Today, I will be talking about an interesting part of Biology which is the skeleton system. But I will be starting with the structure of the skeletal tissues for today and in my next post, I will look deeply into the skeletal system at general.
The structure of skeletal tissues
Bone is an important part of the skeletal system, but there are other tissues associated with it that play a major role in the smooth functioning of the svstem as a whole. These tissues include ligaments, cartilage and tendons. All of the skeletal tissues have distinctive physical properties that adapt them for their functions within your body. In the mammalian embryo, the skeleton is made largely of cartilage tissue. During development this becomes ossified turned into harder, relatively incompressible tissue called bone. Bone is very strong and withstands compression forces very well. When a baby is born, much of the skeleton has already become bone. However, there is still cartilage at the ends of the long bones and this allows the bones to grow for a number of years until the end of puberty. There are some parts in the adult skeleton, such as ears, shaped rings in the trachea, ends of bones at joints, and ends of ribs that remain made of more flexible cartilage.
Skeletons look like dead white structures. However, living bone is very different. It has a rich blood supply. It is constantly being broken down andbuilt up where it is needed in response to the different stresses you impose upon it. Any new activity will cause your bones to be altered slightly. This is brought about by the bone cells. The osteoblasts and osteocytes build up the bone, while the osteoclasts break it down.
So, your skeleton is constantly changing, even as you sit at your school desk. The whole skeleton is replaced over ten years, so no part of an adult human skeleton is more than ten years old.
Living bone is an active, dynamic tissue. It is a composite material (containing more than one substance) made up of bone cells embedded in a matrix of collagen (protein) fibres hardened by
Calcium phosphate, which is deposited within the structure. These hard calcium salts make up 70 percent of the bone. This is how your body manages to mend any breaks in your bones. The bone building cells quickly produce more cells and more matrix, and then calcium salts are deposited to harden things up, until it is a good as new.
Bone tissue is a composite material containing
30 percent organic material (mainly protein, for example collagen)
60 percent inorganic material (mainly calcium phosphate)
10 percent osteocytes (bone cells).
Bone needs to be hard and strong, to support the weight of our body as we move around, but it also needs to be as light as possible. If bones were solid structures, they would be so heavy they would be impossible to move around. However, our bones are not solid they are hollow tubes that are themselves made up of two different types of bone. Compact bone is very dense and heavy, but very strong. Tt is found in areas such as the shafts of the long bones of your body. Much of the rest of the skeleton contains large amounts of spongy bone that has a much lighter, open structure. lt is found in growing regions and in large masses of bone such as the head of the femur (thigh).
How do these strong, rigid structures grow? When you are a small child, there are areas of cartilage in many of your bones, particularly at the top and the bottom of the long bones of your arms and legs. These are the sites where growth takes place, and once your final growth spurt is over they become calcified (calcium salts are deposited) and from then on the whole structure is made of bone. This is one way of aging a skeleton: if there are any cartilage areas, the person was younger than around 18-25 years old, because by that stage the bones are always fully formed.
If children lack calcium when they are growing. they will suffer from the deficiency disease rickets and their bones may not form properly. If older people lack calcium they may suffer from Osteoporosis, where their bones become weak and brittle.
Cartilage
Cartilage is another very strong tissue found in the skeleton. It is flexible rather than rigid. Its structure is rather like bone without the calcium salts, with cartilage cells embedded in a collagen matrix. Much of the skeleton is first formed as cartilage, which is then hardened when calcium
salts are deposited in it. Because cartilage is not rigid, it can be slightly compressed, and this makes it very important to the body as a shock absorber.
Cartilage is found covering the ends of the bones in most joints, and pads of cartilage that act as shock absorbers are found between the vertebrae. It is smooth and slippery and so it reduces friction. Your ears and nose are made of cartilage too.
Ligaments and tendons
Ligaments attach bones to other bones in joints. They form the capsule of the joint that holds the whole arrangement of bones in place. Ligaments have a great deal of tensile strength. This means they can withstand a lot of stretching or pulling They also have a certain amount of elasticity, so that as the bones move within a joint the ligament capsule stretches to allow that to happen
without damage.
They have a great deal of tensile strength, which means they can withstand being stretched. However, they have very little elasticity. This is important, because if tendons stretched, when muscles contracted they wouldnt move the bones, they would simply stretch the tendons. Here is a summary ot the main properties of the skeletal tissues.
. Bone is hardened by calcium salts and resists compression, bending and stretching.
. Cartilage is strong, but not rigid, so it can be compressed and absorb shock.
. Ligaments have tensile strength and some elasticity, so that joints can bend without the bones dislocating. They join bone to bone.
. Tendons have tensile strength and little elasticity They join bone to muscle.
Supporting tissues in plant
Animals are not the only organisms that need supporting and skeletal tissues. Although plants do not move around, they still need support. Trees are supported. Plants that are not woody need to hold up their leaves to capture the sunlight energy for photosynthesis. They need to hold up their flower pollination, and to hold up their fruits so that they can be dispersed. A plant also needs to hold hole body off the ground so that it is less likely to be eaten. Woody plants need support so that they can grow very big. What are the main support tissues in plants and how do they do their job?
For non-woody plants, one of the most important factors in support is turgor
When these cells are turgid, they can support the plant. This is why, when a plant is short of water and the cells become plasmolysed, the plant wilts. The parenchyma cells are no longer turgid, and so they do not give the plant any support.
Collenchyma is another supporting tissue in plants. Collenchyma cells are very similar to parenchyma, but they are more specialised for support. They have extra cellulose on the cell walls particularly in the corners, which make them very rigid and strong. They are also very tightly packed together with no air spaces between them. As a result they provide support for the plant even it they are not furgid. The other main support tissue in non-woody plants is the sclerenchyma. The wall of sclerenchyma cells are heavily thickened with lignin. This kills the cells, but also gives them a lot of strength. They can withstand both stretching and squashing (compressing) without
breaking or buckling.
The final major support tissue in plants is xylem. The xylem vessels are important because they carry water and dissolved minerals from the roots to all the other parts of the plant. The xylem consists mainly of xylem vessels, which are made up of lignified, dead cells.
In woody plants, rings of lignified xylem vessels form the wood, with a thin layer of living cells over the top (the bark). This can support an enormous plant trees such as silk cottons can reach around 10 m in height and giant redwoods (sequoias) can
be up to 85 m tall!
In non-woody plants, the xylem vessels are found as part of the vascular bundles. These help to support the stem and root of the plant along with parenchyma, collenchyma and sclerenchyma.
All of these tissues are important in supporting plants. They are arranged differently in stems and roots, and they are also arranged differently in monocots and dicots.
References
. https://www.kenhub.com/en/library/anatomy/histology-of-skeletal-muscle
. https://en.m.wikipedia.org/wiki/Bone
. https://www.britannica.com/science/bone-anatomy
. https://en.m.wikipedia.org/wiki/Cartilage
. https://www.news-medical.net/amp/health/What-is-Cartilage.aspx
. https://www.healthline.com/health/ligament-vs-tendon
. https://www.medicalnewstoday.com/articles/326858#differences
. http://www1.biologie.uni-hamburg.de/b-online/e06/06.htm
. https://steemit.com/steemstem/@semilore/supporting-tissues-in-plants-functions-and-types
. https://www.toppr.com/guides/biology/anatomy-of-flowering-plants/plant-tissues/