Structure and Function of Joints Flashcards
What are 2 functions of joints?
What are the three main classes of joint?
- Transmit loads so that it isnt painful.
- Allow smooth movement, yet provide stability
Fibrous joint (synarthrosis).
Immobile joints e.g. skull sutures, tooth socket
Cartilaginous joint (amphiarthrosis).
Slightly mobile e.g. intervertebral disc
Synovial joint (diarthrosis).
Freely mobile, allow for lots of free movement e. g. limb joints
What is the annulus fibrosus and what can happen if it prolapses?
In between vertebral bodies, you’ve got annulus fibrosus in the spine
If that prolapses backwards and impinges on the spinal cord, can cause cauda equina = lose sensation in their lower limb, lose control e.g. Of passing urine or opening their bowels.
What are planar and simple hinge joints and what type of movement do they allow?
What are the different types of joint structures?
Synovial joints allow pivot/rotational movement
Give an example of a rotational joint and the specific movement it enables
What can cause issues with the joint here?
Rotation of ? allows ? of the hand?
The first cervical vertebra (atlas) allows the head to turn, and is supported by Odontoid peg (2nd cervical vertebra). Injury here = complete transection.
RA can cause problems at this atlanto-axial junction.
Rotation of proximal radial-ulnar joint allows pronation/supination of hand
What are the types of movement allowed by synovial joints?
saddle vs complex hinge vs ball & socket
Describe the 5 ways to achieve joint stability
? (matching the shapes of bone ends)
? & its ? into ? e. g. ? ligaments of knee.
? ligaments e.g. ? of knee
? to improve congruity, by: (3 things)
Congruity (matching the shapes of bone ends)
Fibrous capsule & its thickenings into extra-articular ligaments e. g. medial and collateral ligaments of knee.
Intra-articular ligaments e.g. cruciate ligaments of knee
Packing to improve congruity, by:
- menisci (semilunar cartilages, knee)
- fat pads (e.g. infrapatellar fat pad of knee)
- Muscles acting across the joint, esp for shoulder stability; shoulder easily dislocated due to poor congruity & slack capsule.
Label this to show the intra-articular structures of the knee
Draw and describe the key features of a synovial joint. Use the femur and tibia as an example.
What happens if there is constant stimulation of the strecth receptors?
Stimulation of stretch receptors by arthritic effusions (swellings)
causes reflex muscle inhibition e.g. of quadriceps —> muscle wasting
Describe features of cartiliage, synovial lining
Cartilage is avsacular and aneural - allows ease of movement without initiating pain.
The synovial lining lines everything around this articulating joint except the cartilage. Also allows ease of movement
What is GAG, give examples
What do the chains form & therefore maintain?
What is GAG produced by
Glycosamino-glycan chain (GAG)
e.g. chondroitin sulphate keratan sulphate, hyaluronan
These chains form a large, negatively charged polymeric structure with a core protein - draws water inside it, maintaining tension & good compressibility
GAG is produced by chrondrocytes (only cell within cartilage)
Label this to show how the sturcture of cartliage is adapted to its function
Apart from lubrication, what is the second function of the synovial fluid?
Synovial lining creates lubrication + ?
? structure - allows certain ? to come through to ? + Allows ? to come into ?
Synovial lining creates lubrication + lymphatic drainage out of a joint
Loosely based structure - allows certain proteins & molecules to come through to provide nutrients into joint + Allows waste products to come into lymphatic drainage
Label the synovial lining structure
Draw and describe the Interface between synovium and joint cavity
various cell types mediate tissue viability within the synovium. What are these cells? + what do these cells do
They create an ? which is in ?.
So, it does not provide ? but allows ?
- macrophages
- synoviocytes
- fibroblasts
They create an interstitial matrix which is in open contact with the synovial fluid. So, it does not provide a continuous cellular barrier but allows it to have a fluid drainage pathway out of the joint itself
define synovial fluid & key features of synovial fluid?
Synovial fluid = an ? of ? generated by ? just below synovial surface.
? are actively secreted by the ?
? - lubricates ? under ?
?=giant ?, Mw 6 ?, hydrated ?. This makes synovial fluid v ?, enabling ?
It creates a high viscosity as it occupies a huge water domain – it’s 2-6mDa in size
Synovial fluid = an ultrafiltrate of plasma generated by fenestrated capillaries just below synovial surface.
Lubricin & hyaluronan are actively secreted by the synoviocytes,
Lubricin - lubricates cartilage under high load & low velocity (boundary lubrication).
Hyaluronan=giant nonsulphated GAG, Mw 6 million, hydrated radius 100-200 nm. This makes synovial fluid v viscous, enabling hydrodynamic lubrication - low load & high velocity - like oil in a car engine.
It creates a high viscosity as it occupies a huge water domain – it’s 2-6mDa in size
As mentioned, synoviocytes activley secrete hyaluronan for boundary lubrication. Describe the structre of hyaluronan
- 2-6 million Da
- single unbranched chain into expanded, random coil
- highly hydrated + viscous
- hydrodynamic lubricant, equivalent of engine oil - high velocity & low load
Describe the pressure and volume of synovial fluid- what can happen to this when things go wrong?
Fluid vol is tiny -fluid film normally 10-100ml thick
Pa varies w joint angle:
subatmospheric in extension
above atmospheric on flexion.
So fluid enters joint in extension and is driven out of it on flexion
Volume increases 10-100x in arthritis - called a joint effusion
In arthritic joint effusion, pa>atmospheric even in extension and pa-angle relation is extremely steep. a min pa at a certain angle determines the the affected joint’s ‘angle of ease’
What does this graph show?
As ? increases - ? increases
Fluid enters joint during ? and leaves the joint during ?. So ? raises intra-articular fluid pressure
But if the fluid keeps building, then the ? and this ? is altered in an ? or ?
As vol increases - pressure increases
Fluid enters joint during extension and leaves the joint during flexion. So flexion raises intra-articular fluid pressure
But if the fluid keeps building, then the angle of ease increases and this pressure angle curve is altered in an arthritic effusion or haemarthrosis (e.g. in haemophilia-blood stained fluid in knee creating a haemarthrosis)
How does synovial fluid form?
What contributes to the synovial fluid?
what provides lubrication?
What happens during flexion?
Forms when synovial fluid pa is low in extension
Capillary bp & plasma colloid pressure contributes to synovial fluid
Hyaluronan made by hyaluronan synthase provides viscous lubrication!
As flexion occurs, the fluid inside a joint increases, so fluid + other waste produces is driven out of joint –> synovium and the lymphatic drainage
Apart from being a lubricant, what is another function of Hyaluronan?
Hyaluronan buffers ? by ?
The ? of hyaluronan is a ?. This helps ? during ?
Hyaluronan buffers fluid loss from joints by reducing fluid drainage rate
The concentration polarisation (filtercake) of hyaluronan is a v large polymeric structure. This helps retain fluid & lubricant during fluid drainage
What are the types of arthiritis?
What is the difference between OA and RA?
what happens to cartilage in an arthritic joint?
Arthroscopy shows that normal cartilage has pearly white appearance.
In arthritis, cartilage becomes fibrillated - comes off the articular surface. If this carries on uncontrolled, you can potentially go down to bone
2 major categories of arthritis include OA and inflammatory arthritis. Describe OA
Osteoarthritis: primarily a ? of ?
Associated w ?, ?, ?
‘?’ and ? (?, sometimes to bone)
It is due to ? and ? loss
Inflammation of ?
Osteoarthritis: primarily a mechanical breakdown of articular cartilage
Associated w ageing, mechanical dysfunction, obesity
‘Fibrillation’ and denudation (erosion, sometimes to bone)
It is due to collagen fibril rupture and aggrecan loss
Inflammation of synovium (synovitis)
2 major categories of arthritis include OA and inflammatory arthritis. Describe inflammatory arthritis
In ?, an ? mechanism triggers ? via mediator release: ?
As inflammation continues, the ?
? can ? the surrounding ?= “?.”
The ? releases ?, which break down proteins, inc ?–> lead to ?.
In RA, an autoimmune mechanism triggers synovial inflammation via mediator release: PGE2, bradykinin, histamine, NO, cytokines
As inflammation continues, the synovium becomes hypertrophic
hypertrophic synovium can invade the surrounding cartilage= “pannus.”
The pannus releases metalloproteinases, which break down proteins, inc collagen–> lead to secondary cartilage erosion.
What happens in an arthritic swelling/joint effusion?
In an arthritic swelling, ? stay in the joint for ?
If arterioles around joint are ?, the ? increases. This→ ? bc of ?
? conc drops + that’s why its difficult to ? once it has reached a certain level
Thus we ? to help ?
In an arthritic swelling, inflammatory mediators stay in the joint for longer
If arterioles around joint are vasodilated, the capillary Pa increases. This→ hot joint bc of inc. blood flow
Hyaluronic acid conc drops + that’s why its difficult to clear this fluid out of the body once it has reached a certain level
Thus we remove patient’s accumulated synovial fluid to help lymphatic drainage to continue over time
