Thehuman skeleton is the internal framework of thehuman body. It is composed of around 270bones at birth – this total decreases toaround 206 bones by adulthood after some bones fuse together, not countingaccessory bones.[1] The bone mass in the skeleton makes up about 14% of the total body weight (ca. 10–11 kg for an average person) and reaches maximum mass between the ages of 25 and 30.[2] The human skeleton can be divided into theaxial skeleton and theappendicular skeleton. The axial skeleton is formed by thespinal column, therib cage, theskull, and associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by theshoulder girdle, thepelvic girdle and the bones of the upper and lowerlimbs.
The human skeleton performs six major functions: support, movement, protection, production ofblood cells, storage of minerals, and endocrine regulation.
The human skeleton is not assexually dimorphic as that of many other primate species, but subtle differences between sexes in themorphology of the skull,dentition,long bones, and pelvis exist. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The humanfemale pelvis is also different from that of males in order to facilitatechildbirth.[3] Unlike most primates, human males do not havepenile bones.[4]
The axial skeleton (80 bones) is formed by thevertebral column (32–34 bones, depending on the number of elements insacrum andcoccyx), the non-cartilage parts of therib cage (12 pairs ofribs and thesternum), and theskull (22 bones; some sources add 7 associated bones).
The upright posture of humans is maintained by the axial skeleton, which transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at thehip joints. The bones of the spine are supported by many ligaments. Theerector spinae muscles are also supporting and are useful for balance.
The appendicular skeleton (126 bones) is formed by the pectoral girdles, the upper limbs, the pelvic girdle or pelvis, and the lower limbs. Their functions are to make locomotion possible and to protect the major organs of digestion, excretion and reproduction.
Functions
The skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals and endocrine regulation.[citation needed]
Support
The skeleton provides the framework which supports the body and maintains its shape. The pelvis, associated ligaments and muscles provide a floor for the pelvic structures. Without the rib cages,costal cartilages, andintercostal muscles, thelungs would collapse.[citation needed]
Movement
The joints between bones allow movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered byskeletal muscles, which are attached to the skeleton at various sites on bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by the nervous system.
It is believed that the reduction of human bone density in prehistoric times reduced the agility and dexterity of human movement. Shifting from hunting toagriculture has caused human bone density to reduce significantly.[5][6][7]
Protection
The skeleton helps to protect many vital internalorgans from being damaged.[citation needed]
The skeleton is the site ofhaematopoiesis, the development ofblood cells that takes place in thebone marrow. In children, haematopoiesis occurs primarily in the marrow of the long bones such as the femur and tibia. In adults, it occurs mainly in the pelvis, cranium, vertebrae, and sternum.[8]
Storage
Thebone matrix can storecalcium and is involved incalcium metabolism, andbone marrow can storeiron inferritin and is involved iniron metabolism. However, bones are not entirely made of calcium, but a mixture ofchondroitin sulfate andhydroxyapatite, the latter making up 70% of a bone. Hydroxyapatite is in turn composed of 39.8% of calcium, 41.4% of oxygen, 18.5% of phosphorus, and 0.2% of hydrogen by mass. Chondroitin sulfate is a sugar made up primarily of oxygen and carbon.[citation needed]
During construction of the York toScarborough Railway Bridge in 1901, workmen discovered a large stone coffin, close to theRiver Ouse. Inside was a skeleton, accompanied by an array of unusual and expensive objects. This chance find represents one of the most significant discoveries ever made fromRoman York. Study of the skeleton has revealed that it belonged to a woman.
Anatomical differences between human males and females are highly pronounced in some soft tissue areas, but tend to be limited in the skeleton. The human skeleton is not assexually dimorphic as that of many other primate species, but subtle differences between sexes in themorphology of the skull,dentition,long bones, and pelvis are exhibited across human populations. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population.[citation needed] It is not known whether or to what extent those differences are genetic or environmental.
Human inter-sex dental dimorphism centers on thecanine teeth, but it is not nearly as pronounced as in the othergreat apes.
Long bones
Long bones are generally larger in males than in females within a given population. Muscle attachment sites on long bones are often more robust in males than in females, reflecting a difference in overall muscle mass and development between sexes. Sexual dimorphism in the long bones is commonly characterized bymorphometric or gross morphological analyses.[citation needed]
Pelvis
The human pelvis exhibits greater sexual dimorphism than other bones, specifically in the size and shape of thepelvic cavity,ilia, greater sciatic notches, and the sub-pubic angle. ThePhenice method is commonly used to determine the sex of an unidentified human skeleton by anthropologists with 96% to 100% accuracy in some populations.[11]
Women's pelvises are wider in the pelvic inlet and are wider throughout the pelvis to allow for child birth. Thesacrum in the women's pelvis is curved inwards to allow the child to have a "funnel" to assist in the child's pathway from the uterus to thebirth canal.
There are many classified skeletal disorders. One of the most common isosteoporosis. Also common isscoliosis, a side-to-side curve in the back or spine, often creating a pronounced "C" or "S" shape when viewed on an x-ray of the spine. This condition is most apparent during adolescence, and is most common with females.[citation needed]
Arthritis is adisorder of the joints. It involves inflammation of one or more joints. When affected by arthritis, the joint or joints affected may be painful to move, may move in unusual directions or may be immobile completely. The symptoms of arthritis will vary differently between types of arthritis. The most common form of arthritis,osteoarthritis, can affect both the larger and smaller joints of the human skeleton. Thecartilage in the affected joints will degrade, soften and wear away. This decreases the mobility of the joints and decreases the space between bones where cartilage should be.[citation needed]
Osteoporosis is a disease of bone where there is reducedbone mineral density, increasing the likelihood offractures.[12] Osteoporosis is defined by theWorld Health Organization in women as a bone mineral density 2.5standard deviations below peak bone mass, relative to the age and sex-matched average, as measured bydual energy X-ray absorptiometry, with the term "established osteoporosis" including the presence of afragility fracture.[13] Osteoporosis is most common in women aftermenopause, when it is called "postmenopausal osteoporosis", but may develop in men and premenopausal women in the presence of particular hormonal disorders and otherchronic diseases or as a result ofsmoking andmedications, specificallyglucocorticoids.[12] Osteoporosis usually has no symptoms until a fracture occurs.[12] For this reason, DEXA scans are often done in people with one or more risk factors, who have developed osteoporosis and be at risk of fracture.[12]
Osteoporosis treatment includes advice to stop smoking, decrease alcohol consumption, exercise regularly, and have a healthy diet.Calcium supplements may also be advised, as mayvitamin D. When medication is used, it may includebisphosphonates,strontium ranelate, and osteoporosis may be one factor considered when commencinghormone replacement therapy.[12]
TheSushruta Samhita, composed between the 6th century BCE and 5th century CE speaks of 360 bones. Books onSalya-Shastra (surgical science) know of only 300. The text then lists the total of 300 as follows: 120 in the extremities (e.g. hands, legs), 117 in the pelvic area, sides, back, abdomen and breast, and 63 in the neck and upwards.[14] The text then explains how these subtotals were empirically verified.[15] The discussion shows that the Indian tradition nurtured diversity of thought, with Sushruta school reaching its own conclusions and differing from the Atreya-Caraka tradition.[15] The differences in the count of bones in the two schools is partly because Charaka Samhita includes 32tooth sockets in its count, and their difference of opinions on how and when to count a cartilage as bone (which both sometimes do, unlike modern anatomy).[16]
Hellenistic world
The study of bones in ancient Greece started underPtolemaic kings due to their link to Egypt.Herophilos, through his work by studying dissected human corpses in Alexandria, is credited to be the pioneer of the field. His works are lost but are often cited by notable persons in the field such asGalen andRufus of Ephesus. Galen himself did little dissection though and relied on the work of others like Marinus of Alexandria,[17] as well as his own observations of gladiator cadavers and animals.[18] According toKatherine Park, in medieval Europe dissection continued to be practiced, contrary to the popular understanding that such practices were taboo and thus completely banned.[19] The practice ofholy autopsy, such as in the case ofClare of Montefalco further supports the claim.[20] Alexandria continued as a center of anatomy under Islamic rule, withIbn Zuhr a notable figure. Chinese understandings are divergent, as the closest corresponding concept in the medicinal system seems to be themeridians, although given thatHua Tuo regularly performed surgery, there may be some distance between medical theory and actual understanding.
Renaissance
Leonardo da Vinci made studies of the skeleton, albeit unpublished in his time.[21] Many artists,Antonio del Pollaiuolo being the first, performed dissections for better understanding of the body, although they concentrated mostly on the muscles.[22]Vesalius, regarded as the founder of modern anatomy, authored the bookDe humani corporis fabrica, which contained many illustrations of the skeleton and other body parts, correcting some theories dating from Galen, such as the lower jaw being a single bone instead of two.[23] Various other figures likeAlessandro Achillini also contributed to the further understanding of the skeleton.
^"Healthy Bones at Every Age".OrthoInfo. American Academy of Orthopaedic Surgeons.Archived from the original on 18 November 2022. Retrieved6 January 2023.
^Fernández, KS; de Alarcón, PA (Dec 2013). "Development of the hematopoietic system and disorders of hematopoiesis that present during infancy and early childhood".Pediatric Clinics of North America.60 (6):1273–89.doi:10.1016/j.pcl.2013.08.002.PMID24237971.
^Buikstra, J.E.; D.H. Ubelaker (1994).Standards for data collection from human skeletal remains. Arkansas Archaeological Survey. p. 208.
^Phenice, T. W. (1969). "A newly developed visual method of sexing the os pubis".American Journal of Physical Anthropology.30 (2):297–301.doi:10.1002/ajpa.1330300214.PMID5772048.
^abcdeBritton, the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston; illustrated by Robert (2010).Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. pp. 1116–1121.ISBN978-0-7020-3085-7.{{cite book}}:|first= has generic name (help)CS1 maint: multiple names: authors list (link)
^WHO (1994). "Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. Report of a WHO Study Group".World Health Organization Technical Report Series.843:1–129.PMID7941614.
