Bone Tissue - Chapter 6 Lecture Notes

The humerus in the arm serves as a typical example of a long bone.
The diaphysis is defined as the shaft or main body of a long bone.
The epiphyses constitute the distal and proximal ends of a long bone.
The metaphyses are the transitional areas where the epiphyses and diaphysis converge and join.
In adolescents, until the cessation of active growth, the epiphysis of long bones contains hyaline cartilage, forming an "epiphyseal growth plate."
- The growth plate is characterized by continuous active cell division, facilitating the elongation of the bone from each end.
In adults, the epiphyseal cartilage is no longer present, signifying that bone elongation has ceased.
- The epiphyseal growth plate transforms into an "epiphyseal line," as the growing cartilage is progressively replaced by calcified bone.
- The epiphyseal line is identifiable both externally and through X-ray imaging.

Compact bone is composed of structural units known as osteons or Haversian systems.
- These systems are formed from concentric lamellae, which are rings of calcified matrix.
Interstitial lamellae are fragments of older osteons that are found between intact osteons.
Outer circumferential lamellae encircle the entire bone, located directly beneath the periosteum.
Inner circumferential lamellae encircle the medullary cavity.
Lacunae are small, microscopic spaces situated between the lamellae which serve as housing for osteocytes.
Canaliculi are tiny channels filled with extracellular fluid that connect adjacent lacunae, allowing for nutrient exchange and waste removal.
The osteon's Central canal (also known as the Haversian canal) contains essential blood vessels and lymphatic vessels.
Perforating (Volkmann's) canals are channels that allow for the transit of blood and lymphatic vessels from the periosteum to the osteon's central canal and to the outer cortex of the bone.

Spongy bone, unlike compact bone, does not contain osteons.
- Instead, its lamellae are organized into a lattice-like network of thin columns called trabeculae.
- The trabeculae of spongy bone are crucial for supporting and protecting the red bone marrow.
- They are strategically oriented along lines of mechanical stress, which enhances the bone's ability to resist stresses without fracturing.
- Hematopoiesis, the process of blood cell production, occurs within the red bone marrow supported by spongy bone.
Within each trabecula of spongy bone, there are lacunae.
- Similar to compact bone, these lacunae contain osteocytes.
- These osteocytes are nourished by blood circulating through the trabeculae, ensuring the health of the mature bone tissue.
The interior of long bones is primarily composed of spongy bone.
- The presence of spongy bone significantly contributes to lessening the overall weight of the bone, an important functional advantage.

Bone tissue is highly vascularized, meaning it is richly supplied with blood.
- Periosteal arteries and veins are responsible for supplying blood to the periosteum and the underlying compact bone.
Nerves typically accompany the blood vessels into the bone tissue.
- The periosteum is particularly rich in sensory nerves.
- These nerves are highly sensitive to tearing or tension, explaining the intense pain experienced when, for example, one bruises their shin due to the periosteum being heavily innervated.