Osseous Tissue (Bones & Joints)

Skeletal System Components & Cells; Bone Structure & Classification; Bone Growth & Remodeling; Calcium Homeostasis; Joints (Articulations);

What are the four main components of the skeletal system?

Bones, Cartilage, Ligaments, Tendons.

What is a Ligament?

Dense connective tissue band that holds bones together at joints (bone to bone)

What is a Tendon?

Dense connective tissue band that attaches muscle to bone

What are the four types of bone cells?

Osteogenic cells, Osteoblasts, Osteocytes, Osteoclasts

What is the function of Osteoblasts?

Bone-forming cells that deposit bone matrix

What is the function of Osteocytes?

Former osteoblasts that act as strain sensors and maintain the bone matrix. They live in spaces called Lacunae.

What is the function of Osteoclasts?

Bone-dissolving cells (crushers) that break down bone for remodeling.

What is the function of Osteogenic cells?

Stem cells that divide to produce new osteoblasts.

What is Compact bone?

The dense outer shell of bone; its structural unit is the Osteon.

What is Spongy (Cancellous) bone?

The loosely organized inner bone; its structural unit is the Trabeculae.

What is found in the spaces of spongy bone?

Red bone marrow.

What is the Diaphysis of a long bone?

The shaft, which provides leverage.

What is the Epiphysis of a long bone?

The enlarged ends, which strengthen the joint.

What is the Periosteum?

The external sheath covering bone (except joints), important for growth and healing.

What is the Endosteum?

The thin membrane lining the marrow cavity.

What is the Medullary cavity?

The space in the diaphysis containing bone marrow.

What is the Epiphyseal plate?

The growth plate of hyaline cartilage in children where bones grow in length.

What are the two types of Ossification (bone development)?

Endochondral and Intramembranous.

What is Endochondral ossification?

Bone development within a pre-existing hyaline cartilage model (e.g., long bones)

What is Intramembranous ossification?

Bone development within fibrous connective tissue (e.g., flat bones of the skull).

How do bones grow in length?

By interstitial growth at the Epiphyseal plate (cartilage grows, then is replaced by bone).

How do bones grow in width?

By appositional growth (osteoblasts on the outside build bone up, osteoclasts inside enlarge the marrow cavity)

What is Bone Remodeling?

The continuous process of bone breakdown (by osteoclasts) and rebuilding (by osteoblasts)

What is Wolff's Law?

The architecture of bone is determined by the mechanical stresses placed upon it.

What three hormones regulate calcium homeostasis?

Calcitriol (Vitamin D), Calcitonin, Parathyroid Hormone (PTH)

What is the function of Calcitriol?

It raises blood calcium levels by increasing absorption from the intestines

What is the function of Parathyroid Hormone (PTH)?

It raises blood calcium levels by stimulating osteoclasts and activating Vitamin D.

What is the function of Calcitonin?

It lowers blood calcium levels by inhibiting osteoclasts.

What is a joint (articulation)?

Any connection between skeletal elements (bone to bone, cartilage to bone, tooth to bone).

What are the three structural classes of joints?

Fibrous, Cartilaginous, Synovial.

What are the three functional classes of joints (by movement)?

Synarthrosis (immobile), Amphiarthrosis (slightly mobile), Diarthrosis (freely mobile).

What is a Synovial joint?

A freely mobile joint where bones are separated by a joint cavity filled with synovial fluid.

What are the six types of Synovial joints?

typically includes Ball & Socket, Hinge, Pivot, Condyloid, Saddle, Plane.

What is Flexion?

Movement that decreases the joint angle.

What is Extension?

Movement that straightens a joint and returns to zero position.

What is Abduction?

Movement away from the midline of the body.

What is Adduction?

Movement toward the midline of the body.

What is Pronation?

Forearm movement that turns the palm to face posteriorly or downward.

What is Supination?

Forearm movement that turns the palm to face anteriorly or upward.

What is Dorsiflexion?

Elevating the toes (as in heel strike).

What is Plantar flexion?

Pointing the toes downward (as in standing on tiptoe).