Lecture 2: Histology of the musculoskeletal system (Baekey) Flashcards
Embryonic vs. Fetal periods of growth
embryonic growth = organogenesis, wheras fetal period of growth = growth of existing organs and structures
what represents the major component of increase in overall body mass during the fetal growth phase?
growth in the musculoskeletal system
ossification/osteogenesis
process of laying down new bone material by osteoblasts
when does ossification in long bones begin in humans?
third month of embryonic development
when does ossification completely finish in humans?
by 25 yrs
epiphysis
end portion of long bone
diaphysis
middle portion of long bone
In which direction does ossification occur in long bones?
moves outward from diaphysis to epiphysis
skull growth in female vs. male baboons
Males continue along the SAME growth trajectory as females, but for a longer period of time
4 mechanisms of growth
1) cell proliferation
2) protoplasmic synthesis
3) water uptake
4) intercellular matrix deposition (i.e. connective tissue, cartilage, bone)
protoplasmic synthesis
new organic matter is created from nutrient supply via biosynthesis
What are ABSOLUTE growth scales used for?
to compare growth within a species
What are RELATIVE growth scales used for?
to compare growth between species
What is scaling?
The relationship b/w overall body size and the relative sizes of various body parts
Geometric vs. elastic scaling
In geometric scaling, all of the proportions stay the same (aka isometry). In elastic scaling, some areas grow disproportionately to others (can be positive or negative allometry)
Allometry
a mathematical tool for analyzing scaling. The study of the relationship b/w size and shape.
positive allometry
when the body part of interest grows faster than whatever it’s being compared to (i.e. the rest of the body)
negative allometry
when the body part of interest grows slower than whatever it’s being compared to (i.e. the rest of the body)
growth pattern of the human brain
fetal phase = isometry
early postnatal = negative allometry
late postnatal = little or no growth
Major tissue components of the MS system
skeletal muscle, cartilage, bone, connective tissue, associated blood vessels and nerves
fetal precursor to skeletal muscle
somite myotomes
fetal precursor to connective tissue
somite dermatomes
fetal precursor to axial skeleton
somite sclerotomes
fetal precursor to appendicular skeleton
lateral plate somatic mesoderm
fetal precursor to skull and branchial arch bone + cartilage
head mesenchyme (largely neural crest)
fetal precursor to skeletal muscle of head and branchial arches 1-3
somitomeres
when do myotome cells become myoblasts?
when they lose the ability to undergo mitosis and begin synthesizing myofibrilar proteins
myotube
an elongated multinucleated muscle fibers formed by fused myoblasts. Synthesizes actin and myosin which self-assemble into thick and thin filaments
3 main steps of skeletal muscle fiber development
1) mesenchymal cells differentiate into myoblasts.
2) myoblasts fuse to form myotubes. Contractile filaments begin to order peripherally
3) nuclei migrate to periphery and cytoplasm is filled with bundles of contractile filaments in banding pattern
3 main layers of muscle
epimysium, perimysium, endomysium
epimysium
(fascia) the outer capsule of muscle
perimysium
inward extensions of epimysium that package groups of muscle cells into fascicles and bring nerves, blood vessels, and lymphatics into the muscle
endomysium
loos connective tissue that surrounds individual multinucleated muscle fibers; brings in capillaries and the smallest division of nerves
metaphysis
transition between the epiphysis and diaphysis
physes =
growth plates. located at metaphysis. An immovable cartilaginous joint (synchondrosis) b/w the epiphysis and diaphysis
characteristics of zone of resting chondrocytes ***
scattered, non-dividing chondrocytes which may serve to weld the growth plate to the epiphysis
characteristics of zone of proliferative chondrocytes ***
- isogenic columns of actively dividing chondrocytes
- site of elongation of the long bone
- more mature chondrocytes located at the diaphyseal end of the columns
characteristics of zone of hypertrophied chondrocytes ***
- narrow zone at diaphyseal end of isogenic columns
- chondrocytes with lacunae are large and intercellular matrix is minimal
- weakest site in the growth plate & major site of fractures
chars. of zone of calcified cartilage ***
- calcium deposition appears as dk. stained matrix
- tidemark visible as border b/w zone of articular cartilage and zone of calcification
osteoblast fx
deposit successive lamellae of bone matrix along margins of trabeculae
osteocyte
an osteoblast that has become trapped inside the deposited matrix. persist as mature bone cells
fx of canaliculi
capture blood supply from haversian canal to supply osteocytes within an osteon
what does tidemark denote?
the border between articular and mineralized (calcified) cartilage
diarthroidal joint
a movable joint
synarthroidal joint
an immovable joint
synovial joint components
components: articulating bone surfaces covered by hyaline cartilage separated by a fluid-filled joint cavity, surrounded by a joint capsule
examples of synovial joint
scapulo-humeral; stifle
symphysis joint components
articular surfaces covered by hyaline cartilage, separated by a pad of fibrocartilage
examples of symphysis joint
intervertebral, pubic symphysis
components of synovial joint capsule
synovial membrane (epithelial-like layer of fibroblasts), synovial fold (infolding of synovial membrane into synovial space), and fibrous layer (dense white fibrous connective tissue that contains elastic fibers)
perichondral ring
where fibrous layer of synovial joint capsule attaches to bone. An area of transition b/w the articular cartilage and the periosteum of the diaphysis
periosteum
membrane that lines the outer surface of all bones
what are tendons composed of?
dense white fibrous connective tissue anchored to bone or muscle
Sharpey’s fibers
collagenous fibers that attach tendons, ligaments, and joint capsules to bone
