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Bone Physiology
Bone tissue (osseous tissue) is a hard tissue, a type of dense connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity.
Bone tissue is made up of different types of bone cells.The structure of a bone has
two parts: the diaphysis and the epiphysis. The diaphysis is the tubular shaft that runs
between the proximal and distal ends of the bone. The hollow region in the diaphysis
is called the medullary cavity , which is filled with yellow marrow. The walls of the
diaphysis are composed of dense and hard compact bone. The wider section at each
end of the bone is called the epiphysis (plural = epiphyses), which is filled with
spongy bone. Red marrow fills the spaces in the spongy bone. Each epiphysis meets
the diaphysis at the metaphysis, the narrow area that contains the epiphyseal
plate (growth plate), a layer of hyaline (transparent) cartilage in a growing bone.
When the bone stops growing in early adulthood (approximately 18–21 years), the
cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal
line.
The medullary cavity has a delicate membranous lining called the endosteum (end- =
“inside”; oste- = “bone”), where bone growth, repair, and remodeling occur. The outer
surface of the bone is covered with a fibrous membrane called the periosteum (peri –
= “around” or “surrounding”). The periosteum contains blood vessels, nerves, and
lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to
bones at the periosteum. The periosteum covers the entire outer surface except where
the epiphyses meet other bones to form joints. In this region, the epiphyses are
canaliculi of other lacunae and eventually with the central canal. This system allows
nutrients to be transported to the osteocytes and wastes to be removed from them.
2 - SPONGY (CANCELLOUS) BONE
Like compact bone, spongy bone , also known as cancellous bone, contains osteocytes
housed in trabeculae (singular = trabecula) (Figure 7). The trabeculae may appear to
be a random network, but each trabecula forms along lines of stress to provide
strength to the bone. The spaces of the trabeculated network provide balance to the
dense and heavy compact bone by making bones lighter so that muscles can move
them more easily. In addition, the spaces in some spongy bones contain red marrow,
protected by the trabeculae, where hematopoiesis occurs.
Remodeling Bone is constantly being created and replaced in a process known as remodeling. This ongoing turnover of bone is a process of resorption followed by replacement of bone with little change in shape. This is done by osteoblasts and osteoclasts. Cells are stimulated by a variety of signals, and together referred to as a remodeling unit. Approximately 10% of the skeletal mass of an adult is remodelled each year.[43]^ The purpose of remodeling is 1 - to regulate calcium homeostasis, 2 - 2 - repair microdamaged bones from everyday stress, and to shape the skeleton during growth.[ citation^ needed ]^ Repeated stress, such as weight- bearing exercise or bone healing The action of osteoblasts and osteoclasts are controlled by a number of chemical enzymes that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape. The cells also use paracrine signalling to control the activity of each other.[ citation needed ] (^) For example, the rate at which osteoclasts resorb bone is inhibited by calcitonin and osteoprotegerin. Calcitonin is produced by parafollicular cells in the thyroid gland, and can bind to receptors on osteoclasts to directly inhibit osteoclast activity. Osteoprotegerin is secreted by osteoblasts and is able to bind RANK-L, inhibiting osteoclast stimulation.[45] Functions of Bone Mechanical
- Protection
- Gives structure
- Facilitates movement
- Facilitates hearing Synthetic
- Contains bone marrow Metabolic
- Stores calcium
- Helps regulate the acid-base balance Mechanical [edit] Bones serve a variety of mechanical functions. Together the bones in the body form the skeleton. They provide a frame to keep the body supported, and an attachment point for skeletal muscles, tendons, ligaments and joints, which function together to generate and transfer forces Bones protect internal organs, such as the skull protecting the brain or the ribs protecting the heart and lungs. bones also have a special role in hearing. The ossicles are three small bones in the middle ear which are involved in sound transduction. Synthetic [edit] The cancellous part of bones contain bone marrow. Bone marrow produces blood cells in a process called hematopoiesis.[34]^ Blood cells that are created in bone marrow include red blood cells, platelets and white blood cells. Metabolic [edit]
- Mineral storage – bones act as reserves of minerals important for the body, most notably calcium and phosphorus. °Determined by the species, age, and the type of bone, bone cells make up to 15 percent of the bone. Growth factor storage – mineralized bone matrix stores important growth factors such as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins and others.[
- Fat storage —marrow adipose tissue (MAT) acts as a storage reserve of fatty acids.[41]
- Acid-base balance – bone buffers the blood against excessive pH changes by absorbing or releasing alkaline saltsDetoxification – bone tissues can also store heavy metals and other foreign elements, removing them from the blood and reducing their effects on other tissues. These can later be gradually released for excretion.
- Endocrine organ – bone controls phosphate metabolism by releasing fibroblast growth factor – 23 (FGF-23), which acts on kidneys to reduce phosphate reabsorption. Bone cells also release a hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.[42]
- Calcium balance—The process of bone resorption by the osteoclasts releases stored calcium into the systemic circulation and is an important process in regulating calcium balance. As bone formation actively fixes circulating calcium in its mineral form, removing it from the
. higher risk of developing rickets in those eat a vegetarian diet that doesn’t include fish, eggs, or milk. Or have trouble digesting milk or have an allergy to milk sugar (lactose). Infants who are only fed breast milk can become deficient in vitamin D as well. Breast milk doesn’t contain enough vitamin D to prevent ricket - pain or tenderness in the bones of the arms, legs, pelvis, or spine - stunted growth and short stature - bone fractures - muscle cramps - teeth deformities, Osteoporosis due to lower-than-normalmaximum bone massand greater-than-normal bone loss.[3]Bone loss increases aftermenopause due to lower levels ofestrogen.[3] Osteoporosis may also occur due to a number of diseases or treatments, includingalcoholism,anorexia,hyperthyroidism,kidney disease , andsurgical removal of the ovaries.[3] Certain medications increase the rate of bone loss, including someantiseizure medications,chemotherapy, proton pump inhibitors,selective serotonin reuptake inhibitors , andglucocorticosteroids.[3]Smokingand too littleexercise are also risk factors. Paget’s disease is the second most common type of bone disease afterosteoporosis. It is a disorder of the bone remodeling process, in which the body absorbs old bone and forms abnormal new bone. ...
- [^ Paget's disease typically occurs in an older population.
- Signs of Paget’s disease of bone include: pain associated with bones and joints, headaches, hearing loss, enlargement or bowing of bones, tingling or numbness
