Embryology of Bone and Muscle Flashcards
Embryonic connective tisse
Mesenchyme
Mesenchyme is derived from _______ and _______
mesoderm and neural crest
defines axes, mechanical role in folding process, signaling role in formation of neural groove/tube, somites (indirectly) and musculoskeletal system (via Shh)
contributes to vertebral bodies and intervertebral discs
Notochord
_______ induces overlying ectoderm to invaginate –> neural groove and tube
notochord
Neural tube induces formation of _____/_____ from paraxial mesoderm
vertebrae/somites
clusters of mesodermal tissue that condense segmentally in rostral to caudal progression. They are derived from paraxial mesoderm.
Somites (somitomeres)
Somitomeres –> Somites
Compact and bound by epithelium = somites
Pairs 1-7 do not compact –> contribute to formation of head and neck
Mesodermal cells from somites migrate and give rise to
Dermomyotome –> dermatomes and myotomes
Sclerotome –> bone and cartilage
Membranous bone formation
Mesenchyme condenses into a very vascular CT. Mesenchymal cells produce matrix containing collagen fibers. Cells differentiate into osteoblasts and begin to lay down mineralized bone matrix, typical in the formation of flat bones (skull).
Endochondral bone formation
Mesenchymal cells differentiate into chondroblasts –> hyaline cartilage model of the (long) bone. Matrix calcifies around the periphery of the shaft. Interiorly, some cells differentiate into osteoblasts and begin to lay down mineralized bony matrix. —Primary ossification center.
Blood vessels invade the diaphysis and stimulate ossification. The diaphysis grows in length toward the ends of the bone. Later, secondary ossification centers form in the ends (epiphyses). The epiphyses grow toward the shaft, leaving a region of hyaline cartilage, the epiphyseal (growth) plate between. Growth of the long bone stops when the cartilage plate has completely ossified.
Timing of ossification centers for long bones
Primary oss centers at week 8 in certain order
Nearly all have primaries at birth
Most secondary centers appear after birth (epiphysis)
Joint formation (overall)
Loose mesenchyme between cartilage models differentiates into fibrous tissue or fibrocartilage. Surrounded by perichondrium .
Synovial joint formation
In synovial joints, programmed cell death (apoptosis) results in joint cavity between adjacent cartilage models. Perichondrium persists as joint capsule, lining differentiates into synovial membrane. Hyaline cartilage persists on articular surfaces.
Marfan Syndrome
Connective tissue disorder - excessive long bone growth
Fibrillin-1 gene mutation
Long, thin limbs
Also can affect heart, vessels, bones, eyes, lungs
Osteogenesis Imperfecta
Defect in type 1 collagen gene Autosomal recessive OR dominant Extreme bone fragility Frequent fractures Hypermobile joints
Achondroplasia
Most common form of dwarfism
Affects long bones
Autosomal dominant or spontaneous mutation of FGFR3 gene
Gigantism
Excessive growth hormone during childhood BEFORE growth plates close
Overal large size, height and organs, normal proportions
Acromegaly
Excessive growth hormone AFTER growth plates closed
Large heavy bones especially hands and feet
Congenital Hip dysplasia/dislocation
Incomplete formation of acetabulum (hip joint)
Legs held in positions that don’t match, less movement, uneven leg length
Axial skeletal system
Skull, vertebral column, ribs/sternum
Appendicular skeletal system
pectoral and pelvic girdles
limbs
Sclerotome cells migrate ________ to form sheath around ______ and ______
ventromedially,
notochord and neural tube
Resegmentation of vertebral column
Caudal part of one segment fuses with rostral part of segment below (around the artery)
i.e. In the primitive stage, the artery appears to separate one vertebra from another. In the definitive stage, the artery lies in the middle of the vertebral body.
Each sclerotome segment is divided into two parts (____ and ______) by _______
Dense caudal and loose cranial part, intersclerotomic (Von ebner’s fissure)
