Skeletal System Overview

Major Functions of the Skeleton

The human skeleton provides the structural framework for the body, supports movement, and protects vital organs. It also serves as a reservoir for minerals and is involved in blood cell production.

• Support: Maintains body shape and posture.

• Protection: Shields organs such as the brain (skull), heart, and lungs (rib cage).

• Movement: Acts as levers for muscles to produce movement.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Houses red bone marrow for hematopoiesis.

Cartilage Tissue

Types and Functional Properties of Cartilage

Cartilage is a flexible connective tissue found in various parts of the body. There are three main types, each with distinct properties and functions.

• Hyaline Cartilage: Most abundant; provides support with flexibility. Found in articular surfaces, costal cartilages, nose, trachea, and larynx.

• Elastic Cartilage: Contains more elastic fibers; maintains shape and flexibility. Found in the ear and epiglottis.

• Fibrocartilage: Highly compressible and strong; resists tension. Found in intervertebral discs, pubic symphysis, and menisci.

Example: The meniscus in the knee is made of fibrocartilage, providing shock absorption.

Major Cartilages of the Adult Skeleton

• Articular cartilage (ends of long bones)

• Costal cartilage (ribs to sternum)

• Nasal cartilage (nose)

• Intervertebral discs

• Pubic symphysis

Cartilage Growth

• Appositional Growth: New cartilage is added to the surface by chondroblasts.

• Interstitial Growth: Chondrocytes within the cartilage divide and secrete new matrix.

Bone Structure and Classification

Bone Classes and Examples

Bones are classified by shape and function:

• Long Bones: Longer than wide (e.g., femur, humerus)

• Short Bones: Cube-shaped (e.g., carpals, tarsals)

• Flat Bones: Thin, flattened (e.g., sternum, skull)

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis)

Gross Anatomy of Bones

• Long Bone: Diaphysis (shaft), epiphyses (ends), metaphysis, medullary cavity, periosteum, endosteum, articular cartilage.

• Flat Bone: Compact bone on exterior, spongy bone (diploë) in the middle.

Bone Marrow and Membranes

• Red Marrow: Hematopoietic tissue, found in spongy bone of flat bones and epiphyses of long bones.

• Yellow Marrow: Fat storage, found in medullary cavity of long bones.

• Periosteum: Outer fibrous membrane covering bone.

• Endosteum: Membrane lining the medullary cavity.

Bone Markings

Bony landmarks indicate sites of articulation, attachment, and passage of nerves/vessels.

• Articulation: Joint surfaces (e.g., condyle, head)

• Attachment: Muscle/ligament attachment (e.g., tuberosity, crest)

• Passage: Foramina for nerves/vessels

Histology and Composition of Bone

Compact vs. Spongy Bone

• Compact Bone: Dense, forms outer layer; contains osteons (Haversian systems).

• Spongy Bone: Porous, contains trabeculae; found in epiphyses and interior of flat bones.

Chemical Composition

• Organic Components: Cells (osteoblasts, osteocytes, osteoclasts), osteoid (collagen fibers).

• Inorganic Components: Hydroxyapatite (calcium phosphate crystals).

Advantages: Organic matrix provides flexibility; inorganic matrix provides strength.

Bone Development and Growth

Ossification Processes

• Intramembranous Ossification: Bone develops from fibrous membrane (e.g., flat bones of skull).

• Endochondral Ossification: Bone replaces hyaline cartilage (e.g., long bones).

Long Bone Growth

• Occurs at epiphyseal plates via proliferation of cartilage and subsequent ossification.

• Appositional growth increases bone diameter.

Bone Remodeling

• Remodeling occurs throughout life, especially at sites of stress.

• Osteoblasts: Build bone.

• Osteoclasts: Break down bone.

• Osteocytes: Maintain bone matrix.

Hormonal Regulation and Wolff's Law

• Hormones: Parathyroid hormone (PTH) increases blood calcium by stimulating osteoclasts; calcitonin lowers blood calcium.

• Physical Stress: Bone adapts to mechanical stress (Wolff's Law).

Negative Feedback Loop: Blood Calcium Regulation

• Low blood calcium stimulates PTH release, increasing osteoclast activity.

• High blood calcium stimulates calcitonin release, increasing osteoblast activity.

Axial and Appendicular Skeleton

Axial Skeleton

• Skull, vertebral column, rib cage

• Protects central nervous system and vital organs

Appendicular Skeleton

• Pectoral girdle, pelvic girdle, limbs

• Facilitates movement

Skull Anatomy

• Major bones: frontal, parietal, temporal, occipital, sphenoid, ethmoid

• Sutures: coronal, sagittal, lambdoid, squamous

• Fossae: anterior, middle, posterior cranial fossae

• Foramina: passageways for nerves and vessels

Facial Bones and Markings

• Maxilla, mandible, zygomatic, nasal, lacrimal, palatine, vomer, inferior nasal concha

• Bone markings indicate articulation and muscle attachment

Vertebral Column

• Regions: cervical (C1–C7), thoracic (T1–T12), lumbar (L1–L5), sacrum, coccyx

• Curvatures: primary (thoracic, sacral), secondary (cervical, lumbar)

• Intervertebral discs: fibrocartilage pads for shock absorption

• Special vertebrae: atlas (C1), axis (C2)

Thoracic Cage

• Bones: sternum, ribs, thoracic vertebrae

• True ribs (1–7), false ribs (8–12), floating ribs (11–12)

• Bony landmarks: costal groove, head, neck, tubercle

Appendicular Skeleton: Upper and Lower Limbs

Pectoral Girdle and Upper Limb

• Scapula, clavicle, humerus, radius, ulna

• Carpal bones (8): scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate

• Metacarpals (5), phalanges (14)

Pelvic Girdle and Lower Limb

• Os coxae (ilium, ischium, pubis)

• Femur, tibia, fibula, patella

• Tarsal bones (7): talus, calcaneus, navicular, cuboid, medial/intermediate/lateral cuneiforms

• Metatarsals (5), phalanges (14)

Example: The talocrural joint is the ankle joint formed by the tibia, fibula, and talus.

Pelvic Differences

• Male pelvis: narrower, deeper, more robust

• Female pelvis: wider, shallower, adapted for childbirth

Bone and Cartilage Development

Classification of Joints

• Fibrous Joints: Bones joined by dense connective tissue; little/no movement (e.g., sutures).

• Cartilaginous Joints: Bones joined by cartilage; limited movement (e.g., symphysis, synchondrosis).

• Synovial Joints: Bones separated by a fluid-filled cavity; freely movable (e.g., shoulder, knee).

Types of Cartilaginous Joints

• Synchondrosis: Hyaline cartilage (e.g., epiphyseal plate)

• Symphysis: Fibrocartilage (e.g., pubic symphysis)

Synovial Joints and Movements

Structural Characteristics of Synovial Joints

• Articular cartilage, joint cavity, synovial fluid, articular capsule, ligaments, nerves, and blood vessels

Types of Synovial Joints

Common Body Movements

• Flexion, extension, abduction, adduction, rotation, circumduction

Bursae and Tendon Sheaths

• Bursae: Fluid-filled sacs that reduce friction between moving structures.

• Tendon Sheaths: Elongated bursae that wrap around tendons.

Ligaments and Joint Stability

• Cruciate Ligaments: Stabilize the knee joint (anterior and posterior cruciate ligaments).

• Labrum: Fibrocartilaginous rim that deepens the socket in ball-and-socket joints (e.g., shoulder).

Summary Table: Bone and Cartilage Types

Key Equations

• Bone Growth Rate:

• Calcium Homeostasis (Negative Feedback):

Additional info: Some details, such as the specific names of carpal and tarsal bones, and the description of Wolff's Law, were inferred for completeness and academic clarity.