Bones give you support, protection of soft internal organs, they assist in movement, they store minerals, produce blood cells, and store chemical energy. They support your body so that you aren't just a clump of skin and organs. Bones are like a framework to hold your body and keep everything attached together. Bones protect your soft internal organs so if you fall your brain won't squish (or any other soft organ). Without bones you wouldn't be able to move, tendons attach your muscles to your bones, so that when your muscles contract the tendon pulls the bone so it will move. The specialized tissue in bones stores minerals like calcium and phosphorus. When necessary the bone will release these minerals into your blood to keep a balance of minerals. Bones have two parts compact bone and spongy bone. The spongy bone contains bone marrow, bone marrow produces blood cells. As you age your red bone marrow becomes yellow bone marrow. Yellow marrow consists of a bunch of adipose cells and of course some blood cells, this creates a chemical energy reserve.
Bones are organs in the skeletal system. They have two parts spongy bone (one the inside) and compact bone (on the outside.) Compact bone is the dense tissue that covers the outside of most bones. It is very hard and is the most strong and supportive part of the bone. Spongy bone is the inside part of the bone, it is less dense. This type of bone is only in short bones and at the ends of long bones. Inside of spongy bone is bone marrow. Bone marrow is what makes the blood cells. Bone marrow is a spongy, fatty tissue it stores stem cells. The stem cells can transform themselves to create red and white blood cells and platelets. You need bone marrow to survive. There are five types of bones; long bones. Short bones, long bones, flat bones, irregular bones, and sesamoid bones are the five types of bone. Short bones are found in your hands and feet, long bones are in your arms and legs they have cartilage at the ends, flat bones are the bones that protect your internal organs like cranium bones and ribs, irregular bones are like vertebrate and some facial bones, and sesamoid bones are small bones in tendons, like in your knee.
Bones are formed during the prenatal development stage. Throughout growth they get harder, bones begin growth at the top of the bone. The bones are softer because it has not been fully turned into bone (this is also called ossified.) They are formed by replacing the existing cartilage. Bones are formed in two ways; IntramembranousOssification and EndochondralOssification. During Intramembranous Ossification mebranous bones come first, they are flat membrane like layers of early connective tissue. Cells called osteoblasts remove calcium from the blood and put it in the bone matrix (cartilage) this causes layers of spongy bone to form around the cartilage. Later in the process the spaces in the spongy bone are filled with bone marrow. Osteoblasts keep depositing calcium into the matrix until surrounded with the calcium. During Endochondral Ossification the original cartilage is replaced.
(other part on next slide)
Theory #1- Early animals with soft bodies had cartilage (at least some did.) This cartilage over time evolved through a process like Intramembranous Ossification. The cartilage became bone and the animals then had bone
Theory #2 (mine and Kristin’s theory)- The earliest animals were single celled, and over time simple invertebrates like sponges evolved. From these simple invertebrates came more advanced ones, with organs and blood. The blood cells had to be made from something like bone marrow, the first step to bone creation. If there were blood there would have to be veins to transport the blood around its body. If one of these more advanced invertebrates got a blood clot, but they had just enough room that the clot didn’t completely stop blood flow or it had become immune to the clots it could start the process. Within the clot would be some of the things that created the blood (that are similar to bone marrow) so this clot hardened just slightly and became the first spongy bone. The blood cells transformed into bone marrow kind of stuff, like bone marrow turns into blood cells and platelets. The calcium in the blood also gathered around this clot/first spongy bone and it added onto the clot. The tissues making up the vein tightened around the clot and hardened with the calcium and phosphorus in the blood. As the animal with this first “blood clot” reproduced, passing on this bone like gene and throughout processes like this the animals were able to grow larger, they needed even more support. And so also over time to adapt to these new needs the outside of the bone became harder; compact bone. Throughout time actual bones evolved from this and the first vertebrates were evolved.