MSK Embryology Lab Flashcards
When does embryo folding occur?
-During week 4
What happens during embryo folding?
-Edges of embryo come together and embryo bends into its recognisable C shape
How does embryo folding occur?
- Folding occurs in 2 directions:
- Laterally; (transverse body folds) driven by somites
- Longitudinally; (head to tail/cephalocaudal) driven by CNS
- Tube like structure created
Why is folding movement important?
-Helps situate forming structures in the correct area of the embryo
What drives embryo folding?
-Growth of the mesoderm
What key structures from ectoderm layer and mesoderm can be seen in early embryo 27 days and where abouts?
- Neural tube: (ectoderm)pretty much in centre at top
- Notochord: (Mesoderm) clump of cells immediately below neural tube
- Paraxial mesoderm: lateral to neural tube (somite)
- Dermamyotome
- Sclerotome
- Myocoele (transient cavity) may be seen between dermamyotome and sclerotome
- Intermediate mesoderm: lies ventrolateral to the somites
- Mesenpheric duct: found laterally, develops into vas deferens in males
- Lateral plate mesoderm: somatic (ectoderm associated) and splanchnic (endoderm associated) laers.
- Splanchnic: continous with extraembryonic mesoderm of yolk sac
- Intraembryonic coeloem
What key structures from endoderm can be seen in early embryo 27 days and where abouts?
- Embryonic endoderm
- Yolk sac endoderm: derived from hypoblast
What is intramembranous ossification and give and it example of where it may occur?
- Relies on mesenchymal stem cells
- No cartilage step
- IN flat bones of skull
- Also allows appositional growth of long bones
Describe the process of intramembranous ossification up to development of osteoblasts?
-Starts with condensation of mesenchymal stem cells, they undergo proliferation and morphological changes and differentiate into osteoprogenitor cells which will develop into osteoblasts.
Describe process of intramembranous ossification from osteoblast development to end?
- Osteoblasts deposit bone matrix which are arranged in bony spicules. Differentiating osteoblasts arrange themselves along the spicules and begin to secrete more bone matrix.
- As more matrix is laid down, spicules increase in size and will fuse. Eventually resulting in trabeculae formation.
What is enchondral bone growth and give and wexample of where it may occur?
- Cartilage model laid down and replaced by bone
- Long bones
Describe process of enchondral ossification in humerus up to chondrocyte degeneration?
- Mesenchymal stem cells condense and differentiate into chondrocytes to lay down cartilaginous model of bone.
- Chondrocytes in middle hypertrophy, calcify and so less nutrients able to pass to it, so they degenerate.
Describe process of enchondral ossification from chondrocyte degeneration?
- Blood vessels take up space left by degenrating chondrocytes (primary ossification centre).
- Osteoblasts can start to lay down bone
- Blood vessels invade epiphysis (secondary ossification centre)
- Eventually (after puberty) centres join and no more growth plate.
How can the embryo age be measured?
- We can use somites up to a point
- But they dissapear after around week 5
- Then crown to rump length
- 200mm is around 24 weeks
How may bone and cartilage be stained?
- H+E and alcian blue
- Stains cartilage blue and bone pinkish
- Alzarin blue can also be used to stain bone
