The skeletal system is our body's framework. Without it we would be a blob of skin, organs, blood vessels, muscles and nerves that would collide with each other and kill us. Many think that bone is just white stuff that keeps our shape normal. However, bones are much more complex than we think they are.
Bones are actually living organisms that have their own lives. They only aid us because it is their nature. We all take them for granted.Every second our body gets rid of old bone cells (resorption) and creates new ones (formation). 
The white bone on the outside of bones is called compact bone (hard bone). Compact bone is made of thousands of tiny rod shaped parts called osteons, which are tightly packed together. Each is thinner than human hair and they are made of layers of hard mineral crystals. Crystals are mainly calcium, phosphate, and carbonate, which are scattered among bundles of threadlike fibers of collagen. Under the compact bone, there is cancellous bone (spongy bone).
It has thousands of tiny holes in it and gives bones their flexibility. In most bones, under the cancellous bone, there is red or yellow jelly-like bone marrow. Red marrow is one of the body's biggest blood cell factories and recycle centers for it creates 2 million red blood cells and tens of thousands of white blood cells every second. Marrow also gets rid of old cells and creates platelets. Yellow marrow stores fat and releases it when needed. 
Muscles are attached to bones with ligaments and tendons, which are flexors. Muscles move bones; they have no power to move on their own.Bone connectors that allow bones to move in different direction are called joints. The categories that joints are divided into are fibrous, cartilaginous, and synovial. Fibrous joints are immovable. Fibrous joints are further down classified into three sub-categories which are sutures, syndemoses and gomphoses. Sutures hold together bones in places such as the cranium (skull). 
Syndemoses hold together the radius and ulna and the tibia and fibula. Gomphoses connect teeth and the sockets in the gums. Cartilaginous joints connect to bones with cartilage such as the disks between the vertebrae and joints that connect the sternum and the ribs. Synovial joints are the most movable of all three categories and are divided into sub-categories just like the fibrous joints. The types of synovial joints are hinge, pivot, gliding, ball and socket, and saddle joints.
Hinge joints such as the elbow or knee can move in one direction like a door. Pivot joints such as the spine or at the neck can twist. Gliding joints such as the ankle or wrist can twist and move up and down. Ball and socket joints such as the shoulder or the hip can move in a hemisphere. Saddle joints such as the base of fingers and toes can move in four different directions. 
The skull protects the brain, the eyes and other sense organs. It consists of twenty nine bones. The bones are linked with sutures. Eight bones make up the cranium. Fourteen are facial bones such as upper jaw, lower jaw, the cheeks, and the nose. Two bones form the upper jaw which is called the maxilla. The mandible or lower jaw can move in all directions but up. They form a crusher together.
The shoulder is biggest joint apart from the knee. It is a synovial ball and socket joint. Though it is one of the most easily dislocated joints, it is very powerful. It connects the humerus (upper arm) with the clavicle (collar bone) and the scapula.
The sternum is what you may know as the breastbone. It is made of two parts, the manubrium and the sternal body. It is connected to the clavicles and the rib cage. 
The rib cage is made of twenty four bones and twelve ribs. It protects organs such as the heart, lungs, liver, kidneys, pancreas, spleen, stomach, intestines, many major arteries, and much more. The first seven ribs are connected to the sternum at the front of the chest with a cartilaginous joint. The next three ribs are connected to the ones above. The last two, called floating ribs are connected to vertebrae. 
Spine is a column of thirty three bones called vertebrae separated by joints called vertebral disks. The spine protects the delicate spinal cord which runs through the hollows in disks. Slipped disks can push on a nerve and cause pain. From the side, the spine looks like an S. It allows us to bend and walk and stand upright.The first and second vertebrae which are found in the neck are called the atlas and the axis. The first seven vertebrae are called cervical vertebrae. The next twelve vertebrae are called thoracic vertebrae. The last 5 are called lumbar vertebrae. 
Humans are the only creatures that have thumbs. Thumbs are very useful in that they allow the user to grip objects by wrapping the thumb and any other finger around an objects.The hand has twenty seven bones which are divided into three groups. The bones in the first group are the phalanges in fingers and the thumb.
The bones in the second group are the carpals in the wrist, and the bones in the last group are the metacarpals in the palm. There are fourteen finger bones, three in each finger, and two in each thumb. There are eight bones in the wrist and there are five bones in the palm.
One of the most common illnesses of the skeletal system is arthritis. There are over 100 different conditions of arthritis. In a case of arthritis, a joint is inflamed. Osteoarthritis occurs when cartilage gets worn out in joints. Rheumatoid arthritis is pain and stiffness in joints. 
Another very common ailment of the bones is a fracture. A fracture is a break in a bone. There are different types of fractures. A compound fracture transpires when a bone shatters or goes through skin. A simple fracture takes place when the bone doesn't go through skin. Fractures usually heal by themselves. Bones are covered by a thin protective layer called periosteum. Blood vessels that run through the periosteum send out blood that will clot and heal broken bones.
Function
The function of the respiratory system is to transport air into the lungs and to facilitate the diffusion of Oxygen into the blood stream. Its also receives waste Carbon Dioxide from the blood and exhales it.
The respiratory system consists of the following structures, divided into the upper and lower respiratory tracts:
Upper Respiratory Tract
• Mouth, nose & nasal cavity: The function of this part of the system is to warm, filter and moisten the incoming air
• Pharynx: Here the throat divides into the trachea (wind pipe) and oesophagus (food pipe). There is also a small flap of cartilage called the epiglottis which prevents food from entering the trachea
• Larynx: This is also known as the voice box as it is where sound is generated. It also helps protect the trachea by producing a strong cough reflex if any solid objects pass the epiglottis.
Lower Respiratory Tract 
• Trachea: Also known as the windpipe this is the tube which carries air from the throat into the lungs. It ranges from 20-25mm in diameter and 10-16cm in length. The inner membrane of the trachea is covered in tiny hairs called cilia, which catch particles of dust which we can then remove through coughing. The trachea is surrounded by 15-20 C-shaped rings of cartilage at the front and side which help protect the trachea and keep it open. They are not complete circles due to the position of the oesophagus immediately behind the trachea and the need for the trachea to partially collapse to allow the expansion of the oesophagus when swallowing large pieces of food.
• Bronchi: The trachea divides into two tubes called bronchi, one entering the left and one entering the right lung. The left bronchi is narrower, longer and more horizontal than the right. Irregular rings of cartilage surround the bronchi, whose walls also consist of smooth muscle. Once inside the lung the bronchi split several ways, forming tertiary bronchi.
• Bronchioles: Tertiary bronchi continue to divide and become bronchioles, very narrow tubes, less than 1 millimeter in diameter. There is no cartilage within the bronchioles and they lead to alveolar sacs.
• Alveoli: Individual hollow cavities contained within alveolar sacs (or ducts). Alveoli have very thin walls which permit the exchange of gases Oxygen and Carbon Dioxide. They are surrounded by a network of capillaries, into which the inspired gases pass. There are approximately 3 million alveoli within an average adult lung.
• Diaphragm: The diaphragm is a broad band of muscle which sits underneath the lungs, attaching to the lower ribs, sternum and lumbar spine and forming the base of the thoracic cavity.