Concept Of Embryology Flashcards
What are the three reasons we study embryology
1) reduces body to its simplest form
2) medical reasons for looking at development
3) see what things are made of and how they develop etc.
How do we study embryology
1) anatomical approach
2) experimental approach
3) developmental approach
Anatomical approach
Careful observation
Experimental approach
Intervention followed by observation
Developmental approach
1) what parts of embryo make what organs
2) huge advances in microscopy
Aristotle proposed what two ways
1) everything is preformed and gets bigger during development
2) new structures arise progressively
What is the first law of Von Baer
General characteristics of the group which an embryo belong develops before special characteristics
What is the second law of Von Baer
General structural relations are likewise formed before the most specific appear
What is the third law of Von Baer
The form of any given embryo does not converge upon other definite forms but separates itself from them
What is the fourth law of Von Baer
The embryo of a higher animal form never resembles the adult of another animal form, such as one less evolved, but only its embryo
What is ontogeny
The entire sequence of events involved in the development of an individual organism
What is phylogeny
The sequence of events involved in the evolutionary development of a species or taxonomic group of organisms
What are the 8 stages involved with ontogeny and phylogeny
1) spermatozoon and oocyte
2) blastula
3) gastrula
4) formation of mesoderm
5) metamerism
6) yolk sac
7) amniotic sac
8) placenta
The dorsal blastopore lip or “the organiser” induces what
An extra embryonic axis containing a new neural tube and eventually a second embryo forms that is linked to the host
What are the three consecutive circles in the dorsal blastopore lip
Presumptive notochord, presumptive somites, presumptive endoderm
What is gastrulation
Cell movements result in a massive reorganisation of the embryo from a simple spherical ball of cells, the blastula, into multi- layered organism
What is the dorsal lip responsible for
Neural induction.
The tissue also has the ability to direct the development of host tissue to form a second neural tube.
What is a blastopore
Opening of the archenteron to the exterior of the embryo at the gastrula stage.
Formed by the invagination of the blastula to form a gastrula
What is the “neural tube”
A hollow structure from which the brain and spinal cord form
Notochord
A cartilaginous skeletal rod supporting the body in all embryonic and some adult chordate animals
Explain the experiment with frogs
- experimental approach
- initial group of cells called the organiser
- cut a bit out and stick it on the other side= secondary area of that differentiation of a 2nd body axis
What is metamerism
An initial sub division of the embryonic body into an ordered series of equal segments (metameres)
It forms the basis of development of vertebrates
What is the process of which somites are formed
Somitogenesis
How are somites paired
They are paired bilaterally and form along the head-tail axis and subdivide
What type of gene indicates where somites start
Hox genes
What is induction (Hans spemann)
The process by which the identity of certain cells influences the developmental fate of surrounding cells
What does the hox code help specify
The AP axis (anterior- posterior)
What is the hox gene
A subset of homeotic genes which regulate the development of anatomical structures in various organisms
How are hox genes identified
1) their protein product is a transcription factor
2) they contain a DNA sequence known as homeobox
3) in animals, the organisation of the hox genes in the chromosome is the same as the order of their expression along the ant-post axis of the developing animal and are thus said to display collinearity
