Yesterday, I went out with a friend to have a drink, and while we were outside I decided to open my coca-cola drink the Nigerian way. Ohh! In case you do not know, the Nigerian way I mean is using your teeth to open the cork of the bottle. Immediately I placed my teeth on the bottle, my lower canine tooth broke a little. I was very down all through the day because I a part of my tooth was gone, and I vowed never to use my teeth again. I am not discussing the teeth today, I am actually discussing the bone but I want to state that the bone isn't metal just as the teeth aren't metal. Also, since they both contain calcium, I felt I should be able to share their similarities and warn that the teeth can be very fragile, and Calcium is not titanium.
Talking about bone. It is the hardest form of collective tissue which is rigid and rich in calcium. It is vascular and has great regenerative power. Talking about skeletons, we have the exoskeleton and the endoskeleton. Exoskeleton covers the entire organism and the organisms may shed them off and regenerate new ones. It is made up of a thin outer protein layer known as the epicuticle, and a thick inner chitin-protein layer known as the procuticle. It is basically found in arthropods which include insects and crustaceans. Endoskeleton is found inside the organism, and these organisms do not shed or regrow these bones. They are found in vertebrates which include man, dogs, monkeys, and so on. Humans have 206 bones with 80 being axial skeletons, and 126 being appendicular skeletons. The axial skeleton includes the skull, the ossicles, the hyoid bone, the sternum, the ribs, and the vertebral column. The appendicular skeleton includes the bones of the upper limbs which are the humerus, radius, carpals, metacarpals, phalanges, and ulna. The shoulder girdle bones are the scapula and clavicle. The shoulder girdle and the upper limb contain 64 bones. The lower limb is made up of the femur, tibia, fibula, tarsals, metatarsals, and phalanges. The bone of the pelvic girdle includes the hip bone. The bones of the lower limb and the pelvic girdle contain 62 bones.
When discussing bones, we need to clarify that they are tissues and there are four types of tissues which are Epithelial Tissues, Muscle Tissues, Nerve Tissues, and Connective Tissues. Bones, tendons, blood, lymphs and fat makeup the connective tissues. bones originate from the mesenchyme, which are from the mesoderm which gives the dermis, adrenal cortex, dura, bones, cartilage, muscles, tendons, blood and lymphs. When talking about the bone, its function cannot be neglected. The serves many purposes including mechanical for attachment of muscles and ligaments, protection for the internal organs, metabolic (calcium and phosphate homeostasis) and hematopoiesis (blood creation). Bones are made up of Diaphesis which is compact bone in the shaft, and Epiphysis which is spongy or cancellous bone at the proximal or distal end of the bone and is covered by Periosteum. Both bones are known as the Lamellar where the Diaphesis gives strenght, and the epiphysis gives flexibility. For imature or people with bones that are diseased, it is known as woven bone. While talking about the types of bones, it is important to discuss the cells in bones which are osteoblast (cells that build up bones), Osteoclast (cells that destroy or cut down bones), and Osteocytes (the sells of the bones that are built or destroyed). Osteoblast originates from the messenchymal stem cells within the marrow. They produce osteoid which builds up bones. The Osteoclast orignate from the monocytes as macrophages, and they are responsible for breaking down bones leaving bony cavities known as howship's Lacunae. Osteoclast is activated by the Osteoblast through the RANK/RANK-L pathway. Bone are composed of Matix which includes Collagen type 1, Osteonechin, Fibronechin, Osteocalcin, and Osteopontin. It is composed of cells which I discussed earlier such as Osteoblast, Osteoclast, and Osteocytes. It is also made up of minerals which are inorganic calcium and Phosphate.
Classifying bones can be Axial or appendicular like i said previously based on positions. Based on structures, they can be Compact bones or Cancellous bones, based on development, bones can be made through intramembranous ossification, or Intracartilagenous ossification. Based on Shapes, bones can be lonf bones (which are found in upper and lower limbs, possessing shafts, with two ends which are the proximal and distal end), flat bones (They are bones of the skull, sternum, and the scapula. They have an outer table made of compact bone, a diploe, and an inner bone known as the inner table), short bones (comprises of the Carpals, the wrist bones,and Tarsals. They do not possess shafts and are made of cancellous bones), irregular bones (these bones include the vertebrae, the hip bone, and some skull bone and are made up of cancellous bone but covered by compact bone), pneumatic bones (paranasal sinuses, and have air filled space), and sesamoid bones (found in the patella, fabella, and pisiform, and function for friction and pressure).
The Haversian system is made of Osteons which is made up of Lamellae. The bone has the haversian canal when cut vertically, and the volkmann's canal horrizontally, allowing blood and lymphs vessels to pass through them, nourishing them. Each blood vessel has a cannaliculi which connects the lacunae together. You might start to wonder what type of blood vessels go into the bones, so let's quickly do that. The Nutrient artery goes into the bone shaft through the nutrient foramen, supplying the bone marrow and the interior part of the shaft. The epiphyseal artery are found around the outer part of the bone or the epiphysis supplying the compact and the spongy area od the bone. The Metaphyseal artery is another bone artery coming from the nutient artery interiorly, and muscular arteries exteriorly, supplying the metaphysis. In children, the metaphyseal artery are end arteries as they do not anastomose or connect and could lead to bone necrosis if damaged in children. The periosteal artery supplies the cortex of the bone. These arteries are found in long bones, but in short bones, only the nutrient and the periosteal arteries are needed. Similar to the arteries, the veins also do the job of taking blood away from the bone, and they follow the same names like the artery depending on where they supply. Bones are supplied by both autonomic and somatic nerves. The somatic nerves are sensory nerves allowing for the ability to sense pain, why the autonomic nerves are responsible for vasomotor fibers which follow the vessels in the bone leading to the constriction of the vessels.