Bones, Bone Structure, and Joints: Study Guide for Anatomy & Physiology

Bones and Bone Structure

Bone Classifications

Bones are classified based on their shape and structure, which relates to their function in the body.

• Long Bones: Longer than they are wide (e.g., femur, humerus). Function in movement and support.

• Short Bones: Nearly equal in length and width (e.g., carpals, tarsals). Provide stability and some movement.

• Flat Bones: Thin, flattened, and usually curved (e.g., sternum, ribs, skull bones). Protect internal organs and provide surfaces for muscle attachment.

• Irregular Bones: Complex shapes (e.g., vertebrae, some facial bones).

• Sesamoid Bones: Small, round bones embedded within tendons (e.g., patella).

Compact vs. Spongy Bone

Bones contain two main types of osseous tissue:

• Compact Bone: Dense and solid, forms the outer layer of bones. Contains osteons (Haversian systems), which are cylindrical structures that provide strength.

• Spongy Bone: Also called cancellous bone, found inside bones, especially at the ends of long bones and in flat bones. Contains a network of trabeculae (thin columns and plates), which help reduce bone weight and provide space for bone marrow.

Articular Cartilage

• Definition: Smooth, white tissue that covers the ends of bones in joints.

• Location: Found at the surfaces of bones where they come together to form joints.

• Function: Reduces friction and absorbs shock in the joint.

• Type: Made of hyaline cartilage.

Hormonal Regulation of Bone Growth

• Calcitonin: Lowers blood calcium levels by inhibiting osteoclast activity and increasing calcium excretion by the kidneys.

• Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating osteoclasts, increasing intestinal absorption, and reducing excretion by the kidneys.

• Growth Hormone: Stimulates bone growth, especially during childhood.

• Sex Hormones (Estrogen and Testosterone): Promote bone growth and later cause epiphyseal plate closure.

Appositional Bone Growth

• Definition: Growth in the diameter or thickness of bones.

• Process: Osteoblasts in the periosteum add new bone tissue to the outer surface, while osteoclasts remove bone from the inner surface, enlarging the medullary cavity.

Bone Formation: Intramembranous vs. Endochondral Ossification

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue. Forms flat bones of the skull, mandible, and clavicle.

• Endochondral Ossification: Bone develops by replacing hyaline cartilage. Forms most bones of the body, especially long bones.

Bone Cells: Osteoblasts vs. Osteoclasts

• Osteoblasts: Bone-forming cells; synthesize and secrete the bone matrix.

• Osteoclasts: Bone-resorbing cells; break down bone tissue, releasing minerals into the blood.

Disorders of Bone Growth

• Pituitary Dwarfism: Short stature due to insufficient growth hormone during childhood.

• Gigantism: Excess growth hormone before epiphyseal plate closure, leading to abnormally large stature.

• Acromegaly: Excess growth hormone after epiphyseal plate closure, causing enlargement of hands, feet, and facial features.

Structure of a Long Bone

• Diaphysis: Shaft of the bone; contains the medullary cavity.

• Epiphysis: Ends of the bone; contains spongy bone and red marrow.

• Metaphysis: Region between diaphysis and epiphysis; contains the epiphyseal plate (growth plate).

• Periosteum: Outer fibrous covering; contains nerves and blood vessels.

• Endosteum: Membrane lining the medullary cavity.

Bone Marrow: Red vs. Yellow

• Red Bone Marrow: Site of hematopoiesis (blood cell formation); found in spongy bone of children and adults (mainly in flat bones and epiphyses).

• Yellow Bone Marrow: Stores fat; found in the medullary cavity of long bones, increases with age as red marrow is replaced.

Hydroxyapatite

• Definition: The main inorganic component of bone matrix, a crystalline calcium phosphate compound.

• Importance: Provides hardness and strength to bone.

• Chemical Formula: $Ca_{10}(PO_4)_6(OH)_2$

Functional Unit of Bone

• Osteon (Haversian System): The structural and functional unit of compact bone, consisting of concentric lamellae around a central canal.

The Skeleton and Joints

Bone Identification and Structures

• Be able to identify major bones and their anatomical features (e.g., femur, humerus, vertebrae, skull bones).

Types of Joints and Movements

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

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

• Synovial Joints: Freely movable joints with a synovial cavity (e.g., knee, shoulder).

Movements at Synovial Joints

• Adduction: Movement toward the midline.

• Abduction: Movement away from the midline.

• Flexion: Decreasing the angle between bones.

• Extension: Increasing the angle between bones.

• Rotation, Circumduction, etc.

Parts of a Synovial Joint

• Articular Cartilage: Covers bone surfaces.

• Joint (Synovial) Cavity: Space containing synovial fluid.

• Articular Capsule: Encloses the joint cavity.

• Synovial Fluid: Lubricates and nourishes the joint.

• Ligaments: Strengthen and support the joint.

The Knee Joint

• Largest and most complex synovial joint.

• Contains menisci (cartilage pads), ligaments (ACL, PCL, MCL, LCL), and bursae.

Arthritis Types

• Osteoarthritis: Degenerative joint disease due to wear and tear.

• Rheumatoid Arthritis: Autoimmune inflammation of joints.

• Gouty Arthritis: Deposition of uric acid crystals in joints.

Blood Calcium Regulation

• Maintained by the skeletal system, digestive system, and urinary system.

Skull and Axial Skeleton

Skull Sutures

• Immovable joints between skull bones (e.g., coronal, sagittal, lambdoid, squamous sutures).

Sinuses

• Air-filled cavities in certain skull bones (frontal, maxillary, ethmoid, sphenoid).

• Function: Lighten the skull, warm and moisten air, enhance voice resonance.

Fontanels

• Soft spots in the fetal and infant skull where bone formation is incomplete.

• Allow for brain growth and passage through the birth canal.

Vertebral Issues

• Osteoporosis: Loss of bone mass, increased fracture risk.

• Osteopenia: Reduced bone mass, less severe than osteoporosis.

• Other vertebral issues: herniated discs, scoliosis, kyphosis, lordosis.

Rib Articulations

• Ribs articulate with thoracic vertebrae and the sternum (via costal cartilage).

Pelvic Girdle

• The ischial tuberosity is the part of the hip bone you sit on.

Male vs. Female Skeleton

• Pelvis: Female pelvis is wider and shallower for childbirth.

• Skull: Male skulls are generally larger and more robust.

• Other differences include bone mass, joint surfaces, and subpubic angle.

Feature	Male Skeleton	Female Skeleton
Pelvic Inlet	Narrow, heart-shaped	Wide, oval
Subpubic Angle	Less than 90°	Greater than 90°
Bone Mass	Heavier, thicker	Lighter, thinner
Skull Features	More pronounced	Smoother, less pronounced

Example: The femur is a long bone, the sternum is a flat bone, and the patella is a sesamoid bone. The knee joint is a synovial joint that allows flexion and extension.

Additional info: Some details, such as the specific names of all bones or the full list of joint types, may require reference to a complete bone list or textbook for comprehensive study.