3.3 lecture - embryology - development of body plan - MacNeil Flashcards
which conceptus layer is always adjacent to maternal blood supply?
syncytiotrophoblast
where is the chorionic cavity in relation to the yolk sac and the amnionic cavity?
chorionic is outside surrounding both yolk sac and amnionic cavity. the chorion is connected to the embryo via the connecting stalk (becomes umbilical cord)
what layers are present in each primary villus extending from the chorion into the decidua? secondary villus?
tertiary villus?
- primary - syncytiotrophoblast and cytotrophoblast
- secondary - syncitiotrophoblast, cytotrophoblast, mesoderm core
- tertiary - synciciotrophoblast, cytotrophoblast, mesoderm core, villous capillaries within mesoderm core
why is week 3 of embryo development the “week of threes” ?
3 cavities - chroionic, definitive yolk sac, amnionic
3 placental layers - syncytiotrophoblast, cytotrophoblast, extraembryonic mesoderm
3 germ layers - ecto, meso, endoderm
3 body axes - craniocaudal, dorsoventral, R/L
function of the:
- amnion
- yolk sac
amnion - line fluid filled amnionic cavity
yolk sac - transfer agent for nutrients, site of primordial germ cells, source of blood cells and blood vessels
epiblast cells that migrate through the primitive groove and migrate cranially in the mesoderm along the cranial caudal axis will form the __
notochord
what cells is the notochord derived from?
epiblast cells that migrate through the primitive groove and migrate cranially in the mesoderm along the cranial caudal axis
what germ layer is the notochord derived from?
mesothelium
another name for the notochord is the…
axial mesoderm
the notochord is important for 3 reasons:
- signals induction of neural tube, somites, and surrounding structures
- vertebral column and base of skull develop around it
- degenerates to leave behind nucleus pulposus of the intervertebral disc
this structure signals the induction of the neural tube, somites, and surrounding structures
notochord
the vertebral column and base of the skull develop around this structure
notochord
this structure ultimately degenerates to leave behind nucleus pulposus of the intervertebral discs in adults
notochord
the location and function of the nucleus pulposus
- located in center of intervertebral discs in adults
- jelly-like structure that functions to distribute compressive loads through hydraulic pressure
T/F during gastrulation, the cells in the ectoderm that will ultimately form the heart migrate to just below the oropharyngeal membrane
false - the heart will be derived from cells of the Mesoderm that migrate Above the oropharyngeal membrane during gastrulation (this cranial end will ultimately fold over so these heart deriving cells are located caudally to oropharyngeal membrane)
what 2 germ layers are fused at the oropharyngeal and cloacal membranes?
ectoderm and endoderm are fused (no mesoderm)
~ what day do the oropharyngeal and cloacal membranes break down?
~ day 26
a solid cord of cells that underlies the developing neural tube forming a midline axis and serves as a basis for the axial skeleton. induces the neural plate and sclerotome portion of the somite
notochord
describe 7 key structures in the sequence in which they arise in the process of neurulation
- neural plate
- axial neural groove / neural folds
- neural crests
- neural tube
- neural crest cells
- primitive brain
- primitive spinal cord
neurulation is…
the process by which the neural tube forms
neurulation begins on day __
day 18
when the notochord thickens and expands mitotically it forms the…
neural plate
folding of the neural plate gives rise to these 2 structures
- axial neural groove
- neural crests
this is where the neuroectoderm merges with the somatic ectoderm during neurulation
neural crests
fusion of neural folds in neurulation results in the formation of…
the neural tube
neural crest cells arise when…
around the time of neural fold fusion to form the neural tube during neurulation, the neural crests detach from the neural tube and migrate into the mesoderm layer
the neural crests detach from the neural tube and migrate into the mesoderm to become…
neural crest cells
describe the fusion that gives rise to the neural tube
- neural folds approach each other
- somatic ectoderm fuses at surface (beginning somewhere mid-axial and zipping up cranially and down caudally)
- neural crest cells detach, migrate into paraxial mesoderm
- neural tube sinks into mesoderm layer
- neural tube folds ventrally to close tube
neural crest cell detachment and migration into mesoderm during gastrulation is an example of what kind of transition?
epithelial to mesenchymal transition
mesenchyme is..
embryonic connective tissue in the mesoderm
T/F fusion of neural folds is due to genetic factors (genes such as sonic hedgehog) and environmental factors (cholesterol and folic acid)
true
what day does closure of the neural tube at each neuropore occur?
Anterior/cranial neuropore: ~day 25
Posterior/caudal neuropore: ~day 28
name the four subdivisions of neural crest derivatives
- cranial
- cardiac
- vagal
- trunk
examples of neural crest derivatives include:
- connective tissue of bones, neck, face skull
- cranial nerve ganglia
- heart septum (cavity wall enclosing heart)
- dentin of tooth
- dermis of head and neck
- dorsal root ganglia
- enteric nervous system
- sympatheitic chain
- adrenal medulla
- Schwann cells (myelin forming cells in PNS)
- glial cells
- malanocytes of skin
- smooth muscle of head region blood vessels
the following are examples of derivatives of what 3rd week structure?
- connective tissue of bones, neck, face skull
- cranial nerve ganglia
- heart septum (cavity wall enclosing heart)
- dentin of tooth
- dermis of head and neck
- dorsal root ganglia
- enteric nervous system
- sympatheitic chain
- adrenal medulla
- Schwann cells (myelin forming cells in PNS)
- glial cells
- malanocytes of skin
- smooth muscle of head region blood vessels
derivatives of neural crest cells
what are the 2 types of ectoderm in week 3 of development
- neuroectoderm
- surface ectoderm
name some derivatives of the surface ectoderm
- epidermis
- nails
- hair
- subcutaneous glands
- mammary glands
- anterior pituitary
- enamel
- lens of the eye
name some derivatives of the neuroectoderm
- central nervous system
- retina
- posterior pituitary gland
- pineal body
the following are all derivatives of what 3rd week structure? • epidermis • nails • hair • subcutaneous glands • mammary glands • anterior pituitary • enamel • lens of the eye
surface ectoderm
the following are all derivatives of what 3rd week structure? • central nervous system • retina • posterior pituitary gland • pineal body
neuroectoderm
what are 2 key regions of the axial mesoderm and why are they important
- cardiogenic mesoderm - at cranial end of embryo, forms heart tubes
- axial rod of mesoderm - forms notochord, which strongly influences formation of nervous system and vertebral column
what is the importance of the cardiogenic mesoderm?
it is the part of the axial mesoderm that forms the heart tubes at cranial and of embryo
what is the importance of the axial rod of the mesoderm?
forms notochord, which strongly influences formation of nervous system and vertebral column
from medial to lateral, what are 4 key longitudinal regions of the mesoderm and what do they give rise to?
- axial mesoderm (heart tubes, notochord)
- paraxial mesoderm (somites)
- intermediate mesoderm (urogenital system)
- lateral plate mesoderm (coelum, viscera)
what does the paraxial mesoderm give rise to?
somites
what does the intermediate mesoderm give rise to?
urogenital system
what does the lateral plate mesoderm give rise to?
- coelum (body cavity)
- connective tissue and muscle of the viscera
- serous membranes
what does the coelum refer to?
the body cavity
what does the viscera refer to?
the internal organs in the main cavities of the body, esp. those in the abdomen, e.g., the intestines
what cells undergo ectodermal to mesenchymal differentiation during neurulation?
neural plate cells
which longitudinal region of the mesoderm is continuous with the extraembryonic mesoderm covering the yolk sac and amnion?
lateral mesoderm
where do first somites arise from the paraxial mesoderm?
in the occipital region
in what kind of sequence to new somites develop from the paraxial mesoderm? until how many somites?
- from cranial to caudal
- until 42 pairs of somites
how is the paraxial mesoderm correlated to age of the embryo during week 3 of development?
age is correlated to the number of somite pairs present
from inner to outer, what 3 structures does each somite form?
- sclerotome -> bone (axial skeleton)
- myotome -> muscle (skeletal muscle)
- dermatome -> connective tissue (dermis of skin)
what is a scleratome derived from and what does it give rise to?
- from somite (from paraxial mesoderm)
- creates axial skeleton (vertebrae, ribs, occipital bone of skull)
what is a myotome derived from and what does it give rise to?
- from somite (from paraxial mesoderm)
- creates skeletal muscle of body, head/neck, and limbs
what is a dermatome derived from and what does it give rise to?
- from somite (from paraxial mesoderm)
- contributes to dermis of skin (connective tissue layer of skin)
what is a key component that migrates with each sclerotome, myotome, and dermatome derived from a somite?
each has its own segmental nerve component migrating with the developing cells
somites and their developing sclerotomes, myotomes, and dermatomes can be classed into what 4 groups?
- occipital
- cervical
- thoracic
- lumbar
what is a dermatomal pattern
area of skin supplied by a single spinal nerve
what happens to the lateral mesoderm in the trunk ~day 17 of development
develops clefts that eventually split it into two layers associated with the endoderm and ectoderm, and the space between the two layers
- splanchnic mesoderm - mesothelial coverings (gut wall)
- somatic mesoderm - (body wall)
- intraembryonic coelum - primitive body cavity
splanchnic mesoderm
formed from the splitting of the lateral mesoderm in the trunk ~day 17, associated with endoderm,, gives rise to mesothelial coverings
intraembryonic coelum
primitive body cavity formed from the splitting of the lateral mesoderm in the trunk into splanchnic mesoderm and somatic mesoderm
what organ system develops from the intermediate mesoderm
urinary & reproductive systems
what is the intermediate mesoderm
in 2-3 week embryo, intermediate mesoderm is mesodermal layer between lateral mesoderm (which is splitting into somatic and splanchnic mesoderms) and the somites / neural tube
-develops into the urinary & reproductive systems
as folding of the intraembryonic coleum forms a horseshoe pointing up, where is the…
- pericardial cavity
- pleural cavity
- peritoneal cavity
- pericardial cavity - bottom of horseshoe ring
- pleural cavity - lateral extensions
- peritoneal cavity - lateral extensions
summarize week 3 development formations
-gastrulation
-major body axes
-notochord
-primordial nervous system (neural tube)
-somites
-cardiogenic area
-primordial body cavity
(still flat trilaminar disk)
summarize completion of embryonic period (weeks 4-8)
morphogenesis
organogenesis
body folding
in what week of development does body folding initiate?
week 4
in embryonic body folding, the oropharyngeal membrane, cardiogenic area, pericardial cavity, and septum transversum (contributes to diaphragm) are relocated to their appropriate positions by what folding process
head folding
in embryonic folding, the cloacal membrane, connecting stalk, and hindgut are relocated to their appropriate positions by what folding process
tail folding
what causes head folding?
differential growth at the neural plate
what causes tail folding?
growth of spinal cord
what causes lateral folding?
growth of somites
as abdominal wall form through lateral folding, part of the endoderm of the yolk sac is incorporated into the embryo as the __
midgut
what is the yolk stalk
connects midgut (part of yolk sac incorporated into body cavity as lateral folding occurs) to yolk sac (hangs outside folding until abdominal wall closes and disconnects yolk sac
3 body cavities in adults
pleural
pericardial
peritoneal
T/F the connecting stalk, which becomes the umbilical cord, is an extension of the yolk sac
false
it is an extension of the chorion
at the end of body folding in the embryonic period, the entire embryo is surrounded by the __, which is itself surrounded by the __
amnionic fluid and amnion
chorionic fluid and chorion
