Skeletal System Chapter 7

Types of Bones (by shape) Long-arm and leg bones Short-”cubelike”-carpals, tarsals Flat-ribs, scapula, some skull Irregular-vertebrae, facial Sesamoid-round- embedded in tendon or ligament-kneecap

Parts of a Long Bone Epiphysis-knob at each end Diaphysis-shaft Articular Cartilage-hyaline cartilage covering end of epiphyses Periosteum-fibrous CT covering bone-has blood vessels Medullary Cavity-opening which runs length of diaphysis-filled with yellow marrow

Compact Bone Tissue-surrounds medullary cavity Spongy Bone (Cancellous) Tissue-has spaces filled with red marrow-located in epiphyses Endosteum-squamous tissue lining medullary cavity and spaces in spongy bone

Microscopic Structure of Bone Compact Bone osteonic systems Haversian (osteonic canals) lacunae with osteocytes lamellae canaliculi Cancellous Bone no osteonic systems plates of bone called TRABECULAE lacunae with osteocytes canaliculi

Bone Growth and Development Bones form by replacing existing connective tissue in one of two ways; 1. Intramembranous ossification - bones begin as sheetlike layers of fibrous c. t. .-see steps in Table 7.1, pg 198 2. Endochondral ossification - bones begin as models of hyaline cartilage

Endochondral Ossification Primary Center of Ossification (in middle of diaphysis)-osteoblasts and blood vessels invade disintegrating cartilage - osteoblasts lay down spongy bone Osteoblasts from periosteum lay down compact bone around primary center (thick)

Osteoclasts carve out medullary cavity Cartilage disintegrates in secondary centers of ossification (in epiphyses) and osteoblasts lay down spongy bone there The area of cartilage between primary and secondary centers of oss. is called the epiphyseal plate/disk (as long as it is present, the bone grows in length) When centers meet, growth in length stops Bone thickness is due to laying down of compact bone under the periosteum

Figure 07.11

Osteoporosis animation

Factors affecting bone growth and development Vitamin D(some is stored in skin and activated by sunlight) - necessary for absorption of calcium from small intestine- a deficiency in children results in rickets; deficiency in adults-->osteomalacea (bone softening) Vitamin A - for bone resorption (osteoclast activity) - deficiency results in retardation of bone development

Ossification video http://www.youtube.com/watch?v=p-3PuLXp9Wg

Vitamin C - needed for collagen synthesis-deficiency results in too little collagen in bone matrix-->thin, fragile bones Thyroid hormone-stimulates replacement of cartilage by bone-too much in child--->stunted growth (premature ossification of epiphyseal plates) Growth hormone-(pituitary gland) stimulates mitotic division of cartilage in epi. plates-deficiency in child-->pituitary dwarfism;too much in child-->giantism; too much in adult--> acromegaly

Sex hormones (estrogens and androgens) - increase bone growth and stimulate ossification of epi. plates (especially estrogens) Physical stress - pull from muscles- stimulates bone tissue to thicken and strengthen (hypertrophy)---lack of exercise causes bone atrophy (become thinner and weaker)

Bone Functions Support & protection Lever System (with muscles) Blood cell formation (hematopoiesis) - in early embryo-yolk sac, then liver & spleen, then red marrow in infant- red marrow (found in most places in bone) Later, some red marrow is replaced by yellow marrow which is for fat storage in adult-red marrow (mostly in spongy bone of skull, ribs, clavicle, scapula, vertebrae, hip)

Storage of salts - most stored as crystals of CaPO4 called hydroxyapetite (Ca++ is important not only in bone hardness, but also in blood clotting, nerve impulse, muscle contraction Low blood Ca++ triggers osteoclast activity High blood Ca++ triggers osteoblast activity Other salts contain Mg, Na, K, Abnormal storage-lead, strontium, radium

Skeletal Organization Axial skeleton-skull, vertebral column, hyoid, ribs, sternum Appendicular skeleton-pectoral and pelvic girdles, limbs

Differences in Male and Female Skeletons Male-heavier, more dense, with more muscle attachments; pelvis is narrower, angle of pubic arch is smaller Female-lighter, less dense, fewer muscle attachments; pelvis is more flared, with larger opening and bigger pubic arch angle

Vertebral Column Normal curvatures: cervical, thoracic, lumbar, and pelvic

Abnormal Curvatures Kyphosis (hunchback) - excessive thoracic curvature Scoliosis - lateral curvature Lordosis (swayback) - excessive lumbar curvature

Other Vertebral Column Disorders Ruptured (herniated) disk - can occur when outer part of intervertebral disk becomes thinner, and inner mass loses firmness - crack occurs in outer, and inner mass oozes out, pressing on nerve Degenerative disk-disks become smaller, more rigid and weaker with age--person becomes shorter--fractures occur more easily