Essay#2 - Structure is critical to proper function. Discuss key structural characteristics, and the various functions provided, for three of the items listed below.
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Many invertebrates lack any specialized skeletal structures. they instead have what is called a "Hydrostatic Skeleton".Organisms have fluid contained inside of their bodies that exerts a pressure and along with their musculature helps to establish a shape. Movement and changes in shape can be achieved by contracting specific muscle groups.
Assuming a constant fluid volume, a change in the width of the animal must be compensated for by a change in length, which is brought about by the increase in internal hydrostatic pressure during muscle contraction. The animal can only attain its initial shape if it is surrounded by a stiff, elastic covering that will spring back to its original shape upon relaxation of the longitudinal musculature (jellyfish, round worm, flat worm) or if it contains opposing muscle groups for the initial shape change (earthworm).
Thus, the “skeletal” system in our hypothetical organism is a fluid. Temporary increases in internal pressure are caused by the contraction of 1 set of muscles, and this temporary pressure increase elongates another set of muscles. Hydrostatic skeletons play a role in the movements made by representatives of nearly every invertebrate phylum.
Some invertebrates have developed the ability to produce a "Shell" over it 's soft tissues for protection (clams, muscles, snails). The makeup of this protective covering is usually composed of calcium carbonate (shell) and tends to limit movement because of it's weight.
Others have taken that idea of a "shell" a step further and produce an "Exoskeleton" that is segmented and composed of a lighter more flexible material called CHITIN. It completely covers all external surfaces and is composed of segments. Having segments offers greater flexibility while still offering some basic protection from potential predators and desiccation.While there is more flexibility than the shell seen in mollusks the exoskeleton is still limiting. Terrestrial arthropods rarely exceed 10cm in length. This is a direct result of the weight imposed. Aquatic arthropods can get substantially larger than 10cm as a result of buoyancy. In addition, in order to grow the arthropod must molt its exoskeleton. The organism is very vulnerable during the molting period.
Many animals have developed the ability to produce an internal skeleton or "Endoskeleton". This offers protection of vulnerable internal organs while still enabling soft sensory organs to be on the external surface as well as offering even more flexibility. The most primitive internal skeletal structure is seen in Echinoderms (sea urchins, sand dollars, star fish). Their internal skeleton is composed of thick plates with limited or no flexibility.
The most recent skeletal system to have evolved is seen a a group of animals called Chordates. During their embryological development a dorsal rod of connective tissue is established that acts as a support structure establishing shape and acting as a place where muscles can attach. In some representatives the notochord disappears as the organism matures, in others it remains, and in the most advanced representatives it develops into the vertebrae of the spine (Vertebrates).
In many animals the skeletal system also acts as a place to store minerals and produce blood cells (marrow). Round bones possess yellow marrow which stores a variety of minerals. Flat bones possess red marrow which contains stem cells responsible for the formation of blood cells.
Cartilage can be found in many of the joints of our skeletal system especially in the knee (meniscus) and vertebrae (disc).
9- What are the functions of cartilage in the joints of the skeletal system?
A membrane can be found lining movable joints. This membrane secretes a lubricating fluid (synovial fluid) that limits friction between the bones. No synthetic lubricant made by humans equals its lubricating properties. If the fluid escapes the joint area it can compromise the lubrication of the joint leading to stiffness, pain, and in advanced cases significantly reduce mobility.