MSK Histology Flashcards
3 TYPES
- SMOOTH - visceral, many body organs and blood vessels
- SKELETAL - voluntary, mainly attached to bony skeleton - striated
- CARDIAC - only at heart, branching/striated
OTHER CONTRACTILES
- PERICYTES (along some blood vessels)
- MYOFIBROBLASTS (scar formation
- MYOEPITHELIAL CELLS (milk @ lactate
SMOOTH MUSCLE
- discrete cells with cell junctions - function as whole
- LONGITDUINAL - FUSIFORM w/ cylindrical nuclei
- TRANSVERSE - ROUND cell and nuclei
- CENTRAL NUCLEUS / NO STRIATIONS
not organised into sarcomeres
- anchored to cell membrane in clumps
- reticulin (collagen T3) rich external lamina / BM that joins cells together
- electrically coupled via gap junctions
- surface receptors for hormonal stimuli
this slide- double layer of smooth muscle @ intestines
SMOOTH MUSCLE ARRANGEMENT AND GAP JUNCTIONS
- each junction = 6 CONNEXON PROTEINS span cell membrane and link interior of adjacent cells
- vital for co-ordinated contraction
- guarded central pore - small molecules to pass from one cell to the next (signal molecules) electrical coupling - freely and quicker than transporting
SKELETAL MUSCLE TERMINOLOGY
- sarcomere - regular repeat structure within myofibrils = interdigitated actin and myosin
- myofibril - small intracellular fibril - sarcomeres joined end to end
- muscle fibre - fusion of many myocytes with 100s of myofibrils. surrounded by common plasmalemma, behaves as single cell - many nuclei
- fasciculus - bundle of muscle fibres surrounded by connective tissue
- endomyosium - lace work of connective tissue between muscle fibres
- perimysium - surrounds group of fibres to form fasciculus
- epimysium - connective tissue around fasciuli to form muscles
MUSCLE FIBRE & LONGITUTIDNAL SKELETAL MUSCLE
- long unbranched
- many nuclei
- LONGITUDINALLY - nuclei at fibre edges
- TRANSVERSELY - aggregated to fasciuli, nuclei at edges
this slide - tongue (with longitudinal muscle fibres)
EXTRINSIC FIBRES - poke out motuh
INTRINSIC FIBRES - manipulate food
myofibrils in register = striations
SKELETAL MUSCLE (TRANSVERSE)
- loosely aggregated to fasciuli by PERIMYSIUM
- nuclei at periphery of fibre
SKELETAL MUSCLE INDIVIDUALLY INNERVATED IN MOTOR UNITS
MITOCHONDRIA BETWEEN MUSCLE FIBRILS WITH MUSCLE FIBRES
MAY SEE GLYCOGEN AND LIPID DROPLETS
SARCOMERE (IRON HAEMATOXYLIN)
- unit structure of sacromere
- Z line to Z line
- thin actin to Z line
- interdigitate thick myosin
- in contraction shortens up to 1/3
- I band - actin only
- A band - actin and myosin
- H band - myosin only (with M line)
- myofibrils run in parallel with sarcomeres in register = STRIATIONS
SARCOMERES JOINED END TO END AND SIDE TO SIDE AT Z-LINE
CARDIAC MUSCLE
- discrete rectangular cells - end to end
- central nuclei
- branch
- connected by intercalated discs - hold cells physically and electrically coupled
- desomosomes
- adherent junctions
- gap junctions
- sarcomes i.e. STRIATED with myofibrils but with different protein isoforms to skeletal
- many mitochondria (ox phos dependent) therefore aerobic respiration only
don’t necessarily have own nerve supply as have innate contractility (SA and AV node regulated)
SARCOMERES
- when stimulated actin fibres slide within th A-band
- brings Z-lines close together
- shortens sarcomere up to 30% - extrinsic work
- tension increases - intrinsic work
- structural protein - titin
between myofibrils:
T-tubules - conduct impulse
sarcoplasmic reticulum - sequester calcium
glycogen/lipid storage
mitochondria - ATP production
UPPER FIBIRL - contractile
LOWER FIBRIL - structural
SKELETAL MUSCLE LONGITUDINAL
- each skeletal muscle fibre = hundreds of myoblasts fused to syncitium
- each fibre = many nuclei under plasmalemma at side of fibre - DISTINGUISHING POINT
this slide -tongue
n.b. small fascicles usuall denote smaller motor units = fine control
SKELETAL MUSCLE TRANSVERSE
- polygonal pink fibres
- arranged in clumps = fascicles
not all skeletal muscle is attached to bone
when skeletal muscles are attached together by fibrous connective tissue = RAPHE
SKELETAL MUSCLE BANDING (IRON HAEMATOXYLIN)
- I band - pale, predominantly actin
- Z line - @ centre of I band
- A band - darker staining, MYOSIN RICH
A band is not actin
@ centre of each A band = paler H band with M line
I stands for ISOTROPIC
A stands for ANISOTROPIC
FIBRE ARRANGEMENT LONGITDUINAL
- striations (myofibrils and repeat sarcolemmas)
- Dark = A band
- Light = I band
- Z lines connected
IN REGISTER
between myofibrils = mitochondria and elements of sarcoplamic reticulum
DYSTROPHIN - binds actin to plasmalemma of muscle cells - structural integrity
FIBRE ARRANGEMENT TRANSVERSE
- actin and myosin appear as dots
- @ I band = small dots only (light)
- @ A band = small and large dots - actin and myosin (dark)
between myofibrils may see parts of T-tubules and sarcoplasmic reticulum. also glycogen and mitochondria.
Z DISC COMPOSITION
lipid = 60% - electrostatically binds proteins
major protein = ALPHA ACTININ
SKELETAL MUSCLE: TYPE 1 & 2(a/b)
most fibres contain all 3 but proportions vary
- TYPE 1 - SLOW TWITCH: oxidative / fatigue-resistant / postural muscles
- TYPE 2a - FAST TWITCH: oxidative / glycolytic - moderately fatigue resistant
- TYPE 2b - FAST TWITCH: depend on glycolytic processes and are therefore fatigue sensitive (SPRINT MUSCLES)
this slide - stained for fibrillar ATPase (DARK BROWN) and greatest in slow twitch with greater number of mitochondria
postural muscles at spine have largest proportion of slow twitch
fingers have highest proportion of fast twitch
SKELETAL MUSCLE: TYPE 1
- type 1 - rows of mitochondria between myofibrils
- fat globules alongside mitochondria used for ATP production
SKELETAL MUSCLE: TYPE 2
- type 2 - fewer/smaller mitochondria
- large reserves of carbohydrates/glycogen
running = anaerobic, therefore uses carbs as energy source
SHARPEY’S FIBRES - TYPE 1 COLLAGEN
- muscles connected to bones via CONNECTIVE TISSUE (MYSIUM)
- either as
- small collagen bundles (SHARPEY’S FIBRES)
- discrete tendons
- Sharpey’s merge with fibrous periosteum of bone and collagenous bone matrix
- spreads muscle force over wide area e.g. rotator cuff at scapular
this slide - oblique = sharpey’s / below = periosteum of bone / lower pale staining cellular layer / upper darker staining fibrous layer
TENDON -TYPE 1 COLLAGEN
- tendons and aponeuroses = condensed parallel bundles of collagen fibres interspersed with fibroblasts
- at end of muscle fasciculi split becoming smaller but more numerous
- connective tissue between more numerous
TENDON = continuation of peri/epimycium
tearing a tendon causes inflammation
inflammation stimulates fibroblasts to synthesise actin (draws would together) and collagen
MUSCLE SPINDLE
- sensory
- embedded within muscle
- small number intrafusal
- surrounding msucle = extrafusal
- separated by connective tissue sheath
intrafusal fibres:
- nerve fibres wound round
- parallel with extrafusal fibres
- relay information about contraction of surrounding muscle
fine movement= smaller motor units and more spindles
CARTILAGE
- cartilage/bone = rigid conenctive tissue (CLOSELY RELATED)
- undifferentiated mesenchymal cell
- cells in dense GAG rich matrix
- variable amounts of collagen and elastic tissue
- FLEXIBLE/COMPRESSIBLE/HARD WEARING
CARTILAGE 2
- surrounded by fibrous capsule - collagen perichondrium
- perichondrium contains undifferentiated progenitor cells (to chondroblast if needed))
3 FORMS
- HYALINE (T2 collagen) - fine collagen and elastic fibres - glassy. POOR STAIN WITH H&E - eg. articular surfaces. all long bones originally H&E
- ELASTIC (T2 collagen and elastic) - irregular arranged elastic fibres VISIBLE
- FIBROUS (T1&2 collagen) - banded collagen eg. intervertebral discs
HYALINE CARTILAGE
- GAG rich
- invisible collagen/elastic - glassy
- clumped chondrocytes in matrix (pale staining lacunae)
- MATRIX BINDS WATER - when compressed exudes water (reabsorbed when pressure released
this slide - trachea
n.b.
- ARTICULAR CARTILAGE has no perichondrium
- hyaline receives nutrients via diffusion from surrounding tissue
ELASTIC CARTILAGE
- larger amounts of elastin
- PINK STAINING STRANDS
- may be fractured (though tougher than hyaline/fibrous
this slide - epiglottis
FIBROUS CARTILAGE
- large amount of collagen arranged in sheets
this slide - IV disc
- thick fibrous outer shell
- more fluid centre
- condrocytes distributed throughout both
- chondrocytes between collagen laminae
OUTER CASING - annulus fibrosus
INNER CASING - annulu pulposus
BONE - T1 CARTILAGE
- mainly collagen (95%) - becomes mineralised (5%)
- synthesised by osteoblasts
- osteoblasts secrete collagen rich matrix - osteoid
- mineralised with hydoxyapetite
- cells trapped in bone -> less active osteocytes
- BONE REABSORBING CELLS - osteoclast (multinucleate/phagocytotic
- bone dynamic - actively resorb bone - continous remodelling
PRIMARY BONE
- randomly organised (woven)
- collagen fibrils - multidirectional
- poor weight/strength ratio
- soon replaced by more organised secondary bone
BONE 2
SECONDARY BONE
- organised
- layers - long axis of hydroxyapetite crystals in parallel with collagen
- collagen fibres at right angles layer to layer - plywood
- INTERNALLY = OSTEONS
- osteons = cylindrical units w/ concentric layers bone and HAVERSIAN CANAL
- HC contains blood vessels and nerves to osteocytes in bone
- osteons continually eroded and replaced
- between osteons = interstitial bone (remnants of previous osteon)
- surrounded by fibrous capsule (periosteum) w/ progenitor cells = healing
- open framework/compact lamellae or osteons
MINERALISED BONE - GROUND SLIDE
- too tough to cut thin
- golden brown haversian canal
- average diameter = 200 microns
- cement line separates each osteon - seals from neighbours - so oxygen/nutrients from HC diffuse throughout osteon
- stops osteocyte contact intra osteon
OSTEOCYTES IN IMPREGNATE BONE
- impregnate with dye
- reveals osteocytes and fine processes (filopodia) through bone
- filopodia make contact with adjactent cells
- passage of nutriets/oxygen etc
- respond to hormones and break down or deposit bone to regulate calcium levels
DECALCIFIED BONE
- dissolve mineral with H2SO4 or EDTA
- mostly condensed collagen left
- HC size increases as bone reabsorbed from osteon
- narrower as new bone deposited
- before puberty
MEMBRANOUS BONES & OSTEOBLATS
- some skull bones formed by direct deposit of bone in condensed mesenchyme = intra-membranous ossification
- easier to recognise osteoblasts
- larger than osteocyte
- dark blue/purple cytoplasm (as large amounts of RNA)
trapped within bone when they lay down new bone - form osteocytes
OSTEOCLASTS (MEMBRANE BONE H&E AND ALCIAN BLUE)
- bone resorbing cells
- active macrophage differentiated from monocytes
- therefore different lineage form osteoblast and osteocyte
- multi-nucleate
- on surface of bone in depression HOWSHIP’S LACUNAE
- primary erosion sites
- LARGER than osteoblast, multinucleate, intense pink stain (to digest bone, need lysosome - eosinophilic)
PROFORMER CARTILAGE
- long bone formation
- cartilaginous proformer -> converted to bone
- long bones not fully developed till after puberty
- hyaline cartilage with fibrous perichondrium contains progenitor cells and chondrocytes
- oxygen and nutrients by diffusion
ENDOCHONDRAL OSSIFICATION
- hyaline cartilage proformer @ 2/3 fetal like
- shaft/diaphysis becomes ossified
- collar penetrated by blood vessels = more osteoprogenitor cells -> osteoblasts and lay down bone
ENDOCHONDRAL OSSIFICATION 2
- secondary centres formed in heads of bones (epiphyses)
- at birth most bones have primary, some secondary
- centres expand = reduces cartilage
- restricted to epiphyseal growth plates
- separates diaphysis from epiphyses
- growth plates extend beyond PUBERTY = bone growth
- epiphyseal cartilage responds to growth hormones and sex hormone
ENDOCHONDRAL OSSIFICATION 3
- @ head of growing long bone
- stages cartilage -> bone
- chondrocytes of resting cartilage divide = zones of progeny (ZONE OF HYPERPLASIA)
- newly formed cells grow eroding cartilage (HYERPTROPHY)
- all that remains are spicules of cartilage (chondrocytes released and resorbed(
- remnant cartilage strands calicified and substrate to osteoblast attachment. osteoblasts lay down primary bone (ZONE OF OSSIFICATION)
- at same time bone eroded and replaced on outside of shaft of bone by appositional growth (= length and girth)
GROWING LONG BONE
- increase in length by adding bone at epiphyseal plate
- additional bone on outside of shaft
- ossification starts at diaphysis
- single epiphyseal growth plaet at distal phalanges of fingers and toes
- carpal and tarsal bones last to ossify @ 7/8yo
DEVELOPING MEMBRANE BONE
- more direct method (intramembranous ossification)
- no cartilage proformer
- @ flat bones of skull -> bone deposited in mesenchyme @ 2/3yo
- small clusters of progenitor cells within mesenchye -> osteoblasts
- deposti isolated islands of bone
- isands coalesce - meshwork of bone
- osteoblasts continue till mesh filled - primary plate of bone
- later eroded and replaced with more organisesd lamellar secondary bone
this slide - skull and brain with immature membrane bone. blue/purple osteoblasts lining holes - synthesise osteoid - profuse endoplasmic reticulum - dark blue
COMPACT MINERALISED BONE
- mature secondary bone
- 5% hyroxyapatite - hard crystalline calcium salt
- contrast by refraction from mineral crystals
MATURE DECALCIFIED BONE
- treat with acid to remove calcium
- inset = bone marrow @ core
- compact lamellar secondary bone stains bright pink (collagen matrix of bone)
- trapped within bone are osteocytes
- surrounded by periosteum
PERIOSTEUM
- outer fibrous
- inner cellular (paler) - rows of dark staining osteoblasts laying down new bone = appositional growth
- site of osteoprogenitor cells
- @ fracture stiumlated to differentiate to chondroblast to cartilage which then undergoes endochondral ossification
