Bone Health, Joint Structure, and Movement: Study Notes for Anatomy & Physiology

Bone Health and Disorders

Rickets

Rickets is a condition characterized by weak, fragile, painful, and deformed bones, primarily affecting children. It is most commonly caused by a deficiency of calcium and/or vitamin D.

• Definition: Rickets is the softening and weakening of bones in children, usually due to inadequate vitamin D, calcium, or phosphate.

• Symptoms: Bone pain, deformities, and increased risk of fractures.

• Causes:

  • Lack of calcium and/or vitamin D

  • Insufficient dietary intake or poor absorption

  • Low exposure to sunlight (which is needed for vitamin D synthesis)

• Vitamin D:

  • Required for the body to absorb calcium from the gut (food/drinks) into the blood.

  • Produced in the dermis of the skin upon exposure to UV sunlight.

  • Also absorbed from foods high in vitamin D (e.g., meats, seafood, eggs, milk, orange juice with added vitamin D).

• Example: Children with rickets may present with bowed legs or other bone deformities.

Osteoporosis

Osteoporosis is a condition of porous, fragile, and deformed bones caused by bone resorption outpacing bone deposition over time. It is most common in older adults.

• Definition: Osteoporosis is a disease in which bone density and quality are reduced, leading to increased risk of fractures.

• Prevalence: Occurs as we age; about 20% of seniors are affected.

• Symptoms: High risk of bone fractures, especially in the hip, spine, and wrist.

• Risk Factors:

  • Low calcium and vitamin D intake

  • Old age

  • Sedentary lifestyle

  • Smoking, alcohol use

  • Genetics (family history, European or Asian ancestry)

  • Small body size (petite individuals)

  • Consuming beverages high in phosphate (e.g., brown colored sodas, sports drinks)

  • Female sex

• Pathophysiology: High blood phosphate triggers the parathyroid glands to secrete parathyroid hormone (PTH), which increases bone resorption.

• Treatments / Prevention:

  • High calcium and vitamin D intake

  • Regular exercise

  • Avoid smoking and excessive alcohol consumption

  • Avoid consuming excess phosphates

• Example: Elderly individuals with osteoporosis may suffer hip fractures after minor falls.

Joints and Articulations

Overview of Joints

Joints, also known as arthroses or articulations, are structures that hold the skeleton together and allow movement between bones.

• Function: Connect bones and permit varying degrees of movement.

• Classification: Joints are classified based on their structure and the type of tissue connecting the bones.

Types of Joints

Joints are categorized into three main types based on their structure and the tissue involved.

Type of Joint	Structure	Examples
Cartilage Joint	Some are hyalin cartilage (e.g., between ribs and sternum); some are fibrocartilage (e.g., between vertebrae, pubic symphysis)	Costosternal joint, intervertebral discs, pubic symphysis
Fibrous Joint	Dense regular connective tissue; two types: A. Sutures (narrow sheets, most skull bones) B. Ligaments (cord/rope-like)	Sutures in the skull, ligaments between bones
Synovial Joint	Complex structure; allows free movement	Knee, shoulder, hip joints

Joint Movements

Types of Movements

Joints allow various types of movements, which are essential for locomotion and daily activities.

• Flexion: Decreasing the angle across a joint (e.g., bending the elbow)

• Extension: Increasing the angle across a joint (e.g., straightening the knee)

• Hyperextension: Increasing the angle across a joint past the standard anatomical position

• Adduction: Moving a body part closer to the body's midline

• Abduction: Moving a body part further from the body's midline

• Circumduction: Cone-shaped movement of a limb

• Rotation: Twisting movement (e.g., turning the head)

• Plantar Flexion: Pointing toes/balls of feet downward

• Dorsiflexion: Pulling toes/balls of feet upward (toward the shin)

Types of Synovial Joints

Synovial joints are further classified based on the shapes of their articulating surfaces and the movements they allow.

Type	Movement	Example
Ball & Socket Joint	Multi-axial movement (flexion, extension, rotation, abduction, adduction)	Shoulder, hip
Hinge Joint	Flexion and extension	Elbow, knee, fingers
Pivot Joint	Rotation around a single axis	Between C1 (atlas) and C2 (axis) vertebrae
Plane Joint	Gliding movements	Intercarpal joints (wrist)
Saddle Joint	Movement in two planes (flexion/extension, abduction/adduction)	Thumb (carpometacarpal joint)
Condyloid Joint	Movement in two planes, no rotation	Wrist (radiocarpal joint)

Additional info:

• Vitamin D synthesis in the skin requires exposure to UVB radiation; deficiency is common in regions with low sunlight.

• Parathyroid hormone (PTH) regulates calcium and phosphate balance in the blood and bones.

• Bone remodeling is a lifelong process involving osteoclasts (bone resorption) and osteoblasts (bone formation).