Histology of the MSK system Flashcards
function of skeletal muscle?
movement, support, protection, thermoregulation, blood circulation
what type of contraction does skeletal muscle do?
voluntary contraction
what is skeletal muscle attached to?
bones and sphincters
what is the entire skeletal muscle surrounded by?
by epimysium (collagenous covering ‘fascia’)
what is the epimysium subdivided into and what are these surrounded by?
1) fascicles (surrounded by perimysium)
2) myofibres (surrounded by endomysium)
what is a skeletal muscle myofibre?
a cellular unit of skeletal muscle
multiple cells fused to form one long tube
multinucleated as a result
sarcolemma?
cell membrane of myofibre
sarcoplasm?
cytoplasm of myofibre cell
what are myofibres made up of?
made up of multiple myofibrils which in turn are formed by many filaments
what type of nuclei does the skeletal myofibre have?
peripheral
if there is lots of protein in skeletal myofibre, what does this mean for staining?
strongly eosinophilic sarcoplasm
Describe the type 1 muscle fibres?
lots of capillaries, mitochondria, myoglobin (gives red colour)
how do the type 1 muscle fibres work?
can contract for long periods with limited energy demand - force contraction is low
Describe the fast twitch (type 2) muscle fibres?
fewer mitochondria and myoglobin (pale colour)
how do type 2 muscle fibres contract?
fast powerful contractions but can’t be sustained for long
subdivided into three subtypes
what are the three types that the type 2 muscle fibre is divided into?
2a oxidative, fatigue resistant
2b glycolytic
2x/c intermediate between these
what do you need to differentiate the subtypes of type 2 muscle fibres?
need special stains e.g. ATPase, NADH, SDH, COX - the differentiation is not visible on routin H&E
in what sections is striation best observed in?
in longitudinal sections
what is striation formed by?
formed by regular arrangement of structural proteins as well as actin and myosin filaments into sarcomeres (contractile unit)
where does a sarcomere span?
spans Z-line to Z-line
what are the proteins in sarcomeres? - they can be three types:
structural
contractile
regulatory
what is the Z-line/disc?
site of attachment of actin
α-actinin, desmin, vimentin
what is the M-line?
site of attachment of myosin
- myomesin
what is the H-band?
only myosin is present (pale with darker M line in middle)
what is the I band?
only actin present (pale region surrounding dark Z-line)
what is the A-band?
overlapping actin and myosin (dark region spanning central Z-line
smooth muscle, type of contraction?
involuntary
what are the functions of smooth muscle?
peristalsis, regulate blood flow, urination respiration
where are smooth muscles found?
GI tract, urogenital tract, respiratory tract, vessels etc.
myocytes?
cells of smooth muscle
not fibres
they are fusiform shaped or ‘spindle shaped’
describe the shape of smooth muscle?
no striation
cigar-shaped
nuclei are centrally located
describe the contractions of the smooth muscle?
contractions have more elasticity than skeletal muscle, but are slower and sustained for long periods with minimal energy requirements
meaning of unitarian?
gap junctions
multiunit?
no gap junctions - so contraction does not spread from one cell to the next
how can we tell dense connective tissue apart from smooth muscle?
shape: much thinner in connective tissue fibrocytes, should be ‘cigar’ in smooth muscle
position: centre of cell in smooth muscle, between collagen fibres in connective tissue
functions of bone?
shape and support, protection, storage (minerals), development and storage of blood cells
describe bones:
dynamic
high tensile strength
relatively lightweight
hardness (matrix - hydroxyapatites) strength (collagen)
what does periosteum do?
lines the outer surface of all bones, two layers
what are the two layers of periosteum?
outer fibrous
inner osteogenic (more cellular)
function of periosteum?
important role in bone modelling, fracture repair
what is the osteoid?
extracellular matrix: 25% water, 25% protein, 50% mineral salts
organic components (glycosaminoglycans, collagen-I fibrils)
inorganic components (hydroxyapatite [combination of Ca, Phosphate]
if the osteoid is mineralised, why is it eosinophilic?
must be decalcified with acid to soften enough for histology
osteogenic cell?
stem cell –> osteoblasts
osteogenic layer of periosteum
osteoblast?
produces osteoid (bone matrix)
line up along osteoid
flat (inactive), ‘teardrop’ (active)
CANNOT divide
osteocyte?
osteoblast surrounded by osteoid
maintains osteoid matrix
stellate processes (communication)
CANNOT divide
osteoclast?
from haemotopoietic cells
(NOT osteogenic cells!)
monocyte lineage: recycles osteoid
multinucleated, eosinophilic (acidic digestive enzymes)
CANNOT divide
Have Howship’s lacunae; digesting osteoid will have a ‘ruffled border’ against the bone
what are the two type of bone cells?
woven (immature) and lamellar (mature)
what are the two sub-types of lamellar bone cells?
compact
spongy (cancellous trabecular)
describe the woven bone cells?
rapidly (fetal growth, repair), increasing osteocytes, haphazard interlacing collagen
describe lamellar bone cell?
decreasing osteocytes, organised collagen fibres
describe the compact lamella bone cell?
dense deposits of matrix with few spaces between matrix elements (e.g. outer shells of the diaphysis and epiphysis)
describe the spongy lamellar bone cell?
aka cancellous trabecular
delicate 3D latticeworks deposits of matrix e.g. interior of the epiphysis, endosteal surface of diaphysis
describe compact bone?
very strong, flexion-resistant bone found along the outer surface, especially diaphysis
what is the structural unit of the compact?
it is the osteon: this converts mechanical force into biochemical stimuli
central (Haversian) canal of compact bone?
runs longitudinally, space for nerve and blood vessels
lamellae of compact bone?
concentric layers around the central canal
lacunae of compact bone?
spaces between lamellae occupied by osteocytes
canaliculi of compact bone?
small channels containing osteocyte stellate processes, radiate from lacunae
cement line of compact bone?
the outer limit of the osteon
the perforating (Volkman) canal of the compact bone?
transverse connecting between adjacent central canals
function of metaphysis and epiphysis of trabecular bone:
transmit forces form joint surfaces to compact bone
is a reservoir for calcium and other minerals
what is trabecular bone lined by?
by endosteum (similar to periosteum)
structure of trabecular bone?
similar structure to compact bone but w/o central canals and is surrounded by marrow
describe woven bone?
haphazard collagen arrangement
more osteocytes than lamellar bone
weak (collagen is not arranged to oppose loading) but faster to form
In adults, indicate some abnormality
describe lamellar bone?
regular arrangement of collagen fibres according to stress from bone loading
fewer osteocytes than woven bone
very strong but slowly remodelled from woven bone
type of cartilage?
hyaline, elastic, fibrous
what lines cartilage - and where doesn’t this line?
perichondrium lines it except at articular surfaces
what are the two layers of perichondrium?
outer fibrous layer
inner chondrogenic layer
