Anatomy and Physiology: The Skeletal System

Composition: The skeletal system consists of bone and cartilage.
Functions Include: - Providing Rigid Support Framework: The skeletal system serves as the structural framework for the human body. - Allowing Movement: Muscles pull on bones for movement, leveraging the skeletal system as levers. - Providing Protection: Bones shield soft internal organs from injury. - Mineral Storage: Bones store minerals within the extracellular matrix. - Energy Storage: Yellow bone marrow stores energy in the form of adipose tissue. - Producing Blood Cells: The skeletal system is involved in the production of blood cells.

Definition: Long bones are defined as bones that are longer than they are wide.
Function: Act as levers to facilitate movement.
Examples of Long Bones: - Humerus: Upper arm bone connecting the shoulder to the elbow. - Femur: Thigh bone, the longest and strongest bone in the body. - Ulna: One of the two bones in the forearm, alongside the radius. - Tibia: The shinbone, larger and stronger than the fibula.

Epiphysis: The end part of a long bone, typically wider than the shaft.
Diaphysis: The long shaft of a bone, the central part.
Metaphysis: The area between the epiphysis and diaphysis, includes the growth plate.
Medullary Cavity: Hollow space within the diaphysis that contains bone marrow.
Epiphyseal Line: Marks the site of the previous epiphyseal plate that is responsible for lengthwise growth.

Periosteum: A dense irregular connective tissue that lines the surface of bones, providing attachment for muscles and ligaments.
Endosteum: A dense irregular connective tissue lining the medullary cavity, involved in bone remodeling.
Articular Cartilage: A smooth layer of hyaline cartilage covering the ends of bones at joints, reducing friction during movement.

Definition: Surface features of bones that provide insights into the bone's function and structure.
Articulating Surfaces: The areas where two bones meet. - Condyle: Rounded surface that articulates with another bone. - Facet: A flat surface for articulation. - Head: A prominent rounded surface, often found at the proximal end of long bones. - Trochlea: Rounded, articulating surface shaped like a pulley.
Depressions: Sunken areas in a bone. - Fossa: An elongated basin. - Sulcus: A groove on the bone surface.
Projections: Parts of the bone that protrude. - Crest: A ridge along the bone. - Epicondyle: A projection off a condyle, providing a site for muscle attachment. - Line: A slight, elongated ridge on the bone. - Process: A prominent feature on the bone. - Ramus: A long extension or branch of the bone. - Spine: A sharp projection. - Trochanter: A rough, round projection found only on the femur. - Tubercle: A small, rounded process. - Tuberosity: A roughened surface area on a bone.
Holes and Spaces: Openings or grooves in the bone. - Canal: A passage within the bone. - Fissure: A slit-like opening through the bone. - Foramen: A hole allowing for the passage of nerves and blood vessels. - Meatus: An opening leading into a canal. - Sinus: An air-filled cavity within a bone.

Definition: A semi-solid connective tissue.
Characteristics: Avascular, meaning it lacks a direct blood supply.
Covered by Perichondrium: A dense irregular connective tissue that contains blood vessels which supply nutrients to the cartilage.

Definition: Solid connective tissue that comprises the skeleton.
Compact Bone: Denser, providing support and protection.
Spongy Bone: Less dense, providing strength and housing red bone marrow in its spaces.

Osteogenic Cells: Stem cells capable of replicating and differentiating into other types of bone cells. - Develop into Osteoblasts: These are bone-forming cells.
Osteoblasts: Cells that synthesize new bone matrix and help in bone formation.
Osteocytes: Mature osteoblasts that are embedded in the bone matrix and located in spaces called lacunae.
Osteoclasts: Cells responsible for the breakdown of bone tissue; involved in bone resorption and remodeling.

Osteon: The fundamental structural unit of compact bone. - Comprised of rings of calcified matrix known as concentric lamellae. - Concentric lamellae surround a central canal containing blood vessels, contributing to nourishment and strength.
Blood Vessels in Central Canal: These vessels are connected to the periosteum via perforating canals, allowing for nutrient exchange.

Trabeculae: The structural units forming a lattice-like network within spongy bone. - Orientation: These beams align according to stress lines to enhance bone strength.
Spaces: The interstitial spaces within trabeculae are where red bone marrow is found and where hematopoiesis (blood cell formation) occurs.

Ossification: The process of bone formation. - A cartilage or membranous model is essential for this process as new bone tissue develops on this model.
Types of Ossification: - Intramembranous Ossification: Involves the transformation of connective tissue membranes into bone. - Endochondral Ossification: Involves the transformation of hyaline cartilage into bone.

Definition: The continuous process in which bones undergo breakdown and formation. - Bone is cyclically broken down and new bone material is created, aiding in mineral availability and homeostasis.
Triggers for Remodeling: - Influences include physical activity, injury, and other stresses placed on the bone. - Bones remodel to increase in strength along lines of mechanical resistance.

Fracture: A break in a bone.
Steps in Bone Repair: - Hematoma Formation: Prevents blood loss and serves as the initial response to fracture. - Cartilage Callus Formation: Soft tissue builds a new template for bone formation over the fracture site. - Replacement of Callus with Bone: The soft callus is incrementally replaced with hard bone tissue. - Building of Compact Bone: Compact bone is established around the periphery of the fracture site for support.

Calcium Storage: Calcium ions are stored in the extracellular matrix of bone.
Conditions: - Hypocalcemia: Low blood calcium levels that may lead to muscle cramps and osteoporosis. - Hypercalcemia: High blood calcium levels that can result in kidney stones and cardiovascular issues.
Hormonal Regulation: - Parathyroid Hormone (PTH): Stimulates osteoclasts, enhancing bone resorption and raising blood calcium levels. - Calcitonin (CT): Inhibits the activity of osteoclasts, promoting bone formation and lowering blood calcium levels.

Effect of Exercise: - Regular physical stress leads to stronger and denser bones due to increased muscle engagement and loading.
Consequences of Lack of Exercise: - Sedentary lifestyle results in weaker, lighter bones and increased fracture risk due to decreased mineral density.

At the conclusion of this chapter, you should be able to: - List the classes of bones along with examples for each class. - Describe the anatomy of both compact and spongy bones in detail. - Discuss the mechanisms behind bone growth and formation processes. - Outline the procedure of fracture repair comprehensively.