Editing Human skeleton (section)

==Functions==

The skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals and endocrine regulation.{{Citation needed|date=September 2024}}

===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 cartilage]]s, and [[intercostal muscle]]s, the [[human lungs|lungs]] would collapse.{{Citation needed|date=September 2024}}

===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 by [[skeletal muscle]]s, 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 to [[agriculture]] has caused human bone density to reduce significantly.<ref>{{cite magazine |title=Switching Farming Made Human Bone Skeleton Joint Lighter |url=http://www.smithsonianmag.com/science-nature/switching-farming-made-human-joint-bones-lighter-180953711/?no-ist |url-access=subscription |archive-url=https://web.archive.org/web/20150321112852/https://www.smithsonianmag.com/science-nature/switching-farming-made-human-joint-bones-lighter-180953711/ |archive-date=21 March 2015 |last=Thompson |first=Helen |magazine=[[Smithsonian (magazine)|Smithsonian]] |date=23 December 2014 |access-date=16 July 2024}}{{cbignore}}</ref><ref>{{cite web |url=http://www.world-science.net/othernews/141223_skeleton.htm |url-status=dead |archive-url=https://web.archive.org/web/20150316080428/http://www.world-science.net/othernews/141223_skeleton.htm |archive-date=16 March 2015 |title=Light human skeleton may have come after agriculture |access-date=16 July 2024 |website=World Science}}{{cbignore}}</ref><ref>{{cite web|url=http://blogs.discovermagazine.com/d-brief/2014/12/22/with-the-advent-of-agriculture-human-bones-dramatically-weakened/|title=With the Advent of Agriculture, Human Bones Dramatically Weakened|date=22 December 2014|access-date=4 March 2017|archive-date=13 March 2017|archive-url=https://web.archive.org/web/20170313214116/http://blogs.discovermagazine.com/d-brief/2014/12/22/with-the-advent-of-agriculture-human-bones-dramatically-weakened/|url-status=dead}}</ref>

===Protection===
The skeleton helps to protect many vital internal [[organ (anatomy)|organs]] from being damaged.{{Citation needed|date=September 2024}}
* The skull protects the [[human brain|brain]]
* The [[vertebrae]] protect the [[spinal cord]].
* The [[rib cage]], [[vertebral column|spine]], and [[sternum]] protect the [[lungs]], [[heart]] and major [[blood vessel]]s.

===Blood cell production===
The skeleton is the site of [[haematopoiesis]], the development of [[blood cells]] that takes place in the [[bone 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.<ref>{{cite journal|last=Fernández|first=KS|author2=de Alarcón, PA|title=Development of the hematopoietic system and disorders of hematopoiesis that present during infancy and early childhood.|journal=Pediatric Clinics of North America|date=Dec 2013|volume=60|issue=6|pages=1273–89|pmid=24237971|doi=10.1016/j.pcl.2013.08.002}}</ref>

===Storage===
The [[Osteon|bone matrix]] can store [[calcium]] and is involved in [[calcium metabolism]], and [[bone marrow]] can store [[iron]] in [[ferritin]] and is involved in [[Human iron metabolism|iron metabolism]]. However, bones are not entirely made of calcium, but a mixture of [[chondroitin sulfate]] and [[hydroxyapatite]], 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|date=September 2024}}

===Endocrine regulation===
Bone cells release a [[hormone]] called [[osteocalcin]], which contributes to the regulation of [[blood sugar]] ([[glucose]]) and [[body fat|fat deposition]]. Osteocalcin increases both [[insulin]] secretion and sensitivity, in addition to boosting the number of [[insulin-producing cell]]s and reducing stores of fat.<ref>{{cite journal |doi=10.1016/j.cell.2007.05.047 |title=Endocrine Regulation of Energy Metabolism by the Skeleton |year=2007 |last1=Lee |first1=Na Kyung |last2=Sowa |first2=Hideaki |last3=Hinoi |first3=Eiichi |last4=Ferron |first4=Mathieu |last5=Ahn |first5=Jong Deok |last6=Confavreux |first6=Cyrille |last7=Dacquin |first7=Romain |last8=Mee |first8=Patrick J. |last9=McKee |first9=Marc D. |last10=Jung |first10=Dae Young |last11=Zhang |first11=Zhiyou |last12=Kim |first12=Jason K. |last13=Mauvais-Jarvis |first13=Franck |last14=Ducy |first14=Patricia |last15=Karsenty |first15=Gerard |journal=Cell |volume=130 |issue=3 |pages=456–69 |pmid=17693256 |pmc=2013746}}</ref>