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It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The matrix is hardened by the binding of inorganic mineral salt, calcium phosphate, in a chemical arrangement known as bone mineral, a form of calcium apatite. [8] [9] It is the mineralization that gives bones rigidity. Bone is actively constructed and remodeled throughout life by specialized bone cells known as osteoblasts and osteoclasts.
The cell body varies in size from 5–20 micrometers in diameter and contain 40–60 cell processes per cell, [4] with a cell to cell distance between 20–30 micrometers. [3] A mature osteocyte contains a single nucleus that is located toward the vascular side and has one or two nucleoli and a membrane. [ 5 ]
Cell type % cell count: Erythrocytes (red blood cells) 84.0 Platelets: 4.9 Bone marrow cells 2.5 Vascular endothelial cells: 2.1 Lymphocytes: 1.5 Hepatocytes: 0.8 Neurons and glia: 0.6 Bronchial endothelial cells: 0.5 Epidermal cells: 0.5 Respiratory interstitial cells: 0.5 Adipocytes (fat cells) 0.2 Dermal fibroblasts: 0.1 Muscle cells: 0.001 ...
This is a list of human anatomy mnemonics, categorized and alphabetized.For mnemonics in other medical specialties, see this list of medical mnemonics.Mnemonics serve as a systematic method for remembrance of functionally or systemically related items within regions of larger fields of study, such as those found in the study of specific areas of human anatomy, such as the bones in the hand ...
In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots. Each lacuna is occupied during life by a branched cell, termed an osteocyte, bone-cell or bone-corpuscle. Lacunae are connected to one another by small canals called canaliculi. A lacuna never contains more than one osteocyte.
The axial skeleton (80 bones) is formed by the vertebral column (32–34 bones; the number of the vertebrae differs from human to human as the lower 2 parts, sacral and coccygeal bone may vary in length), a part of the rib cage (12 pairs of ribs and the sternum), and the skull (22 bones and 7 associated bones).
A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed. These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. The sesamoid bones protect tendons by helping them overcome compressive forces.