SKELETAL TISSUE AND PHYSIOLOGY

CARTILAGE Connective tissue Fibers embedded in firm gel Avascular Chondrocytes lie in lacunae Nutrients delivered by diffusion

3 TYPES Fibrocartilage – menesci of knee and between vertebrae Elastic – external ear and epiglottis Hyaline – articular, chondral, laryngeal, tracheal and bronchial

FUNCTIONS OF SKELETON Support Protection Movement –bones and joints – levers Mineral reservoir – Ca++, Phosphorus Hemopoiesis – blood cell formation

TYPES OF BONES Long – humerus, femur, ulna, radius, tibia, fibula Short – carpals and tarsals Flat – skull, ribs, patella, scapula Irregular – vertebrae, facial bones, hyoid

MACROSCOPIC STRUCTURE OF LONG BONES Diaphysis – main shaft like portion; hollow, cylindrical, thick compact bone Epiphysis(-es) – end of long bones – bulbous shape provides generous space for muscle attachments – spongy (cancellous) bone filled with yellow marrow except in proximal epiphyses of humerus and femur (red)

Articular cartilage – thin layer of hyaline cartilage that covers joint surfaces of epiphyses – shock absorber Periosteum –dense, white fibrous membrane that covers bone everywhere but joint surfaces – Sharpey’s fibers penetrate bone – muscle fibers interlace with these providing a firm anchor – BVs from periosteum nourish bone –

- OSTEOBLASTS (bone building cells) compose inner periosteum 5. Medullary cavity – marrow containing cavity in diaphysis 6. Endosteum – membrane lining medullary cavity

                                                                             

SHORT, FLAT AND IRREGULAR BONES Cancellous bone covered w/compact bone Red marrow fills spaces in cancellous bone inside a few irregular and flat bones (vertebrae and sternum) Needle aspiration – diagnostic tool

BONE TISSUE Connective tissue – cells, fibers (collagen) and calcified matrix More matrix than cells; lots of collagen Strength of cast iron, 1/3 the mass

BONE MATRIX Inorganic salts – APATITE (crystals of calcium and phosphate) gives bone its hardness – oriented to resist stress Organic matrix – collagen and ground substance – amorphous mixture of protein and polysaccharides

MICROSCOPIC STRUCTURE OF BONE Compact bone composed of Haversian system Lamellae – concentric cylinders of calcified matrix Lacunae – small spaces containing tissue fluid in which osteocytes lie between lamellae Canaliculi – small canals radiating from lacunae, connecting them to each other and the Haversian canal

Haversian canal – extends through center of each Haversian system – blood and lymph transport O2 and nutrients to bone cells - BVs from periosteum penetrate bone via Volkmann’s canals; arteries supply marrow Cancellous bone – NO Haversian systems; weblike arrangement of marrow filled spaces separated by trabeculae (thin processes of bone)

BONE MARKINGS DEPRESSIONS AND OPENINGS Fossa Sinus Foramen Meatus Sulcus

B. PROJECTIONS AND PROCESSES 1. Condyle 2. Head 3. Trochanter 4. Crest 5. Spinous process 6. Tuberosity 7. Tubercle

DEVELOPMENT OF BONE - OSTEOGENESIS 1. Intramembranous ossification happens in connective tissue membrane Includes broad flat bones of the skull Membrane like layers of primitive connective tissue appear at the site of future bone Layers supplied with blood – connective tissue cells arrange themselves around the blood vessel

These cells differentiate into osteoblasts Osteoblasts deposit bony matrix – produce spongy bone Osteoblasts become surrounded by bony matrix – in lacunae, osteocytes Osteoblasts on inside of periosteum give rise to compact bone

2. Endochondral Formed from hyaline cartilage model Periosteum develops, enlarges, and forms subperiosteal collar 1o ossification center develops as cartilage begins to calcify and BVs enter rapidly changing cartilage model at midpoint of diaphysis Ossification proceeds from diaphysis to epiphysis Bone grows in length

2o ossification center appears at epiphyses and growth proceeds from epiphysis to diaphysis Until bone length growth is complete, a layer of cartilage (epiphyseal cartilage) remains between diaphysis and epiphysis Epiphyseal cartilage thickens during growth periods This cartilage ossifies – osteoblasts make organic bone matrix, matrix calcifies – bone grows longer

Tibial epiphysis

BONE GROWTH AND RESORPTION Bone growth – diameter Osteoclasts Osteoblasts Ossification and resorption occur concurrently In adult years, rate = Childhood and adolescence, ossification > resorption 35- 40 years, resorption > ossification

BONE FRACTURES AND REPAIRS Fracture – break in bone’s continuity Simple – skin unbroken Compound – skin broken Alignment = reduction Closed reduction = fracture set without opening skin Open reduction – requires surgical incision Osteomyelitis Kids – greenstick fractures – bone cracked

HEALING OF FRACTURES Dead bone – removed by osteoclasts or serves as framework for CALLUS (repair tissue) Callus – periosteal and endosteal cells differentiate into chondroblasts and osteoblasts Callus binds broken ends – callus tissue is eventually replaced by normal bone