mesodermal tissue derivatives

8/9/2019 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

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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

mesodermal tissue derivatives

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