Chapter 6 Skeletal System.docx

Skeletal System A. Functions 1. Support – arches of feet, vertebral column, pelvis 2. Protect softer tissues – skull, ribs, pelvis 3. Act as levers for movement 4. Hemopoiesis - production of blood cells 5. Mineral storage and homeostasis – calcium, phosphate 6. Adipose storage 7. Skeletal muscle at...

Skeletal System A. Functions 1. Support – arches of feet, vertebral column, pelvis 2. Protect softer tissues – skull, ribs, pelvis 3. Act as levers for movement 4. Hemopoiesis - production of blood cells 5. Mineral storage and homeostasis – calcium, phosphate 6. Adipose storage 7. Skeletal muscle attachment sites 8. Hormone production – osteocalcin (see pg. 176) B. Bone Classification According to general location: 1. Axial skeleton – bones in the long axis of the body. Includes bones of skull, vertebral column and bony thorax (rib cage). ***Details to be studied in lab*** 2. Appendicular skeleton – bones of the upper and lower limbs as well as the bones that connect them to the axial skeleton (girdles). ***Details to be studied in lab*** According to shape: 1. Long - greater length than width. Typically have a middle shaft region with two expanded ends. Most but not all bones of the limbs. 2. Short – somewhat cubed shape, nearly equal in length and width. Include wrist and ankle bones. 3. Sesamoid – A type of short bone that develop in tendons. vary in number Include patella and bones in tendons of hand and foot. 4. Flat – thin, flattened bones that are usually curve. Includes scapula, ribs, hip bones and most cranial bones. 5. Irregular – complex shapes that do not fit any of the above types Include vertebrae, some facial bones. 6. Sutural – develop within joints of the cranium. vary in number ***Details to be studied in lab*** C. Bone Structure Parts of a Long bone (examples: humerus, femur) 1. diaphysis - shaft region of a bone 2. epiphysis – expanded end regions (plural: epiphyses) 3. articular cartilage – layer of hyaline cartilage on the outside of the ends of the epiphyses. Acts to decrease friction and shock absorption. 4. periosteum - fibrous, vascular bone covering. Functions include attachment sites for tendons and ligaments, anchors blood vessels to bone surface, bone development and bone tissue repair. Anchored to underlying bone tissue by way of perforating (Sharpey’s) fibers. 5. medullary cavity – cavity in diaphysis containing yellow bone marrow. 6. yellow bone marrow – fat (energy) storage in adults 7. endosteum – fibrous lining of the medullary cavity 8. compact bone – the outer external bone tissue. Resists compression and bending forces. See pages 181–184 structure: osteons, lamellae, interstitial lamellae, circumferential lamellae, osteocytes, lacunae, canaliculus, central canal *** see lab models*** 9. spongy bone- irregular bony plates (trabeculae) found underneath the compact bone of the epiphyses and inner bone tissue of the diaphysis (lining medullary cavity). Reduces weight of skeleton 10. red bone marrow – where hemopoiesis occurs. found in the spaces between trabeculae of spongy bone. Parts of a Flat bone (example: cranial bone) Spongy bone sandwiched between two layers of compact bone. Red bone marrow present within spongy bone. Periosteum covering outer surface of both layers of compact bone. D. Bone Tissue Cells 1. osteoprogenitor (osteogenic) cells – stem cells found in periosteum and endosteum. Very actively dividing (mitosis) cells. Some daughter cells become osteoblasts while others remain as osteogenic cells. 2. osteoblasts – bone forming cells. Mitotically active bone cells releasing matrix. 3. osteocytes – mature bone maintenance cells. Maintain calcium homeostasis 4. osteoclasts – giant multinucleated cells that reabsorb (break down) bone matrix. Contain a ruffled border surface that releases digesting enzymes into matrix when physically in contact with bone tissue. E. Bone Composition 1. Bone cells 2. Matrix Organic portion of matrix: Osteoid – type I collagen fibers gel-like ground substance Inorganic portion of matrix: Mineral Salt (hydroxyapatites) – tightly packed needle-like calcium phosphate crystals around collagen fibers. Responsible for bone hardness. Mineralization of bone tissue occurs when osteoblasts secrete enzymes that cause hydroxyapatite crystals to form and bond together in the matrix. F. Bone Development Ossification – the process of forming bone tissue Types of Ossification: Intramembranous Ossification – bone develops between membranes Endochondral Ossification- bone develops within hyaline cartilage Intramembranous Development / Ossification - examples: flat bones 1. sheet like masses of connective tissue form in embryo 2. osteoblasts form in between the sheets. 3. osteoblasts begin to lay down matrix around themselves 4. spongy bone is produced between the membranes 5. the sheet like membranes persist to become the periosteum 6. osteoblasts on the inner surface of the periosteum lay down compact bone over the spongy bone. Endochondral Development / Ossification 1. formation of a hyaline cartilage model in embryo. 2. a. periosteum (perichondrium) starts to develop around model. b. primary ossification center starts to develop in middle of model. 3. a. formation of compact bony collar around model. b. medullary cavity begins to appear as blood vessels grow into model delivering osteoclast cells. c. secondary ossification enter begins at the ends of the model. 4. cartilage cells in the epiphyseal disk (plate) undergo mitosis which results in increase in bone length due to expanding cartilage in disk. (Interstitial Growth -pg174) 5. primary and secondary ossification centers overtake disk and bone becomes completely ossified. G. Factors Affecting Bone Growth 1. Nutrition Vitamin A needed for bone resorption Vitamin C needed for proper collagen synthesis and deposition Vitamin D needed for proper gut calcium absorption 2. Physical/ Mechanical Stress - stimulates osteoblast activity 3. Hormones * Thyroid Hormones - excessive amounts can cause premature ossification * Sex Hormones – gonad produced hormones that stimulate growth and ossification * Growth Hormone (GH)– pituitary gland hormone that stimulates epiphyseal disk (plate) growth. *Excessive GH in children - can cause pituitary giantism (see fig. 16.6) *Insufficient GH in children - can cause pituitary dwarfism (see fig. 16.6) *Excessive GH in adults - can cause acromegaly (see pg. 616) G. Bone Fractures / Bone Repair Complete fracture – bone broken all the way through Incomplete fracture – not broken all the way through Basic Types of Fractures: 1. Simple (closed) fracture – a complete fracture that does not penetrate through the surface of skin. 2. Compound (open) fracture – a complete fracture that breaks through the surface of the skin. 3. Comminuted fracture – a complete fracture with many fracture pieces. 4. Greenstick fracture – an incomplete fracture that starts out transverse. Steps in Fracture Repair (see pg. 191 for details) 1. Fracture hematoma 2. Fibrocartilaginous callus 3. Bony callus 4. Bone remodeling H. Blood Calcium Homeostasis (endocrine controlled) Normal blood calcium levels = 9-11mg/ 100ml blood Blood calcium levels above 11mg/ 100ml blood = Hypercalcemia Blood calcium levels below 9mg/ 100ml blood = Hypocalcemia Hormones involved: 1. Calcitonin - increased release by thyroid gland when blood calcium levels increase (high) Functions: decrease blood calcium levels by a. stimulating osteoblast activity (pulls calcium from blood to deposit in new bone tissue) b. decrease osteoclast activity (less bone demineralization so less calcium enters bloodstream) 2. Parathyroid Hormone (PTH) - increased release by parathyroid glands when blood calcium levels decrease. Functions: increase blood calcium levels by a. stimulating osteoclast cell activity (more calcium enters blood) b. decrease osteoblast cell activity (pull less calcium from blood) c. stimulates calcium absorption from the gut (increases blood Ca+) d. causes kidneys to conserve calcium (decrease urine output of Ca+) So, we can see that blood calcium levels are maintained by the opposing effects of these two hormones. It is not a situation in which one is secreted while the other is not secreted, but by increasing or decreasing the current hormone amounts being secreted at the moment in response to changing blood calcium levels.