Histology Flashcards
describe 3 features of skeletal muscle cells
striated
unbranched (long tubes)
Multinucleate (forms a syncytium - several cells loose membranes between them to form one giant cell)
where do nuclei sit in skeletal muscle cells?
at the periphery, just under the membrane (sarcolemma)
how big are skeletal muscle?
1000 - 200,000 microns
usually entire length of muscle
how are muscle fibres grouped?
grouped into fascicles
a muscle contains several fascicles
what are the 3 types of connective tissue in a muscle?
each muscle cell surrounded by endomysium
each fascicle surrounded by perimysium
whole muscle body surrounded by epimysium
breakdown of muscle structure?
muscle > muscle fascicle > muscle fibre > myofibrils > sarcomeres > actin and myosin
what else is contained within a muscle?
blood vessels, nerves, lymphatics
myosin vs actin band?
myosin = A band (thicker/darker) actin = I band (lighter)
what causes striation in skeletal muscle?
optical illusion
regular arrangement of sarcomeres (myosin and actin bands) means dark and light bands line up (z lines in registry)
how can a whole muscle cell (very long) be supplied via one neuromuscular junction?
they are able to conduct action potential
how does a motor neuron supply a motor unit?
branches near its termination and each branch ends in a neuromuscular junction at a muscle cell
components of type 1 fibres?
lots of mitochondria and myoglobin as they are aerobic
“red fibres”
components of type 2x fibres?
few mitochondria and less myoglobin as they don’t need as much oxygen bc they are anaerobic
“white fibres”
characteristics of cartilage?
semi-rigid and deformable
permeable
avascular (nourished by diffusion through ECM)
characteristics of bone?
rigid
not permeable
nourished by blood vessels that pervade the tissue (highly vascular)
what are cartilage cells?
chondrocytes
chondroblasts when immature/producing
where are chondrocytes found?
lacuna
- maintain extra cellular matrix
what are the components of the extra cellular matrix (ECM)?
most common form of cartilage (hyaline)
75% water
25% organic material
what composes the organic material in ECM?
60% type 2 collagen
40% proteoglycan aggregates (made up of GAGs)
what are the 3 types of cartilage?
hyaline (most common)
elastic (flexibility)
fibrocartilage
what is fibrocartilage?
mix between type 1 and type 2 cartilage
bands of dense type 1 with small amounts of cartilaginous ECM
where is hyaline cartilage found?
articular surfaces tracheal rings costal cartilage epiphyseal growth plates precursor to bones in foetus
give 5 functions of bone?
support levers for movement protection of organs calcium store (95% of calcium) Haemopoiesis (blood cell production)
how does cauliflower ear arise?
damage to vasculature in ear due to repeated trauma which is replaced with scar tissue
how is bone involved in blood cell production?
in utero blood production begins in bone marrow before birth and by time of birth, bone marrow (red) is the site of haemopoiesis
By early twenties - only the axial skeleton and limb girdle is involved in blood production
what makes up bone?
65% bioapatitie (calcium phosphate)
23% collagen
10% water
2% non-collagen protein
cancellous/trabecular bone vs cortical bone?
cancellous = at epiphyses of bone, fine meshwork cortical = outer dense shell, makes up diaphysis (shaft)
how does bone remodel?
throughout life at different rates throughout body (except from cochlear area)
what makes up bone?
round groupings of lamellar bone called osteons
canal in the middle (heversion canal) containing blood vessel
larger spaces between the osteons in trabecular bone
what is a volkmans canal?
horizontally running canals with blood vessels supplying heversion canals
what are osteons?
groups of lamellar bodies
usually product of later bone remodelling
forms layers in bone
how are cortical and cancellous bone different?
similar bone cells
main difference is presence of spaces (marrow cavities)
what gives osteons their strength?
background of collagen running in different directions
what are cannuliculi?
little cell processes (like dendrites) that cross the osteon and allow communication with other cells and connection to blood vessels in heversion canal
keeps the cells alive within a solid matrix
what is a cement line?
marks boundary of osteon
are heversion canals found in trabecular bone? why?
no
cells are close enough to vessels etc as the struts of bone are thin and close enough to the marrow spaces that they don’t need a separate blood supply
name 4 cells of bone
osteoprogenitor cells
osteoblasts
osteocytes
osteoclasts
which cells lay down new bone?
osteoblasts
which cells are living within the matrix in bone?
osteocytes
what are osteoprogenitor cells?
serve as a pool of reserve osteoblasts on bone surfaces (e.g under periosteum)
what are osteoclasts?
large multinucleated cells found on bone surface which reabsorb bone
describe the cutting cone remodelling mechanism
osteoclasts group together and drill down into bone forming a large tunnel
blood vessel grows into the tunnel, bringing with it osteoblasts which line the tunnel and lay down new lamellar bone
heversion canal is formed
how do osteoblasts form new bone?
they secrete Osteoid (collection of organic compounds of bone matrix - collagen, GAGs, proteoglycans etc)
Osteoid is mineralized over time in extracellular space
what is the main component of bone mineral?
calcium phosphate
where is bone built from?
can only grow at the surface
bone is added to at the surface
what is woven bone?
initial layed down bone either during development or fracture healing
chaotic organisation of collagen fibres - no lamellar structure
later destroyed by osteoclasts and replaced by lamellar bone
type 1 vs type 2 collagen?
type 1 = most common, found in most connective tissues (e.g - tendon)
type 2 = finer, forms a 3D meshwork instead of aggregating into linear bundles like type 1
where are osteoclasts derived from?
macrophage lineage
can fuse to form a giant cell
