bone (osseous tissue) ( os' e-us): a connective tissue that forms in the bony skeleton. Bones are organs because they contain tissues.
During development of the embryo, the human skeleton is made up of cartilages and fibrous membranes, but most of these early supports are soon replaced by bone. early life
There are 206 named bones of the human skeleton . They are divided into the axial and appendicular groups. fact
the axial skeleton These bones form the vertical axis of the body. They function in protection and support of the body and body parts. bones of the axial skeleton : <ul>- skull bones - vertebral column - rib cage </ul>
the appendicular skeleton These bones comprise the upper and lower limbs of the body, and the bones that connect limbs to the axial skeleton. They function in movement. Bones of the appendicular skeleton: <ul>- shoulder bones - Hip bones - Arms and hands - Legs and feet </ul>
fact Bones support, protect, and allow for movement of the body. Uncommonly known: <ul>- Bones store minerals (including calcium and phosphate) and distribute them to the rest of the body - Hematopoiesis (blood cell formation) occurs in the red marrow of certain bones - Bones store triglycerides (fat) in the yellow marrow of certain bones </ul>
bone markings All bones have bone markings. The external surfaces of bones display projections, depressions and openings—they are not smooth. Bone markings are the sites for muscle, ligament and tendon attachment. They also serve as passageways for blood vessels and nerves.
bone textures Bones are made up of 2 layers that differ in texture and function: <ul>- Compact bone: external layer of the bone that is very dense, appearing to be smooth and solid but actually is filled with passageways for nerves, blood vessels, and lymphatic vessels - Cancellous bone: internal layer of the bone that looks spongy; this spongy layer contains the red or yellow bone marrow </ul>
bone classifications <ul>- Long bones: longer than they are wide; have a shaft with 2 ends. All limb bones (except knee cap, wrist and ankle bones), including finger and toe bones - Short bones: cube-shaped or sesame seed-shaped (sesamoid bones). Include wrist and ankle bones - Flat bones: thin, flat and often curved. The breastbone, shoulder blades, ribs and skull bones are flat bones - Irregular bones: all other bones; have complicated shapes. Included are the hip bones and vertebrae </ul>
long bone structure Long bones are mainly comprised of a shaft, 2 ends and membranes. <ul>- Diaphysis: the shaft of a long bone; constructed of compact bone and envelopes a marrow cavity. In adults, this cavity stores yellow marrow (fat) - Epiphyses: the bone ends of a long bone; constructed of compact bone externally and spongy bone internally. Contains cartilage at joints for cushion during movement - Periosteum & Endosteum: double-layered membrane that lines the external and internal long bone respectively; contain bone-forming cells and bone-destroying cells. Responsible for the growth and health of bones </ul>
short, irregular & flat bone structure Consist of thin plates covered in periosteum (membrane); contain compact bone externally and spongy bone internally. Have no shaft or epiphyses, and contain red or yellow marrow.
blood cell production <ul>- Hematopoietic tissue (red marrow) is mostly found within spongy bone of long bones and flat bones - In adults, blood cell production occurs primarily in the heads of the femur and humerus bones (long bones), and in the sternum (flat bone) and hip bone (irregular bone) - Yellow marrow can convert itself into to red marrow if a person becomes anemic and needs more red blood cells </ul>
bone cells 4 types of cells make up bone tissue: <ul>- Osteogenic cells: stem cells that undergo mitosis to generate more bone cells, plus create osteoblasts and osteoclasts - Osteocytes: Maintain bone matrix; act as sensors of bone deformation or other bone damage and alert bone repairing cells - Osteoblasts: Bone-forming cells; secrete bone matrix and create new bone - Osteoclasts: Bone-destroying cells; break down and phagocytize (eat) demineralized matrix and dead osteocytes </ul>
bone formation <ul>Bone formation happens in 4-5 main stages: 1. Bone tissue begins to develop and replace fibrous membranes and cartilage at about week 8 of embryonic development 2. Cartilage in the center of the bone calcifies and develops cavities 3. The periosteal bud (contains a nutrient-rich artery and vein, lymphatic vessels, nerve fibers, red marrow elements and bone cells) begins to form and invade cavities, secreting bone matrix </ul>
bone formation <ul>4. The forming bone continues to grow this way throughout the fetal period (week 9 until birth) 5. Shortly before or after birth, cavities and spongy bone form in the epiphyses of long bones and bone cells continue to secrete bone matrix. This phase does not happen in short bones, and this phase happens continually in irregular bones </ul>
fact Most bones stop growing during adolescence. Some facial bones, especially those of the nose and lower jaw, continue to grow almost to no end throughout life.
hormones Until young adulthood, bone formation is controlled by hormones. <ul>- Growth hormone is the most important stimulus of bone growth during infancy and childhood - Thyroid hormones regulate the activity of growth hormone, making sure bones grow at proper proportions - At puberty, the sex hormones testosterone and estrogen promote the growth spurt typical of adolescence and induce masculinization or feminization - During the end of adolescence, sex hormones then trigger closure, ending bone growth </ul>
bone disease When there is an imbalance or dysfunction with bone remodeling cells or other aspects of bone formation, a variety of bone diseases can occur. <ul>- Osteomalacia: “Soft bones;” includes several disorders in which bone minerals (calcium) are not deposited so bones soften and weaken, such as Rickets - Rickets: A bone disorder in children where bones grow too rapidly so bone deformations occur. Caused by insufficient calcium or Vitamin D </ul>
<ul><li>Osteoporosis: A group of diseases in which bone destruction by osteoclasts outpaces bone deposit by osteoblasts. Bones become so fragile that the smallest amount of pressure can cause bones to break
Paget's Disease: Occurs when excessive bone is deposited by osteoblasts, and this production is not matched by the breaking down of bone by osteoclasts which results in abnormally high ratios of spongy bone. The spine, pelvis, femur and skull most often become deformed </li></ul>bone disease
Sources “ Human Anatomy & Physiology, Pearson International Edition, Eighth Edition.” Marieb and Hoehn. 2010.
Images McGraw-Hill Companies. www.mcgraw-hill.com/ National Library of Medicine and International Osteoporosis Foundation. www.nlm.nih.gov/ Nucleus Communications, Inc. 2003. www.nucleusinc.com Visual Dictionary Online. www.visualdictionaryonline.com
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