3 - Tissue Mechanics and Injury Flashcards
What is the definition of a tissue?
It is an aggregate of cells that have a similar structure and function
What are the 4 types of tissues?
Connective Tissue
Epithelial Tissue
Muscle Tissue
Nervous Tissue
What is another name for connective tissue?
Inert Tissue
True or false: all joints in the body are made up of connective tissue?
True
What are some examples of connective tissue?
Bones, Bursae, Capsules, Cartilage, Discs, Meniscus, Ligaments, Tendons
What is the extracellular matrix (ECM)?
It attracts and binds water, supporting substances for fibrous and cellular components
Contributes to the overall strength of the connective tissue
What are the different components of the ECM?
Fibrous component (collagen and elastin)
Collagen Type 1
Collagen Type 2
What is collagen?
a white fibrous tissue with steel-like strength. It is very rigid
What is elastin?
It is a yellow fibrous tissue with elastic properties
What is collagen type 1?
Thick fibers with little elongation
They resist tensile forces quite well
What is collagen type 2?
thinner less stiff fibers, they resist compression and shear forces
What makes up the cellular component of tissues?
Resident cells and circulating cells
What are resident cells?
Depends on what type of tissue they are in but they are cells that are always present
Examples: Fibroblasts (collagen) Osteoblasts (bone) and Chondroblasts (cartilage)
What are circulating cells?
They appear when a tissue is inflamed or damaged
What are some examples of circulating cells?
Lymphocytes
Macrophages
What is the ECM to Cell component ratio in ligaments?
Cells make up 10-20%
ECM makes up 80-90%
What is the make up of a ligament? Like what type of fibers is it composed of?
Primarily Type 1 Collagen fibers
They are densely packed
Arranged in the line with the applied tensile force (may have varying directions of the ligament depending on the direction of the force ex. MCL)
What is the ECM to Cell component ratio in tendons?
Similar to ligaments, 10-20% cells and 80-90% ECM
What is the make up of a tendon? Like what type of fibers is it composed of?
Has more type 1 collagen fibers than ligaments as it has to withstand stronger tensile forces
Its fibers are aligned in one direction
What is the fibrocartilaginous junction?
It is the gradual change in tendon structure which is divided into 4 zones.
It diffuses the load at the tissue-bone interface to help prevent injury
What are the four zones of the fibrocartilaginous junction?
Zone 1 - Tendon
Zone 2 - Uncalcified fibrocartilage
Zone 3 - Calcified fibrocartilage
Zone 4 - Bone
What is the musculotendinous junction?
It is where muscles intertwine with the tendon
It is very sensitive to mechanical conditions and becomes flatter with low load
What is hyaline cartilage?
It is composed of type 2 collagen and compresses the proteoglycan molecules that hold onto water during loading
It also lines articulating bones and distinguishes synovial joints
It is avascular and gets nutrients with compression
What are the three zones of articular cartilage?
Zone 1 - parallel fibers, smooth, reduced friction, distribute forces
Zone 2 - mesh like to hold water and helps absorb compression forces
Zone 3 - Perpendicular fibers to zone 1, it securely holds the calcified cartilage
What are the features of fibrocartilage?
Mostly type 1 collagen fibers. has a limited blood supply and relies on compression for nutrient diffusion.
What are the features of bones
Primarily type 1 collagen. Supplied by calcium
Has 2 layers: cancellous (spongy) and compact (cortical)
Has both osteoblasts (lay down new bone) and osteoclasts (break down bone)
What are the different types of loads you can place on a tissue?
Compression Tension Bending (tension and compression) Torsion Shear
True or false: only some connective tissues are viscoelastic?
False, ALL connective tissues are viscoelastic
What is creep?
A continuous change in shape with prolonged force application
What is stress relaxation?
a tissue is stretched to a fixed length and held constant; the force needed to maintain that length reduces over time
What is strain-rate sensitivity?
That more force is required to deform a tissue rapidly versus slowly
True or false: cortical bone withstands greater force with less deformation than cancellous bone?
True
True or false: the amount of strain required to reach failure is more in cortical bone than cancellous bone?
False it is less in cortical bone
What defines a stress fracture?
Frequent loading of low magnitude
What can lead to complete failure of bone?
A single load of high magnitude
What determines the amount of force that a tendon can resist and the amount of elongation it can undergo?
It’s cross sectional area, material and tendon length
What does continuous compression do to tendons?
It modifies the composition to more resemble cartilage. It creates a shift from type 1 collagen to type 2 reducing its tensile strength resistance
How do you increase thickness and strength of a ligament?
By loading it with intermittent tensile loads
What three things does cartilage have to do to resist load?
Stress developed in the fibrillar portion of the ECM
Swelling pressures developed in the interstitial fluid
Frictional drag resulting from fluid flow through the ECM
A contractile unit is also known as a ______?
Sarcomere
What starts the cross bridge cycle?
An action potential releases Ca2+ and that exposes the binding sites between actin and myosin
How is active tension developed?
By the active contractile elements of the muscle
What are the factors that affect if more cross bridges form or not?
Frequency of motor unit firing
Number of motor units firing
Size of motor units firing
Diameter of the axon
How is passive tension developed?
By the non-contractile components of the muscle
What are the parallel elastic components that help contribute to the tension
Epimysium
Perimysium
Endomysium
What are the series elastic components of passive tension?
Tendons (when the muscle is stretched the tendon is pulled as well)
True or false: there is a direct relationship between the tension development and the muscle length?
True
What does optimal length mean?
Means the muscle is capable of developing a maximal tension
