Bones, The Skeletal System, & Articulations

Functions of the Skeletal System

1. Support: Stable framework for body structure. 2. Protection: Shields vital organs. 3. Movement: Bones as levers for muscles. 4. Storage: Reservoir for minerals and fat. 5. Hematopoiesis: Blood cell formation in marrow. 6. Acid-base homeostasis: Regulates pH balance.

Types of Bones

1. Long Bones: Elongated shape (e.g., femur). 2. Short Bones: Nearly equal lengths (e.g., carpals). 3. Flat Bones: Thin and curved (e.g., sternum). 4. Irregular Bones: Complex shapes (e.g., vertebrae).

Diaphysis

The central shaft of long bones primarily composed of compact bone.

Osteocytes

Mature bone cells that reside in lacunae and maintain bone matrix.

Intramembranous Ossification

Direct formation of bone from mesenchymal tissue, important for flat bones.

Endochondral Ossification

Replacement of hyaline cartilage with bone for long bone development.

Bone Remodeling Factors

1. Sex Hormones: Promote bone formation. 2. Age: Affects remodeling efficiency. 3. Dietary Factors: Nutrient intake essential for bone health.

Axial Skeleton

Comprises 80 bones including skull, ribs, sternum, and vertebrae.

Appendicular Skeleton

Includes 126 bones such as girdles and limb bones for movement.

Support

The skeletal system provides a stable framework for the body, cradling soft organs and allowing for upright posture.

Protection

The skeleton acts as a shield for vital organs, such as the skull protecting the brain and the ribcage protecting the heart and lungs.

Movement

Bones serve as levers for muscle action, with joints allowing flexible movement for activities like walking and grasping.

Storage

Bones act as reservoirs for minerals like calcium and phosphorus and store adipose tissue for energy.

Hematopoiesis

The process of blood cell formation that occurs in red bone marrow, producing red blood cells, white blood cells, and platelets.

Acid-base Homeostasis

Bones help regulate the body’s pH balance by absorbing or releasing minerals.

Long Bones

Bones longer than they are wide, consisting of a diaphysis and epiphyses, examples include femur and humerus.

Short Bones

Nearly equal in length and width, providing stability and support, such as carpals and tarsals.

Flat Bones

Thin and often curved bones that provide extensive surfaces for muscle attachment and protection, like the sternum and ribs.

Irregular Bones

Complex shaped bones that serve multiple functions, such as the vertebrae and some facial bones.

Diaphysis

The central shaft of long bones composed primarily of compact bone, providing strength and support.

Epiphysis

The ends of long bones covered with articular cartilage to facilitate joint movement.

Articular Cartilage

Smooth tissue covering the ends of bones in synovial joints, reducing friction.

Periosteum

A dense membrane covering bone surfaces containing blood vessels and nerves, essential for bone health.

Medullary Cavity

Hollow space within the diaphysis filled with yellow marrow, serving as a fat storage depot.

Osteocytes

Mature bone cells residing in lacunae that maintain bone matrix and regulate mineral content.

Osteoblasts

Immature bone-forming cells that produce the bone matrix and are vital during growth.

Osteoclasts

Large multinucleated cells that resorb bone tissue, critical for bone remodeling.

Compact Bone

Dense tissue forming the outer layer of bones, providing strength and protection.

Spongy Bone

Lightweight bone tissue found in the epiphyses, providing structural integrity and a site for hematopoiesis.

Intramembranous Ossification

Bone formation from mesenchymal tissue, mainly forming flat bones like the skull.

Endochondral Ossification

Replacement of hyaline cartilage with bone, essential for the development of long bones.

Bone Remodeling

The process of bone deposition and resorption, crucial for calcium regulation and adaptation to stress.

Axial Skeleton

Comprises 80 bones including the skull, ribs, sternum, and vertebrae, providing support and protection.

Appendicular Skeleton

Comprises 126 bones, including limb bones and girdles, facilitating movement and support.

Synarthroses

Completely immovable joints, providing stability, such as cranial sutures.

Amphiarthroses

Slightly movable joints allowing limited flexibility, such as the pubic symphysis.

Diarthroses

Freely movable joints, such as synovial joints like the knee and shoulder.

Fibrous Joints

Joints characterized by dense connective tissue with no joint cavity, such as sutures.

Cartilaginous Joints

Bones connected by cartilage allowing limited movement, like synchondroses.

Synovial Joints

joints with a fluid-filled cavity allowing extensive mobility, critical for diverse movements.

Flexion

Decreases the angle between body parts, such as bending the elbow.

Extension

Increases the angle between body parts, like straightening the knee.

Abduction

Moves a limb away from the body's midline, such as raising arms sideways.

Adduction

Moves a limb toward the midline of the body, like bringing arms down to the sides.

Bone Deposition

New bone formation through osteoblasts, essential for growth, healing, and adaptation.

Bone Resorption

Breakdown of bone tissue by osteoclasts, crucial for calcium regulation and reshaping bones.