The Human Endoskeleton: Our Hard “Dried Body” Lying Within Help
Introduction The Human Endoskeleton: Our Hard “Dried Body” Lying Within
If we humans are just a “bag of bones,” then, having discussed the “bag” (skin), we now need to consider the bones! Recollect that crabs, lobsters, and other arthropods have soft bodies that are covered and protected by a tough exoskeleton of the substance, chitin. The skeleton or “hard dried body” is on the outside, like a coat of mail or battle armor. Human beings and most other vertebrates, however, have taken the exactly opposite approach to these arthropods in protecting their delicate internal organs from physical trauma and injury. They possess an endoskeleton ( EN -doh- skel -uh-tun), or “hard dried body within” ( endo -).
A big peach, in a plant-sense, has its own form of endoskeleton – a rock-hard inner pit (Figure 13.4). As explained in Chapter 9, a ripened fruit, such as a nice round, pinkish peach, is actually the fleshy wall of a plant ovary, which encases and protects the seeds holding the delicate plant embryos. In peaches, the stony pits are the seeds that contain the early embryos for germinating new peach trees.
In humans and our animal relatives, the endoskeleton is comprised of many individual bone organs (and the joints made between them). But instead of protecting a delicate plant embryo, bones in the skull or cranium protect the soft eyes and brain. And bones in the thorax or chest wall protect the relatively soft heart and lungs.
In both the peach and the human body, a very thin, tough integument or skin ensheaths a large quantity of relatively soft flesh. And lying deep within this fleshy mass is a protective peach pit or (in the case of vertebrate animals) a protective endoskeleton.
Humans, of course, have a much more complex body plan, compared to peaches! Our skeleton is subdivided into two main portions. An axial skeleton (discussed back in Chapter 12) lies within the head, neck, and body trunk. Conversely, an appendicular ( ah -pen- DIK -you-ler) skeleton lies within the body appendages (ah- PEN -dah- jes ) or limb “attachments.” The appendicular skeleton consists of the bones in the upper appendages (the shoulders, arms, wrists, and hands), as well as those in the lower appendages (the hips, legs, ankles, and feet). Taken together, the axial and appendicular skeletons make up the “hard dried body” or endoskeleton lying “within” us.
And being chordates, our vertebral columns stiffen and support us from the inside, rather than from the outside.
Practice problems for these concepts can be found at: Skins And Skeletons Test
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