Tissues and Cartilage

• There are four basic types of tissue: epithelium, connective, muscle, and nervous.
• An embryo's skeleton is mainly cartilage, which is replaced by bone as childhood ends.

Types of Cartilage

• Elastic cartilage regains its natural shape after stretching.
• Hyaline cartilage is the most abundant type, also known as articular cartilage.
• Fibrocartilage is the strongest type of cartilage.
• A lacuna is a space that protects chondrocytes.
• Chondrocytes maintain the integrity and strength of cartilage by collecting nutrients and producing waste.
• Hyaline cartilage has no fibers.
• Elastic cartilage has elastic fibers.
• Fibrocartilage has collagen fibers.

Terms:

• Chondro = cartilage.
• Osteo = refers to bone.
• Blast = immature cell undergoing mitosis and growing.
• Cyte = a mature cell that is not growing.

Factors Regulating Bone Growth:

• Hormones and vitamins are needed to regulate bone growth.
• Vitamin D increases calcium absorption from the gut.
• Parathyroid hormone (PTH), from four glands, increases blood calcium.
• Calcitonin decreases blood calcium, opposing PTH.
• Growth hormone and thyroid hormone modulate bone growth.
• Sex hormones cause growth spurts at adolescence and the closure of epiphyses.

Bones:

• Bones enable skeletal muscles to attach, facilitating movement.
• They protect internal organs and store minerals.

Bone Functions:

• Support, movement, protection, mineral storage, blood cell formation, and energy storage.
• Red bone marrow makes blood cells, and yellow bone marrow stores fat.

The Periosteum

• The periosteum is a dense fibrocellular membrane covering the exterior bone surface, made of two layers.
• The outer fibrous layer is dense fibrous tissue.
• The inner cellular layer contains elastic fibers, blood vessels, nerve fibers, and dormant osteoblasts.
• Functions include protection, nutrition to bones, and regeneration in fracture healing via osteoblasts.

The Endosteum

• The endosteum is a thin cellular membrane lining most bones and the medullary cavity.
• It contains osteoblasts, osteoclasts (bone-destroying cells), and stem cells.
• Functions include lining the bone marrow, regulating bone remodeling, and providing a niche for hematopoiesis (blood cell formation).

Bone Anatomy:

• Compact bone is hard, and spongy bone is soft.
• Compact bone makes up the hard outer layer. It gives bones a smooth, white appearance, making up 80% of the total bone mass.
• Spongy bone is weaker, less dense, and more flexible than compact bone. It weighs 20% of total bone mass and is highly vascular.
• The osteon, also known as the Haversian system, is the basic structural unit of compact bone tissue.
• The central canal runs lengthwise through the bone, containing nerves and blood vessels that supply the bone.
• Concentric lamellae are composed of a calcified matrix plus inorganic salts and organic material.
• Lacunae are small spaces in bone tissue where mature cells called osteocytes are imprisoned.
• Osteocytes maintain the bone matrix, metabolism, and mineral homeostasis.
• Canaliculi are small canals that extend from lacunae in many directions, connecting other lacunae and providing communication and nutrient delivery in the central canal.

Classification of Bones by Shape:

• Long, short, irregular, sesamoid, and flat.
• The skeletal system is divided into axial and appendicular regions, with 80 and 126 bones, respectively.
• Babies have 300 bones, while adults have 206.

Count of Bones:

• Skull: 22+6+/- floating bone.
• Vertebrae: 26, protect the spinal cord.
• Ribs: 24.
• Sternum: 1.