Cartilage and Bone: Skeletal System Structure

Cartilage and Bone: Skeletal System Structure

• Skeletal system components include bone and cartilage.

Skeletal System Functions

• Support
• Movement
• Protection
• Hemopoiesis
• Compact bone contains osteons and spongy bone does not.
• Compact bone is comprised of collagen and ground substance.

Bone Shapes

• Examples of flat bones include the sternum and ribs.
• Examples of boxy bones are the patella.
• Examples of long bones are the femur, ulna, and metacarpals
• Sphenoid vertebrae are considered irregular bones

Compact Bone

• An osteon is a structural unit of compact bone containing a central canal with blood vessels and nerves, as well as osteocytes residing in lacunae.
• Concentric lamellae are mineralized extracellular matrix rings within the osteon.
• Canaliculi are tiny canals in compact bone
• The ECM in each concentric lamella is composed of collagen and ground substance.

Spongy Bone

• Spongy bone (or cancellous bone) is made up of thin plates or struts called trabeculae
• Red bone marrow is found in spongy bone.
• Spongy bone lacks osteons, but maintains osteocytes within lacunae.
• Tiny canaliculi travel through the parallel lamellae in spongy bone.
• The ECM is each parallel lamella contains trabeculae and red bone marrow.

Cartilage Review: Hyaline Cartilage

• Provides smooth surfaces for movement.
• Supports soft tissue
• It serves as a model for bone growth.
• Locations include the trachea, larynx, costal cartilage, gristle, and the ends of small bones.

Fibrocartilage

• Resists compression and absorbs shock in some joints.
• Functions to resist compression and absorb shock in some joints
• Located in intervertebral discs, pubic symphysis, and menisci of knee joints.

Elastic Cartilage

• Maintains structure and shape while permitting flexibility.
• Located in the external ear and epiglottis of the larynx.

Growth Patterns in Cartilage

• Interstitial growth is internal growth via chondrocytes dividing via mitosis.
• Appositional growth occurs from the periphery.
• Chondrocytes inhibits angiogenesis, which impacts cartilage repair and healing because blood vessels supply oxygen and nutrients to the damaged area.

Bone Cells

• Osteoprogenitor cells are stem cells that make a new committed cell/osteoblast when they divide
• Osteoblasts are immature bone cells.
• Osteocytes are mature bone cells found in lacunae that maintain bone health.
• Osteoclasts are giant "bone eaters" important in bone resorption; derived from monocytes.

Osteolysis

• Osteolysis is a resorption.
• Elevated calcium levels will be happen from catrilage released from the ground substance within the lamellae into the blood

Osteopenia

• A normal loss of bone density expected with age.
• Osteoblast activity declines, but osteoclasts maintain their activity level leading to an imbalance.
• Cisgender women lose about 8% of bone mass after age 30, while cisgender males lose about 3% per decade.

Osteoporosis

• A disease associated with porous bones.
• Sex hormones are linked to bone density with estrogen stimulating osteoblasts.
• Individuals with functioning ovaries entering menopause experience a drop in estrogen levels, leading to decreased bone density and vulnerability to osteoporosis.
• Calcium intake and weight-bearing exercise are the best

Osteoclasts

• Bone eaters that secrete hydrochloric acid to dissolve calcified matrix.
• Their lysosomes contain digestive enzymes to help dissolve collagen.

Anatomy of a Long Bone

• Osteon organization in compact bone contributes to bone strength.

Anatomy of a Long Bone: Cross Section

• Dense Regular Connective Tissue builds a ligament.

Intramembranous Bone Formation

• Fibrous or dense CT is present first.
• Committed stem cells become osteoprogenitor cells.
• Osteoprogenitor cells differentiate and become osteoblasts.
• Osteoblasts secrete extracellular matrix
• Trapped osteoblasts become mature osteocytes
• Occurs in locations like the skull.
• Fontanels are soft spots in the skull that allow the skull to be flexible

Endochondral Bone Formation

• Hyaline cartilage is replaced with bone.
• The primary ossification center is located in the diaphysis
• Secondary ossification centers are located in the epiphysis
• The epiphyseal disk is the location where growth occurs
• Bones increase in girth through appositional growth.

Factors Affecting Bone Health

• Hormones
• Nutrition
• Exercise
• Age

Bone Remodeling

• Occurs with a renewal rate of up to 18% per year.
• Bone formation and resorption processes tend to occur at about the same rate, in response to stress
• Age affects remodeling rate and osteopenia, where osteoblast activity declines but osteoclasts maintain their activity level, leading to higher bone resorption than formation and a loss in bone density.

Bone Repair

• Occurs after a break with a hematoma blood clot forming between broken bones six to eight hours after the break.
• A fibrocartilaginous callus forms between broken bones at about three weeks.
• A bony callus forms after about three months.

Disorders of the Skeletal System

• Osteopenia is a normal loss of bone density expected with age with osteoblast activity declines but osteoclasts maintain their activitylevel so imbalance is expected.
• Osteoporosis porous bones where sex hormones are linked to bone density so an individual's endocrine system

Osteomalacia and Rickets

• Osteomalacia in adults and rickets in children involves softening of the bones due to insufficient bone mineralization; ECM isn't strong enough. Common symptom is bowed legs.
• Caused by insufficient levels of vitamin D, impairing absorption of calcium from the diet

Osteomyelitis

• Inflammation of the bone and marrow where infections are usually caused by staphylococcus aureus bacteria
• Infection of the bone usually caused by staphylococcus aureus bacteria
• Symptoms include fever, chills, and pain.
• Treatment involves antibiotics and surgery to remove dead bone tissue.

Scurvy

• A nutritional deficiency caused by prolonged lack of Vitamin C.
• Vitamin C is essential for the production of collagen, which involved with bone health, especially at the joints

Joints/Articulations

• This section introduces six key terms related to Joints/Articulations

Joint Classification based on Function

• Synarthrosis: No movement between bones such as teeth in the mandible and sutures between skull bones
• Amphiarthrosis: Little movement between bones such as intervertebral disks.
• Diarthrosis: Freely moveable joints such as the knee, elbow, fingers, shoulder, hip etc

Joint Classification based on Structure

• Fibrous joints: Bones are held together by fibrous CT
• Cartilaginous: Bones are held together by Cartilage
• Synovial: Synovial membrane and joint capsule are between bones

Functional Classifications of Joints

• Diarthroses: Joints that move freely! (Ex: elbow, shoulder, fingers, knee, hip)
• Synarthroses: Joints that don't move at all. (Ex: suture, teeth, & epiphyseal disks)
• Amphiarthroses: Joints that are able to move a little bit (think about compression types of movement) (Ex: Intervertebral discs & pubic symphass)

Fibrous Joints

• Sutures are exemplified by the coronal, sagittal, lambdoid, and squamous sutures located on the skulls.
• Gomphosis is exemplified by teeth and bone held together in an alveolus.
• Syndesmosis is a sheet of fibrous/dense connective tissue known as the interosseous membrane anchoring the radius and ulna in the antebrachium, or the tibia to the fibula.

Cartilaginous Joints

• Cartilaginous joints form where two bones are joined by cartilage.
• Symphyses are exemplified by pubic symphysis
• Synchondroses are exemplified by a growth plateepiphyseal disk where cartilage separates the epiphysis.

Synovial Joints

• Ends of bones are covered with hyaline cartilage
• A joint capsule isolates/creates the joint cavity separating the two bones
• The capsule is lined internally by a fluid producing synovial membrane and internally by fibrous connective tissue
• Meniscus: fibrocartilage pads that adds stability to joint and acts as shock absorber providing a broader distribution of force.
• Bursae synovial fluid-filled structures that reduce friction where ligaments, muscles, tendons, or bones rub together

Synovial Joints

• Ball-and-socket joint example: head of femur with acetabulum (hip joint)
• Gliding/plane joints: joints between carpals or tarsals
• Hinge: elbow, knee, or finger joints
• Condylar joints: mandible-skull joint, between phalanges and metacarpals
• Saddle joint: Thumbs grasping objects
• Pivot joints: C1 and C2 vertebrae with the dens pivot point, proximal end of the radius in the ulna

Diarthrotic Movements at Synovial Joints

• Flexion and extension (plus hyperextension)
• Dorsiflexion and plantarflexion
• Abduction and adduction
• Supination and pronation
• Rotation
• Eversion and inversion
• Protraction and retraction
• Elevation and depression
• Circumduction

Joint Disorders

• Sprain: Injury to ligaments, where the collagen fibers of the dense regular connective tissue are damaged.

Joint Dislocation and Separations

• Bones are not in the correct position.
• Damage to cartilage, ligaments, and or joint capsule. Need to consider.

Slipped Discs

• Compression of the intervertebral discs
• Damage to supporting ligaments associated with vertebral column
• Can cause/allow the disk "core" to buige out of place and put pressure on nerves

Bursitis

• Inflammation of the bursa
• Associated with friction, repetitive movements, and or trauma

Arthritis

• Arthritis - general term for any inflammation
• Osteoarthritis- old patients, degeneration and wear tear. Friction due to articular cartilage being unhealthy
• Rheumatoid arthritis-autoimmune women: immune system attacking the joints, scar tissue forming at these sites of injury.