SKELETAL SYSTEM Parts of the Skeletal System 1. 2. 3. 4. Bones Joints Cartilages Ligaments – fibrous cords that bind the bones together at joints. 2 Subdivisions of the skeleton 1. Axial Skeleton - the bones that form the longitudinal axis of the body 2. Appendicular Skeleton - the bones of the limbs and girdles that attach them to the axial skeleton. FUNCTIONS OF THE BONES 1. Support the body 2. Protect Soft organs - Skull and vertebrae protect brain and spinal cord - Rib cage protects thoracic cavity organs 3. Attached skeletal muscles allow movement 4. Store Minerals and fats - Calcium and phosphorus - Fat in the internal marrow cavity 5. Blood Cell formation (hematopoiesis) CARTILAGE Articular cartilage - type of hyaline cartilage that covers the end of bones 2 Types of Cartilage Growth: 1. Appositional growth - chondroblasts in the perichondrium, and outside edge of the existing cartilage. 2. Interstitial growth - chondrocytes in the center of the tissue and in-between the existing cells BONE MATRIX - - - Mature bone matrix is normally about 35% organic and 65% inorganic material. The organic material consists primarily of collagen and proteoglycans. The inorganic material consists primarily of a calcium phosphate crystal called hydroxyapatite. The collagen and mineral components are responsible for the major functional characteristics of the bone. Osteogenesis Imperfecta - - 3 Types of Cartilages 1. Hyaline Cartilage 2. Fibrocartilage 3. Elastic Cartilage - Cartilage Making cells: 1. Chondroblast (young) 2. Chondrocyte (mature) Most cartilage is covered by a protective connective tissue sheath called the perichondrium. Also known as brittle bone disorder. It is caused by mutations that yield reduced or defective type I collagen. Type I collagen is the major collagen of bone, tendon, and skin The mildest and most common form of OI is called type I, wherein it is caused by too little formation of normal type I collagen (collagendeficiency disorder). BONE CELLS Osteochondral progenitor cells – are stem cells that can become osteoblasts or chondroblasts. Osteoblast – bone forming cells. - They produce collagen and proteoglycans. - Also releases matrix vesicles, which contain high concentrations of calcium and phosphorous. Short Bones - Generally cube-shaped (Carpals & Tarsals) - Osteocytes – mature bone cells. Osteoclasts – bone destroying cells. - They perform reabsorption, or breakdown, of bone that mobilizes crucial calcium and phosphate ions for use in many metabolic processes. - Irregular Bones – Irregular shape (Vertebrae & Hip Bones) - CLASSIFICATION OF BONES - The adult has 206 bones 2 basic types of osseous (bone) tissue 1. Compact bone - Dense, smooth, and homogeneous 2. Spongy bone - Small needlelike pieces of bone - Many open spaces Bones are classified on the basis of shape into four groups: 1. 2. 3. 4. Long Flat Short Irregular Long Bones - Typically longer than they are wide (Femur & Humerus) - Shaft with enlarged ends Contain mostly compact bone; spongy bone at ends All of the bones of the limbs (except wrist, ankle, and kneecap bones) are long bones Flat Bones - Thin, flattened, and usually curved (Ribs & Sternum) - Has two thin layers of compact bone sandwiching a layer of spongy bone between them Contain mostly spongy bone with an outer layer of compact bone Sesamoid bones are a type of short bone that form within tendons (patella) Do not fit into other bone classification categories. STRUCTURE OF BONE Diaphysis – makes up most of bone’s length - Composed of compact bone Periosteum – outside covering of the diaphysis - Fibrous connective tissue membrane Perforating (Sharpey’s) fibers secure periosteum to underlying bone - Passages for nerves and blood vessels CATEGORIES OF BONE MARKINGS Projections or processes—grow out from the bone surface - Terms often begin with “T” Depressions or cavities—indentations - Terms often begin with “F” Microscopic anatomy of spongy bone Epiphysis - Composed mostly of spongy bone enclosed by thin layer of compact bone. Articular Cartilage – Covers the external surface of the epiphyses - A glassy hyaline cartilage, which provides a smooth surface Epiphyseal line - Remnant of the epiphyseal plate - Seen in adult bones Epiphyseal plate – Flat plate of hyaline cartilage seen in young, growing bone - Causes lengthwise growth of a long bone Endosteum – Lines the inner surface of the shaft - Made of connective tissue Medullar cavity – cavity inside the shaft - Contains yellow marrow (mostly fat) in adults Contains red marrow for blood cell formation in infants until age 6 or 7 Bone Markings - Reveals the sites of attachments for muscles, tendons, and ligaments - Composed of small, needlelike pieces of bone called trabeculae and open spaces Has lots of open spaces filled by marrow, blood vessels, and nerves Lacunae – Cavities in bone matrix that house osteocytes. Lamellae – Concentric circles of lacunae situated around the central (Haversian) canal. Central (Haversian) canal – Opening in the center of an osteon Osteon (Haversian system) – A unit of bone containing central canal and matrix rings Canaliculi - Tiny canals - Radiate from the central canal to lacunae Perforating (Volkmann’s) canal – Canal perpendicular to the central canal Ossification, or osteogenesis - is the process of bone formation; occurs by appositional growth on the surface of previously existing material, either bone or cartilage - Occurs on hyaline cartilage models or fibrous membranes, and Long bone growth involves two major phases 2 Types of Ossification 1. Intramembranous ossification – The making of bone within connective tissue membranes. - Responsible for making flat bones 2. Endochondral ossification – The process of making bone within cartilage. 3. Primary ossification center – Located in the diaphysis 4. Secondary ossification center – Located in the epiphysis Cells involved with ossification: - Chondrocytes – cartilage-making cells Osteoblasts Osteocytes Endochondral Ossification: 1. Hyaline cartilage provides a framework for bone formation 2. Periosteum forms; osteoblasts invade the primary ossification center 3. Osteoblasts in the primary ossification center produce spongy bone; other osteoblasts below the periosteum produce compact bone 4. Spongy bone in the diaphysis is broken down by osteoclasts; medullary cavity is formed; after birth secondary ossification center appear in the epiphyses 5. Bone continues to grow in length and width as long as the epiphyseal plate (growth plate) is present 6. Bone is fully formed and has stopped growing; epiphyseal line remains By birth, most cartilage is converted to bone except for two regions in a long bone 1. Articular cartilages 2. Epiphyseal plates New cartilage – is formed continuously on external face of these two cartilages Old cartilage – is broken down and replaced by bony matrix Appositional Growth - Bones grow in width Osteoblasts in the periosteum add bone matrix to the outside of the diaphysis Osteoclasts in the endosteum remove bone from the inner surface of the diaphysis Bone growth is controlled by hormones, such as growth hormone and sex hormones Bones are remodeled throughout life in response to two factors: 1. Calcium ion level in the blood determines when bone matrix is to be broken down or formed 2. Pull of gravity and muscles on the skeleton determines where bone matrix is to be broken down or formed CALCIUM ION REGULATION Parathyroid Hormone (PTH) – Released when calcium ion levels in blood are low - Activates osteoclasts Osteoclasts break down bone and release calcium ions into the blood Hypercalcemia (high blood calcium levels) prompts calcium storage to bones by osteoblasts. When PTH binds to these receptors, osteoblasts respond by producing receptor activator of nuclear factor kappaB ligand (RANKL). RANKL is expressed on the surface of the osteoblasts and combines with receptor activator of nuclear factor kappaB (RANK) found on the cell surfaces of osteoclast precursor stem cells. Osteoclast production is inhibited by osteoprotegerin (OPG), which is secreted by osteoblasts and other cells. Increased PTH causes decreased secretion of OPG from osteoblasts and other cells. Thus, increased PTH promotes an increase in osteoclast numbers by increasing RANKL and decreasing OPG. Conversely, decreased PTH results in fewer osteoclasts by decreasing RANKL and increasing OPG. Calcitonin – Secreted from the thyroid gland when blood calcium ion levels are too high. Nutrition - Certain vitamins are important to bone growth in very specific ways. - - Vitamin D is necessary for the normal absorption of calcium from the intestines Insufficient vitamin D in children causes rickets Rickets – a disease resulting from reduced mineralization of the bone matrix. Osteomalacia – adult rickets; softening of bones due to calcium depletion. Vitamin C is necessary for collagen synthesis by osteoblasts. - In children, Vitamin C deficiency can retard growth. In both children and adults, vitamin C deficiency can result in scurvy. HORMONES 1. 2. 3. - Growth Hormone Thyroid Hormone Reproductive Hormones Estrogen and testosterone initially stimulate bone growth, which accounts for the burst of growth at puberty. - Females usually stop growing earlier than males because estrogens cause quicker closure of the epiphyseal plate than testosterone. BONE FRACTURES Fracture: break in a bone Types of bone fractures: 1. Closed (simple) fracture – is a break that does not penetrate the skin 2. Open (compound) fracture – is a broken bone that penetrates through the skin. Bone fractures are treated by reduction and immobilization - - Closed reduction: bones are manually coaxed into position by physician’s hands Open reduction: bones are secured with pins or wires during surgery Healing time is 6 – 8 weeks Hematoma Formation - When a bone is fractured, the blood vessels in the bone and surrounding periosteum are damaged and hematoma forms. - A hematoma is a localized mass of blood released from blood vessels but confined within an organ or space Hyoid bone – Closely related to mandible and temporal bones - The only bone that does not articulate with another bone THORACIC CAGE Bony thorax, or thoracic cage, protects organs of the thoracic cavity Consist of 3 parts: 1. 2. 3. Sternum Ribs True Ribs (pairs 1-7) False Ribs (pairs 8 – 12) Floating Ribs (pairs 11 – 12) Thoracic Vertebrae JOINTS - Joints – are commonly named according to the bones or portions of bones that join together. Example: temporomandibular joint – between the temporal bone and the mandible Some joints are given the Greek or Latin equivalent of the common name, such as cubital (elbow/forearm) joint. CLASSES OF JOINTS 1. Fibrous Joints - Sutures Syndesmoses Gomphoses 2. Cartilaginous Joints - Synchondroses Symphyses 3. Synovial Joints - Plane or Gliding Joint Saddle Joint Hinge Joint Pivot Joint Ball-and-socket joint Ellipsoid joint FIBROUS JOINTS - The articulating surfaces of two bones united by fibrous connective tissue - No joint cavity; no movement Sutures - Seams found only between the bones of the skull - - - In newborn, some of the sutures have a membranous area called a fontanel (“little fountain”) Fontanels make the skull flexible during the birth process and allow for growth of the head after birth. When a suture becomes fully ossified, it becomes a synostosis. Synostosis results when two bones grow together across a joint to form a single bone. Syndesmoses - A slightly movable type of fibrous joint - The bone are farther apart than in a suture and are joined by ligaments Some movement may occur because the ligaments are flexible Gomphoses - Are specialized joints consisting of pegs that fit into sockets - Periodontal ligaments: the connective tissue bundles between the teeth and their sockets Synchondroses - Consist of two bones joined by hyaline cartilage. Sympheses – Consist of fibrocartilage uniting two bones Synovial Joints - Contain synovial fluid and allow considerable movement between articulating bones Plane joint or Gliding joint – consist of two flat bone surfaces of about equal size between which a slight gliding motion can occur. Saddle joint – consists of two saddle-shaped articulating surfaces oriented at right angle to each other. Hinge joint – a uniaxial joint in which a convex cylinder in one bone is applied to a corresponding concavity in the other bone. Pivot joint – a uniaxial joint that restricts movement to rotation around a single axis. Ball-and-socket joint – consists of a ball (head) at the end of one bone and a socket in an adjacent bone into which a portion of the ball fits Ellipsoid joint – a modified ball-and-socket joint; the articular surfaces are ellipsoid in shape TYPES OF MOVEMENTS Gliding movements – the simplest of all types of movement Angular movements: 1. Flexion – a bending movement that decreases the angle of the joint to bring the articulating bones closer together. 2. Extension – a straightening movement that increases the angle of the joint to extend the articulating bone 3. Hyperextension - extension of a joint beyond 180 degrees 4. Plantar Flexion – movement of the foot toward the plantar surface, as when standing on the toes 5. Dorsiflexion - movement of the foot toward the shin, as when walking on the heels 6. Abduction – to take away; movement away from the midline 7. Adduction – to bring together; movement toward the midline Circular Movements: 1. Rotation – the turning of the structure around its long axis - Example: rotating the head to shake the head “no” 2. Pronation – the word prone means lying facedown 3. Supination – the word supine means lying faceup 4. Circumduction – a combination of flexion, extension, abduction, and adduction
