Synovial fluid The synovial fluid helps protect the joint from mechanical injury and contains hyaluronic acid and lubricin Danning, In a healthy joint, the synovial fluid is very viscous and clear, and is either colourless or a pale straw colour.
Water is able to enter the joint very easily during inflammation but, once it mixes with hyaluronic acid, it cannot leave as quickly Robson and Syndercombe Court, — as such, although it may only take a few hours for the joint to swell, it can take a few days for that swelling to subside. The synovial fluid may become infected by a haematogenous blood-borne spread of bacteria, extension of an adjacent infection or direct inoculation following trauma or an invasive procedure.
This is known as septic arthritis and can damage the synovium or cartilage. Rheumatoid arthritis This is an autoimmune inflammatory arthropathy that affects the synovium. It occurs more often in smokers and is three times more common in women than men Ralston and McInnes, Clinical onset is characterised by the abnormal production of cytokines and inflammatory mediators such as interleukin 1, interleukin 6, interleukin 15 and tumour necrosis factor Ralston and McInnes, This causes the synovium to become inflamed and hypertrophied so the synovial villi become thickened and fuse together to form a pannus.
The pannus invades the surrounding tissue such as the cartilage, ligaments and joint capsule , which this can lead to progressive destruction of the joint Danning, Rheumatoid arthritis can also affect periarticular structures, including tendon sheaths and bursas, as well as having extra-articular manifestations.
Osteoarthritis The articulating surfaces in synovial joints are coated with approximately mm of hyaline cartilage, which provides a smooth surface and reduces friction during movement. This helps distribute the weight across the joint, reducing friction and damage to the bone surface Robson and Syndercombe Court, Osteoarthritis is a degenerative condition involving focal loss of the articular cartilage, so the cartilage becomes less efficient at protecting the ends of the bone Ralston and McInnes, Over time, this can cause bony surfaces to rub together on movement, causing pain and audible crepitus.
As the bone attempts to compensate for the loss of articular cartilage, it produces new bone to try and stabilise the joint.
This results in bone thickening under the remaining cartilage sclerosis and formation of osteophytes at the joint margins, which can reduce the range of movement of the joint. Supporting ligaments Synovial joints are designed to permit movement while, at the same time, maintaining balance, strength and stability. They vary in structure and the type of movement they permit — Table 2 summarises the different types. The stability of the joint depends on its shape, the number and position of supporting ligaments around it, their strength and the tension they exert Tortora and Derrickson, Supporting ligaments are described according to their position in relation to the capsule extracapsular or intracapsular.
Excessive tension on ligaments, such as moving the joint beyond its functional range of movement, can cause them to stretch and may mean they sprain or tear. Ligament damage can compromise joint stability and function. Prolonged disuse of the joint, for example due to immobilisation in a cast or through bed rest, often gives reduced flexibility of the ligaments and tendons, as well as muscular atrophy Tortora and Derrickson, This may lead to reduced mobility of joints and difficulties with functional activity.
Unlike skeletal muscle, smooth and cardiac muscles are not under voluntary control Soames and Palastanga, Skeletal muscle is innervated by the somatic motor nerves to simulate voluntary movement, whereas cardiac and smooth muscles are innervated by the autonomic nervous system.
Skeletal muscle The anatomy of skeletal muscle is shown in Fig 1. Skeletal muscle fibre cells are narrow, but can be long Danning, and each fibre has its own connective tissue covering called the endomysium Soames and Palastanga, The muscle fibres are in bundles known as fascicles, which are held together by a layer of connective tissue called the perimysium. These are grouped together to form muscles, bound by a sheath of fibrous connective tissue known as the epimysium.
The epimysium merges with the perimysium to form the muscle tendon, which attaches the muscle to the periosteum of the bone. The site where tendons and ligaments insert to the bone is known as the enthesis; this is the site commonly affected in seronegative spondyloarthro-pathies for example, ankylosing spondylitis, psoriatic arthritis and reactive arthritis. Seronegative arthropathies are a type of arthritis that do not have rheumatoid factor antibodies.
Bursas are fluid-filled sacs located at sites where there may be shearing forces, such as when muscles and tendons pass over, or around the edge of, bone — for example, in the shoulder subacromial bursa or the hip trochanteric bursa Robson and Syndercombe Court, Bursas allow structures to glide smoothly over each other, reducing friction during movement. Many muscles are named according to their various characteristics, such as: brevis short , longus long , maximus large and minimus small.
These help to limit joint dislocation and restrict improper hyperextension and hyperflexion. Also made of fibrous tissue are bursae. Musculoskeletal system : Image depicting the human muscular system skeletal muscle. Learning Objectives Explain the purpose of the musculoskeletal system.
The skeleton serves as the main storage system for calcium and phosphorus. The skeleton also contains critical components of the hematopoietic blood production system and fat storage. These functions occur in red marrow and yellow marrow, respectively.
To allow motion, different bones are connected by articulating joints. Cartilage prevents the bone ends from rubbing directly on to each other while the muscles contract to move the bones associated with the joint. Key Terms red marrow : Red marrow or medulla ossium rubra, consists mainly of hematopoietic tissue, and gives rise to red blood cells RBCs , platelets and most white blood cells WBCs. All cellular blood components are derived from HSCs.
Skeletal System A human skeleton : Image as overview of the human skeletal system. Muscular System Muscles contract shorten to move the bone attached at the joint. Three types of muscle tissue exist in the body. These are skeletal, smooth, and cardiac muscle. Humans have three different kinds of muscle: Skeletal muscle is attached by cord-like tendons to bone, such as in the legs, arms, and face.
Skeletal muscles are called striated pronounced: STRY-ay-ted because they are made up of fibers that have horizontal stripes when viewed under a microscope. These muscles help hold the skeleton together, give the body shape, and help it with everyday movements known as voluntary muscles because you can control their movement.
They can contract shorten or tighten quickly and powerfully, but they tire easily. Smooth, or involuntary, muscle is also made of fibers, but this type of muscle looks smooth, not striated.
We can't consciously control our smooth muscles; rather, they're controlled by the nervous system automatically which is why they're also called involuntary. Examples of smooth muscles are the walls of the stomach and intestines, which help break up food and move it through the digestive system. Smooth muscle is also found in the walls of blood vessels, where it squeezes the stream of blood flowing through the vessels to help maintain blood pressure.
Smooth muscles take longer to contract than skeletal muscles do, but they can stay contracted for a long time because they don't tire easily. Cardiac muscle is found in the heart. The walls of the heart's chambers are composed almost entirely of muscle fibers. Cardiac muscle is also an involuntary type of muscle. Its rhythmic, powerful contractions force blood out of the heart as it beats. How Do Muscles Work? Joints are classified by their range of movement: Immovable, or fibrous, joints don't move.
The dome of the skull, for example, is made of bony plates, which move slightly during birth and then fuse together as the skull finishes growing. Between the edges of these plates are links, or joints, of fibrous tissue. Fibrous joints also hold the teeth in the jawbone. Partially movable, or cartilaginous pronounced: kar-tuh-LAH-juh-nus , joints move a little. They are linked by cartilage, as in the spine. Each of the vertebrae in the spine moves in relation to the one above and below it, and together these movements give the spine its flexibility.
Freely movable, or synovial pronounced: sih-NO-vee-ul , joints move in many directions. The main joints of the body — such as those found at the hip, shoulders, elbows, knees, wrists, and ankles — are freely movable. They are filled with synovial fluid, which acts as a lubricant to help the joints move easily.
Three kinds of freely movable joints play a big part in voluntary movement: Hinge joints allow movement in one direction, as seen in the knees and elbows. Pivot joints allow a rotating or twisting motion, like that of the head moving from side to side. Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone.
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