mesodermal tissue derivatives
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MESODERMAL TISSUE AND ITS DERIVATIVESMESODERMAL TISSUE AND ITS DERIVATIVES
Begin with somite as mass with hollow center
radial arrangement of cells
shape changes with time
extend dorsoventrally; flatten mediolaterally
myocoelmyocoel: spherical long vertical slit
Consequences:
inner and outer walls parietal and visceral layers of lateral plate
outer wall dermatome dermis
inner wall skeletongenous tissue and voluntary striated muscle
inner wall later subdivides
sclerotomesclerotome and myotomemyotome
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Muscle segmentation from somite segmentation
Hermann and Heinz; Studies ofMuscle Development. Annals NY Acad. Sci 1952
Great mass increase 40 84 hours
Cell # increase: 8x103 121x103
No DNA or RNA or protein increase
Dilution of cells = 1.7
5 6 days very little change
Day 11 new trend (chart on next slide)
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DAY PN/Cell Cell Mass (mg x 10-7) RNA
9 7.10 13.6 5.28
10 9.45 12.6 3.79
12 7.45 13.6 3.89
13 7.60 13.1 4.28
14 9.95 14.0 4.37
15 10.50 12.2 3.72
16 11.20 13.1 3.90
17 14.20 13.2 4.00
18 13.40 11.5 3.83
19 18.10 14.6 4.36
20 25.70 22.6 5.45
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Coelom and MesenteriesCoelom and Mesenteries
Coelom --- splitting of lateral plate Somatic (parietal) and splanchnic layers(visceral)
Doral mesentery
Ventral mesentery
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Retroperitoneal
Ventral mesogastrium
Falciform ligament
Transverse septum
Pleural channels
Pleural cavities
Pleuropericardial fold
Pleuroperitoneal fold
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MUSCLE DEVELOPMENTMUSCLE DEVELOPMENT
3 TYPES OF MUSCLE TISSUE
Striated, voluntary muscleSmooth, involuntary muscle
Cardiac muscle
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MUSCLE DEVELOPMENT
Striated, voluntary muscle tissue
Somatic mesoderm and head mesoderm
exceptions: Ciliary muscles and Iris neural crest
Christ, et. al. (1977); Chevallier (1977): Chick/Quail experiments
Cells represent a syncytium from fusion of mononucleated myoblasts
Myoblasts differentiated elongate in parallel clusters
Cells fuse myotubes = multinucleated muscle fibers
Cytodifferentiation specific contractile proteins after fustion
Parallel myofilaments (actin and myosin)
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RestrictionRestriction cells in epiblast or in primitive streak stage
(chick development)
Holtzer, et. al. begin with founder cells
Internally controlled genetic program
Founder cells
clones
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Formation ofMuscles (the organs)
Common origin: paraxial mesoderm
Migration of myogenic cells: pathway not controlled
by information in the myogenic cells.
Muscle blastemaMuscle blastema
Mix myogenic cells from different regions
Morphogenesis controlled by connective tissues
Intrafusal muscle fibersIntrafusal muscle fibers
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Cardiac muscleCardiac muscle
Splanchnic mesoderm
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Smooth muscleSmooth muscle
General Rule:General Rule: smooth muscle differentiates from any type of
mesoderm surrounding the epithelial component
Blood vessels: somatic mesoderm; Iris: sphincter pupulae from ectoderm
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AXIAL SKELETONAXIAL SKELETON
3 PHASES AXIAL SKELETON FORMATION
1. Notochord
2. Cartilage (related to notochord; some independent
Cyclostomes; Elasmobranchs end development
3.Cartilage replaced by bone
all other fish; all tetrapods
Cartilage from sclerotome = segmentalSclerotome (mesoderm) mesenchyme
Mesenchyme forms sheath around notochord (lose
segmentation
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Arcualia form (condensation of mesenchyme near notochord
and spinal cord
Double pairs: (Next slide for graphic)dorsolateral pairdorsolateral pair
grow up around spinal cord neural
arches
ventrolateral pairventrolateral pair
grow down (tail) hemal arches
caudal artery/vein
grow laterally (cervical/thoracic)
ribrudiments
Centrum (body) from both pairs around
notochord
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Dorsolateral
arcualia
Ventrolateral arcualia
Centrum
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Extirpation ExperimentsExtirpation Experiments
Remove notochord vertebral column irregular
Remove spinal cord vertebrae do not form
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Transplantation ExperimentsTransplantation Experiments:
Neural tube to second host dorsolateral mesoderm neural
arches form
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Grafted
spinal cord
Induced
neural
arch
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Substitute somitesSubstitute somites (increase number per segment
increases # muscle segments spinal ganglia (not a
strict correspondence)
# neural arches correspond to number of ganglia
Neural crest repulses skeletogenous mesenchyme
Two cartilage segments form between each ganglion
another structure(s) act on vertebral formation?
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HEAD REGIONHEAD REGION
TrabeculaeTrabeculae (Prechordal cartilages)
Neural crest
Prechordal mesoderm
Parachordal cartilagesParachordal cartilages
Mesenchyme from sclerotome
Sense Organ CapsulesSense Organ Capsules (nose, eye, ear)
Skeletogenous mesenchyme
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From Weichert: Anatomy of the Chordates
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PAIRED LIMBSPAIRED LIMBS
Derived from:
Lateral plate mesoderm
Epidermis
Somites
Also includes nerves, blood vessels, lymphatics and other structures
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Beginning of the limb saga: lateral plate mesoderm
somatic layer thickens
mass separates from lateral plate = cell
migration
cells transform into mesenchyme
position of thickenings varies in different groups
Amniotes mesenchyme along entirelength of body to form Wolffian ridges
thickest anteriorly and posteriorly
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Epidermis thickens over mesenchymal massesEpidermis thickens over mesenchymal masses
entire length of Wolffian Ridgesridge subsides in intermediate regions
remains in regions of limb buds
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Mesoderm determined shortly after closure ofMesoderm determined shortly after closure of
neural tubeneural tube
Any epidermis can participate in limb formation
Mesoderm component is critical
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Epidermis is not passiveEpidermis is not passive
Ectodermal Apical Ridge (higher vertebrates)(next slide for illustration)
Ridge cells more RNA and glycogen
Ridge cells very high levels of alkaline
phosphatase
Ridge indispensible for normal outgrowth
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TrypsinTrypsin--Versene ExperimentsVersene Experiments
Trypsin removes epidermis intact
Versene removes epidermis in flakes; mesoderm
unaffected
Recombine components (epidermis and mesoderm
stick readily to each other
Mesoderm (leg-bud); Ectoderm (wing-bud) graft to flank of
third embryo forms a leg (determined by the mesoderm)
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Competence for Limb DevelopmentCompetence for Limb Development
Entire flank
Amphibians
Introduction of inducer limb development
Inductor used: Ear vesicle
Other organs also used: hypophysis, olfactory sac
Determination of limb mesoderm
With other parts of mesodermal mantle
flank
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Limb DifferentiationLimb Differentiation
Start at time when width = length subordinate parts begin to
form
1st: distal end flattens even more than the flat limb bud
rounded end
becomes pentagonal
points become digits
cellular necrosis between digits
macophages remove dead cells
DS-1
DS-2
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DS-1
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DS-2
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Rotation of LimbRotation of Limb
Flexor surface ventral, extensor surface is dorsal
Limb elongates and rotates
flexor surface posterior to posterodorsal
Flexures develop
Preaxial edge is anterior (red line on diagram) a
Elongates and bends at future elbow (knee) b and c
Another, less pronounced flexure at carpus (tarsus)
DS-3
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a b c
DS-3
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INTERNAL CHANGES IN LIMBINTERNAL CHANGES IN LIMB
Mesenchyme initially uniform distribution
thins out some areas
thickens other areas = future bones
converted to procartilage
Limb skeleton proximo-distal direction
stylopodium (humerus/femur) first
zeugopodium (radius-ulna/tibial-fibula) next
autopodium (carpus-digits/tarsus-digits) much later
sequence does not hold in autopodium
metacarpals/metatarsals (larger) first
carpals/tarsals (smaller) slow
digits return to proximo-distal sequence
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Limb GirdlesLimb Girdles
Develop intimately with limb
limb does not need to be present
if limb is absent no articulation forms
Additional mesenchyme needed to complete limb
lower edge of myotome supplies mesenchyme for muscles
Fish: muscle buds enter limb and fuse (common mass) = myoblast
secondary condensation to form muscles
Amphibians, reptiles, birds and mammals individual cells migrate
into limb
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Bone formationBone formation
Endochondral
Intramembanous
Osteoblasts
Osteoclasts
Osteogenic fibers
Histology web site: http://camilolab.slu.edu/444/histology.html
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1
23
4
5
6 7 8
THE ZONES (FROM ENDS OF CARTILAGETHE ZONES (FROM ENDS OF CARTILAGE
TOWARD PRIMARY OSSIFICATION CENTER)TOWARD PRIMARY OSSIFICATION CENTER)
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1.1.Quiescent (Reserve) ZoneQuiescent (Reserve) Zone
Primitive hyaline cartilage
Slight, slow growth
Extensive at first progressively smaller
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2.2. Proliferative ZoneProliferative Zone
Active mitotic zone
Cells divide, daughter cells divide, etc.
Forms rows of cells
Rows parallel with long axis of cartilage
Rows add cells at distal (free) end
Cells in rows are crowded, flattened,
separated by very little matrix
More matrix between rows
Arrangement adds length not breath to
cartilage mass
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3.3. Maturation ZoneMaturation Zone
Mitosis ceases
Cells and lacunae enlarge (cuboidal shape)
Increases length even more
This growth is interstitial
Maturing cells produce more phosphatase and
glycogen
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4.4. Calcification ZoneCalcification Zone
Deeply basophilic, calcified matrix
Zone is narrow
Cells at peak of life cycle
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5.5. Regressive ZoneRegressive Zone
Cartilage cells dying
Matrix between cells dissolving (open uplacunae)
Thicker plates of cartilage not eroded
significantly
Vascular primary marrow extends into newspaces
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6. Ossification Zone6. Ossification Zone
Osteoblasts migrate to calcified cartilage
Rapid deposition of bone
Adds to spongy bone already present
7. Osseus Zone7. Osseus Zone
Zone of endochondral bone from ossification
region to primary center
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8. Resorptive Zone8. Resorptive Zone
Advance of ossification toward cartilage offset
Compensatory resorption of bone
Resorption at oldest (proximal) end of
bony mass
Keeps mass of spongy bone nearly
constant
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