Topic 2 Human Reproductive Anatomy: Notable Exceptions to General Embryonic Patterns Flashcards
1
Q
a. Gray Crescent
b. Gastrulation
c. Yolk
A
Steps of Frog Embryonic Pattern
2
Q
- Sperm penetrates frog egg → reorganization of cytoplasm → pigmented cap of animal pole rotates towards the point of penetration while a gray crescent shape region forms opposite of the point of penetration.
- The gray crescent experiment - in early cleavage, each individual cell could develop into a frog only if it had some portion of the gray crescent
A
Gray Crescent
3
Q
- Blastopore forms at the border between the gray crescent and the vegetal pole. During gastrulation, cells migrate over the top edge of, and into, the blastopore through a process called involution, forming the dorsal lip in the same region previously occupied by the gray crescent. The blastocoel disappears and is replaced by the archenteron. The bottom edge of the blastopore → ventral lip, side → lateral lip
A
Gastrulation
4
Q
- More extensive than sea urchin; cells from the vegetal pole rich in yolk material form a yolk plug near the dorsal lip
- Note that the dorsal lip is important experimentally. Normally, these cells give rise to the notochord. In the dorsal lip transplanted experiment, dorsal lip cells were translated from a donor to a recipient embryo at a location corresponding to its future belly. The embryo developed two notochords - a normal dorsal one, and a second one along the belly that could give rise to a second embryo, formed partly from recipient tissue! This showed that the cells which ordinarily form the belly could be induced to develop structures different from their ordinary fate
A
Yolk
5
Q
a. Blastodisc
b. Primitive streak
A
Steps of Bird Embryonic Pattern
6
Q
- Flattened, disc shaped region that sits on top of the yolk; cleavage occurs here. The yolk of a bird egg is very large and is not involved in cleavage
A
Blastodisc
7
Q
- (also found in mammalian embryos) when gastrulation begins, invagination occurs along a line called the primitive streak. As cells migrate into here, the result is an elongated blastopore rather than a circular one as in sea urchins and frogs.
A
Primitive Streak
8
Q
a. Blastocyst
b. Trophoblast
c. Embryonic Disc
A
Humans and most other mammals embryonic patterns
9
Q
- The blastula stage consists of two parts: an outer ring of cells (trophoblast) and inner cell mass (embryonic disc)
- The inner cell mass forms the epiblast and hypoblast. The epiblast gives rise to the endoderm, ectoderm, and mesoderm. The trophoblast consists of a double layer of cells, and is the precursor of the placenta.
A
Blastocyst
10
Q
- Accomplishes implantation by embedding into the endometrium.
a. Produces human chorionic gonadotropin (hCG) to maintain estrogen and progesterone production from the corpus luteum, which maintains the endometrium
b. The trophoblast later forms the chorion, which eventually forms the placenta by fusing with the endometrium. By the end of the first trimester, the placenta reaches full development and secretes its own estrogen and progesterone so hCG lowers.
A
Trophoblast
11
Q
- Within the cavity created by the trophoblast, the inner cell mass clusters at one pole and flattens into the embryonic disc, analogous to the blastodisc of birds and reptiles.
a. The primitive streak develops → gastrulation → development of embryo + extra-embryonic membranes (except the chorion)
b. Basically, aquatic vertebrates form the blastopore, and terrestrial vertebrates form the primitive streak!
A
Embryonic Disc
12
Q
- Contrary to what some illustrations may imply, the hypoblast actually only gives rise to the extra-embryonic endoderm (umbilical vesicle/ allantois/yolk sac). The definitive (intra-embryonic) endoderm is actually formed from invagination of the epiblasts displacing the hypoblast. Note that the chorion develops from the trophoblast + extra embryonic mesoderm layers
A
Note
