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Skeletal structure and function

Skeletons support and protect our bodies. Bugs have exoskeletons outside their bodies, while humans have endoskeletons inside. Our bones are in axial (skull, ribcage, spine) and appendicular (arms, legs) groups. Bone marrow makes blood cells; more specifically, red marrow makes blood and yellow marrow stores fat. Created by Tracy Kim Kovach.

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  • piceratops seedling style avatar for user Callum Kennedy
    is the red and/or yellow bone marrow housed inside of the cancellous bone?
    (14 votes)
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  • blobby green style avatar for user tanzil rubab
    why does it pain when our bones break? do they have nerves or anything else, other than bone marrow, going through them?
    (20 votes)
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  • leaf red style avatar for user Kyle B.
    Are the scapula and clavicle part of the Appendicular or Axial skeleton?
    (14 votes)
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  • leaf green style avatar for user Bhavana Mashetty
    I was told that when a bone is broken majorly, doctors take a chunk of bone from the pelvic girdle and patch it up. So when this happens, won't the haemopoeisis get disturbed. And will it cause any irregularities in the structure of that bone?
    (12 votes)
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  • starky sapling style avatar for user jshao
    I've read about rickets which is when your bones start bending. What causes this. i just can't remember what causes rickets.
    (6 votes)
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    • duskpin ultimate style avatar for user ♫Northstar♫
      So rickets is a bone disorder, then why is it concerned with vitamin D?... now you may intake sufficient calcium and phosphorus but to draw nutrition out of them, your body needs vit D. When that's missing, your body draws calcium from your bones which makes your bones decalcified. This causes rickets. Hope this helps.
      (9 votes)
  • leafers sapling style avatar for user Roxylabastida
    Why do bones really break if we have layers of skin on us?
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  • marcimus red style avatar for user Khadija Ebied
    is the shoulder bone part of the appendicular or axial skeleton?because in my science book the shoulder bone is a part of appendicular skeleton but i am not sure.
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  • blobby green style avatar for user elijahsanchez
    so what is the sholder bone called
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  • duskpin tree style avatar for user Evan Reese Lyas
    What's the differnce between hip and pelvis?
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  • piceratops tree style avatar for user thewizeraven
    The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together.[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 the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

    The human skeleton performs six major functions: support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation.

    The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology 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.[citation needed] The human female pelvis is also different from that of males in order to facilitate childbirth.[3] Unlike most primates, human males do not have penile bones.[4]

    Main article: Axial skeleton
    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).

    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 the hip joints. The bones of the spine are supported by many ligaments. The erector spinae muscles are also supporting and are useful for balance.

    Main article: Appendicular skeleton
    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.

    The skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals and endocrine regulation.

    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, and intercostal muscles, the lungs would collapse.

    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 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 to agriculture has caused human bone density to reduce significantly.[5][6][7]

    The skeleton helps to protect many vital internal organs from being damaged.

    The skull protects the brain
    The vertebrae protect the spinal cord.
    The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.
    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.[8]

    The bone matrix can store calcium and is involved in calcium metabolism, and bone marrow can store iron in ferritin and is involved in 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.

    Endocrine regulation
    Bone cells release a hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat deposition. Osteocalcin increases both insulin secretion and sensitivity, in addition to boosting the number of insulin-producing cells and reducing stores of fat.[9]

    Sex differences

    During construction of the York to Scarborough Railway Bridge in 1901, workmen discovered a large stone coffin, close to the River 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 from Roman 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 as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology 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.

    A variety of gross morphological traits of the human skull demonstrate sexual dimorphism, such as the median nuchal line, mastoid processes, supraorbital margin, supraorbital ridge, and the chin.[10]

    Human inter-sex dental dimorphism centers on the canine teeth, but it is not nearly as pronounced as in the other great 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 by morphometric or gross morphological analyses.

    The human pelvis exhibits greater sexual dimorphism than other bones, specifically in the size and shape of the pelvic cavity, ilia, greater sciatic notches, and the sub-pubic angle. The Phenice 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. The sacrum 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 the birth canal.

    Clinical significance
    See also: Bone disease
    There are many classified skeletal disorders. One of the most common is osteoporosis. Also common is scoliosis, 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.

    Main article: Arthritis
    Arthritis is a disorder 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. The cartilage 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.

    Main article: Osteoporosis
    Osteoporosis is a disease of bone where there is reduced bone mineral density, increasing the likelihood of fractures.[12] Osteoporosis is defined by the World Health Organization in women as a bone mineral density 2.5 standard deviations below peak bone mass, relative to the age and sex-matched average, as measured by Dual energy X-ray absorptiometry, with the term "established osteoporosis" including the presence of a fragility fracture.[13] Osteoporosis is most common in women after menopause, when it is called "postmenopausal osteoporosis", but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids.[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 may Vitamin D. When medication is used, it may include bisphosphonates, Strontium ranelate, and osteoporosis may be one factor considered when commencing Hormone replacement therapy.[12]
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Video transcript

So in this video we're going to be talking about skeletal structure and then the function of those skeletons and specifically human skeletons is what we're interested in but before we talk about human skeletons let's talk about bug skeletons or the skeletons of arthropods are insects and so I'm going to draw a little ladybug here and our little ladybug being an arthropod has what is called an exoskeleton and the XO and XO skeleton actually first the fact that this skeleton is outside of the ladybug so "exo" is actually Greek for outside or external humans on the other hand we are vertebrates and as vertebrates we have this amazing network of bones located on the interior of our bodies and so we have what are called endo skeletons and endo is greek for within or inner referring to the location of the skeleton is being inside of our bodies as opposed to outside now as humans our endoskeleton performs a variety of pretty vital functions the first of which is it supports our body and provides a framework for movement so what does this mean are our body is supported by the network of our bones which allows us to sit up and stand and provide some sort of structure for our body and then the limbs of our body in particular and various joints in our body provide a framework for movement that allows you to run around to kick a soccer ball to type on a keyboard another important function of our skeleton is that it protects our most vital organs so if you look at the skull for example it houses our brain and the ribcage it protects our heart and lungs and other organs and the third function of our skeleton is is that it performs a variety of physiological roles in our body namely the storage of calcium and what is called hematopoeisis, which is the production of all the cellular components within our blood so our blood is made up of many different components plasma proteins among other things and the cellular components of our blood which are red blood cells white blood cells and platelets are all formed within the bone marrow of my bones and so those are the main functions of the bones that form our skeleton now one way of classifying bones is differentiating between those that form the axial skeleton and then those that form the appendicular skeleton now the axial skeleton is made up of our skull and ribcage and our vertebral column that is the axial skeleton it forms sort of the axis of our body right right in the center down the midline and then the bones of the forelimbs and our pelvis form what is called the appendicular skeleton and so go are four appendages form the appendicular skeleton which is attached to our central or axial skeleton another classification system for the bones in our skeleton is the difference between flat bones and long bones now what are flat bones some examples of flat bones are the bones that make up your skull the different bones that make up your ribs and then also the bones in your pelvis and so flat bones really are describing the shape of the bone these bones are made up of an inner spongy or cancellous bone and then the outer shell is made up of compact bone there's an inner spongy cancellous bone in an outer shell of compact bone and flat bone serve primarily to protect our organs and serve as a site for him at 0 police's now long bones on the other hand some examples of those would be the humerus in your upper arm or say the femur and your lower leg and if I draw a long bone out here there are a few different terms to be familiar with when you're referring to different parts of the long bone the long middle portion of a long bone is called the diathesis and then the end of a long bone is called the APIs and there is the small area of bone in between the two are in the middle of the diathesis and the purposes is called the metaphysis and the metathesis contains the growth plate which is present in the long bones of children and these long bones are made up of the same inner spongy cancellous bone with an outer shell of compact bone just like flat bones and these long bones really are the ones that provide a framework for movement like we talked about before and they also serve as a side of hematopoiesis. And speaking of hematopoiesi, where exactly does this Hematopoiesis occur? I mentioned that it occurs in bone marrow which is contained within bones and there are two different types of bone marrow there is what is called red bone marrow and then yellow bone marrow now red bone marrow serves as the primary site for hematopoiesis, which makes sense because the red blood cells from hematopoiesis actually make red bone marrow look red to the naked eye so you can remember that red bone marrows for blood or hematopoiesis and you can typically find red bone marrow within flat bones and then in the epiphyses of long bones. And then yellow bone marrow on the other hand is primarily a site for fat storage made up of fat cells called adipocytes and generally you can find yellow bone marrow within the diocese of long bones