Study Guide: Bones and Skeletal Tissue (Anatomy & Physiology)

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Bones and Skeletal Tissue

Characteristics of Cartilage

Cartilage is a specialized connective tissue found in various locations throughout the body. It provides support, flexibility, and cushioning in joints and other structures.

Type of Cell in Cartilage	Does Cartilage Contain Blood Vessels? Nerves?	Name 3 Types of Cartilage	Which Type is Most Plentiful in the Body?
Chondrocytes & Chondroblasts	No vessels, no nerves; nutrients diffuse through the matrix	Hyaline, elastic, fibrocartilage	Hyaline cartilage

Functions of Bone

Bones are rigid organs that serve multiple essential functions in the human body.

Support: Provides structural framework for the body.
Protection: Shields vital organs (e.g., skull protects brain, ribs protect heart and lungs).
Movement: Acts as levers for muscles to produce movement.
Mineral Storage: Stores minerals such as calcium and phosphorus.
Blood Cell Production: Produces red and white blood cells (hematopoiesis) in bone marrow.
Fat Storage: Stores energy in the form of adipose tissue in yellow marrow.
Hormone Production: Osteocalcin production helps regulate insulin secretion, glucose homeostasis, and energy expenditure.

Bone Parts

Bones have distinct anatomical regions, each with specific functions and characteristics.

Compact Bone: Solid, heavy, and hard. Forms the outer layer and shaft of long bones. Optimized for strength and hardness.
Spongy Bone (Cancellous Bone): Trabecular, honeycomb-like structure. Spaces filled with marrow, found in the ends of long bones.
Epiphysis: Ends of long bones; includes proximal and distal regions.
Epiphyseal Plate: Growth plate made of hyaline cartilage; site of bone lengthening during childhood and adolescence.
Articular Cartilage: Hyaline cartilage covering bone ends at joints, reducing friction.
Periosteum: Double-layered membrane covering the outer surface of bones; contains fibrous and osteogenic layers.
Fibers: Collagen fibers anchor periosteum to bone matrix.

Bone Markings

Bones display various markings that serve as attachment points for muscles, passageways for nerves and blood vessels, and articulation surfaces.

Tuberosity: Large, rounded projection; may be roughened.
Tubercle: Small, rounded projection.
Crest: Narrow, prominent ridge.
Condyle: Rounded articular projection.
Fossa: Shallow depression in bone.
Sinus: Cavity within bone, lined with mucous membrane.
Notch: Indentation at the edge of a bone.
Foramen: Round or oval opening through bone.

Bone Cell Types and Functions

Bone tissue contains several specialized cell types, each with unique roles in bone formation, maintenance, and resorption.

Osteoblasts: Immature bone cells that deposit minerals to form new bone; become osteocytes.
Osteocytes: Mature bone cells located in lacunae within the lamellae; maintain bone tissue.
Osteoclasts: Multinucleated cells derived from white blood cell lineage; responsible for bone resorption.

Endochondral Ossification

Endochondral ossification is the process by which bone tissue is created from a cartilage template, primarily during fetal development and childhood.

Bones begin as hyaline cartilage models.
Osteoblasts form a bone collar around the cartilage.
Cartilage in the center calcifies and develops cavities.
Periosteal bud invades the cavities, forming spongy bone.
Medullary cavity forms as ossification continues.
Epiphyses ossify, leaving hyaline cartilage only at the articular surfaces and epiphyseal plates.

Bone Growth in Children

Bones grow in length at the epiphyseal plate, which maintains a constant thickness by balancing cartilage growth and replacement by bone tissue.

Epiphyseal plate closure marks the end of bone growth: typically at age 18 for females, 21 for males.

Hormonal Regulation of Bone

Bone metabolism is regulated by hormones that control calcium levels and bone remodeling.

Hormone	Effect on Blood Calcium	Effect on Osteoblasts/Osteoclasts	Other Notes
Calcitonin	Decrease	Stimulates osteoblasts, inhibits osteoclasts	Calcitonin is released when blood calcium is high; promotes bone deposition.
Parathyroid Hormone (PTH)	Increase	Stimulates osteoclasts, inhibits osteoblasts	PTH is released when blood calcium is low; promotes bone resorption.

Wolff's Law of Bone

Wolff's Law states that bone grows or remodels in response to mechanical stress. Bones strengthen in areas where stress is greatest, adapting to the demands placed on them.

Weight-bearing exercise and muscle activity stimulate bone growth.

Stages of Bone Fracture Healing

Bone healing occurs in four main stages following a fracture:

Hematoma Formation: Blood clot forms at the fracture site.
Fibrocartilaginous Callus Formation: Soft callus of cartilage and fibrous tissue bridges the fracture.
Bony Callus Formation: Osteoblasts produce new bone, replacing the soft callus with hard bone.
Bone Remodeling: Bone is reshaped to restore its original structure.

Types of Bone Fractures

Bone fractures are classified based on their characteristics and severity.

Compound (Open) Fracture: Bone ends penetrate the skin.
Closed (Simple) Fracture: Bone ends do not penetrate the skin.
Comminuted Fracture: Bone fragments into three or more pieces; common in older adults.
Spiral Fracture: Ragged break caused by excessive twisting forces.
Greenstick Fracture: Incomplete break; common in children.

Rickets

Rickets is a preventable disease caused by vitamin D deficiency, leading to impaired bone mineralization in children.

Symptoms: Bowed legs, pelvic and rib cage deformities, enlarged and abnormally long bones.
Prevention: Adequate vitamin D intake and exposure to sunlight.

Osteoporosis

Osteoporosis is a disorder characterized by low bone density and increased bone resorption, resulting in fragile bones.

Risk Factors:
1. Decreased sex hormone
2. Insufficient bone stress
3. Poor diet (low calcium, vitamin D, protein)
4. Smoking
5. Genetics
6. Hormone-related conditions (diabetes, hyperthyroidism)
7. Alcohol and certain medications
Diagnosis: DEXA scan measures bone density; T-score < -2.5 indicates osteoporosis.
Treatment: Hormone replacement therapy (HRT), bisphosphonates (inhibit osteoclasts).

Vocabulary Table: Bone and Skeletal Tissue

Vocab Term	Use in a Sentence	Synonym	Reminds me of...
Osseous tissue	His osseous tissue was deteriorating due to osteoporosis.	Bone	Tree rings in a trunk
Spongy bone	Spongy bone is found at the two ends of long bones.	Cancellous bone	Honeycomb
Chondrocytes	Chondrocytes maintain the cartilage matrix in joints.	Cartilage cells	Bubble-like cells in spaces
Osteoblasts	Osteoblasts build new bone during growth and repair.	Bone-forming cells	Construction workers
Osteoclasts	Osteoclasts break down bone to release calcium into the blood.	Bone-destroying cells	Pac-Man eating bone

Key Equations

Rate of Bone Formation:
Rate of Bone Resorption:

Additional info:

Some content was expanded for clarity and completeness, including definitions and examples.
Hormonal regulation table includes inferred details for PTH, which is standard in A&P.