Chapter 6 Skeletal System
Chapter 6 Skeletal System BIOL 243 001
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This 6 page Class Notes was uploaded by Kaitlin Notetaker on Sunday February 21, 2016. The Class Notes belongs to BIOL 243 001 at University of South Carolina taught by Lewis Bowman in Spring 2016. Since its upload, it has received 43 views. For similar materials see Human Anatomy and Physiology I in Biology at University of South Carolina.
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Date Created: 02/21/16
Sunday, February 21, y Skeletal System 206 bones in the human body • the skeleton is divided into two portions: 1. axial skeleton comprised of the skull, vertebral column and thoracic cage • forms longitudinal axis; supports head, neck and trunk; and protects brain, spinal cord and thoracic organs 2. appendicular skeleton comprised of the bones of the limbs and their girdles • each limb is composed of 3 major segments connected by movable joints characteristics of the skeleton: • endoskeleton skeletons is inside the body (an exoskeleton is like a cockroach) • bones are a connective tissue cells found in bone are: • osteoblasts and osteocytes synthesize bone • osteoclasts breakdown bone • extracellular matrix ground substance consists of various salts: calcium phosphate, calcium carbonate • hard and resists compression various fibers: many collagenous fibers to provide tensile strength classification of bones: • according to structure long bones arm, forearm, leg and thigh 1 Sunday, February 21, y bones skull, ribs and sternum short bones carpals and tarsals irregular bones vertebrae • long bone epiphysis “head” of long bones • proximal (closer to origin) and distal (farther from origin) diaphysis shaft of the long bones • hollow and contains yellow bone marrow fat rticula cartilage hyaline cartilage on the surface of epiphyses periosteum connective tissue membrane that surrounds bone • inner layer is rich with osteoblasts endosteum lining on the inside that separates bone and bone marrow • two types of bone structure 1. compact bone on the surface of all bones • few air spaces, very dense, very strong • organization: supplied with nutrients because of highly organized structure which allows nerves and blood vessels to run through osteon (Haversian) system group of parallel hollow tubes of bone matrix • central (Haversian) canal blood vessels and nerves that run through osteons • nutrients diffuse through cracks (canaliculus) to supply the cells (osteocytes) with amino acids and oxygen • lamellae different layers of bone 2 Sunday, February 21, y 2. spongy bone on the inside of bones except in diaphysis • many air spaces, weaker than compact helps the bones to resist stress • is the location of red bone marrow hemophoiesis red blood cell formation • no osteons but osteocyte cells are present in small cavities in bone matrix called lacunae yellow bone marrow located on inside of diaphysis • fat (not really bone) Bone Development • 1. endochondral ossification the hyaline cartilage of the embryonic skeleton is constructed into bone hyaline cartilage will degenerate (die) and the membrane (perichondrium) is converted into a periosteum • a) a bony collar forms around the diaphysis (shaft) on the outside of the hyaline cartilage model, encasing it • b) cartilage inside diaphysis calcifies and develops cavities which will form spongy bone • occurs outside to inside formation for nearly all bones in the body except skull and facial bones • 2. intramembraneous ossification starts with a matrix of fibers (mostly collagenous); osteoblasts invade matrix of fibers and make spongy bone • then remodeled and compact bone forms 3 Sunday, February 21, y • occurs from inside to outside • increase in the length of long bones (growth) before birth, diaphyses are ossified (converted to bone) after birth, epiphyses are ossified • leave a plate of hyaline cartilage between diaphysis and epiphysis epiphyseal plate “growth plate” cells in the growth zone are triggered by growth hormones to divide rapidly to lengthen long bone the surrounding cartilage will calcify then ossify to produce new bone and growth • complications with epiphyseal plate ituitar giant continued release of growth hormone and growth of epiphyseal plate pituitary dwarf stopped release of growth hormone too early and long bones are shorter than normal • remodeling bones are continually being broken down and rebuilt ccurs by remodeling packets that contain osteoclasts (break down bone) and osteoblasts (synthesize bone) • osteoclasts erode bone by creating an acidic environment which dissolves calcium and establishes conditions where bone will break down • bone deposition organic layer (glycoproteins, collagen, elastic fibers) are laid down first • mineralization various calcium precipitates are laid down processes active in controlling remodeling • hormonal mechanisms keeps calcium levels in blood maintained 4 Sunday, February 21, y i calcium levels decrease, parathyroid hormone is released by parathyroid gland that stimulates the osteoclasts to enhance breakdown of bone in order to release calcium into the blood i calcium levels increase, calcitonin is released by the thyroid to inhibit osteoclasts • response to stress stress has a signaling pathway for bone to be deposited to strengthen Bone Complications • rickets vitamin D deficiency D is necessary for the consumption of calcium and phosphorous which forms and strengthens bones • osteoporosis balance of breakdown and synthesizing (not synthesizing, just breakdown) bones become brittle and beak easily, loss of bone mass most common in postmenopausal females • fractures types : • simple bones are broken into two pieces (in half) • compound (one of more) of bones are protruding through the skin • comminuted splintering (broken into lots of pieces) • depressed bones are pushed inward (in skull) healing occurs in stages • 1. hematoma (blood clot) is formed • 2. fibroblast and chondroblasts invade and generate a fibrocartilaginous callus 5 Sunday, February 21, y • 3. osteoblasts invade to form a bony callus (similar to spongy bone) • 4. bone remodeling takes place and compact bone is deposited on outside 6
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