Bones and the Skeletal System Review
Skeletal System Introduction
The skeletal system is composed of:
Bones
Cartilages
Joints
It forms the internal framework of the body, providing support, protection, movement, and other crucial functions.
Cartilage
Location in the Adult Body
Aids in support of the body through cushioning.
It is a tough but flexible tissue that withstands twisting and compressive forces.
Specific locations include:
External ear
Articular cartilage (at the ends of most bones at movable joints)
Between vertebrae (intervertebral discs)
Articular discs
Epiglottis
Nose
Costal cartilage (connecting ribs to sternum)
Pubic symphysis
Larynx
Airways
Cartilage Matrix
Cartilage is a connective tissue with an extensive extracellular matrix (ECM).
It consists primarily of water, ranging from 60\% to 80\%, which allows it to return to its original shape once compressed.
The specific cells in cartilage are called chondrocytes.
Each chondrocyte resides in a space known as a lacuna.
Notably, cartilage contains no nervous innervation or blood vessels, making its healing process slower.
Types of Cartilage
There are three main types of cartilage in the body:
Hyaline Cartilage:
Characterized by being flexible and resilient.
Found in articular cartilage, costal cartilage, and respiratory cartilage.
Elastic Cartilage:
Highly bendable due to a high concentration of elastic fibers.
Located in the epiglottis and the outer ear.
Fibrocartilage:
Designed to resist both compression and tension forces.
Found in the knee menisci and the annulus fibrosus of intervertebral discs.
Bones
Functions of Bones
Support and Protection: Provides a framework for the body and protects internal organs.
Levers for Movement: Serves as attachment sites for muscles and tissues, creating levers for movement.
Hematopoiesis: The process of blood cell production occurs within the bone marrow.
Storage of Mineral and Energy Reserves: Primarily stores calcium and phosphate, essential minerals for various bodily functions.
Bones as Organs
Bones are classified as organs because they contain several different types of tissues:
Bone Tissue: A specialized connective tissue with an extensive ECM composed of:
An organic component (e.g., cells like osteoblasts, osteocytes) for tensile strength.
An inorganic component (e.g., mineral salts, specifically hydroxyapatites) for hardness.
Bone tissue is dynamic and continuously undergoes remodeling.
This process involves:
Osteogenic cells: Stem cells that differentiate into bone-forming cells.
Osteoblasts: Responsible for depositing the organic material of the bone matrix.
Osteocytes: Mature bone cells surrounded by the matrix, maintaining bone tissue.
Osteoclasts: Cells responsible for breaking down bone tissue.
Nervous Tissue: Contains nerves that innervate the bone.
Blood Tissue: Contains blood vessels that supply nutrients and remove waste.
Cartilage: Articular cartilage is found at the ends of bones in joints.
Epithelial Tissue: Lines blood vessels within the bone.
Bone Shapes
Flat Bones: Thin and may be slightly curved (e.g., skull bones, sternum).
Irregular Bones: Have elaborate and complex shapes (e.g., vertebrae, hip bones).
Long Bones: Characterized by a shaft and two ends, longer than they are wide (e.g., femur, humerus).
Short Bones: Roughly cube-shaped (e.g., carpals, tarsals).
Sesamoid Bones: A special type of short bone that forms within a tendon (e.g., patella).
Compact and Spongy Bone
Compact Bone (also known as cortical bone):
Appears solid to the unaided eye but contains many microscopic passageways for blood and lymphatic vessels and nerves.
The structural unit of compact bone is the osteon (or Haversian system), a cylinder of bone tissue.
Found as the external layer on all bones and forms the bulk of the diaphysis (shaft) of long bones.
Spongy Bone (also known as trabecular bone):
Structural units are trabeculae, which are flat, needle-like or plate-like bone pieces that form a network of