EMBRYOLOGY Flashcards
the branch of biology that studies the prenatal
development of gametes (sex cells),
fertilization, and development of embryos and
fetuses.
embryology
“Ontogeny recapitulates phylogeny”,
theorizes that the stages an animal embryo undergoes
during development are a chronological replay of that
species’ past evolutionary forms.
Ernst Haeckel
“Recapitulation is not the only relationship between
embryos and ancestors”
Gavin de Beers
✓Embryonic structures may or may not be present from their ancestors or descendants.
✓Embryonic structures - vestigial (lost); or retained to adulthood.
✓Developmental stages may be repeated in earlier stage but not in later stages.
✓Developmental sequence may or may not be altered in the descendant.
Gavin de Beers
are an organism’s reproductive cells or sex cells
gametes
gametes are __, and each cell carries only one copy of each chromosome
haploid
process of formation of gametes
gametogenesis
cells that produces testosterone in the presence of
luteinizing hormone (LH).
Leydig cells
is a “nurse” cell of a seminiferous tubule and helps in the process of spermatogenesis
Sertoli cell
is the final stage of spermatogenesis, which sees the maturation of spermatids into mature spermatozoa
spermiogenesis
an endocrine structure that continuously release hormones responsible for the thickening of the endometrium in the uterus.
corpus luteum
Is the fusion of haploid gametes, egg and sperm, to form the diploid zygote
fertilization
step-by-step process of fertilization
(1) sperm makes contact with egg
(2) acrosome reacts with zona pellucida
(3) acrosome reacts with perivitelline space
(4) plasma membranes of sperm and egg fuse
(5) sperm nucleus enters egg
(6) cortical granules fuse with egg plasma membrane, which renders the vitelline layer impenetrable to sperm
the formation of the blastomeres
cellulation (cleavage)
The process by which the zygote undergo repeated
mitotic cell division
cleavage
is a mass of 16 totipotent cells in a spherical
shape
morula
spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel).
blastula
EPIBLAST or EPIMERE; developing embryo
nourished by the vegetal pole (dorsal cells–ECTODERM)
animal pole
HYPOBLAST or HYPOMERE or developing yolk;
nourishes the embryo GUT
(ventral cells–ENDODERM)
vegetal pole
(4) classifications of egg based on the amount of yolk
alecithal
microcithal
mesolecithal
macrolecithal/polylecithal
classification of egg based on the amount of yolk
egg contains no yolk
alecithal
classification of egg based on the amount of yolk
egg contain small or negligible amount of yolk
microlecithal
classification of egg based on the amount of yolk
eutherian mammals
alecithal
classification of egg based on the amount of yolk
amphioxus, tunicates
microlecithal
classification of egg based on the amount of yolk
egg contins moderate amount of yolk
mesolecithal
classification of egg based on the amount of yolk
dipnoi, petromyzon
mesolecithal
classification of egg based on the amount of yolk
egg contains high mount of yolk
macrolecithal/polylecithal
classification of egg based on the amount of yolk
reptile, birds
macrolecithal/polylecithal
(2) distribtion of yolk
isolecithal/homolecithal
telolecithal
distribtion of yolk
A very little amount of yolk present and is
uniformly distributed through out the egg
isolecithal/homolecithal
distribtion of yolk
echinoderm, amphioxus, mammals
isolecithal/homolecithal
distribtion of yolk
Egg contains moderate or large amount of yolk,
distribution of yolk is unequal (concentrated in
the Vegetal pole)
telolecithal
(2) influence of yolk on cleavage
holoblastic
meroblastic
influence of yolk on cleavage
Type of cleavage furrow bisects the entire egg.
holoblastic (complete) cleavage
influence of yolk on cleavage
Type of cleavage furrow restricted to the active
cytoplasm found either in the animal pole (macrolecithal egg).
meroblastic (incomplete) cleavage
type of cleavage found
birds fish
meroblastic (incomplete) cleavage
type of cleavagefound
amphibians mammals
holoblastic (complete) cleavage
cleavage in amphibians (4) structures
mesolecithal
vegetal pole
animal pole
blastocoel
cleavage in amphibians
holoblastic; unequal-sized blastomeres
mesolecithal
cleavage in amphibians
larger blastomeres; nourishes the
embryo; slower development
vegetal pole
cleavage in amphibians
smaller blastomeres; developing
embryo
animal pole
cleavage in amphibians
towards animal pole
blastocoel
cleavage in birds/aves (4) structures
macrolecithal
vegetal pole
animal pole
narrow blastocoel
cleavage in birds/aves
“meroblastic” (partial cleavage); unequalsized blastomeres
macrolecithal
cleavage in birds/aves
large size yolk mass; too great to be penetrated by cleavage furrow
vegetal pole
cleavage in birds/aves
is relatively small (blastoderm)
animal pole
Process in which the single-layered blastula is reorganized into a multilayered structure known as the gastrula.
gastrulation
Cell found inside the blastocyst (is the mass of cells that give rise to the definitive structures of the embryo)
inner cell mass (ICM)
Cells found outside the blastocyst (provide nutrients to the embryo and develop into a large part of the placenta).
trophoblast
cleavage in mammals
microlecithal
cleavage in mammals
holoblastic; unequal-sized blastomeres
microlecithal
is a structure formed in the early development
of mammals
blastocyst
__ result in a massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism.
Cell movements
important outcomes of gastrulation
- Formation of the three (3) embryonic germ layers.
- Formation of the embryonic gut (archenteron).
- Appearance of the major body axes.
(3) germ layers
ectoderm
mesoderm
endoderm
the middle germ layer
mesoderm
the outermost germ layer
ectoderm
the innermost germ layer
endoderm
the ectoderm forms the (4)
skin
brain
nervous system
other external tissues
the mesoderm forms the (3)
muscle
skeletal system
circulatory system
the endoderm forms the (2)
the lining of:
gut
other internal organs
Multipotent stromal cells that can differentiate into a
variety of cell types
mesenchymal stem cell
Unspecialized pack of tissue of a developing embryo and its cells enter into the formation of specialized
tissues
mesenchymal stem cell
multiple differentiation potential of MSCs (10)
cartilage
bone
adipose
muscle
nerve
myocardium
liver
cornea
trachea
skin
having a body derived from only two embryonic cell layers (ectoderm and endoderm, but no mesoderm)
diploblastic
having a body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm)
triploblastic
diploblastic/triploblastic
spondes
coelenterates
diploblastic
diploblastic/triploblastic
all multicellular animals (except sponges and coelenterates)
triploblastic
Animals in which the blastopore becomes the mouth
protostome
Animals in which the blastopore becomes the anus
deuterostome
prostosome/deuterostome
primitive invertebrates
protostome
prostosome/deuterostome
echinoderms and chordates
deuterostome
proces of gastrulation
(1) gastrulation begins when cells in the region of the gray crescent move inward, forming the dorsal lip of the future blastopore
(2) cells of the animal pole spread out, pushing surface cells belowthem toward and across the dorsal lip. these cells move into the itnerior of the embryo, where they form the endoderm and mesoderm
(3) the archenteron expands, destroying the blastocoel. the blastospore lip forms a circle, with cells moving to the interior all around the blastopore; the yolk plug is visible through the blastopore.
process of neurulation
(1) notochord forms from mesoderm cells soon after gastrulation is complete
(2) signals from notochord cause inward folding of ectoderm at the neural plate
(3) ends of neural plate fuse and disconnect to form an autonomous neural tube
Refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.
neurulation
It is the process by which the three germ tissue layers of the embryo, which are the ectoderm, endoderm, and mesoderm, develop into the internal organs of the organism
organogenesis
the embryo at the stage neurulation is termed as
neurula
Migration of primordial germ cells (Mesenchyme).
organogenesis
embryo
Establishes the head and tail
holoblastic embryo
embryo
3 germ layers spread faced down on the uncleaved yolk
meroblastic embryo
organogenesis: endoderm (3)
foregut
midgut
hindgut
organogenesis: endoderm
major structures formed by the foregut
epithelium: oral cavity, nasal cavity, pharynx, gill, esophagus, lung
organogenesis: endoderm
major structures formed by the midgut
visceral organs: stomach, liver, gall bladder, pancreas, intestines, germ cells of gonads (ovary & testis), part of the yolk sac membrane, part of the allantois
organogenesis: endoderm
major structures formed by the hindgut
urinary bladder; cloaca/anus
organogenesis: mesoderm (7) layers
outer epimere - dermatome
middle epimere - myotome
inner epimee - sclerotome
chordamesoderm
intermediate mesoderm
somatic hypomere
splanchnic hypomere
organogenesis: mesoderm
outer epimere - dermatome
skin dermis
organogenesis: mesoderm
middle epimere - myotome
muscles: axial, appendicular, ranchiomeric, hypobranchal
organogenesis: mesoderm
inner epimere - sclerotome
vertebral column
organogenesis: mesoderm
chordamesoderm
notochord
organogenesis: mesoderm
intermediate mesoderm
kidney; urogenital ducts
organogenesis: mesoderm
somatic hypomere
bones: ribs, sternum, appendicular skeleton, some appendicular muscles, parietal peritoneum (outer abdominal wall); genital ridge; part of amnion and chorion
organogenesis: mesoderm
splanchnic hypomer
blood, heart, gut, smooth muscle, visceral peritoneum (inner abdominal wall); yolk sac and allantois
organogenesis: ectoderm (4)
somatic ectoderm
neural plate ectoderm
epidermal placodes
ectomesenchyme (neural crest)
organogenesis: ectoderm
somatic ectoderm
skin epidermis; teeth enamel; stomodeum (mouth); proctodeum (anus/cloaca); gill epitheleum; part of amnion and chorion
organogenesis: ectoderm
neural plate ectoderm
brain; spinal cord
organogenesis: ectoderm
epidermal placodes
capsules; olfactory; optic; otic; epibranchial capsules; neuromast (electroreceptors organs); gnaglia of some cranial nerves
organogenesis: ectoderm
ectomesenchyme (neural crest)
spinal ganglia; splanchnocranium; neurocranium (part); dermatocranium (part); teeth dentine; eye cornea; chromatophores (pigment cells); branchiomeric muscle; aortic arches; heart septum (divides the right and left side of heart)
- membranes which assist in the development of the embryo.
- originate from the embryo, but are not considered part of it.
- typically perform roles in nutrition, gas exchange, and waste removal
extraembryonic membranes
- Eggs are laid in water; yolk sac is the only fetal membrane formed.
- Yolk sac – formed from 3 germ layers to absorb the yolk into the body
- Respiration and excretion are direct contact with the environment
fish
- Mammals that produce a shelled egg like their reptilian ancestors.
- Spiny anteater (echidna) and Duckbill platypus
mammals: monotremes
- Pouched mammals (no typical placenta), Marsupials (Kangaroo, Wombat).
- Embryo is poorly supplied with yolk, yolk sac provides a rudimentary connection to the mother’s blood (food, oxygen, and other essentials).
- The young are born in a very immature state (they are able to crawl into a pouch on the mother’s abdomen, attach themselves to nipples, and drink milk from her
mammary glands).
mammals: metaherian
- Placental mammals.
- The extraembryonic membranes form a placenta and umbilical cord (connect the embryo to the mother’s
uterus) - Placenta functions include gas exchange, metabolic transfer, hormone secretion, and fetal protection.
mammals: eutherian
reptiles and birds (4 structures of egg)
amnion
yolk sac
chorion
allantois
reptiles and birds
protects the embryo in a sac filled with amniotic
fluid
amnion
reptiles and birds
contains yolk —the sole source of food until
hatching (mixture or proteins and lipoproteins)
yolk sac
reptiles and birds
lines the inner surface of the shell (which is
permeable to gases) and participates in the exchange of
O2and CO2between theembryo and the outside air
chorion
reptiles and birds
stores metabolic wastes (chiefly uric acid) of the
embryo and participates in gas exchange.
allantois
