Study Guide: Skeletal Tissue and Bone Structure

Skeletal Tissue and Bone Structure

Major Bones and Bone Markings

The human skeleton is composed of various bones, each with unique markings that serve as attachment points for muscles, ligaments, and tendons. Understanding these markings is essential for identifying bones and their functions.

• Trochanter: A large, rough projection found on the femur.

• Trochlea: A smooth, grooved articular process shaped like a pulley, found on the humerus.

• Other markings: Include condyles, epicondyles, tuberosities, and foramina.

• Application: Markings help in lab identification and understanding joint movement.

Gross Anatomy of Long Bones

Long bones have distinct regions that contribute to their growth and function.

• Diaphysis: The shaft of the bone, providing support and structure.

• Epiphysis: The ends of the bone, involved in joint articulation.

• Metaphysis: The region between diaphysis and epiphysis, containing the growth plate.

• Medullary cavity: The central cavity within the diaphysis, containing bone marrow.

Periosteum and Endosteum

These are connective tissue membranes that cover and line bone surfaces.

• Periosteum: A dense, fibrous membrane covering the external surface of bones, except at joints. It contains nerves, blood vessels, and osteogenic cells.

• Endosteum: A thin membrane lining the internal surfaces of bones, including the medullary cavity. It is involved in bone growth and remodeling.

Blood Vessels of Long Bones

Blood supply is crucial for bone health, growth, and repair.

• Nutrient arteries: Enter through nutrient foramina to supply the diaphysis.

• Metaphyseal and epiphyseal arteries: Supply the ends of the bone.

• Periosteal vessels: Supply the outer compact bone.

Red vs. Yellow Marrow

Bone marrow exists in two forms, each with distinct functions.

• Red marrow: Found in the epiphyses and flat bones; responsible for hematopoiesis (blood cell formation).

• Yellow marrow: Found in the diaphysis; primarily stores fat and can convert to red marrow if needed.

Vertebrae and Their Markings

The vertebral column consists of several vertebrae, each with unique features.

• Number of vertebrae: 33 total (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal).

• Markings: Include spinous process, transverse process, vertebral foramen, and articular facets.

Microscopic Features of Long Bone

Under the microscope, long bones reveal complex structures essential for strength and function.

• Osteon (Haversian system): The fundamental unit of compact bone, consisting of concentric lamellae around a central canal.

• Lamellae: Layers of bone matrix.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae for nutrient exchange.

Long Bone vs. Spongy Bone

Bones are classified based on their structure and function.

• Long (compact) bone: Dense, strong, and forms the outer layer of bones.

• Spongy (cancellous) bone: Porous, found at the ends of long bones and inside flat bones, providing support and flexibility.

Bone Cells and Their Functions

Bone tissue contains specialized cells responsible for growth, maintenance, and remodeling.

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteoclasts: Break down bone matrix for remodeling and calcium release.

Intramembranous Ossification

This process forms flat bones, such as those of the skull, directly from mesenchymal tissue.

1. Mesenchymal cells cluster and differentiate into osteoblasts.

2. Osteoblasts secrete bone matrix, forming ossification centers.

3. Matrix calcifies, trapping osteoblasts as osteocytes.

4. Trabeculae form, and periosteum develops.

Endochondral Ossification

This process forms most bones, including long bones, from a cartilage template.

1. Cartilage model develops.

2. Chondrocytes enlarge and die; matrix calcifies.

3. Blood vessels invade; osteoblasts form bone matrix.

4. Primary and secondary ossification centers develop.

5. Cartilage is replaced by bone, except at articular surfaces and growth plates.

Growth of Long Bones

Long bones grow in length at the epiphyseal (growth) plate through endochondral ossification.

• Chondrocytes proliferate and enlarge at the growth plate.

• Matrix calcifies, and osteoblasts replace cartilage with bone.

• Bone growth continues until the growth plate closes after puberty.

Impact of Nutrition on Bones

Nutrition plays a vital role in bone health and development.

• Vitamin A: Essential for osteoblast activity and bone growth.

• Vitamin D: Promotes calcium absorption for bone mineralization.

• Calcium and phosphorus: Key minerals for bone strength.

Example: Deficiency in vitamin D can lead to rickets, a disease characterized by weak and deformed bones.