Tendon Structure Flashcards
What is vascularture of a tendon like?
No direct blood supply but not completely a vascular
How do tendons get their nutrients
Diffusion from synovial fluid
What are the three different blood supplies for tendons/
Osteotendious junction
Vessels surrounding connective tissue
Musculotendious junction
What is the innervature of the tendon like?
Branches from muscle belly and the skin
Branches are parallel to tendons axis
Nerves are localised in paratenon, epitenon, endotenon
What is the function of a tendon and the one exception
To connect bone to muscle
Transmit muscle force to bone
Help compress force
In lining of abdominal wall there is no muscle but tendons
How do tendons passively transfer force from muscle to bone?
Muscle mass is near proximal part of body, so mass of limb is lower
Neurovascular bundles are as short as possible to prevent damage
What type of connective tissue are tendons?
Dense connective tissue
What are the two different types of tendons
Positional
Elastic
What are the uses, examples and structure of positional tendons
Stiffer, less elastic so bones can be pulled back together and support the joint
Example is common digital tendon (helps extend carpus and digits)
What are the uses, examples and structure of elastic tendons
Used to absorb shock landings
Mostly in forelimb
Usually on flexor tendons like deep digital flexor tendon and superficial digital flexor tendon
What are the uses, examples and structure of elastic tendons
Used to absorb shock landings
Mostly in forelimb
Usually at flexor points like deep digital flexor tendon and superficial digital flexor tendon
What is the TIOM (suspensary ligament)
NOT A LIGAMENT BUT A VERY TENDIOUS MUSCLE!
Function is to support fetlock joints and prevent hyper extension
What is the weird bit sticking out behind dogs leg?
Common Calcaneon tendon
What is the manica flexoria
Links the DDFT and SDFT
SDFT forms a sheath to allow DDFT to run through it
Where is the manica flexoria
From foot to a third of the way up the cannon
What is a bursae
Bag of synovial fluid
Detached from joint and attached under the tendon to stop it from rubbing on bone
What is the function of a tendon sheath?
Layer/ tunnel of synovial membrane around a tunnel
Secretes synovial fluid as lubricant
What is the mesotenon?
Two sides of bursae meet and so blood vessels can’t get in
Why do sheathed tendons have less chance of healing?
Only internal blood supply is available
Blood supply from mesotenon neurovascular bundle only
What is an adhesion?
band of scar tissue that joins two internal body surfaces that are not usually connected
What happens is a sheath is torn when healing a tendon
Healing is accelerated
More chances of adhesions
Impacts gliding function
Why don’t tendons tend to rupture as much as muscles?
Tensile strength of tendon much higher than that of a muscle
What may weaken a tendon?
Chronic injuries and stretching
What may happen to a tendon if heavy exercise
Mineralises
Why may Cushing syndrome lead to a rupture
High glucocorticoid levels inhibits collagen synthesis
What is the composition of tendons like?
65-80% collagen
2% elastin
1-5% proteoglycans
30% water
What type of collagen is in tendons?
Type 1
How is collagen synthesised
- A triple helical structure called pro collagen is made inside the fibroblasts
- Once outside the cell, pro collagen is trimmed to make an insoluble molecule
- Collagen fibres self assemble outside of cell into fibrils. PG place as bridge fibrils to strengthen them
- Bundles of fibrils assemble into a collagen fibre
What is the epitenon?
The outer covering of a tendon within its sheath. Most important structure in the tendon repair process. Connective tissue and defined tendon unit
What is the endotenon?
A loose acellular tissue carrying blood vessels that surrounds small bundles of collagen fibers throughout the tendon
What is the paratenon?
The loose connective tissue surrounding the entire tendon, which allows the tendon to slide. Supplies the majority of a tendon’s blood supply.
What is the function of Tenocytes?
Sense mechanical loads transmitted by tendons or ligament through their contact with fibres
Can respond by altering composition of the extra cellular matrix
What are the two types of tendon insertion
- Indirect (fibrous)- simple
- Direct (fibrocartilagneous)- complicated
How does indirect insertion work?
Attached to periosteum (membrane around bone)
Bone at insertion point is immature and constantly remodelling
Collagen fibres of tendon/ ligament connect with fibres in bone
Low angle of insertion
How does direct insertion work?
Gradation from tendon to fibrocartilage to mineralized fibrocartilage to bone
Collagen fibres carry on into bone at high angle and don’t stop at periosteum
What are tenocytes and their functiom
Fibrocytes inside the tendons
Responsible for the crimp of secondary bundles
In contact with each other and pull on collagen fibres
What is crimp and why is it Important?
Allows collagen fibres to stretch during compression
Crimped when relaxed
Not crimped when load added
Seen in secondary bundles
What gives tendons the following properties?
- ability to stretch
- elasticity
-shock absorbance
- water content and proteoglycans
- springy helical collagen molecules
- crimp
What is the importance of cross linking fibres by GAGs
Aligns and lacks the fibres correctly
Allows collagen fibres to slide under each other under load
What is a proteoglycans
Several GAGs joined to a core protein
Core proteins are then joined to a hyaluronan spine to create a large complex
What is the importance of proteoglycans
Can bind with collagen to create a mesh work
Can bind to water to create gel like properties
What is the function of large proteoglycans?
Large swelling potential
Resists compression
Binds Cations and water
What is the function of small PG
Tensile strength
Binds growth factors
What is cartilage oligometric matrix protein (COMP)
Glycoprotein found in tendons and ligaments
Resists load
Helps form fibrils
Organises collagen network
At what % strain does the SDFT rupture
12-21%
What changes stiffness/ elasticity of tendon?
Crimp angle of fibrils
Fibril diameter
Composition of extracellular matrix
What is TIMP
Enzyme that breaks down collagen cross links
How does a tendon transfer energy?
temporarily storing elastic energy, then releasing this energy to do work on the muscle
What is exercise induced hyperthermia of a tendon
Elastic energy transferred to heat energy
Causes cell death of fibroblasts
What affects elasticity and ultimate tensile force
• Molecular composition and arrangement of tendons.
• Age.
• Exercise (short-term and long-term).
• Loading (speed of exercise, height of jump).
• Training intervals (time for repair and adaptation)
When do tendons mature
2 years of age
How does exercise affect tendons
Short term —>affects collagen arrangement and water distribution
Long term—> affects COMP, GAG levels, affects cross sectional area
