SKELETON TISSUE AND STRUCTURE

Functions of the Skeletal System Support Provides the framework for the attachment of other organs Storage of minerals Calcium ions: 98 % of body’s calcium ions are in the bones Phosphate ions

Functions of the Skeletal System (cont.) Blood cell production Leverage Muscles pulls on bones to produce movement Protection Ribs protect heart and lungs Skull protects the brain Vertebrae protect the spinal cord Pelvic bones protect the reproductive organs

Bone Classification a)Long Bones b)Short Bones c)Flat Bones d)Irregular Bones e) Sesamoid Bones TARSAL BONE PARIETAL BONE Vertebral bone patella

Parts of a Long Bone epiphysis distal proximal diaphysis compact bone spongy bone -Branching plates are called trabeculae ENDOSTEUM, Lines medullary cavity, which contains marrow: red, yellow articular cartilage PERIOSTEUM, fibrous outer layer -> ligaments

The Histological Organization of Mature Bone The matrix of bone Calcium phosphate eventually converts to hydroxyapatite crystals hydroxyapatite Collagen fibers (1/3 of bone matrix) Collagen and hydroxyapatite make bone tissue strong Bone cells

The Cells of Mature Bone Osteocytes Mature bone cells They control Ca 2+ storage and release Sit in depressions called lacunae Surrounded by a matrix called lamellae Small channels extending from the osteocytes to the blood capillaries are called canaliculi

The Cells of Mature Bone (cont.) Osteoblasts (remember: blasts “build”) These are Immature bone cells Found on the inner and outer surfaces of bones Secrete osteoid, protein mixture that forms the organic matrix of bone. Bone is formed when osteoid mineralizes. Osteoblasts are involved in making new bone. This is a process called osteogenesis (ossification)

The Cells of Mature Bone (continued) Osteoprogenitor cells Found on the innermost layer of the periosteum and the inner lining of the endosteum Differentiate to form new osteoblasts Heavily involved in the repair of bones after a break Osteoclasts Multinucleated cells Secrete acids, which dissolve the bones. (osteolysis)

Two Types of Osseous Tissue Compact bone (dense bone) Forms the walls of bone; conducts stress along the Length of the bone Spongy bone (trabecular, or cancellous, bone) Open network of plates Surrounds the medullary cavity Provide strength w/o weight JPG×G×

Compact Bone (details) Consists of osteons Basic functional unit of bone Consists of: Central canal – place where blood vessel runs through Canaliculi – projections from osteocyte Osteocytes – bone cells Lacunae – small cavity containing osteocyte Lamellae – concentric rings of matrix (calcium phosphate) Osteons are sometimes called Haversian systems. The central canal is sometimes called the Haversian canal.

The photo shows the femur. Trabeculae of spongy bone Endosteum Lamellae Canaliculi opening on surface Spongy bone Forms branching plates called trabeculae Supports the marrow

Structure and Function of Bone Periosteum Outer surface of the bone Isolates and protects the bone from surrounding tissue Provides a route and a place for attachment for circulatory and nervous supply Actively participates in bone growth and repair Attaches the bone to the connective tissue network of the deep fascia Endosteum (plural endostea) connective tissue that lines the surface of the bony tissue that forms the medullary cavity of long bones © 2015 Pearson Education, Inc.

Figure 5.4a Anatomy and Histology of the Periosteum and Endosteum © 2015 Pearson Education, Inc. a The periosteum contains outer (fibrous) and inner (osteogenic) layers. Collagen fibers of the periosteum are continuous with those of the bone, adjacent joint capsules, and attached tendons and ligaments. Joint capsule Osteogenic layer of periosteum Fibrous layer of periosteum Endosteum Compact bone Circumferential lamellae Periosteum Fibrous layer Osteogenic layer Canaliculi Lacuna Osteocyte Perforating fibers

Bone Development Intramembranous Ossification connective tissue becomes osteoblasts  osteocytes in lacunae e.g. broad, flat bones, such as skull bones (except mandible) Endochondral Ossification (most bones) Hyaline cartilage forms a model bone Cartilage decomposes, and periosteum develops from connective tissue (see next slide)

Epiphyseal Plate Area of cartilage in the metaphysis Cartilage near the diaphysis is converted to bone The width of this zone gets narrower as we age Marks the former location of the epiphyseal cartilage © 2015 Pearson Education, Inc. X-ray of the hand of a young child. SEE EPIPHYSEAL PLATES X-ray of the hand of an adult. SEE epiphyseal lines.

Increasing the Diameter of a Developing Bone Inner layer of the periosteum differentiates to form osteoblasts and adds bone matrix to the surface This forms circumferential lamellae to the outer surface Osteons form Bone continues to enlarge in diameter APPOSITIONAL BONE GROWTH

Bone Development and Growth There are four major sets of blood vessels associated with the long bones Nutrient vessels Metaphyseal vessels Epiphyseal vessels Periosteal vessels © 2015 Pearson Education, Inc.

REALIZE THAT THERE IS A CIRCULATORY SUPPLY TO THE BONE © 2015 Pearson Education, Inc. Metaphysis Epiphyseal artery and vein Metaphyseal artery and vein Nutrient artery and vein Periosteal arteries and veins Periosteum Connections to superficial osteons Metaphyseal artery and vein Articular cartilage Periosteum Compact bone Medullary cavity Nutrient foramen Branches of nutrient artery and vein Epiphyseal line Vessels in Bone Also, where blood vessels enter, nerves enter

Bone markings include: Projections Depressions Fossa Openings Sinuses/canals/fissures/foramen Processes Trochanter/crest/spine/line/tubercle/tuberosity/ head/neck/facet/condyle/trochlea © 2015 Pearson Education, Inc.

Examples of Bone Markings (Surface Features) Skull, sagittal section Skull, anterior view Openings Sinus or antrum: A chamber within a bone, normally filled with air Meatus or canal: A passageway through the substance of a bone Fissure:An elongated cleft Foramen: A rounded passageway for blood vessels and/or nerves Process:Any projection or bump Elevations and Projections Ramus:An extension of a bone making an angle to the rest of the structure

Examples of Bone Markings (Surface Features, cont.) Ramus Head: The expanded articular end of an epiphysis, often separated from the shaft by a narrower neck Processes formed where tendons or ligaments attach Processes formed for articulations with adjacent bones Fossa Foramen Pelvis Head Neck Humerus Condyle Femur Depressions Neck: A narrower connection between the epiphysis and diaphysis Facet: A small, flat articular surface Condyle: A smooth, rounded articular process Trochlea: A smooth, grooved articular process shaped like a pulley Trochanter: A large, rough projection Crest: A prominent ridge Spine: A pointed process Line: A low ridge Tubercle: A small, rounded projection Tuberosity: A rough projection Sulcus: A narrow groove Fossa: A shallow depression

Factors Regulating Bone Growth Nutrition Calcium ions Phosphate ions Magnesium ions Citrate Carbonate ions Sodium ions Vitamins A, C, D (calcitriol) Hormones: parathyroid and calcitonin hormones Growth hormone (somatotropin) simulates Excessive – acromegaly Insufficient - dwarfism Estrogen and testosterone stimulate

Remodeling of Bone Realignment of teeth can change the shape of tooth sockets Increased muscular development Bone changes occur due to stress Stressed bones become thicker and stronger Inactivity causes degeneration © 2015 Pearson Education, Inc. Physical stress is good

Rickets/Osteomalacia A disease caused by lack of vit D softening/weakening of bone Can be treated with Calcium green leafy vegetables,!

Osteoporosis = loss of bone density. hollow/brittle bones Causes Lack of exercise < calcium Age Sex hormone deficiencies Osteoclasts break down osteocytes to give the body Calcium