SKELETAL SYSTEM Osteology study of bones Bone is

SKELETAL SYSTEM • Osteology – study of bones • Bone is a vascular, innervated connective tissue • cartilage is a nonvascular, non-innervated connective tissue • Skeletal system is derived from mesoderm

Bone functions 1. support/structure 2. protection 3. movement 4. mineral storage – calcium, phosphorous , magnesium 5. hemopoiesis – blood cell formation 6. triglyceride storage

Long bone anatomy humerus, femur, etc (typically appendicular) 1. diaphysis – shaft 2. epiphysis (es) – bulbous ends 3. metaphysis (es) – between 1&2 *contains epiphyseal plate in youth*

4. articular cartilage (hyaline) friction reduction at joints 5. periosteum (dense irregular) wraps outer bone surface 6. endosteum lines medullary cavity 7. medullary cavity - in diaphysis contains yellow marrow 8. yellow marrow triglycerides (fat) 9. compact bone – “compact” “surface” bone 10. spongy bone – porous normally in epiphyses in adult long bones

11. red marrow – hemopoietic tissue found in spaces of spongy bone

• *compare long bones to flat bones which have two layers of compact bone and one layer of spongy bone • *analogous to a sandwich : compact =slices of bread spongy = filler

Bone matrix *nonliving, cellular products- composes most of bone 1. mineral salts (50%)– calcium phosphate(hydroxyapatite), calcium carbonate, magnesium hydroxide, fluoride, sulfates - results in the hardness of bone -minerals arrive via blood 2. collagen(25%) - results in tensile strength of bone - secreted by osteoblasts (bone cells)

Bone cells 1. Osteogenic - mitotic, one daughter differentiates, other maintained as osteogenic (like stem cells) Located beneath periosteum and endosteum. 2. Osteoblast – formed directly from osteogenic cells - bone “builder” – produces/secretes collagen 3. Osteocyte – retired osteoblast - most mature, true bone cell - resides in matrix (lacuna) until death ________________________ 4. Osteoclast - * not related to previous cells - made of fused monocytes (wbc’s) - bone destoyer -secretes enzymes to dissolve matrix

Compact Bone *compact bone is superficial bone *consists of Haversian Systems (Osteons) 1. Haversian Canal – penetrating blood vessel 2. Canaliculus (i) – liquid (H 2 O) filled canals connecting Haversian canals to lacunae 3. Lacuna (ae) – space containing an osteocyte (cave) 4. Lamellae – surrounding rings of matrix

Spongy Bone spongy bone is deep to compact bone *porous * no true Haversian system, has only 1. canaliculi 2. lacunae 3. lamellae *spongy bone is arranged into thin strands called trabeculae

Bone Formation – osteogenesis or ossification A- Intramembranous Ossification *bone forming from soft tissue – no cartilage* *forms cranial skull bones and possibly the clavicles a) mesenchymal osteogenic osteoblasts bone

B- Endochondral Ossification *future bone composed of hyaline cartilage, then converted to bone *most bones of the body form by endochondral ossification a) mesenchymal chondroblasts hyaline cartilage osteogenic osteoblasts bone

Steps of endochondral ossification 1) primary ossification center -located in the middle of the future bone -dying cartilage cells trigger the penetration of cartilage by a blood vessel -ossification proceeds superficial to deep

2) secondary ossification centers -located inside of epiphyses -ossification proceeds deep to superficial *overall results growth plate in metaphysis & articular cartilage on epiphyses WHY?

Nutrients for healthy bones A) VITAMINS 1) vitamin C - collagen synthesis -osteoblast osteocyte differentiation 2) vitamin B 12 – collagen synthesis 3) vitamin K - collagen synthesis 4) vitamin A - increased osteoblast activity 5) vitamin D- calcification (rickets) and calcium absorption

• B) MINERALS Calcium, phosphorous, magnesium, fluoride, iron, manganese

Fractures / Repair / Healing A) Fracture types – see handout *a fracture is any break or crack in a bone 1. simple(closed) fracture does not break skin 2. compound (open) fracture breaks skin as well as bone 3. greenstick fracture one side breaks, other side bends common in youth

4. comminuted fracture fragments at break site, usually requires surgery 5. impacted fracture(compression) two ends of bone driven into each other 6. stress fracture tiny, often microscopic cracks in a bone painful, overuse injury

7. Spiral fracture - ragged break due to twisting force 8. Epiphyseal fracture - break at growth plate (epiphyseal plate) 9. Depressed fracture - broken bone pressed inward (skull)

7. Colle’s Fracture common sports injury (falling while running) radius breaks near wrist distal portion of radius(near hand) moves posterior to rest of radius 8. Pott’s Fracture common ankle injury sole of foot moves laterally fracture to tibia (medially) as well as fibula

5 stages of healing 1. Fracture hematoma stage blood clots at break site – can take several hours. Why? 2. Procallus stagebroken area becomes vascular

3. Fibrocartilaginous stage fibrocartilage holds broken ends together (approx 3 weeks) 4. Bony callus stage ( 3 -4 mo. ) fibrocartilage replaced by spongy bone 5. Remodeling stage spongy bone slowly converted to compact bone (months)

Reduction -realigning broken ends of bone 1) open reduction – surgical 2) closed reduction - nonsurgical

Bone growth A) length epiphyseal plate is ossified on side of diaphysis cartilage cells proliferate on side of epiphysis B) thickness matrix forms around blood vessel on surface of bone vessel becomes a Haversian canal

Hormones affecting bones. 1. PTH (parathyroid hormone) - increases blood calcium levels -”pulls” calcium from bones by stimulating osteoclast activity 2. CT (calcitonin) - lowers blood calcium levels -increases bone calcium levels -may slow osteoclast activity -most effective in youth

Cartilage *matrix is similar to bone ----- collagen and water * but different ----- chondroitin sulfate and hyaluronic acid (GAG’s) rather than mineral salts *GAG = glycosaminoglycan

2. Collagen for tensile strength other components for resilience

3. a)hyaline - shiny, glassy, most common in human body Locations: trachea, nose, bone joints, growth plates, larynx, rib cage Functions: Support, cushion, glide

4. ELASTIC Cartilage: most elastin* Locations: Epiglottis, External ear Functions: structure , flexibility

5. c)fibrocartilage – very abundant collagen Functions: resists compression , structure Locations: meniscus, vertebral disks, bone repair

6. cartilage is an avascular connective tissue and lacks a direct nerve supply

7. a)chondrocyte – mature cartilage cell in lacuna within cartilage matrix b)chondroblasts – secretes collagen - analogous to osteoblast c) Perichondrium – analogous to periosteum