Lecture Notes: Bones as Organs

Overview

• Bones contain various tissue types: osseous tissue, cartilage, fibrous connective tissue, nervous tissue, epithelial tissue, and muscle tissue.
• Bones are considered organs due to the presence of multiple tissue types.

Bone Structure

1. Hierarchical Levels of Bone Structure
   • Gross Anatomy: Examination of bone textures.
     • Compact Bone: Dense, smooth, solid, found along bone margins.
     • Spongy Bone: Interior parts, made of trabeculae, allows resistance from multiple planes.

Types of Bones

1. Short, Irregular, and Flat Bones

   • Found in the skull, consist of thin plates of compact bone with spongy bone, known as diplo, in the middle.
   • Periosteum: Connective tissue covering for blood vessels and nerves.
   • Endosteum: Connective tissue layer between compact and spongy bone.
   • No shafts or epiphysis; spongy bone may contain red bone marrow but lacks a cavity.
   • Hyaline cartilage present at joints.

2. Long Bones

   • Diaphysis: Shaft with a hollow medullary cavity, mainly compact bone.
   • Metaphysis: Region where bone grows, consists of spongy bone.
   • Epiphyseal Line/Plate: Cartilage that facilitates bone growth in length.
   • Epiphysis: Contains compact bone on the outside and spongy bone inside.
   • Marrow Types:
     • Red Bone Marrow: Found in spongy bone, site for hematopoiesis.
     • Yellow Bone Marrow: Found in medullary cavity, fat storage.
   • Periosteum and Endosteum play significant roles in the structure and function.

Membranes Associated with Bones

1. Periosteum

   • White, double-layered membrane covering external bone surfaces except at joints.
   • Consists of dense, irregular connective tissue with collagen fibers (Sharpies fibers) that secure it to the bone matrix.
   • Contains an osteogenic layer with undifferentiated osteogenic cells.
   • Serves as an attachment point for tendons and ligaments.
   • Contains nutrient arteries and nerve fibers.

2. Endosteum

   • Delicate membrane lining the interior surface of compact bone and trabeculae of spongy bone.
   • Contains osteogenic cells for bone repair and remodeling.

Bone Marrow

• Red Bone Marrow

  • Important for blood cell formation, found in small cavities in flat bones and ends of long bones.
  • Present in medullary cavities of newborns; can convert from yellow marrow under anemic conditions.

• Yellow Bone Marrow

  • Contains fat, found in hollow medullary cavities of long bones.

Conclusion

• Bones, with their complex structure and various tissue types, serve multiple roles including the formation of blood cells, fat storage, and providing structural strength and support.