Bones and Skeletal Tissues Part 1

Bones and Skeletal Tissues Part 1

• The skeletal system is an interconnected network of bones, ligaments, and tendons.
• This system provides support and protection for the body.
• The human skeleton is comprised of 206 bones.

Objectives

• The objectives include describing bone classification.
• Discussing the functions of the skeletal system.
• Identifying the four types of bones.
• Identifying various bone cells.

Skeletal Cartilages

• Cartilage does not contain blood vessels or nerves.
• Perichondrium surrounds cartilage, supplying nutrients.
• Three types of skeletal cartilages are hyaline, elastic, and fibrocartilage.

Types of Cartilage

• Hyaline cartilage: Provides support, flexibility, and resilience; most abundant.
• Elastic cartilage: Similar to hyaline, but includes elastic fibers.
• Fibrocartilage: Contains collagen fibers for great tensile strength.

Respiratory Tube Cartilages in Neck & Thorax

• Found in the respiratory system.

Growth of Cartilage

• Appositional growth: Cartilage cells secrete matrix on the external face of existing cartilage.
• Interstitial growth: Chondrocytes divide and secrete new matrix, expanding cartilage internally.
• Calcification occurs during normal bone growth and old age.

Bones of Skeleton

• Two main groups:
  • Axial skeleton: Bones of the skull and vertebrae, mainly flat and irregular, protect organs like the brain, heart, and lungs, and support the body.
  • Appendicular skeleton: Bones of the limbs and girdles.

Parts of the Axial Skeleton

• Skull: Protects the brain.
• Vertebrae: Protect the spinal cord and help maintain upright posture.
• Ribs: Protect the lungs and heart; intercostal muscles move against the ribs for breathing.

Classification of Bones by Shape

• Long bones: Longer than wide (e.g., humerus).
• Short bones: Cube-shaped (e.g., carpals, tarsals).
• Flat bones: Thin, flat, slightly curved (e.g., skull bones).
• Irregular bones: Complicated shapes (e.g., vertebra, sphenoid).

Long Bones

• Found in the limbs.
• Each bone is a body (diaphysis) and extremities (epiphyses).
• The wall consists of dense tissue.
• A medullary canal contains marrow.

Divisions of the Skeletal System

• Divided into two:
  • Axial: central, protects vital organs.
  • Appendicular: skeleton of the extremities.

Structure of a Long Bone

• Diaphysis (shaft): Compact bone collar surrounds the medullary cavity, which contains yellow marrow in adults.
• Epiphyses (ends): Spongy bone interior, epiphyseal line (remnant of growth plate), articular cartilage on joint surfaces.

Membranes of Bone

• Periosteum: Outer fibrous layer. Inner osteogenic layer contains bone-forming cells (osteoblasts), bone-destroying cells (osteoclasts), and stem cells. Nerve fibers, nutrient blood vessels enter via nutrient foramina, secured to underlying bone by Sharpey's fibres.
• Endosteum: Delicate membrane on internal surfaces of bone; contains osteoblasts and osteoclasts.

Bone Textures

• Compact bone: Dense outer layer.
• Spongy bone: Honeycomb of trabeculae.

Location of Hematopoietic Tissue (Red Marrow)

• Adult red marrow is in trabecular cavities of the heads of the femur and humerus, and diploë of flat bones.
• Infant red marrow is in medullary cavities and all spaces in spongy bone.

Microscopic Anatomy of Bone - Cells of Bone

• Osteogenic cells: Stem cells that differentiate into osteoblasts.
• Osteoblasts: Bone-forming cells.
• Osteocytes: Mature bone cells.
• Osteoclasts: Cells that break down bone matrix.

Microscopic Anatomy of Bone - Compact Bone

• Haversian system (osteon): Weight-bearing, column-like matrix tubes, Haversian/central canal (contains blood vessels and nerves).
• Lamellae (matrix tubes). Perforating/Volkmann's canals connect blood vessels and nerves. Lacunae (small cavities containing osteocytes). Canaliculi (hair-like canals connecting lacunae and central canal).

Microscopic Anatomy of Bone - Spongy Bone

• Trabeculae: Align along lines of stress; contain irregularly arranged lamellae,osteocytes, and canaliculi. Capillaries in endosteum supply nutrients.

Chemical Composition of Bone - Organic

• Osteogenic cells, osteoblasts, osteocytes, osteoclasts.
• Osteoid—organic bone matrix secreted by osteoblasts(proteoglycans, glycoproteins).
• Collagen fibers provide tensile strength and flexibility.

Chemical Composition of Bone - Inorganic

• Hydroxyapatites (mineral salts): 65% of bone mass.
• Mainly calcium phosphate crystals.
• Responsible for hardness & compression resistance

Factors Contributing to Bone Growth

• Nutrition (mainly calcium).
• Exposure to sunlight (promotes vitamin D production for calcium absorption).
• Hormonal secretion (e.g., growth hormone).
• Physical exercise (increases bone density and strength).

Bone Markings: Projections

• Sites of muscle and ligament attachments.
• Tuberosity, crest, trochanter, line, tubercle, epicondyle, spine, process.

Bone Markings: Depressions and Openings

• Meatus (canal-like passageways), sinus (cavity within a bone), fossa (shallow, basin-like depression), groove (furrow), fissure (narrow, slit-like opening), foramen (round or oval opening).

Explore the foundational concepts of the skeletal system in this quiz. You will learn about bone classification, the four types of bones, and the various bone cells. Additionally, we will cover the characteristics and types of skeletal cartilages.