History of Embryology Flashcards
what begins before the completion of anatomical development?
physiology
what was meant by Aristotle when he coined vital heat?
fluids from each parent mixing to form a offspring
name the 6 challenges that early embryologists faced
- differentiation
- morphogenesis
- growth
- reproduction
- evolution
- environmental stresses
Aristole described the 2 historically important models of development known as
- preformation
- epigenesis
define epigenesis
organs form “de novo”
define preformation
organs are present in miniature form within the gametes
preformation is aka
homonculus
what were some of the characteristics believed by preformationist homunculus?
- sperm or egg carries info. to form the adult being
- no changes due to environment can occur
first to observe the Primary Germ Layers in the chicken embryo species and that the germ layers give rise to specific organ systems
Karl Ernst von Baer & Christian Pander
what proved the end of the preformation theorist?
advancements in microscopes and staining techniques
what constitutes the primary germ layers?
- ectoderm
- mesoderm
- endoderm
define ectoderm
outer most layer that produces the epidermis of the skin and forms the brain and nervous system
define mesoderm
middle layer that generates blood, kidneys, heart, bones, muscle, & connective tissues
define endoderm
innermost layer forming the epithelium
what are the 2 primary cell types from which other cells, tissues, and organs develop?
- epithelial cells
- mesenchymal cells
define morphogenesis
the formation of the structural components in the body
- how differentiated cells become organized into tissues and organs
define malformations
Genetic alterations that cause abnormalities
define teratogens
agents responsible for disruptions at the gene level causing abnormalities and malformations to the developing fetus
give an example of a teratogen
thalidomide
embryology focuses on the ___________ changes whilst development focuses on the __________ changes.
anatomical
physiological
define growth
the expansion of an organism in length and circumference
growth implies ONLY multiplication of …….. and NOT changes in …………
- cells
- cellular/tissue anatomy
what 3 things does differentiation describe
- cell/ tissue changes to become specialized
- how one cell become different cell types
- how DNA segments are regulated
how are DNA segments regulated
w/ acetylation and adenylation
apoptosis is
programed cell death
ontogeny is aka
life history
oocyte is known as the
ovum
the ovum changes from oogonium to
primary then secondary oocyte
define pronuclei
is haploid (23 chromosomes)
spermatozoa is the
mature sperm
zygote is aka
the fertilized ovum
In what region of the oviduct does fertilization typically occur?
oviduct: fallopian tube
in the ampulla region
“curved” part of the fallopian tube
what is meant by polyspermia?
multiple sperm cells fertilizing a single egg
what are the 5 stages of embryonic development?
- cleavage
- blastulation
- gastrulation
- neurulation
- organogenesis
describe cleavage
- the creation of morula
- zygote divides forming blastomeres (single cells)
describe bastulation
creation of bastula
describe gastrulation
- creation of gastrula
- beginnings of 3 germ layers which form organs & body structures
describe neurulation
creation of neurual w/ neural plate
- key parts of the nervous system
the neurual then turns into
a neural tube
the neural tube turns into
the central and peripheral nervous system
as the zygote begins to divide ______ are formed
blastomeres
during cleavage cells look alike in
morphology
- not necessarily size
the morula is made up of
12 or more blastomeres
when does the morula form?
3-4 days following fertilization as the embryo enters the uterus from the uterine tube
a blastocyst is a
type of bastula found in mammals
in humans. when the morula enters the uterus what forms?
a fluid-filled cavity (blastocoel)
- appox. 5 days after fertilization
the formation of a blastocoel results in the formation of the… and an outer ring of blastomeres termed the
- inner cell mass (ICM)
- trophoblast
the ICM becomes the
body of the new offspring
define embryo
human baby during the first 8 weeks of gestation
when is the developing baby most susceptible to teratogenic and congenital anomalities
during the embryo phase
what is known as all parts of the blastocyst that includes the embryo and all its developing structures
conceptus
define primordium
the first apparent indication of an organ or structure
define fetus
the human baby from the 9th week of gestation until the birth of the child
Aristotle first used the terms
zygote and vital heat
define embryology
the anatomical changes that occur during development from conception to birth
define development
the physiological and molecular events that occur during growth and differentiation of the embryo
define differentiation
how one cell becomes many diff. kinds of cell types and how DNA segments are switched on and off
blastomeres all look alike in _________ but not necessarily the same ______.
morphology
size
each blastomere contains the full
compliment of genetic information
a blastomere is
diploid
describe organogenesis
creation of organs
define inner cell mass (ICM)
mass of blastomeres that forms at one pole of the blastula
the ICM is AKA the
embryonic stem cells
define trophoblast
bastomeres which form the mem. and structures such as the placenta, allantois, chorion
