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Skeleton

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A skeleton is…

Hominoidea (Ape) skeletons

 

Axial skeleton

Bones of the head and trunk of a vertebrate

Appendicular skeleton

All of the bones connected to the axial skeleton; these are the bones of our appendages.

The skull

The skull isn’t one bone; it is made of several bones fused together.

What are bones made of?

Although bones in museums are dry and hard,  the bones in your body are different. Those are alive, growing.

The outer surface of bone is the periosteum (pare-ee-OS-tee-um). It’s a thin, dense membrane that contains nerves and blood vessels that nourish the bone.

The next layer is compact bone. Smooth, hard. The part you see when you look at a skeleton.

Within that are layers of cancellous (KAN-sell-us) bone, which looks like a sponge.

In many bones the innermost part is the marrow. It is sort of like a thick jelly, and its job is to make blood cells.

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How does bone maintain it’s strength? Remodeling

Every day there is physical stress and vibrations acting on our bones.

Bones develop micro cracks. Over time these cracks join together to make longer cracks. Eventually the cracks become long enough, and the bone would spontaneously break, even while just walking

Osteoclasts – Cells that secrete acid, breaking down bone and releasing calcium ions.

From the Greek ὀστέον, osteon (“bone”) and κλαστός, clastos (“broken”)

Osteoclasts degrading bone

Osteoblasts – Cells that grab calcium ions and fuse them (with other atoms) into new bone.

From the Greek ὀστέο, osteo (“bone”) and βλαστάνω, blastanō (“growing”)

They build a mineral, hydroxylapatite. Ca10(PO4)6(OH)2

Osteoblasts remodeling bone

Bone marrow makes blood cells

How many bones do humans have?

A baby’s body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults have. Some of a baby’s bones are made partly or entirely of cartilage (say: KAR-tel-ij). This cartilage is soft and flexible. During childhood, as you are growing, the cartilage grows and is slowly replaced by bone, with help from calcium.

By the time you are about 25, this process will be complete. After this happens, there can be no more growth — the bones are as big as they will ever be. All of these bones make up a skeleton that is both very strong and very light.

http://kidshealth.org/kid/htbw/bones.html

Hand bones

This is a human hand from the outside – my own, after a hiking “incident” 😉

Hand with damage from hiking accident

Hand with damage from hiking accident

This is an X-ray of the same hand; the doctors were making sure that none of my bones were broken. (None were, although there was some damage to the tissues.)

Hand with damage from hiking accident

Hand with damage from hiking accident

Sample questions

Feb 2016 MCAS.  When astronauts are in low-gravity environments, their bodies begin to release stored calcium. As a result, which of the following most likely occurs when an astronaut returns to Earth?

A. The risk of inflamed tendons increases.
B. The chance of breaking a bone increases.
C. The stomach’s level of functioning decreases.
D. The blood’s ability to carry oxygen decreases.

Feb 2016 MCAS. An altered form of the structural protein collagen causes a condition in which bones are weak and break easily. Which of the following are components of collagen?

A. amino acids .   B. fatty acids .   C. monosaccharides .   D. nucleotides

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