Bones

• Flat bones are two compact bone sections with spongy bone in between them. An example of this bone is the frontal bone.
• An example of short bones are your carpal and tarsal bones.
• An example of a sesamoid bone is your patella.
• An example of a sutural bone is your flat bone in your cranium.
• An example of an irregular bone is your vertebra.
• Long bones have a medullary cavity with yellow bone marrow. The tips have spongy bone and the shafts have compact bone. An example of a long bone is your femur.
• Fossa are indentations where tendons and ligaments attach.
• Foramen are openings and depressions in bone for the passage of blood vessels and nerves.
• The epiphysis is the wide part at the end of a long bone. It contains mostly spongy (trabecular) bone.
• The diaphysis is the shaft of a long bone and it has a wall of compact bone. The central space is known as the medullary cavity.
• The metaphysis is where the diaphysis and epiphysis meet.
• About 1/3 of bone mass is collagen.
• Osteogenic cells/osteoprogenitors are mesenchymal cells that differentiate into other types of cells. They line the medullary cavity.
• Osteogenic cells/osteoprogenitors line the medullary cavity.
• Osteocytes are in ostoens in compact bone. They are found in lacunae and help to mantain protein and mineral content of the bone, and communicate via gap junctions connected with caniliculi.
• Osteoblasts help to produce new bone matrix and become osteocytes.
• Osteoclasts remove and store bone matrix and release materials into the blood as needed.
• Osteons are the functional unit of compact bone, they are the circles are the top of compact bone.
• The central canal is in the middle of each osteon.
• The perforating canal is perpendicular to the surface of bone. It carries vessels into deep bone and the matrix.
• The lamellae are the layers of bone matrix. Concentric lamellae surround the central canal. Interstitial lamellae fill the space between osteons. Circumferential lamellae surround the outer and inner bone surfaces.
• Calcium phosphate makes up 2/3 of bone. Collagen makes up 1/3 of bone mass. Cells make up a very small portion of a bone.
• The periosteum covers the outside of bones, except with joint cavities. Fibers are interwoven with those of tendons.
• Perforating fibers in the periosteum become incoporated into bone tissue and increase the strength of attachments.
• Tendons, ligaments, and aponeuroses attach to the periosteum.
• The endosteum is an incomplete layer of cells that lines the medullary cavity. It also covers trabeculae of spongy bone and the central canals of compact bone.
• The endosteum is active during bone growth, repair, and modeling.
• Spongy bone matrix forms an open network of trabeculae which lacks capillaries and venules.
• Red blood marrow fills spaces between trabeculae. Yellow bone marrow is found in other sites of spongy bone and stores fat.
• Most bones form through endochondral ossification which is when the primary ossification center, which forms the medullary cavity, develops inside the hyaline cartilage framework. Cartilage turns into bone.
• The secondary ossification center is the center of calcification in the epiphyses of long bones.
• The epiphyseal line is an indicator of the boundary between the epiphysis and the diaphysis.
• Interstitial growth is in the length. Appositional growth is in width.
• Intramembranous ossification makes flat bones as the ossification centers merge and trap blood vessels forming compact bone.
• Bone remodeling occurs throughout life and helps manage balance of calcium ions and phosphorus. It recycles and renews the bone matrix. Calcium and phosphorus help to make up the inorganic calcium matrix that provides rigidity and collagen provides flexibility.
• Vitamin C: collagen synthesis. Vitamin A: stimulates osteoblast activity. Vitamin K, B12: synthesis of bone proteins.
• Calcium is important to many physiological processes like muscular contraction, strengthening the skeleton, and sending impulses via NT.
• Kidneys secrete calcitriol which allows the intestines to absorb more in the case of low calcium concentration, which allows its concentration in the blood to increase. Kidneys swcrete less calcitriol to have less absorbed by intestines if there is high calcium concentration.
• The first horomone that is released if there is low calcium ion concentration is PTH which is secreted by parathyroids. If there is high calcium ion concentration, the thyroid glands secrete calcitonin.
• The intestines absorb calcium ions as dictated by calcitriol release by the kidneys.