Skeletal

BIO 163: Basic Anatomy and Physiology Ch. 6: Skeletal System and Joints Functions ● ● Support Protect Movement Storage ● Blood cell production - Skeletal System Components Bones Hyaline cartilage type of cartilage associated with bone development Tendons: connect muscles to bones Ligaments: connect bones to bones - Bone Histology - Bone Matrix Minerals Fat in yellow bone marrow Bone, cartilage, tendons, and ligaments: all connective tissues. Characteristics determined by composition of their extracellular matrix. Matrix contains: collagen, ground substance, and other organic molecules, as well as water and minerals. Red bone marrow Bone matrix is about 35% organic and 65% inorganic material by weight. Organic material: collagen & proteoglycans Collagen provides flexibility & strength - Inorganic material: calcium phosphate crystal called hydroxyapatite - Bone Cells THREE types of cells in bone: 1.Osteoblasts: responsible for the formation of bone and the repair and remodeling of bone. Produce collagen and proteoglycans. - 2+ Secrete high concentrations of Ca and phosphate ions, forming crystals called hydroxyapatite. The formation of new bone by osteoblasts is called ossification. - 2. Osteocytes: cells that maintain bone matrix Mineral component gives bone compression (weight-bearing) strength Account for 90-95% of bone cells - long life spans 3. Osteoclasts: bone-destroying cells. Contribute to bone repair and remodeling by removing existing bone, called bone reabsorption. 2+ Bone breakdown is important for mobilizing Ca putting calcium in the blood when needed Lacunae spaces within the bone matrix that house Osteocyte cell bodies Canaliculi narrow, long spaces that house Osteocyte cell extensions Bone Histology ● Osteoprogenitor cells ● Spongy and Compact Bone ● L Osteoblasts Osteocytes Osteoclasts ● Lamellar bone: mature bone Aka osteogenic cell L Bone can be classified according to the amount of bone matrix relative to the amount of space within the bone: 1 Spongy Bone Trabeculae interconnecting rods or plates of bone that comprises Spongy bone Between the trabeculae are spaces, filled with bone marrow & blood vessels. Reduces weight of bone Organized into thin, concentric sheets or layers, called lamellae. Compact Bone 1 1.Spongy bone has less bone matrix and more space within the bone 2. Compact bone has more bone matrix and less space Types of Bones Compact bone is the solid, outer layer surrounding each bone. Functional unit of compact bone is an osteon: composed of concentric rings of matrix surrounding a central canal. Central canals contain blood vessels, nerves, and loose connective tissue Structure of a Long Bone Diaphysis: center portion of the bone which is composed of compact bone surrounding a hollow center called the medullary cavity Spongy bone tissue lines the medullary cavity Ends of a long bone are called epiphyses Contain mostly spongy bone, with an outer layer of compact bone. Epiphyseal plate: located between the epiphysis and the diaphysis. Growth in bone length occurs at the epiphyseal plate. When bone stops growing in length, the epiphyseal plate becomes ossified and is called the epiphyseal line. Ossification (Osteogenesis) Bone formation in the fetus follows two processes: Intramembranous ossification starts within embryonic connective tissue membranes. Endochondral ossification starts with a cartilage model. Both types of bone formation can result in compact or spongy bone. Intramembranous Ossification Forms skull bones Intramembranous ossification occurs when osteoblasts begin to produce bone within connective . Ⓡ Endochondral Ossification ● tissue. Osteoblasts line up on the surface of connective tissue fibers & begin depositing bone matrix to form trabeculae. . Process begins in areas called ossification centers: trabeculae radiate out from these centers. Two or more ossification centers exist in each flat skull bone Ⓡ Bone Growth in Length and Width Endochondral bone formation: bone formation within a cartilage model. Cartilage model is replaced by bone. Initially formed is a Primary ossification center, which forms bone in the diaphysis of a long bones Secondary ossification center forms bone in the epiphysis Occurs in all bones except skull There are 2 types of bone growth that occurs by cartilage growth: - - 1. Appositional Growth → chondroblasts in the inner chondrogenic layer add new cartilage to the outside edge of the existing cartilage Leads to increase in bone width - Interstitial Bone Growth Growth in the length of a bone, major source of increased height in an individual, occurs in the epiphyseal plate. 2. Interstitial Growth → chondrocytes in the center of the tissue divide & add more matrix in between the existing cells Leads to increase in bone length Appositional Bone Growth Occurs throughout life as bone is remodeled to meet the physical demands Bone growth occurs by the deposition of new bone lamellae onto existing bone or other connective tissue. Occurs through endochondral ossification Occurs only during childhood As osteoblasts deposit new bone matrix on the surface of bones between the periosteum and the existing bone matrix, the bone increases in width, or diameter. This process is called appositional growth Bone Remodeling Bone remodeling involves: 1. Removal of existing bone by osteoclasts and 2. Deposition of new bone by osteoblasts Occurs in all bones Responsible for: changes in bone shape, bone repair, adjustment of bone to stress, & calcium ion regulation Allows bone to adapt to the body's changing requirements Bone Repair (Healing) 1. Broken bone causes bleeding and a hematoma forms. 2. A callus forms which is a bone cartilage network between and around the bone fragments. 3. Woven, spongy bone replaces the callus. 4. Compact bone replaces the spongy bone. Bone and Calcium Homeostasis: maintained by parathyroid hormone (PTH) and calcitonin Parathyroid Hormone (PTH) ● Calcitonin ● ● 2+ Secreted by the parathyroid gland when blood Ca levels are too low Increases formation and activation of osteoclasts, the principal bone-reabsorbing cells 2+ ● ● 2+ Stimulates reabsorption of Ca from urine in the kidney, reducing the amount of Ca excreted in the urine. Skeletal System and Divisions 2+ Secreted from the thyroid gland when blood Ca levels are too high 2+ Rapidly lowers blood Ca levels by inhibiting osteoclast activity The Axial Skeleton 80 bones Including: Adult skeleton= average 206 total bones Bones are segregated into the axial skeleton and the appendicular skeleton Vertebral Column The vertebral column, or spine, is the central axis of the skeleton, extending from the base of the skull to slightly past the end of the pelvis. In adults, it usually consists of 26 individual bones, grouped into five regions 7 cervical vertebra 12 thoracic vertebra 5 lumbar vertebra 1 sacrum 1 coccyx • Atlas: - Axis: Skull Hyoid Auditory ossicles (Ear) Vertebral Column Thorax-sternum and ribs - nd First vertebra holds head Second vertebra rotates head Functions of Vertebral Column • Supports body weight a Vertebral Curvatures • The adult vertebral column has four major curvatures: cervical, thoracic, lumbar and sacrococcygeal. Primary curves-curves posteriorly The thoracic region • ↑ Protects the brain & spinal cord Allows spinal nerves to exit the spinal cord Provides a site for muscle attachment Provides movement of the head and trunk * The Appendicular Skeleton - Secondary curves- curves anteriorly The cervical region The lumbar region The sacral and coccygeal regions together 126 bones Including: Articulations Pelvic Gender Differences Pectoral girdles Pelvic girdles Upper limbs (arms and hands) Lower limbs (legs and feet) Articulations (joints): where two bones come together. Classified two ways: Structurally: fibrous, cartilaginous, or synovial, based on major connective tissue type that binds the bones together & whether a fluid-filled joint capsule is present. Functional categories: synarthroses, amphiarthroses, or diarthroses, based upon degree of motion Joint Classification - HOWE Structural connective tissue type Fibrous: united by fibrous connective tissue Cartilaginous: united by means of cartilage Synovial: joined by a fluid cavity, most joints of the appendicular skeleton Functional degree of motion Synarthrosis: non-movable joint Ex. skull Amphiarthrosis: slightly movable joint Ex. Between vertebrae Diarthrosis: freely movable joint • Ex. knee, elbow, wrist