Bone Resorption and Cartilage Growth

Bone Resorption

• Osteoclasts destroy bone matrix using proteases and hydrogen ions
• Proteases break down organic matrix components
• Hydrogen Ions contribute to the acidic environment that dissolves inorganic components of bone matrix
• Occurs when blood calcium levels are low
• Transcytosis: Transporting macromolecules across the interior of a cell
• Resorption lacuna: Empty spaces left behind after bone matrix is broken down by osteoclasts

Cartilage Growth

• Interstitial growth: Occurs within the cartilage itself, allows growth from within
• Appositional growth: Occurs at the outer surface of cartilage, allows growth in width
• Chondrocytes: Mature cartilage cells residing in lacunae
• Chondroblasts: Immature cartilage cells that actively synthesize and secrete new matrix
• Perichondrium: Outer layer of connective tissue surrounding cartilage, contains stem cells that differentiate into chondroblasts
• Hyaline cartilage: Type of cartilage found in joints, nose, and trachea

Endochondral Ossification

• Process of bone formation that replaces cartilage with bone
• Occurs in long bones
• Epiphyseal plate: Growth plate located at the ends of long bones
• Articular cartilage: Hyaline cartilage covering the ends of bones in joints, allows for smooth movement
• Spongy bone: Porous bone tissue found at the ends of long bones
• Compact bone: Dense bone tissue found in the shafts of long bones
• Medullary cavity: Space within the shaft of long bones that contains bone marrow
• Periosteum: Outer layer of connective tissue surrounding bone, contains stem cells that differentiate into bone cells

Regulating Blood Calcium Levels

• Parathyroid hormone (PTH) released in response to low blood calcium levels
• PTH stimulates osteoclast activity, increasing bone resorption and releasing calcium into blood
• PTH also stimulates the kidneys to increase calcium reabsorption from urine
• Calcitriol: Active form of vitamin D, promotes calcium absorption from the intestines
• Calcitonin: Released from the thyroid gland in response to high blood calcium levels
• Calcitonin inhibits osteoclast activity, reducing bone resorption and lowering blood calcium levels
• Calcitonin stimulates kidneys to increase calcium excretion in urine

Osteoporosis

• Reduced bone mass: Compromises normal bone function
• Weakened bones: Prone to fractures
• Factors contributing to osteoporosis: age, race, menopause, smoking
• Osteopenia: Reduced bone density, occurs with age
• Hormonal decline: Contributes to bone loss with age

Bone Fracture and Repair

• Fracture: Break in bone
• Occurs due to unusual stress or impact
• More common with age due to weakened bones
• Stress fracture: Thin break caused by repetitive loads
• Pathologic fracture: Occurs due to underlying disease or condition
• Simple fracture: Bone breaks but does not penetrate the skin
• Compound fracture: Bone breaks and penetrates the skin

Bone Repair

• Fracture hematoma: Blood clot that forms at the fracture site
• Fibrocartilaginous (soft) callus: Forms around the fracture site, made of cartilage and fibrous tissue
• Hard callus: Forms as the soft callus is replaced by bone
• Bone remodeling: Process of reshaping and strengthening the bone after healing
• Periosteum: Plays a role in bone repair by providing cells and nutrients
• Medullary cavity: Contributes to the formation of new bone tissue

Articulations

• Articulations, or joints, are where bones meet.
• They allow for movement and stability.

Joint Classification

• Structurally categorized based on the presence or absence of a joint cavity and the type of connective tissue:
  • Fibrous
  • Cartilaginous
  • Synovial
• Functionally categorized based on the range of movement:
  • Synarthrosis (immovable)
  • Amphiarthrosis (slightly movable)
  • Diarthrosis (freely movable)

Fibrous Joints

• Connected by dense connective tissue.
• Lack a joint cavity.
• Include:
  • Sutures: Found between bones of the skull. Become ossified in adults, forming synostoses.
  • Syndesmoses: Connected by ligaments, allowing for slight movement. Example: distal tibiofibular joint.
  • Gomphoses: Peg-and-socket joints, found between teeth and their sockets.

Cartilaginous Joints

• Connected by cartilage.
• Lack a joint cavity.
• Include:
  • Synchondroses: Connected by hyaline cartilage. Example: first sternocostal joint, epiphyseal plates.
  • Symphyses: Connected by fibrocartilage. Example: intervertebral discs, pubic symphysis.

Synovial Joints

• Contain a joint cavity filled with synovial fluid.
• Freely movable (diarthroses).
• Key structures:
  • Articular capsule: Encloses the joint, preventing separation of bones. Has two layers: outer fibrous layer and inner synovial membrane.
  • Articular cartilage: Covers the ends of bones, reducing friction and acting as a shock absorber.
  • Joint cavity: Space between the bones, filled with synovial fluid.
  • Synovial fluid: Lubricates, provides shock absorption, and nourishes articular cartilage.
  • Ligaments: Strengthen and stabilize the joint. Can be extrinsic or intrinsic.
  • Bursae: Fluid-filled sacs that cushion and reduce friction between bones, tendons, ligaments, and muscles.
  • Fat pads: Protect and cushion the joint.

Types of Synovial Joints

• Plane: Allow for gliding movements. Example: intercarpal joints.
• Hinge: Allow for flexion and extension. Example: elbow joint.
• Pivot: Allow for rotation. Example: radioulnar joint.
• Condylar: Allow for flexion, extension, adduction, abduction, and circumduction. Example: knee joint.
• Saddle: Allow for movement in two planes. Example: carpometacarpal joint of thumb.
• Ball-and-socket: Allow for movement in all planes. Example: shoulder and hip joints.

Clinical View: Arthritis

• Group of diseases that cause joint inflammation and degeneration.
• Symptoms: joint swelling, pain, and stiffness.
• Types:
  • Gouty arthritis: Caused by high uric acid levels.
  • Osteoarthritis: Degenerative condition caused by cartilage breakdown.
  • Rheumatoid arthritis: Autoimmune disorder that inflames the synovial membrane.

Shoulder Joint

• Consists of three joints:

  • Glenohumeral joint: Ball-and-socket, allows for a wide range of movement.
  • Acromioclavicular joint: Plane joint, allows for slight gliding movements.
  • Sternoclavicular joint: Saddle joint, allows for elevation, depression, and circumduction.

• Shoulder separation: Dislocation of the acromioclavicular joint.

Knee Joint

• Largest and most complex joint in the body.
• Hinge joint, allows for flexion and extension.
• Contains:
  • Medial and lateral menisci: C-shaped fibrocartilage pads that act as shock absorbers.
  • Anterior and posterior cruciate ligaments: Provide stability and prevent excessive movement.
  • Tibial collateral and fibular collateral ligaments: Prevent side-to-side movement.

Knee Ligament and Cartilage Injuries

• Tibial collateral ligament injury: Common, usually caused by a blow to the outside of the knee.
• Anterior cruciate ligament (ACL) injury: Very common, often occurs when the knee is hyperextended.
• Menisci injury: Can occur due to blows or overuse.
• Unhappy triad: Triple injury of the ACL, tibial collateral ligament, and medial meniscus, often caused by a lateral blow to the knee.

Ankle Joint

• Talocrural joint.
• Hinge joint, allows for dorsiflexion and plantarflexion.
• Stabilized by ligaments:
  • Deltoid ligament: Medial side, strong.
  • Lateral ligament: Lateral side, weaker.
  • Tibiofibular ligaments: Stabilize the ankle joint.

Ankle Sprains and Pott Fractures

• Sprain: Stretching or tearing of the lateral ligaments, usually caused by overinversion.
• Pott fracture: Overeversion of the ankle, causing fracture of the medial malleolus and fibula.

Articulations

• Bones are too rigid to bend, they meet at joints called articulations
• Joints are different shapes and have different supporting structures
• Joints allow different types and ranges of movement
• Joints are the points where bones, bone and cartilage, or bone and teeth meet

Classification of Joints

• Joints are classified based on whether there is a joint cavity, and the type of connective tissue
• Joints can be Fibrous, Cartilaginous, or Synovial
• Joints are classified based on their range of motion: Synarthrosis, Amphiarthrosis, and Diarthrosis
• Synarthrosis - No movement
• Amphiarthrosis - Limited movement
• Diarthrosis - Free movement

Fibrous Joints

• Fibrous joints are connected by dense regular connective tissue
• Fibrous joints have no joint cavity
• Fibrous joints are synarthrosis or amphiarthrosis
• Fibrous joints become ossified in adults - synostoses

Cartilaginous Joints: Sympheses

• Cartilaginous joints lack a joint cavity
• Cartilaginous joints are amphiarthroses
• Cartilaginous joints have cartilage between articulating bones
• Cartilage between articulating bones can be hyaline or fibrocartilage
• Cartilage in these joints acts as shock absorbers and resist compression and tension

Cartilaginous Joints: Synchondroses

• First Sternocostal joint is firmly united to the manubrium, which provides stability to the rib cage
• Costochondral joints connect the ribs and costal cartilage
• Costochondritis is inflammation of the costochondral joints
• The epiphyseal plate is a cartilaginous joint
• Some synchondroses ossify over time

Synovial Joints

• Synovial joints are the most common in the body
• Synovial joints have a joint cavity, space between bones
• Synovial joints are all diarthroses
• Synovial joints are all diarthroses and have key features:
  • Articular capsule, strengthens joints to prevent being pulled apart
  • Articular cartilage, lacks perichondrium, reduces friction, acts as a cushion to absorb joint compression, prevents damage to the ends of bones
  • Joint cavity, space permitting separation of bones
    • Synovial membrane secretes synovial fluid
    • Synovial fluid is viscous and oily
    • Synovial fluid is secretions from synovial membrane cells and filtrate from plasma
    • Synovial fluid lubricates articular cartilage, acts as a shock absorber, nourishes and removes wastes from articular chondrocytes
  • Sensory nerves and blood vessels, innervate and supply articular capsule and ligaments
    • Proprioceptors, detect stretch and movement of a joint
    • Nociceptors, detect damaging or potentially damaging stimuli

Classification of Synovial Joints

• Classified by shape of surfaces and movement allowed:
  • Uniaxial joint, movement along one axis
  • Biaxial joint, movement along two axes
  • Multi-axial joint, movement along multiple axes
• Joints can be classified from least to most mobile:
  • Plane joints, simplest synovial articulation, least mobile diarthrosis, uniaxial, limited movement in one plane, articular surfaces are flat, e.g., intercarpal and intertarsal joints
  • Hinge joints, uniaxial, permits movement in one plane, like a door hinge, e.g., elbow, knee, and interphalangeal joints
  • Pivot joints, uniaxial, bone rotates on longitudinal axis relative to a second bone, e.g., proximal radioulnar joint, e.g., dens of axis and anterior arch of atlas
  • Condylar joints, biaxial, oval convex surface articulating with concave surface, e.g., metacarpophalangeal joints of fingers and thumb
  • Saddle joints, biaxial, convex and concave surfaces resemble saddle shape, greater range of movement than condylar or hinge joints, e.g., carpometacarpal joint of the thumb
  • Ball and socket joints, multiaxial, spherical head of one bone fits into cuplike socket, e.g., coxal and glenohumeral joints, most freely mobile

Temporomandibular Joint

• The Temporomandibular joint (TMJ) is the only mobile joint in the skull
• The TMJ has a loose articular capsule, articular disc of fibrocartilage, articular tubercle, Sphenomandibular ligament, Tempromandibular ligament
• TMJ movements include depression/elevation, protraction/retraction, and excursion.

TMJ Disorders

• TMJ disorders are common
• TMJ disorders most commonly caused by alterations in ligaments securing the joint
• TMJ disorders can cause clicking or popping as the mouth opens and closes

Shoulder Joint

• The glenohumeral joint is commonly called the shoulder joint
• The glenohumeral joint permits the greatest range of motion of any joint in the body
• The glenohumeral joint is most unstable and the most frequently dislocated joint
• The glenohumeral joint is supported by the rotator cuff muscles, which encircle the joint and fuse with the articular capsule
• glenohumeral joint has a fibrocartilaginous glenoid labrum, a loose articular capsule, a coracoacromial ligament, a coracohumeral ligament, glenohumeral ligaments, the tendon of the long head of the biceps brachii, and abundant bursae

Dislocation of the Glenohumeral Joint

• Dislocation of the glenohumeral joint is common due to its instability
• Dislocation of the glenohumeral joint usually occur when a fully abducted humerus is struck
• A dislocated glenohumeral joint appears flattened and "squared-off"
• The humeral head is anterior and inferior to the glenohumeral joint capsule

Elbow Joint

• The elbow joint is a hinge joint composed of two articulations :
  • humeroulnar joint, trochlea / trochlear notch
  • humeroradial joint, capitulum / radial head
• Both are enclosed within a single articular capsule
• The elbow joint is very stable due to interlocking bony surfaces, a thick articular capsules, and multiple ligaments
• The elbow joint is not as mobile as some other joints

Ligaments of the Elbow Joint

• The elbow joint only allows flexion and extension
• Stress to the elbow joint can damage the ligaments, for example:
  • It can be damaged from a fall onto an outstretched hand with the elbow joint partly flexed
  • It may cause a dislocation from stress and impact

Subluxation of the Head of the Radius

• Subluxation is an incomplete dislocation
• Subluxation involves contact alteration between joint surfaces but remains in partial contact
• A doctor can maneuver the radial head back into the annular ligament

Coxal Joint

• The hip joint is the articulation between the head of the femur and acetabulum of the os coxa
• The hip joint has an acetabular labrum, a fibrocartilaginous ring, an articular capsule, a ligament of the head of femur
• The hip joint is more stable and less mobile than the glenohumeral joint
• The hip joint is supported by the articular capsule, ligaments, and muscles
• Retinacular fibers are ligamentous fibers of the articular capsule.

Hip Joint: Intracapsular Spiraling Ligaments

• The hip joint is very stable in the extended position
• The hip joint permits flexion, extension, abduction, adduction, rotation, and circumduction

Femoral Fracture

• Femoral fractures are often referred to incorrectly as "fractured hip"
• Femoral fractures rotate laterally and are shorter than the other leg
• Intertrochanteric fractures
  • are extracapsular fractures
  • usually occur in younger to middle-aged individuals due to trauma
• Subcapital fractures
  • occur within the hip articular capsule
  • usually occur in elderly individuals with osteoporosis
  • may result in tearing of the retinacular arteries and avascular necrosis in the region

Knee Joint

• The knee joint is the largest and most complex diarthrosis
• The knee joint is primarily a hinge joint
• The knee joint is composed of two separate articulations:
  • tibiofemoral joint
  • patellofemoral joint
• The knee joint does not have a unified capsule or joint cavity
• The articular capsule is reinforced by the quadriceps tendon
• The patellar ligament and fibular collateral ligament prevent hyperadduction
• The tibial collateral ligament prevents hyperabduction

Cruciate Ligaments

• The cruciate ligaments prevent anterior and posterior movement of the tibia relative to fixed femur
• The anterior cruciate ligament extends from anterior intercondylar area of tibia to lateral condyle of femur
• The posterior cruciate ligament extends from posterior intercondylar area of tibia to medial condyle of femur

This quiz covers key concepts of bone resorption and cartilage growth, including the roles of osteoclasts, proteases, and hydrogen ions in bone matrix breakdown. Additionally, it examines processes like interstitial and appositional growth in cartilage, along with the functions of chondrocytes and chondroblasts. Test your understanding of these essential biological processes.