Embryology Flashcards
when is a mature ovum release?
ovulation
what is fertilization?
process of sperm joining egg
describe the process of fertilization
- sperm makes contact w egg
- acrosome reacts w zona pellucida & creates a space
- plasma membranes of sperm & egg fuse
- sperm nucleus enters egg
- cortical granules fuse w egg plasma membrane, renders plasma membrane impenetrable to other sperm
what is a zygote?
single celled fertilized egg (day 1)
what is cleavage?
cell division: zygote to blastocyst
what are daughter cells?
products of cell division called blastomeres
what is a morula?
32 cell (blastomeres) embryo
describe the blastocyst stage (day 4-5)
- trophoblast pumps fluid into cell to form fluid-filled vesicle (blastocoele)
- fluid pushes inner cell mass to one end of tropoectoderm (embryonic pole)
- hypoblast cells line & feed blastocoele
what is the epiblast?
inner cell mass of blastocyst
what is the trophoblast?
external cell layer of blastocyst
what is the blastocoele?
yolk sac that will feed embryo for several weeks
what are hypoblasts?
cells that line & feed blastocoele
what occurs on day 5-9 of implantation?
blastocyst interacts with uterine wall:
- giant cells from trophoblast implant in uterine wall
- rest of trophoblast gives rise to placenta & membranes
- blastocoele feeds embryo for several weeks
what is an embryonic bilaminar disc?
2 distinct layers of embryo at beginning of week 3:
epiblast (outer region of blastocyst)
hypoblast (borders blastocoele)
what is gastrulation?
formation of 3 embryonic germ layers from cells of epiblast
describe the process of gastrulation
- cells migrate through rift in epiblast called primitive streak
- form endoderm, then mesoderm, remaining epiblast cells become ectoderm
what tissues are formed by the ectoderm?
CNS
PNS
ANS
outer layer of skin
what tissues are formed by the mesoderm?
connective tissue (bone, cartilage, muscle, adipose)
what tissues are formed by the endoderm?
GI tract
lungs
liver
what is neurulation and when does it occur?
formation of notochord & neural tube (week 3)
describe the process of neurulation
- cells migrate through Henson’s node forming notochord
- notochord signals to overlying ectoderm to thicken to form neural plate
- neural plate begins to fold at midline (neural groove), closing to form neural tube
how does the notochord form?
via mesoderm cells that migrate through Henson’s Node
what is Henson’s node?
collection of cell bodies at anterior end of primitive streak
what is the neural tube?
- cavity for formation of CNS
- vertebral column & skull form around tube
what are neural tube defects?
failure of neural tube to close due to folic acid deficiency
what are 2 types of spina bifida?
- occulta (no protrusion of CNS/meninges)
- cystica (protrusion of CNS/meninges)
name 2 types of spina bifida cystica lesions
meningocoele
myelomeningocoele
meningocoele lesion
protrusion of meninges through defect in spine
myelomeningocoele lesion
protrusion of spinal cord & meninges through defect in spine
what is anencephaly?
failure of skull to form in which missing skull cap & cerebral cortex (incompatible with life)
what is encephalocoele?
failure of skull to form in which part of brain/meninges forms in a sac outside of skull
skeleton & articulations derive from ____
mesoderm
what is paraxial mesoderm?
mesoderm lateral to neural tube & notochord
what happens to paraxial mesoderm by 20 days in utero?
organizes into 42-44 segments
lateral plate mesoderm gives rise to ____
body wall/limbs
what are somites?
- compact aggregates of paraxial mesoderm
- appear as bead-like elevations along dorsal surface
- form cranial to caudal
how are somites divided?
- sclerotome: skeletal system
- myotome: muscular system
- dermatome: deeper layers of skin, adipose tissue
how many primary ossification centers in typical vertebrae?
3
how many secondary ossification centers in typical vertebrae?
5
describe primary ossification centers
- body (centrum)
- neural arch = 2 centers that meet at dorsal midline to form SP, fuse w body anteriorly
describe secondary ossification centers
- tips of each TP
- one at tip of SP
- 2 ring shaped annular epiphyses at top & bottom of vertebrae
where are growth plates located in vertebrae?
between primary & secondary ossification centers
describe vertebrae at birth
- 3 primary ossification centers are distinct
- joined by cartilage
vertebrae by age 1
neural arches fused
vertebrae by age 6
- arches fused to bodies
- accommodates growing spinal cord
when do secondary ossification centers appear?
puberty
when do primary ossification centers begin to fuse?
by age 21
- annular epiphyses
- presacral complete by age 25
- sacrum complete by 23
ossification of atlas (C1)
- 2 primary ossification centers (left & right): bulk of posterior arch & lateral mass
- halves of posterior arch fuse by age 4
- anterior arch appears at year 1 & joins lateral masses between 5-9 years
ossification of axis (C2)
- same ossification centers as typical, plus 2 for dens (appear in 4-5th month in utero)
- at birth: centrum, dens, neural arches
- primary centers fused by age 6
ossification centers of sacrum
- body: from primary center of centrum & 2 epiphyseal plates
- vertebral arches: from 2 primary ossification centers
- other centers: laterally for upper 3-4 segments for costal segments
- secondary centers on each lateral surface (1 auricular surface, 1 lateral edge)
timing of ossification of sacrum
- age 2-5: neural arches join w bodies, lower segments 1st
- age 16: annular epiphyses for bodies, 18-20 lateral epiphyses (IVD separate bodies)
- age 18: synostosis of discs begins, proceeds cranially
ossification of coccyx
each segment has its own ossification center:
- 1 - soon after birth
- 2 - age 5-10
- 3 - age 10-15
- 4 - age 14-20
name the 5 stages of lung development
- embryonic
- pseudoglandular
- canalicular
- saccular
- postnatal
lungs are derived from ____
endoderm
lung development
embryonic stage
- week 3: lung bud develops from foregut, divide into lobar buds
- week 8: lobar buds divide & form bronchiopulmonary segments
- buds lined by endodermally derived endothelium that differentiates into epithelium that lines airways & alveoli
lung development
pseudoglandular stage
weeks 7-18
- conductive airways formed by progressive branching
- 13 weeks: cilia appear in proximal airways
lung development
canalicular stage
16-25 weeks: gas exchanging portion of lung is formed & vascularized
lung development
saccular stage
25 weeks to birth: development of primitive saccules that become alveoli after birth
lung development
postnatal stage
birth & after: maturation of alveoli
development of heart
truncus arteriosus
divides & gives rise to aorta & pulmonary trunk
development of heart
bulbus cordis
right ventricle
development of heart
primitive ventricle
left ventricle
development of heart
primitive atrium
anterior portions of L & R atria & both auricles
development of heart
sinus venosus
- posterior walls of atria
- SA node
- coronary sinus
