Lecture 1 Bones Flashcards
What is the embryonic origin of bones, connective tissue and skeletal muscle?
The mesdoderm of the trilaminar disc
What are 6 functions of bone?
Support: skeleton provieds framework for maintaining posture.
Protection: ribs protect lungs + heart, skull protects brain, vertebrae protects spinal chord, bony pelvis protects pelvic structures
Metabolic: homeostasis of calcium and phosphate. Storage and release of these is under endocrine control
Storage: Reservoir for calcium + phosphate. Bone also contains large amountsof protein (collagen) and bone marrow is rich in fat. It is a site of storage for some growth factors and cytokines.
Movement: Occurs at joints. Bones act as an attachment site for muscles and tendons which use bones as levers. Shape of articulating surfaces determines the range of movement.
Haematopoiesis: (generation of RBC’s) in the cavities of bones
Where are the sites of haematopoiesis in adults and children?
Children: long bones (femur/tibia)
Adult: pelvis, skull, vertebrae, sternum.
What type of muscle is a skeletal muscle?
Straited muslce. Under voluntary control.
What are the functions of skeletal muscle?
- locomotion (contraction of muscles across a joint leading to movement)
- posture (postural muscles maintain equilibrium, allowing us to stand upright)
- metabolic (fast + slow twitch fibres, glycogen metabolism)
- venous return (muscles in leg compress deep veins propelling blood back to heart)
- heat production (shivering- generation of heat)
- continence (muscles of pelvic floor are responsible for maintenance of urinary/faecal continence)
What types of connective tissue are there in the MSK?
Tendons, ligaments, fascia, cartilage (hyaline/fibrocartilage), synovial membrane.
what are tendons, ligaments and fascia?
Tendon: connects muscle to bone (force-transmission from contracting muscle to bone to which they’re attached)
Ligament: bone to bone (prevent excessive amount of movement and support joints)
Fascia: sheets of connective tissue (create compartments, some sheets are very tough so protect underlying structures)
What types of cartilage are present in MSK?
Hyaline (articular)
- found on ends of bones
- smooth, creates frictionless motion at joint
- this combined with the synovial fluid, creates extremely low friciton
Fibrocartilage:
- higher collagen content
- shock absorption
- increasing bony congruity
What is bony congruity?
Creating a complementary shape of bony surfaces to improve stability
What is the synovial membrane?
Produces synovial fluid which lubricates the joints.
Found within joints, bursae and tendon sheaths.
What is a bursa?
Small sac lined by synovial membrane containing synovial fluid.
- provides cushion between, bones/tendons/muscle at a joint
- reduces friction
What are tendon sheaths?
Elongated bursae that wrap around tendon reducing friction associated with movement of tendon.
What are the cellular compartments of bone?
- osteocytes
- osteoblasts
- osteoclasts
- fibroblasts
- macrophages
- mast cells
- adipocytes
How does bone differ from other connective tissue?
It contains calcium phosphate. CaPO4 (hydroxyapatite), which mineralises the extracellular matrix,and offers rigidity.
What is the major fibre type in bone?
Collagen. Not significant amounts of elastin.
What does the ground substance consist of in bone?
Water, GAG’s, proteoglycans
What gives bone its mechanical properties?
Collagen: tensile strength
Calcium phosphate: compressive strength
What is the function of osteoblasts?
Synthesise new bone, deposit osteoid.
They then deposit calcium phosphate into osteoid to make bone.
What does osteoid contain?
Collagen, osteocalcin, osteopontin
What do osteoclasts do?
Secrete acidic chemicals to dissolve the osteoid, forming a pit on the surface of bone.
The minerals in ionic form are absorbed into the osteoclast which releases them into extracellular fluid from where they enter the blood. (resorption)
What type of cell are osteoclasts and how do they form?
Multinucleate cells.
Formed by the fusion of progenitor cells of macrophage lineage.
What occurs when an osteoclast becomes active?
The surface they are in contact with ruffles, increasing the surface area for absorption of minerals.
What are osetocytes?
When osteoblasts become trapped in bone matrix. Osteocytes are trapped inside a lacunae and become involved in signalling processes.
How do osteocytes communicate with each other?
Via filapodia which extend through canaliculi of the bone (microscopic canals between lacunae of bone)
What are the 2 types of bone?
Compact/cortical- dense outer layer
Spongy/cancellous- interior of bone, consist of trabeculae (thin spicules of bone), meshwork is filled with bone marrow in living bone.
How many bones does an adult skeleton contain?
206
What are the 2 skeleton divisions?
Axial: longitudinal, bottom of spine up to head including ribcage
Appendicular: bones up upper and lower limbs (inclusing pelvis)
What are the different bone shapes?
Long (ulna/radius), flat (skull-parietal bone), short (carpals), irregular (vertebrae), sesamoid (patella)
Where do you find long bones?
In the appendicular skeleton. Act as rigid levers adn are positioned in space by the action of muscles.
What are the different regions of the bone?
Diaphysis: shaft of the long bone
Metaphysis: bone flares out at each, lies adjacent to the growth plate
Epiphysis: on the other side of the growth plate (distal-close to torso/proximal-further away from torso)
What is the bone covered in?
At the articulating surfaces are covered in hyaline cartilage, remainder of the bone is covered in periosteum.
Medullary cavity lined with endosteum.
What is the epiphyseal line?
It replaces epiphyseal plate (growth plate) which is found in children.
What is the medullary cavity filled with?
Full of red bone barrow in children-involved in haematopoiesis.
In adults it is full of yellow bone marrow due to high fat content.
What is the blood supply to the bone marrow?
Nutrient artery. Enters the bone via the nutrient foramen, near the middle of the diaphysis.
What are short bones and their function?
As long as they are wide.
Provide stability, when working together they provide a wide range of movement.
e.g. carpal bones in wrist, tarsal bones in ankle
What are flat bones and their function?
Protect internal organs.
Provide a large area for attachment of muscles.
e.g.skull, pelvis, sternum & ribs (thoracic cage)
What are irregular bones and their function?
Complex shape which helps protects internal organs
Vary in shape
e.g. vertebrae
What are sesamoid bones and their function?
Bones embedded in tendons. Protect tendons from stress and wear.
Act as fulcrum
e.g. patella, tendons of feet/hands
Which bones have no growth plate/epiphysis?
Short, flat, irregular, sesamoid.
These all consist of 2 layers of compact bone with layer of spongy bone between them and the bone marrow being contained between the trabeculae.
Are there other arteries other than the nutrient artery that supply bone?
Periosteal arteries: supply the periosteum and outer 1/3 of the cortex of the bone.
Metaphyseal arteries: enter at side attachment of joint capsule which is continuous with the periosteum
Epiphyseal artery
What is the difference between the metaphyseal arteries in adults and children?
Children: these artieries don’t cross the growth plate (epiphyseal plate of cartilage), so a secondary ossification centre in epiphysis is completely dependent on the epiphyseal artery.
Adult: epiphyses fuses, an anastomosis formed between the epiphyseal and metaphyseal arteries.
What is avascular necrosis & the causes?
Death of bone due to loss of blood supply.
Causes:
-fracture
-alcoholism
-excessive steroid use
-trauma
-radiation (obliteration of small arteries)
-thrombosis
-hypertension
-decompression sickness (small bubbles of nitrogen form which can impede blood supply)
How is bone remodelled?
Change in the balance of osteoclasts and osteoblasts.
-occurs in response to environmental factors (exercise)
What is a joint?
Articulation between 2 or more bones.
Most mobile joints are the least stable.
What are the 3 types of joints?
Fibrous
Cartilaginous
Synovial
What are fibrous joints and give examples:
United by collagen fibres.
Limited mobility
High stability
e.g. sutures of skull, betweem roots of tooth and mandible bone
What are cartilaginous joints and give examples:
Joints that use cartilage to unite bones.
Found in the midline of the body and epiphyseal plates of long bones
Primary:completely immobile (epiphyseal growth plates, first sternocostal joint b/w sternum and first rib)
Secondary (symphyses): pad of fibrocartilage between them (pubic symphysis, intervertebral discs)
What is a synovial joint?
Has a joint cavity containing synovial fluid.
Articulating surfaces usually covered in hyaline cartilage.(prevents friction, resists compressive forces)
- provides lubrication to articular surfaces
- high degree of mobility, are widespread
What are the exceptions to the rule of articulating surfaces in synovial joints being covered by hyaline cartilage?
Atypical synovial joints. Covered with fibrocartilage.
e.g. sternoclavicular joint (sternum and clavicle)
What is the fibrous capsule?
Surrounds the synovial joint.
- composed of collagen
- encloses the joint (except where it is interrupted by synovial protrusions which form bursae)
- stabilises the joint, resists dislocation but permits movement
- continuous with periosteum of adjacent bones
What is the synovial membrane?
Thin, highly vascularised membrane which produces synovial fluid, it lines the joint capsule and any exposed osseous surfaces.
It lines tendon sheaths and bursa.
It DOES NOT line articular cartilage/meniscus/intra-articular discs-fibrocartilage which separated synovial cavities allowing separate movements to occur in each one.
What are the different types of synovial joints?
Plane, saddle, hinge, pivot, ball & socket, condyloid (ellipsoid)
What is a plane joint?
2 flat surfaces against each other.
- allow movement in several directions in a single plane
e. g. carpal bones in the wrist
What is a condyloid joint?
2 elliptical bowls
- elliptical shape prevents rotation
e. g. radiocarpal joint (b/w radius and carpals)
What is a saddle joint?
2 bones fitting togther like a saddle and a person
- allows movement in 2 planes at the same time
e. g. 1st carpometacarpal joint at base of thumb
What is a hinge joint?
Allows flexion and extension without sliding
- movement in one anatomical plane
e. g. elbow joint b/w humerus and ulna (hinge synovial joint)
What is a pivot joint?
Peg with a ring shaped hole
- rotational motion without gliding
e. g. atlanto-axial, joint b/w 1st & 2nd cervical vertebrae allows head to rotate whilst maintaining stability of neck
What is a ball and socket joint?
Allows stable movement in several directions without slippage
- most mobile (flexion, extension, adduction, abduction, rotation, circumduction)
e. g.hip/shoulder
What is circumduction?
Combination of all the movements in other planes
What is the function and composition of synovial fluid?
Functions:
- reduce friction
- shock absorber
- transport nutrients/remove waste from articular cartilage
Composition:
- clear, viscous, slightly alkaline
- volume less than half a mm
- contains hyaluronic acid, lubricin, proteinases & collagenases
What does the knee joint contain?
An intra-articular fibrocartilaginous menisci
What is the blood supply like in a joint?
Articular cartilage: avascular
Fibrous capsule/ligaments: poor blood supply
Synovial membrane: rich blood supply (maintain flow of nutrients via synovial fluid to cartilaginous surfaces)
What affects the range of motion of the joints?
- structure/shape of articulating bones
- strength and tension of ligaments
- arrangement of muscles around the joint
- apposition of neighbouring tissue
- effect of hormones
- disuse of a joint
How do synovial joints develop?
During the 6th week.
-areas of mesenchyme within growing limb buds begin to differentiate into hyaline cartilage
Synovial joints will form between adjacent cartilage regions
- cells at inter zone undergo apoptosis to form the joint cavity
- surrounding cells from the perichondrium form the joint capsule and peri articular ligaments emerge (continuous with the periosteum)
What does the knee joint contain?
Some cartilage within the joint is preserved and develops intra-articular ligaments (anterior/posterior cruciate ligaments)
What is a first class lever?
Seen where the load is in equilibrium. Force is applied on the opposite side of the fulcrum to the effort. (see-saw)
e.g. head on the top of neck (posterioir neck muscles contract to raise the load of the facial and jaw skeleton-forward and backward movement of head with spine as fulcrum)
What is a second class lever?
Load being lifted lies between the fulcrum and the effort applied.
e.g. standing on tip toes (calf muscle is effort, load is it bottom of foot, fulcrum is the toes)
What is a third class lever?
When the effort is applied between the fulcrum and the load.
e.g. elbow ( elbow joint is fulcrum, biceps is the effort, the weight of the forearm is the load)
What do you see in joints where you want to generate very high forces?
In equilibruim F1 x D1 = F2 x D2
Therefore if you want to increase F2 you must decrease D2 or increase D1/F1
e.g. seen in animals which dig (aardvarks-long olecranon process, strong muscles, short limbs) to maximase power
