Skeletal System
Bones, cartilages, ligaments, and connective tissues.
Functions of Skeletal System
Support, storage of minerals (calcium) and lipids (yellow marrow), blood cell production (red marrow), protection, and leverage (force of motion).
Sutural Bones
Small, irregular bones; found in between the flat bones of the skull.
Irregular Bones
Have complex shapes; examples are spinal vertebrae.
Short Bones
Small and thick; examples are ankle and wrist bones.
Flat Bones
Have thin, parallel surfaces; found in skull, sternum, ribs, and scapulae.
Long Bones
Long and thin; found in arms, legs, hands, feet, fingers, and toes.
Sesamoid Bones
Usually small, and flat; develop inside tendons near joints of knees, hands, and feet.
Depressions
Bone markings along bone surface.
Elevations (projections)
Where tendons and ligaments attach; at articulations with other bones.
Tunnels
Where blood and nerves enter bone.
Diaphysis
The shaft, heavy wall of compact bone; contain a central space called medullary (marrow) cavity.
Epiphysis
Wide part at each end of long bone where they articulate with other bones; mostly spongy bone and covered with compact bone.
Metaphysis
Where the diaphysis and epiphysis meet.
Bone (Osseous) Tissue
Dense, supportive connective tissue that contains specialized cells; produce solid matrix of calcium salt deposits around collagen fibers.
Minerals in Bone Matrix
Two-thirds of bone is calcium phosphate which reacts with calcium hydroxide to form crystals of hydroxyapatite, which incorporates other calcium salts and ions.
Canaliculi
Form pathways for blood vessels; exchange nutrients and waste.
Periosteum
Covers outer surfaces of bones; consists of outer fibrous and inner cellular layers.
Matrix Proteins in Bone Matrix
One-third of bone matrix is protein fibers.
Bone Cells
Make up only 2% of bone mass; contain osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts.
Osteoprogenitor Cells
Mesenchymal stem cells that divide to produce osteoblasts; located in endosteum, the inner cellular layer of periosteum. Assist in fracture repair.
Osteoblasts
Immature bone cells that secrete matrix compounds (osteogenesis). Osteoid- matrix produced by osteoblasts but not yet calcified to form bone. Osteoblasts surrounded by bone become osteocytes.
Osteocytes
Mature bone cells that maintain the bone matrix, live in lacunae, are between layers (lamellae) of matrix, and connect by cytoplasmic extensions through canaliculi in lamellae; do not divide. Functions: to maintain protein and mineral content of matrix, a
Osteoclasts
Secrete acids and protein-digesting enzymes; giant, multinucleate cells. Dissolve bone matrix and release stored minerals (osteolysis). Derived from stem cells that produce macrophages.
Homeostasis
Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance. More breakdown that building, bones become weak. Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone.
Compact Bone
Osteon is the basic unit; osteocytes are arranged in concentric lamellae around a central canal containing blood vessels, and have perforating canals (carry blood vessels into bone and marrow).
Circumferential Lamellae
In compact bone. Lamellae wrapped around the long bone. bind osteons together.
Spongy Bone
Does NOT have osteons; the matrix forms an open network of trabeculae (which have no blood vessels), the space in between trabeculae is filled with red bone marrow (which has blood vessels, forms red blood cells, and supplies nutrients to osteocytes. Cont
Weight-Bearing Bones
The femur transfers weight from hip joint to knee joint, causing tension on the lateral side of the shaft, and compression on the medial side.
Periosteum
Covers all bones except parts enclosed in joint capsules; made up of an outer, fibrous layer and an inner, cellular layer. Contain perforating fibers: collagen fibers of the periosteum that connect with collegian fibers in bone, attach tendons, and ligame
Endosteum
An incomplete cellular layer that lines the medullary (marrow) cavity, covers trabeculae of spongy bone, lines central canals; contain osteoblasts, osteoprogenitor cells, and osteoclasts. Active in bone growth and repair.
Osteogenesis
Bone formation.
Ossification
The process of replacing other tissues with bone; Endochondral and Intramembranous.
Calcification
The process of depositing calcium salts; occurs during bone ossification and in other tissues.
Endochondral Ossification
Ossifies bone that originate as hyaline cartilage, seven main steps in endochondral ossification.
Intramembranous Ossification
Also called Dermal Ossification, occurs in the dermis; produces dermal bones such as mandible and clavicle.
Metaphyseal Vessels
Supply the epiphyseal cartilage, where bone growth occurs.
Periosteal vessels
Blood to superficial osteons, secondary ossification centers.
Lymph and Nerves
The periosteum also contains networks of lymphatic vessels and sensory nerves.
Bone Remodeling
Skeleton replaces mineral reserves, recycles and renews bone matrix, involves osteocytes, osteoblasts, and osteoclasts. Bone continually remodels, recycles, and replaces. Deposition > removal= bones stronger. Removal > Replacement= bones weaker.