MSK embryology Flashcards
when does embryonic folding generally happen?
week 4 of development
how does embryonic folding occur?
occurs in 2 directions
-lateral folding is driven by somites
-cephalocaudal / head and tail folding which is driven by CNS, particularly brain
-folds happen simultaneously and close the body wall of the embryo and create a tube like structure
closes the body wall and creates a tube like centre
how are embryos staged?
the the number of smote pairs they have
what makes up the amnionic membrane?
continuous should join at the top. embryo membrane to extra embryonic membrane. encloses a space where amnionic fluid should be
what is the function of the amnionic space and fluid?
protection, remains until birth, this is the fluid that leaks when ‘water breaks’
what is in the centre of the neural tube?
neural canal
what is the mantle zone of the neural tube?
where it is more cellular, made up of neuroblasts, cells going under mitosis, future grey matter of CNS
what does the marginal zone form?
white matter of CNS
what are the 3 main parts of the mesoderm?
paraxial
lateral plate
intermediate
what is the notochord?
signalling centre during development of mesoderm and CNS, sends out signals to mesoderm to tell it to differentiate
transient structure
parts go on to form nucleus pulpous
what mesoderm is adjacent to neural tube?
paraxial mesoderm
how many blocks of paraxial mesoderm are there?
2, these go on to form somites
what kind of sequence do the somites form in?
cranial caudal sequence
what are the somites?
transient structures that appear and disappear, differentiate to give different structures in MSK
what are the zones of the somite?
dermomyotome
sclerotome
what is the dermomyotome?
outer part of somite
goes on to form dermis of skin and skeletal muscle
can have spaces
more cellular
what is the sclerotome?
ventral part of somite
more cellular that dermomyotome
where does somite come from?
paraxial mesoderm
what does the sclerotome go on to form?
vertebrae and ribs
what does interimediate mesoderm connect?
connects paraxial mesoderm to somatic and lateral plate mesoderm
what does intermediate mesoderm differentiate into?
uriogential structures
what is the big space in the middle of the embryo?
dorsal aorta, blood cells in the aorta
what is the lateral plate mesoderm
most lateral in the embryo
been pushed apart into 2
where is the somatic lateral plate mesoderm?
directly under the one or two laters thick of ectoderm
where is the sphlanic LPM?
continuity with endoderm
at the bottom of embryo on the outside
what is the endoderm?
forms lining of primitive gut
endothelial sheet that gets bent to form tube when embryo folds up
what’s the difference between the yolk sac cells and endoderm cells?
cells are different shapes
endoderm - bigger and more organised and tighter packed
where does the initial blood vessel development occur?
in the yolk sac
generally when does yolk sac fall off?
week 17-18
what is appositional growth?
increase in girth/width of a bone - seen during development and in fractures. Chondroblasts deposit collagen matrix on cartilage beneath the periosteum and add bone widthwise.
what is interstitial growth?
increase in length. This is a result of growth plate of cartilage model during growth period up until puberty
what is endochondral ossification?
cartilage model is laid down as a precursor to bone
what is intramembranous ossification?
cartilage not involved, condensation of mesenchyme straight to bone
what is mesenchyme?
Connective tissue formed from mesoderm. Highly migratory and essentially a stem cell population for the musculoskeletal system
what are osteprogenitor cells?
Osteoprogenitor cells, also known as osteogenic cells, are stem cells located in the bone that play an important role in bone growth and repair. These cells are the precursors to the more specialised bone cells osteocytes and osteoblasts and differentiate from mesenchymal stem cells.
what is the myotome?
part of the somite that forms the muscles (confusing as a myotome in adulthood is the group of muscles that a single spinal nerve innervates)
how does intramembranous ossification work?
relies on mesenchymal stem cells present within the developing bone. Mesenchymal stem cells can differentiate straight into osteoblasts, so allowing intramembranous ossification to occur without needing a cartilage step.
what bones are formed by inramembranous ossification?
flat bones of skull and face and clavicles
how do long bones grow?
intramembranous ossification
how does intramembranous ossification begin?
begins with condensation of the mesenchymal stem cells. They undergo proliferation and undergo morphological changes and differentiate into osteoprogenitor cells which will in turn develop into osteoblastsThe osteogeneic cells start to deposit bone matrix which are arranged in bony spicules. The differentiating osteoblasts arrange themselves along the spicules and begin to secrete more bone matrix. As more matrix gets laid down, the spicules increase in size and will fuse together. As these grow, they will fuse with more and more spicules and this results in the formation of trabeculae.
what is the metaphysis?
transitional zone that connects the epiphysis and diaphysis of the growing long bone
when do somites disappear?
5 weeks
how are embryos measured after week 5?
crown rump length
what is crown rump length
straight line between the two points to measure fetal size
when does the fetal period begin?
week 8
what age is a foetus of 200mm crown rump length suspected to be?
24 weeks
what is the first stage of bone development in the embryo?
-intramembranous ossification of the outside ends of bone, inside is cartilage
-chondrocytes get bigger and leave spaces within shaft
-cartilage matrix calcifies
-less nutrients get to chondrocytes and begin to die
-blood vessels invade into these spaces (primary ossification centre)
-blood vessels bring in osteoprogenitor cells which begin to lay down bone
-bone marrow forms
-eventually blood vessels invade epiphyses - secondary ossification centres
what does alcian blue do?
stains cartilage blue
where is the growth plate?
separating diaphysis and epiphysis
zone of reserve cartilage?
resting cartilage
what is the period of proliferation?
chondrocytes become more ordered and line up onto of each other, more proliferation in cartilage
what is the period of maturation?
get bigger in size but mitosis stops
zone of hypertrophy?
vacuole within the chondrocyte as they begin to lay down matrix, depositing minerals and calcified matrix, surrounds large cells
when calcified hard matrix lays down chondrocytes begin to die
what is the role of osteoclasts?
absurd anything not needed
change shapes of new bone
what are the zones of the growth plate?
resting cartilage
proliferation of chondrocytes
maturation - no more mitosis
zone of hypertrophy, cells enlarge and form vacuoles
cartilage degeneration
osteogenic activity
what are osteoclasts?
are large multinucleated cells, with a ‘ruffled border’ that resorb bone matrix, as shown in the diagram above. They are important for remodelling, growth and repair of bone. (clast - greek ‘to break’).
where are osteoclasts derived from?
They are derived from blood monocytes/macrophages which are derived from haematopoetic cells in the bone marrow. The precursors are often released as monocytes into the blood stream and they then collect at sites of bone resorption, where they fuse to form multinucleated osteoclasts, stick to the surface of bone, and break down the bone matrix.
what do osteoclasts secrete?
have prominent Golgi apparatus, and vesicles. They secrete enzymes such as carbonic anhydrase which acidifies the matrix and causes it to decalcify, and hydrolyses which breaks down the matrix once it is decalcified. Other cell types help to phagocytose and get rid of the debris
what do osteoblasts do?
synthesize the bone matrix and are responsible for its mineralization. They are derived from osteoprogenitor cells, a mesenchymal stem cell line.
what are smaller osteoclasts or osteoblasts?
osteoblasts
where do vertebra form from?
sclerotome
the amnion is an extra embryonic membrane what germ layer is it a continuation of?
ectoderm
what type of mesoderm fuses to close the body wall of the embryo during folding?
somatic lateral plate mesoderm
