Chapter 7 (1)

• The skeletal system is composed of bones, cartilage, and ligaments. Cartilage is the forerunner of most bones as it covers many joint surfaces of mature bone. Ligaments hold bones together at joints. And tendons attach muscle to bone.
• Functions of the Skeleton include: Support, Protection, Movement, Electrolyte balance, Acid–base balance, and Blood formation.
• SUPPORT: The bones of the limbs and vertebrae support the body; jaw bones support teeth; some bones support viscera. PROTECTION: of the brain, spinal cord, heart, lungs, and more. MOVEMENT: limb movements, breathing, and other movements depend on the bone.
• ELECTROLYTE BALANCE: for calcium and phosphate levels. ACID-BASE BALANCE: the skeleton buffers blood against large pH changes by altering phosphate and carbonate salt levels. BLOOD FORMATION: red bone marrow is the chief producer of blood cells.
• Bone (osseous tissue) is connective tissue with the matrix hardened by calcium phosphate and other minerals. Mineralization or calcification is the hardening process of bone. Individual bones (are also organs) consist of bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.
• The types of bone: Long bone (are longer than wide and have rigid levers acted upon by muscles; crucial for movement e.g femur), short bone (are approximately equal in length and width and glide across one another in multiple directions e.g NOT the finger bones but the carpals and tarsals(phalanges)), flat bone (are thin, curved plates that protect soft organs e.g the sternum), and irregular bone (are elaborate shapes that do not fit into other categories e.g the coccyx).
• The types of bones diagram:

  
• Compact bone is the dense outer shell of the bone. WHILE Spongy (cancellous) bone is loosely organized bone tissue found in the center of ends and center of shafts of long bones and the middle of nearly all others. It is covered by more durable compact bone. The skeleton is three-fourths compact bone and one-fourth spongy bone by weight.
• Features of long bones include: Long bone, Epiphyses and diaphysis, Compact and spongy bone, Marrow cavity, Articular cartilage, and Periosteum.
• The diaphysis is the shaft that provides leverage. The medullary cavity (marrow cavity) is the space in the diaphysis of a long bone that contains bone marrow. The epiphyses are enlarged ends of a long bone and they strengthen the joint and anchor ligaments and tendons.
• Articular cartilage is the layer of hyaline cartilage that covers the joint surface; it allows the joint to move more freely. The nutrient foramina are minute holes in the bone surface that allow blood vessels to penetrate through.
• The periosteum is the external sheath covering most of the bone. There is the outer fibrous layer of collagen and the Inner osteogenic layer. With the outer fibrous layer of collagen, some fibers are continuous with tendons and there are perforating fibers that penetrate the bone matrix. With the inner osteogenic layer of bone-forming cells, it is important to bone growth and the healing of fractures.
• The endosteum is a thin layer of reticular connective tissue lining the marrow cavity. It has cells that dissolve osseous tissue and others thatdeposit it.
• The epiphyseal plate (growth plate) is the area of hyaline cartilage that separates epiphyses and diaphyses of children’s bones. It enables growth in length. The epiphyseal line is in adults, and it is a bony scar that marks where the growth plate used to be.
• A diploe is a spongy middle layer that absorbs shock and its marrow spaces are lined with endosteum.
• There are Four principal types of bone cells: Osteogenic cells, osteoblasts, osteocytes, and osteoclasts. Bone is connective tissue that consists of cells, fibers, and ground substances.
• Osteogenic cells are stem cells found in the endosteum and inner layer of the periosteum. They arise from embryonic mesenchymal cells and multiply continuously and give rise to most other bone cell types.
• Osteoblasts build bones by synthesizing a soft organic material that hardens through mineral deposition. They increase in number when there is stress on the bones, reinforcing them. Osteoblasts also produce osteocalcin, a hormone that stimulates insulin secretion in the pancreas and increases insulin sensitivity in adipocytes, limiting the growth of adipose tissue.
• Osteocytes are former osteoblasts that have become trapped in the matrix they deposited. Lacunae are tiny cavities where osteocytes reside. Canaliculi are little channels that connect lacunae. The cytoplasmic processes of osteocytes reach into canaliculi and contact processes of neighboring cells. Gap junctions allow for the passage of nutrients, wastes, and signals. And some osteocytes reabsorb bone matrix while others deposit it. They act as strain sensors, which when stressed, produce biochemical signals that regulate bone remodeling (shape and density changes that are adaptive).
• Osteoclasts are bone-dissolving cells found on bone surface. They develop from the same bone marrow stem cells that give rise to blood cells (different origin from other bone cells). Very large cells formed from the fusion of several stem cells have multiple nuclei in each cell. The ruffled border (large surface area) faces bone. The cells often reside in resorption bays (pits in the bone surface) and Dissolving bone is part of bone remodeling.