Skeletal System Anatomy & Physiology PDF

Skeletal System Anatomy & Physiology Skeletal System This system has the following components: bones, cartilage, tendons, and ligaments. Skeleton – framework and gives shape to the body, support an...

Skeletal System Anatomy & Physiology Skeletal System This system has the following components: bones, cartilage, tendons, and ligaments. Skeleton – framework and gives shape to the body, support and protects the internal organs* Functions: 1. Body support – the skeleton supports the body against gravity. It largely determine the body’s shape.** 2. Body movement – the skeleton is a system of muscle operated levers. Skeletal System Functions: 3. Organ protection – the bone is hard and protects the organs it surrounds. 4. Blood cell production – many long bones contain cavities filled with red bone marrow, a tissue that produces red blood cells, white blood cells and platelets. The yellow bone marrow replaces the red bone marrow. 5. Mineral storage – the bone stores calcium and phosphorus. If blood levels of these minerals decrease, the minerals are released from bone into the blood. Adipose tissue is also stored within bone cavities. If needed, the lipids are released into the blood and used by other tissues as a source of energy. Bones Bones are hard connective tissue forming the substance and structure of the skeleton. The adult skeleton is composed of 206 bones.* Bone Cells 1. Osteoclasts – bone destroying cells that break down the bone. Bone reabsorption or bone resorption – is the breakdown of bone and is important for mobilizing crucial calcium and phosphate ions for use in many metabolic processes. As bone is broken down, the calcium goes back into the blood. 2. Osteoblasts – bone forming or bone building cells that produce collagen and secrete matrix vesicles that contain calcium and phosphate. Ossification – the formation of new bone by osteoblasts. It occurs by appositional growth on the surface of previously existing material, either bone or cartilage. Bone matrix produced by the osteoblasts covers the older bone surface and surrounds the osteoblast cell bodies and extensions. The result is a new layer of bone. Bone Cells Bone collagen – is the living protein matrix laid down by the osteoblasts. Collagen forms a living web-like protein matrix. This living collagen provides the scaffolding for bone formation. This living protein collagen web becomes mineralized to make bones strong and appear to be hard. Bone Cells 3. Osteocytes – mature bone cells accounting for 90 – 95% of bone cells and has a life span of 25 years. These cells are connected to neighboring osteocytes through their cell extensions.* Lacunae – spaces within the bone matrix where osteocyte cell bodies are housed. Canaliculi – long narrow spaces where osteocyte cell extensions are housed. Nutrients and gases can pass through the small amount of fluid surrounding the cells in the canaliculi and lacunae or pass from cell to cell through the gap junctions connecting the cell extensions.** Bone Cells Bone Tissues Bones can be classified according to the amount of bone matrix relative to the amount of space within the bone. 1. Compact bone – has more bone matrix and less space than spongy bone. It is dense and looks smooth and homogenous making a solid outer layer surrounding each bone. Blood vessels enter the substance of the bone itself. Lamella – thin concentric sheets or layers of organized arrangement of collagen fibers approximately 3 – 7 micrometers thick. Bone Tissues 2. Spongy bone – appears porous, has less bone matrix and more space than compact bone. It is composed of small needlelike pieces of bone and lots of open space. Trabeculae – interconnecting rods or plates of bone found in spongy bone. Between the trabeculae are spaces, filled with bone marrow and blood vessels. Bone Tissues Bone Tissues Bone Classifications 1. Long bones – typically longer than they are wide. They have a shaft with heads at both ends. Long bones are mostly compact bones. Most of the bones of the upper and lower limbs are long bones. 2. Short bones – are generally cube shaped and contain mostly spongy bone. The wrist and ankle bones are examples. 3. Irregular bones – bones that to not fit into the other categories such as the vertebrae and facial bones. 4. Flat bones – are thin, flattened, and usually curved. They have two thin layers of compact bone sandwiching a layer of spongy bone between them. Examples are certain skull bones, the ribs, the breastbone, and the shoulder blades. Bone Classifications Structure of Long Bones 1. Osteon or haversian system – the functional unit of a long bone. It is composed of concentric rings of matrix, which surround a central tunnel and contain osteocytes. Central canal or haversian canal – contains blood vessels, nerves, and loose connective tissue. This is surrounded by lamellae rings of bone matrix. Volkmann canal or perforating canal – contains blood vessels and delivers blood to the central canals of the osteons. The perforating canals run perpendicular to the length of the bone. Structure of Long Bones 2. Diaphysis – the center portion of the bone and is composed primarily of compact bone. Medullary cavity – a hollow center surrounded by the diaphysis. It is where red bone marrow and/or yellow bone marrow are stored. Red bone marrow – site of blood cell formation Yellow bone marrow – adipose tissue for storage of fats 3. Epiphysis – the ends of the long bones. The epiphyses are mostly spongy bone, with an outer layer of compact bone. Epiphyseal plate or growth plate – is located between the epiphysis and the diaphysis where growth in bone length occurs. Epiphyseal line – the ossified epiphyseal plate resulting from the stopping of bone growth in length Structure of Long Bones 4. Periosteum – a connective tissue membrane covering the outer surface of a bone. The outer fibrous layer is dense irregular collagenous connective tissue that contains blood vessels and nerves. The inner layer is a single layer of bone cells, including osteoclasts and osteoblasts. 5. Endosteum – a single cell layer of connective tissue that lines the internal surfaces of all cavities within bones, such as the medullary cavity of the diaphysis and the smaller cavities in spongy and compact bone. The endosteum also includes osteoblasts and osteoclasts. Structure of Long Bones Structure of Other Bones Short and irregular bones have a composition similar to the epiphyses of long bones – compact bone surfaces surrounding a spongy bone center with small spaces that are usually filled with marrow. Short and irregular bones are not elongated and have no diaphyses. However, certain regions of these bones, such as the processes (projections), have epiphyseal growth plates and therefore small epiphyses. Structure of Other Bones Sinuses – within some of the flat and irregular bones of the skull are air-filled spaces. Sinuses are lined by mucous membranes. Bone Remodeling Bone Remodeling It is the process of replacing old bone with new bone. Osteoclasts remove old bone and osteoblasts deposit new bone. Bone remodeling is involved in several important functions, including bone growth, changes in bone shape, adjustment of the bone to stress, bone repair, and body calcium ion regulation.* Bones are remodeled continuously in response to changes in 2 factors: Calcium levels in the blood Pull of gravity and muscles on the skeleton** Bone Remodeling Bone Growth Bones increase in size only by appositional growth which is the formation of new bone on the surface of older bone or cartilage. Bone Length Growth Long bones and bony projections increase in length because of growth at the epiphyseal plate. In a long bone, the epiphyseal plate separates the epiphysis from the diaphysis. Long bones grow by creating new cartilage via interstitial growth in the epiphyseal plate. This is followed by appositional bone growth on the surface of the existing cartilage. Bone Length Growth Bone Growth Bone Width Growth Osteoblasts from the periosteum lay down bone beneath it to form a series of ridges with grooves between them, following appositional bone growth. As the osteoblasts continue to produce bone, the ridges increase in size, extend toward each other, and meet to change the groove into a tunnel which is lined by the endosteum. This endosteum had previously been the periosteum before the growth in bone width and formation of grooves along the outer surface of the bone occurred. Osteoblasts from the endosteum lay down bone to form lamellae to fill in the tunnel, enclosing the blood vessel, and produces the osteon. Bone Width Growth Gross Anatomy Axial skeleton – bones located along the central axis of the body. It consists of bones of the head, vertebral column, and rib cage. It also protects the brain, the spinal cord, and the viral organs housed within the thorax. Appendicular skeleton – consists of the appendages and the bones that support them. It is made up of the bones of the upper limbs, the lower limbs, and the two girdles: pectoral girdle and pelvic girdle. It allows movement of appendages and supports weight in an upright position. Gross Anatomy Skull Skull Hyoid Vertebral Column Thoracic Cage Pectoral Girdle Upper Limb Pelvic Girdle Pelvic Girdle Lower Limb Other Structures 1. Ligament – an elastic band of tissue that connects bone to bone and provides stability to the joint. 2. Tendon – a band of tissue that connects muscle to bone. 3. Cartilage – soft, gel-like padding between bones that protects joints and facilitates movement. Hyaline cartilage – most bones in the body start out as a hyaline cartilage model, growth in bone length and bone repair often involve making hyaline cartilage first, then replacing it with bone. Articular cartilage – hyaline cartilage that covers the ends of bones where they come together to form joints, has no blood vessels or nerves. Ligament & Tendon Cartilage Other Structures 4. Joint – or articulations holds the bones together securely but also give the rigid skeleton mobility. Functional classification: Classification focuses on the amount of movement allowed by the joint. Synarthroses – immovable joints Amphiarthroses – slightly movable joints Diarthroses – freely movable joints Joints Joints Structural classification: Classification is according to the major connective tissue type that binds the bones together and whether a fluid-filled joint capsule is present. Fibrous joints – are immovable and slightly movable joints connecting the bones with fibrous tissue. The best example are the sutures of the skull. The irregular edges of the bones interlock and are bound together by connective tissue fibers allowing no movement to occur. Fibrous Joints Joints Structural classification: Cartilaginous joints – are immovable and slightly movable joints connecting the bone ends with cartilage. Examples of this joint type are the intervertebral joints of the spinal column, where the articulating bone surfaces are connected by discs of fibrocartilage. Cartilaginous Joints Joints Structural classification: Synovial joints – freely movable joints with bone ends are separated by a joint cavity containing synovial fluid. Most joints that unite the bones of the appendicular skeleton are synovial joints, reflecting the far greater mobility of the appendicular skeleton compared with the axial skeleton. Synovial fluid – serves as protection and lubrication of the joints. It reduces friction during movement. Synovial Joints Synovial Joints Range of Motion Range of motion describes the amount of mobility that can be demonstrated in a given joint. Active range of motion – is the amount of movement that can be accomplished by contracting the muscles that normally act across a joint. Passive range of motion – is the amount of movement that can be accomplished when the structures that meet at the joint are moved by an outside force. Range of Motion Range of Motion Range of Motion Range of Motion Range of Motion