From Wikipedia, the free encyclopedia Embryology
Embryology
• The middle layer, or mesoderm, gives rise to the
muscles, skeleton and blood system.
• The outer layer of cells, or ectoderm, gives rise to the
nervous system and skin.
In humans, the term embryo refers to the ball of dividing
cells from the moment the zygote implants itself in the
uterus wall until the end of the eighth week after con-
ception. Beyond the eighth week, the developing human
is then called a fetus. Embryos in many species often
appear similar to one another in early developmental
stages. The reason for this similarity is because species
1 - morula, 2 - blastula have a shared evolutionary history. These similarities
among species are called homologous structures, which
are structures that have the same or similar function and
mechanism having evolved from a common ancestor.
History
1 - blastula, 2 - gastrula with blastopore; orange - ectoderm,
red - endoderm.
Embryology (from Greek ἔμβρυον, embryon, "unborn, em-
bryo"; and -λογία, -logia) is a science which is about the
development of an embryo from the fertilization of the
ovum to the fetus stage. After cleavage, the dividing cells,
or morula, becomes a hollow ball, or blastula, which de-
velops a hole or pore at one end.
In bilateral animals, the blastula develops in one of
two ways that divides the whole animal kingdom into
two halves (see: Embryological origins of the mouth and
anus). If in the blastula the first pore (blastopore) be- Human embryo at six weeks gestational age
comes the mouth of the animal, it is a protostome; if the
first pore becomes the anus then it is a deuterostome. As recently as the 18th century, the prevailing notion
The protostomes include most invertebrate animals, in human embryology was preformation: the idea that
such as insects, worms and molluscs, while the deuteros- semen contains an embryo — a preformed, miniature
tomes include the vertebrates. In due course, the blastula infant, or "homunculus" — that simply becomes larger
changes into a more differentiated structure called the during development. The competing explanation of em-
gastrula. bryonic development was epigenesis, originally proposed
The gastrula with its blastopore soon develops three 2,000 years earlier by Aristotle. Much early embryology
distinct layers of cells (the germ layers) from which all came from the work of the great Italian anatomists: Al-
the bodily organs and tissues then develop: drovandi, Aranzio, Leonardo da Vinci, Marcello Malpighi,
• The innermost layer, or endoderm, gives rise to the Gabriele Falloppio, Girolamo Cardano, Emilio Parisano,
digestive organs, lungs and bladder. Fortunio Liceti, Stefano Lorenzini, Spallanzani, Enrico
Sertoli, Mauro Rusconi, etc.[1] According to epigenesis,
1
From Wikipedia, the free encyclopedia Embryology
the form of an animal emerges gradually from a relative-
ly formless egg. As microscopy improved during the 19th
century, biologists could see that embryos took shape
in a series of progressive steps, and epigenesis displaced
preformation as the favored explanation among embry-
ologists.[2]
Finally Karl Ernst von Baer discovered the mam-
malian ovum in 1827.[3][4][5] Modern embryological pio-
neers include Charles Darwin, Ernst Haeckel, J.B.S. Hal-
dane, and Joseph Needham. Other important contribu-
tors include William Harvey, Kaspar Friedrich Wolff,
Heinz Christian Pander, August Weismann, Gavin de
Beer, Ernest Everett Just, and Edward B. Lewis.
After the 1950s, with the DNA helical structure being
unravelled and the increasing knowledge in the field of
molecular biology, developmental biology emerged as a
field of study which attempts to correlate the genes with
morphological change, and so tries to determine which
genes are responsible for each morphological change
that takes place in an embryo, and how these genes are
regulated.
Histological film 10 day mouse embryo Vertebrate and invertebrate
embryology
Many principles of embryology apply to both inverte-
brate animals as well as to vertebrates.[6] Therefore, the
study of invertebrate embryology has advanced the
study of vertebrate embryology. However, there are
many differences as well. For example, numerous inver-
tebrate species release a larva before development is
complete; at the end of the larval period, an animal for
the first time comes to resemble an adult similar to its
parent or parents. Although invertebrate embryology is
similar in some ways for different invertebrate animals,
there are also countless variations. For instance, while
spiders proceed directly from egg to adult form many in-
sects develop through at least one larval stage
Modern embryology research
Currently, embryology has become an important re-
search area for studying the genetic control of the de-
velopment process (e.g. morphogens), its link to cell sig-
nalling, its importance for the study of certain diseases
and mutations and in links to stem cell research.
See also
• Ontogeny
• Embryogenesis
• Recapitulation theory
• Prenatal development
Beetle larvae • Protostomes
• Deuterostomes
2
From Wikipedia, the free encyclopedia Embryology
• Germ layers [6] Parker, Sybil. "Invertebrate Embryology," McGraw-
• Epigenesis (biology) Hill Encyclopedia of Science & Technology (McGraw-
• Developmental biology Hill 1997).
• Cell signalling Embryology - History of embryology as a science."
• Hedgehog signaling pathway Science Encyclopedia. Web. 06 Nov. 2009.
• Morphogens .
• Embryo drawing "Germ layer." Encyclopædia Britannica. 2009. Ency-
clopædia Britannica Online. 06 Nov. 2009
References .
[1] Massimo De Felici, Gregorio Siracus, The rise of
embryology in Italy: from the Renaissance to the early
20th Century, Int. J. Dev. Biol. 44: 515-521 (2000).
Further reading
[2] Campbell et al. (p. 987) • Apostoli, Pietro; Catalani, Simona (2011). "Chapter
[3] K. J. Betteridge (1981). "An historical look at 11. Metal Ions Affecting Reproduction and
embryo transfer". Reproduction. The Journal of the Development". In Astrid Sigel, Helmut Sigel and
62:
Society for Reproduction and Fertility 62 1–13. Roland K. O. Sigel. Metal Ions in Toxicology. Metal Ions
http://www.reproduction-online.org/content/62/ in Life Sciences. 8. RSC Publishing. pp. 263–303.
1/1.full.pdf+html. "Three years later, the Estonian, doi:10.1039/9781849732116-00263.
Karl Ernst von Baer, finally found the true • Scott F. Gilbert. Developmental Biology. Sinauer, 2003.
mammalian egg in a pet dog (von Baer, 1827)." ISBN 0-87893-258-5.
[4] Lois N. Magner (2005). History of the Life Sciences. • Lewis Wolpert. Principles of Development. Oxford
New York. Basel: Marcel Dekker. p. 166. University Press, 2006. ISBN 0-19-927536-X.
http://books.google.com/
External links
books?id=EnG0gshuCBAC&printsec=frontcover&dq=History+of+the+Life+Sciences&hl=et&ei=6feXTp_PG-
_44QSOkJCZBA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CC0Q6AEwAA#v=onepage&q&f=false.
[5] Alex Lopata (2009). "History of the Egg in • Indiana University’s Human Embryology Animations
Embryology". Journal of Mammalian Ova Research 26 26: • What is a human admixed embryo?
2–9. http://www.bioone.org/doi/full/10.1274/ • UNSW Embryology | UNSW Embryology Large
jmor.26.2. resource of information and media
• Definition of embryo according to Webster
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Categories:
• Embryology
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