Tissues of the musculoskeletal system Flashcards
What is the most abundant protein in the body?
Collagen
What characterizes the features of connective tissue generally?
Relative abundance of extracellular matrix as compared with cellular mass
What is the tertiary structure of collagen?
Triple helix made up of three separate polypeptide molecules called alpha chains
What are the primary components of the extracellular matrix?
Collagen, proteoglycans, elastin
What is the basic structure of proteoglycans?
Core protein with one or more covalently attached glycosaminoglycan side chains
What are the two major families of proteoglycans?
Large aggregating and small leucine rich
What is the composition of elastic fibers?
Composed mainly of elastin. The monomeric component of elastin is tropoelastin
How much elastic deformation can elastic fibers undergo?
70% of the resting length (maximum extension of 220% before loss of resting length)
What other components of the extracellular matrix are essential for elastin formation?
Presence of fibrillin microfibrils and fibronectin
What cells comprise the basic multicellular unit of bone?
Osteoblasts, osteoclasts, osteocytes
Where does most bone remodelling occur?
On cortical or trabecular surfaces
What are the two predominant forms of bone in the adult?
Cancellous and cortical
Where do osteoblasts, osteoclasts and osteocytes reside?
Osteoblasts: periosteal and endosteal membranes.
Osteocytes: are terminally differentiated osteoblasts encased in bone
Osteoclasts: exist on the bone surface
What is the water, mineral and organic matter content of bone?
Low water content (5-10%), high mineral content (70%), remainder is inorganic matter
What accounts for the majority of the organic matrix in bone?
Collagen (90%). Predominantly type 1
What is the primary mineral component of bone?
Calcium hydroxylapatite
What components of bone provide stiffness and strength to resist compressive and tensile stresses?
Compressive stresses: mineral component.
Tensile stresses: organic component (hence why bone is week in tension)
What are the two types of bone formation?
Lamellar bone and woven bone
What is the water content of articular cartilage?
70%
On a dry weight basis what is the composition of articular cartilage?
50% collagen, 35% proteoglycans, 10% other glycoproteins. Chrondrocytes make up 5-10% of articular cartilage by volume
What is the predominant type of collagen in articular and fibrocartilage?
Articular: type 1
Fibrocartilage: type 2
What are the layers of articular cartilage?
Unmineralized zones:
Zone 1: Superficial zone: chondrocytes are small and axes are parallel to joint surface. Collagen is fibrils are densely packed and also parallel.
Zone 2: Transitional zone: chondrocytes are larger and rounded. Collagen fibrils form a mesh like structure.
Zone 3: Radiate zone: chondrocytes and collagen fibrils are larger and orientated perpendicular to the joint surface.
Tide mark: separates the unmineralized and mineralized zones.
Zone 4: Calcified cartilage/mineralized zone
Are proteoglycans more or less abundant with depth in the articular cartilage?
More abundant deeper, and provide resistance to compressive stresses. Tensile stresses are predominantly mitigated by collagen fibrils.
Does fibrocartilage contain a high or low quantity of proteoglycans?
Relatively low quantity. Characterized by chrondrocytic cells suspended in a dense ECM
What are the three different types of tendon in the body?
Aponeuroses, positional tendons (stiff) and energy storing (most elastic)
What is the composition of ligaments or tendons?
Tenocytes or ligamentocytes are elongated fibroblastic cells that are aligned with collagen fibers. ECM predominantly composed of type 1 collaged. Numerous proteoglycans.
What are the biomechanical characteristics of tendons/ligaments?
Anistrophic, viscoelastic (creep recovery and stress relaxation)
What are the two types of entheses?
Fibrous (incorporated into periosteum) or fibrocartilaginous (bony attachment via a fibrocartilaginous precursor)
What is the major cellular component of muscle?
Intracellular myofibrillar proteins (ECM makes up a small proportion)
What are the basic functional units of muscle?
Myofiber is made up of myofibrils that are composed of sarcomeres (overlapping regions of actin and myosin that longitudinally slide in response to stimulation from a motor axon - release of calcium from sarcoplasmic reticulum in response to ACh binding on sarcolemma).
The cell membrane of myofibers is the sarcolemma, with nuclei positioned immediately adjacent. The sarcoplasmic reticulum surrounds myofibrils within a myofiber.
Myofibers are then bundled into muscle fibers (surrounded by endomysium). Then fasicles (surrounded by perimysium). Then muscle bellies (surrounded by epimysium). These connective tissue structures compose the ECM of skeletal muscle.
What are the two basic types of muscle fibers?
Slow twitch (type 1): relies predominantly on oxidative metabolism.
Fast twitch (type 2): variable reliance on oxidative metabolism
What connective tissue structure is predoninantly responsible for transmission of muscle force?
Perimysium
