What is the 16 cell stage called?
A
Morula
13
Q
Describe the Morula.
A
16 cell stage
Had defined inner and outer cells
Inner cells = inner cell mass (embryo)
Outer cells = outer cell mass (trophoblasts, which will be the placenta)
14
Q
What cells will become the placenta?
A
Trophoblasts
15
Q
What will the inner cells of the morula become?
A
Embryo
16
Q
What will the outer cells of the morula become?
A
Trophoblasts, which will become the placenta
17
Q
What happens to the Morula?
A
Makes its way into the uterus, enlarges and becomes a blastocyst
18
Q
The first cleavage is completed about how many hours after fertilization?
A
30 hours
19
Q
Morula develops how many days after fertilization?
A
3-4 days after fertilization
20
Q
When does the blastocyst form?
A
4.5-5 days after fertilization
21
Q
When does implantation occur?
A
About 6 days after fertilization
22
Q
Fertilization occurs how many hours after ovulation?
A
12-24 hours after ovulation
23
Q
What happens when the morula enters the uterine cavity?
A
Fluid penetrates into the intercellular spaces of inner cell mass. Space becomes a single cavity called the blastocele
24
Q
Blastocele
A
Single cavity that is formed when fluid penetrates into the intercellular spaces of inner cell mass when morula enters the uterine cavity
Internal fluid filled space
25
What is the blastocyst comprised of?
Trophoblast
Blastocele
Embryoblast
26
Trophoblast
Outer covering; formed form cells of the outer cell mass. Cells flatten and eventually form the epithelial wall of the blastocyst; will be come the placenta
27
Embryoblast
Inner cell mass; located at one pole
28
How long does the blastocyst remain free in the uterus?
2 days
29
When does implantation occur?
Day 6 after fertilization
30
Trophoblastic cells over the embryoblast pole penetrates between what?
Epithelial cells of the uterine wall
31
Blastocyst attaches to the uterine epithelium and subsequently what? How is it oriented?
Endometrium; oriented os the inner cell mass is near the endometrium
32
What is the sequence of events for implanation?
1. Trophoblast cells over embryoblast pole penetrate between epithelial cells of uterine wall
2. Blastocyst attaches to uterine epithelium and subsequently the endometrium
3. Oriented so the inner cell mass is near the endometrium
33
At what day is the Blastocyst partially embedded?
At day 8
34
What are the two layers that the trophoblast cells over the embryoblast differentiate into?
1. Syncytiotrophoblast
| 2. Cytotrophoblast
35
Syncytiotrophoblast
One of the two layers that the trophoblast cells over the embryoblast differentiate into; multi-nucleated, outer zone (no cell boundaries)
36
Cytotrophoblast
One of the two layers that the trophoblast cells over the embryoblast differentiate into; mononucleated cells, inner layer (distinct cells)
37
What do the two layers that the trophoblast cells over the embryoblast become part of?
Part of the chorion (one of the fetal membranes)
38
What does the inner cell mass (embryoblast) differentiate into?
Hypoblast layer
| Epiblast layer
39
Hypoblast layer
Layer of small cuboidal cells adjacent to the blastocyst cavity; one of two layers that the inner cell mass (embryoblast) differentiates to
40
Epiblast Layer
Layer of high columnar cells adjacent to amniotic cavity; one of the two layers that the inner cell mass (embryoblast) differentiates to
41
What's another name for the hypoblast layer?
Entoderm
42
What's another name for the epiblast layer?
Ectoderm
43
What happens at Day 11-12?
* Completely embedded.
* Cells of Synctiotrophoblast penetrate deeper into endothelial lining of maternal capillaries
* Capillaries are congested and dilated (sinusoids)
* Causes blood to flow through the trophoblastic system
* Beginning of the uteroplacental circulation
44
What are sinusoids?
Congested and dilated capillaries
45
Cytotrophoblast proliferates to form what?
Amnion
| Amniotic Cavity
46
Amnion
Thin protective membrane that surrounds the developing embryo; from the cytotrophoblast
47
Amniotic Cavity
Space, eventually filled with fluid; from the cytotrophoblast
48
When does Gastrulation start?
Day 8
49
What is Gastrulation?
```
Process of establishing 3 germ layers
ICM Differentiates:
-Ectoderm
-Endoderm
-Mesoderm
```
50
What are the major embryonic tissues from which all tissues and organs of the body develop?
- Ectoderm
- Endoderm
- Mesoderm
51
Gatrulation starts with the formation of what?
Primitive streak on the epiblast
52
When is the primitive streak on the epiblast clearly visible as a narrow groove?
Day 15-16
53
What cells migrate to the primitive streak?
Cells of the epiblast migrate to the primitive streak
54
What happens to the cells of the epiblast that migrate to the primitive streak?
Attach and become flask-like
Detach from epiblast and slip beneath it
Inward movement/cause invagination
Cells displace the hypoblast (creates endoderm)
Other lies between the epiblast and the new endoderm (mesoderm)
Cells remaining in the epiblast (ectoderm)
55
What is the source of the germ layers?
Epiblast
56
Inner cell mass is now called what as amniotic cavity starts to form?
Embryonic Disc
57
What is the layer of cells of the inner cell mass closest to the amniotic cavity?
Ectoderm
58
What is the layer of inner cell mass that borders the blastocele?
Endoderm
59
What is the layer that lies between the ectoderm and endoderm?
Mesoderm
60
What does the ectoderm become?
Skin, teeth, mouth glands, nervous system, some endocrine glands
61
What does the endoderm become?
Epithelium of digestive tract, respiratory system, bladder, vagina, urethra
62
What does the mesoderm become?
All connective tissue, the muscular, skeletal, lymphatic and circulatory systems
63
When does the cardiovascular system appear in the embryo? What else is significant at this point?
Middle of the 3rd week; at this point the embryo is no longer able to survive via diffusion alone
64
What system reaches a functional state long before any of the other systems?
Cardiovascular System
65
How does the vascular system develop?
From a simply symmetrical plexus, into an asymmetrical complex system of arteries, veins and capillaries.
66
Describe the size of the embryonic heart in relation to the size of the embryo.
The size of the embryonic heart in relation to the size of the embryo is enormous compared to an adult heart in an adult size body.
67
Where do the progenitor heart cells lie?
In the epiblast; adjacent to the cranial end of the primitive streak
68
Where do the progenitor heart cells move?
Through the streak and into the splanchnic layer of the mesoderm (day 16-18)
69
What do the progenitor heart cells form?
Horse-shoe shaped cluster of cells called the primitive heart field (PHF); will form blood islands and cardiac myoblasts
70
Primitive Heart Field (PHF) specified on both sides to become what?
Atria, LV, RV, conus cordis, truncus arteriosus
71
Where do the conus and truncus come from? When do they show up?
Secondary Heart Field; show up around Day 20-21
72
What do blood islands nad cardiac myoblasts form?
blood cells and blood vessels
73
Blood islands unite and form a horse-shoe shaped tube. Describe it.
Endothelial cell lines; surrounded by myoblasts
74
More blood islands appear bilaterally, parallel and close to the midline. What will these form?
Dorsal aortas
75
What does the intraembryonic celom (body cavity) eventually become?
Pericardial cavity
76
How is the intraembryonic celom formed?
By the joining of small (initially isolated) spaces which appear in the lateral mesoderm
77
Intraembryonic celom has bilateral cavities tha do what?
Extend cranially and fuse with each other forming a horseshoe-shaped cavity
78
When does heart development start? Where does it occur?
At the end of the 3rd week of gestation; occurs in the ventral region of the emrbyo, inferior to the foregut
79
Scattered masses of angiogenic cells appear where?
In the mesenchyme derived from PHF; occurs ventral (in front of) the intraembryonic celom.
80
The anterior part of the celom will develop what?
The pericardial cavity
81
Angiogenic cells form what? Which do what?
Clusters (blood islands), which increase in size and number; acquire a lumen, unite and form a plexus of blood vessels. From this plexus, bilateral endocardial tubes develop
82
The endocardial tubes unite to form a common tube called what?
Primitive Heart Tube
83
By what day does the single heart tube start to beat?
day 21-22
84
What is happening as the heart tube continues to elongate?
Cells are added form the secondary heart field to the cranial end of the tube; process is essential for normal function of part of the RV, the conus cordis and the truncus arteriosus; also essential for looping
85
What happens if lengthening of the heart tube doesn't occur?
Where outflow tract defects come from; DORT, VSD, TOF, PA, PS
86
What will eventually give rise to the dorsal aortas?
Other blood islands that appear inferior to the endocardial tubes
87
What will the dorsal aortas connect to? What part of the heart do these establish?
Will connect with the endocardial tubes, establish the arterial end of the heart
88
What will the other end of the future endocardial tubes make contact with?
Vielline veins (via the sinus venosus) and establish a venous pole
89
At what day have the tubes fused together and a single heart tube begins to beat?
Day 21-22
90
At day 23, the newly formed heart tube starts to do what?
Bend; cephalic part bends ventrally, caudally and to the right. Cardual part bends dorsalcranially and to the left.
91
Where does the heart tube bulge into at day 23?
Into the pericardial cavity
92
Where is the heart tube attached to?
Dorsal wall by mesoderm
93
What happens to the mesderm around day 23, which is attached to dorsal wall?
Eventually ruptures, leaves heart tube suspended in the pericardial cavity
94
What are the regions of the heart tube?
```
Dorsal aorta and aortic sac
bulbus cordis
primitive ventricle
atrioventricular sulcus
paired primitive atria
sinus venosus
```
95
What does the dorsa aortia and aortic sac become?
The common outflow tract
96
What is the bulbus cordis?
Primitive RV
97
What is the primitive ventricle?
Primitive LV
98
Atrioventricular Sulvus divides what?
Atria from the ventricles
99
What will the paired primitive atria form?
Common atria
100
What will the sinus venosus eventually form?
Coronary Sinus and oblique vein of the LA
