Musculoskeletal System Purpose
- Provides protection to internal organs and important structures e.g. ribcage for heart and lungs, vertebral column for spinal cord
- Works with the nervous system to induce voluntary movement
-Provides structural support to the body - Site of homeostasis and haemotopoeisis
Bone
Bone is a type of connective tissue that is distinguished by the mineralisation of the bone matrix. There are 206 bones in the adult human body, made up of short, long, flat and irregular bones.
Muscle
Muscle is a type of contractile tissue which provides support to the body and enacts voluntary and autonomous movements.
Cartilage
Cartilage is a soft, flexible material typically located on the epiphysis of some bones. They act as a shock absorber and prevent friction from occurring between two bones, ensuring smooth movement.
Ligament
Ligaments connect bone to bone
Tendon
Anchor bone to muscle, and help determine the amount of force necessary to induce a contraction.
Components of Bone
- Calcium phosphate - in the form of hydroxyapatite crystals.
- Collagen fibres - provides protection and support
- Ground substance - for bone growth and maintenance
- Bone cells – helps with the building, breakdown and maintenance of bone.
Compact Bone
- Made up of densely packed haversian systems, which are concentric layers of bone matrix. In the middle of a haversian system is the central canal, containing blood vessels and nerves.
-It is the denser, strong tissue of bone and located just under the peritoneum. - Provides strength, structure and the ability to withstand compressive force.
Spongey Bone
- Less dense and made up of columns of bone known as trabeculae, interspersed with cavities.
- Within these cavities is red bone marrow which is the site of haematopoiesis (production of blood cells – thrombocytes, leukocytes and erythrocytes.)
- Characterised by its porous, honey-comb like structure.
- Usually found towards the centre of the bone
- Individuals typically have a combination of spongy bone and compact bone.
Peritoneum
Fibrous tissue that covers the entirety of the bone. For protection and support.
Red Bone Marrow
- site of haematopoiesis, or the production of blood cells. (erythrocytes, thrombocytes, leukocytes)
- children have red bone marrow in all bones. As we age, only some long bones contain it. e.g. legs, arms
- As we age, red bone marrow is replaced by yellow blood marrow which is predominantly made up of adipose tissue.
- Contains haemopoietic cells which divide to form red blood cells (erythrocytes) , white blood cells (leukocytes), platelets (thrombocytes)
Classification of Bone
Long Bone – Bones that are longer than they are wide e.g. femur
Short Bone - Smaller bones that are usually square-shaped or cuboid . e.g. metacarpals in wrist
Flat bones – bones that are usually curved e.g. bones in the skull
Irregular Bones – Bones that do not fit in the above categories e.g. ver
Axial Skeleton
Contains the bones that are necessary for protection and support of vital organs and structures e.g. rib cage for heart and lungs or vertebral column for spinal cord, cranium for brain
Appendicular Skeleton
Contains the bones that interact with the environment. e.g. bones in the legs and arms.
Osteoclast
A type of cell in the bone that releases digestive enzymes to break down the bone in the instance of damage, mechanical stress or hormone signalling.
Osteoprogenitor Cells
Reside in the bone tissue and are precursor to osteoblasts. They are formed from stem cells found in the red bone marrow.
Osteoblast
A type of cell that releases bone matrix and collagen fibres to rebuild bone removed by osteoclasts. Also calcifies the bone.
Osteocytes
A type of cell that maintains the integrity of the bone. After osteoblasts have been completely surrounded by bone matrix, they become osteocytes. They sit within small divots known as lacuna and extend processes throughout the bone to detect pressrue.
Bone Remodelling (ARRFQ)
- Activation: Mechanical stress, damage or hormone signalling enables osteoclasts to enter the area of bone to be removed.
- Resorption: Osteoclasts release digestive enzyme to break down bone matrix. They form a divot in the bone known as Howship’s lacuna.
- Reversal: Cells in the bloodstream signal osteoblasts to the area of bone formation
- Formation: Osteoblasts release collagen fibres and bone matrix to build up the bone.
- Quiescence: Osteoblasts become osteocytes once surrounded by bone.
Bone remodelling is the process of breaking down and reforming bone where damage has occurred, mechanical stress, hormone signalling and to maintain mineral homeostasis.
Hormones That Contribute to Calcium Homeostasis
- Parathyroid Hormone (PTH) – triggers osteoclasts to breakdown bone matrix to release calcium into the blood stream. (when low on calcium)
- Calcitonin – Inhibits osteoclast activity. (when high calcium levels in the blood)
-Testosterone/Oestrogen – For growth, inhibits osteoclasts activity and promotes osteoblasts to build bone. - Vitamin C - Enhances calcium absorption from the gut and promotes bone mineralisation
Joints
Joints define the area in which two bones meet. There are different kind of joints dependent on the bones involved and their roles.
Allow for structural support and sometimes movement.
Fibrous Joints
Bones that are joined by dense, fibrous connective tissue with no joint cavity. Very stiff to immovable
Cartilaginous Joints
Bones are joined by cartilage, with no joint cavity, allowing limited movement. e.g. intervertebral discs
Synovial Joints
Bones that are joined by a fluid-filled joint cavity, surrounded by a capsule and supported by ligaments. Allows for a wide range of movement. e.g. knee, elbow
