BIOL124 - Lecture 8/9

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  • Created on: 11-03-16 21:45
What is organogenesis?
Development of organs
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What is gastrulation?
Cell movements which produce gut and three primary germ layers
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What is cleavage?
Cell division in early embryo
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What is Sea Urchin cleavage like?
It has rapid divisions. The blastomeres are all the same size and have equal divisions. Holoblastic division occurs.
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What is holoblastic cleavage?
It is when divisions divide the entire cell. Blastomeres become smaller with each division.
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What is Amphibian cleavage like?
It has unequal holoblastic division - blastomeres in animal pole are smaller than blastomeres in vegeral pole because of presence of yolk in vegetal hemisphere.
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What are the names of the hemispheres of amphibian cleavage?
Animal hemisphere and vegetal hemisphere
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What is Meroblastic cleavage?
When the cleavage plane does NOT bisect yolk.
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After the cleavage stage comes...
Blastula formation
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What are the two types of cells that make up the chick blastodisc
The epiblast and the hypoblast
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Is the Blastocoel nearer the Animal pole or the Vegetal pole?
It is nearer the Animal pole
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What does gastrulation form?
The primary germ layers: ectoderm, mesoderm and endoderm
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What does the ectoderm form?
The epidermis of Skin, the nervous system pituitary gland, adrenal medulla, jaws and teeth and germ cells.
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What does the mesoderm form?
The Notochord, muscular system, skeletal system, circulatory and lymphatic systems, excretory and reproductive systems and the dermis of skin.
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What does the endoderm form?
The epithelial lining of gut and associated organs. Epithelial lining of respiratory, excretory and reproductive tracts.
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The archenteron of the sea urchin egg forms what?
The digestive tube which leads to the mouth and the anus (from the blastopore)
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In amphibians, what is the first sign that the organism is gastrulating?
It is the movement of cells from the outside to the inside. A little took is formed, a line. At this stage, cells don't know whether they'll be ectoderm, mesoderm or endoderm.
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Cells on the equator always develop into what?
The mesoderm.
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What happens during amphibian ...?
Cells move from the outside to the inside of the blastocoel. It isn't centrally located because the yolk. It is in the animal pole, in a region called the dorsal lip of the blastopore
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What happens after the formation of a took?
Cells move up over the top of the blastocoel. As these cells are moving over this, they are dragging a tube (forming the arcenteron (gut)). The blastocoel shrinks and moves to one side.
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What is the cavity that runs through the yolk of the fertilized egg called?
The primitive streak - this is formed by cells moving from the outside to the inside, through the fluid filled cavity.
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What is invagination?
Cells moving inside to the blastocoel
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Where does the primitive streak run into?
The blastocoel. The first cells to go through the streak are able to displace some of the hypoblast cells.
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The first cells to go through the streak are able to displace some of the hypoblast cells and will form what type of cells?
The endoderm
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The next set of cells to go through the streak will form what?
The mesoderm
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Cells that do not go though the streak and stay on top will form what?
The ectoderm
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There are cells to one side of the developing part in them middle which are not part of the chicken, they will form the...
Extra embryonic membrane
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In chick extraembryonic membranes, what do the cells do?
Cells from the side come up over the top to form the amnion. You get other membranes that grow up and around the yolk, forming the yolk sac.
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In the chick extraembryonic membrane, what is the chorion?
It is the outermost membrane
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In humans, when is the first cleavage division?
It is 24-30 hours after fertilisation.
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What type of division is it in humans? What is formed?
It is holoblastic division and two blastomeres are formed
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What happens to the 2 blastomeres after a day?
They divide to form 4 blastomeres.
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By day 3, the blastomere is called a...
Early Morula
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By day 4, it is called an...
Advanced morula
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What happens after 5 days to the blastocyst? It is termed "Hatching".
It digests a hole in the zona pellucida and emerges. This is called hatching.
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Is implantation possible before hatching?
No -
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What makes up the blastocyst?
The inner cell mass (embryoblast), the blastocoel and the trophoblast.
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What does the inner cell mass develop into?
It develops into the embryo.
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What does the trophoblast form?
Part of the placenta.
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Implantation occurs after how many days?
6 -7
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During implantation, what does the blastocyst burrow into?
The endometrium
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During implantation, where is the inner cell mass in the blastocyst?
Next to the endometrium.
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After implantation the inner cell mass rearranges into 2 layers of cells, what are these? And what do they make up?
They are the hypoblast and epiblast layers. They make up the bilaminar embryonic disc.
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After 12 - 15 day, what occurs?
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What happens during gastrulation?
The primitive streak forms in the dorsal epiblast and defines anterior/posterior and left/right of embryo.
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What are the steps of organogenesis?
1.) Notochord develops from dorsal mesoderm2.)Induction of neural plate from ectoderm layer above the notochord.3.) A neural groove and neural folds form from the dorsal ectoderm.4.)The neural folds rise up, meet and fuse to form the neural tube.
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What does the neural tube become?
It becomes the CNS (central nervous system).
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What happens in neurulation in amphibians?
The neural plate folds to become a neural fold. This then goes on to bring together the ectoderm which forms the neural crest. This is now the outer layer of the ectoderm.
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Neurulation in humans- What happens?
The Neural plate folds to form the neural groove and the neural fold. The neural folds meets with the other side forming a neural tube.
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Development requires signals, what for?
Growth, morphogenesis and differentiation.
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What does induction mean?
When the fate of one cell is influenced by another.
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What is determined by induction?
Positional information - cells need to know where they are, so they develop into the correct structures.
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What is Spemann's Organiser?
It was an experiment that found that transplantation of a second organiser causes induction of another joined entire embryo.
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In this experiment, what was the organiser?
It was the dorsal lip of the blastopore
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What was the structure of the conjoined embryo?
It had two notochords and 2 neural chords.
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How does the organiser alter cell fate?
BMP 4 is uniformly distributed in late blastula and causes VENTRAL development. Chordin and Noggin stop action of BMP 4 and allow dorsal development.
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Give another example of induction:
Induction of neural plate
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BMP 4 is expressed throught the blastula. What releases inhibitors of the BMP?
The organiser region
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BMP antagonists induce neural fate but something else is also needed for neural plate formation, what is this?
FGF (Fibroblast Growth Factors)
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In chicks, which gene does FGF activate?
The Churchill gene. Churchill expression causes activation of Sox2 (first neural plate development marker).
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induction is also present in the anterior-posterior axis of development in the vertebrate limb - what does it develop into
A proximal shoulder or distal
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What does distal mean
Furthest from the body
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What is AER?
Apical Ectodermanl Ridge - it is required for limb outgrowth, it secretes fibroblast growth factor family proteins
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What is ZPA?
It is Zone of polarising Activity - it control anterior posterior digit formation via induction
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What would happen if you inserted donor ZPA into the other side of a limb bud that already had ZPA?
Limbs would grow on either side of the limb bud.
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What is Shh?
Sonic Hedgehog
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Where is Shh found?
It is found in the zone of polarising activity.
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What does Shh do?
It was found that Shh, found within the ZPA, is responsible for the limb growth,
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Card 2


What is gastrulation?


Cell movements which produce gut and three primary germ layers

Card 3


What is cleavage?


Preview of the front of card 3

Card 4


What is Sea Urchin cleavage like?


Preview of the front of card 4

Card 5


What is holoblastic cleavage?


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