the skeletal system. - buried w/in the muscles - functions are: a.) provide a rigid framework for...
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The Skeletal System
Chapter 6-8
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- buried w/in the muscles
- functions are:
a.) provide a rigid framework for protection
b.) support structure for the body
c.) movement
d.) storage
e.) blood cell formation
- living organs bec they change & help the body respond to a changing envir – allows us to grow
The Primary Organs are the BONES:
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At birth the bones are made of CARTILAGE – gradually this cartilage will become transformed into bones – calcification makes the bones hard
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- Osteoblasts (bone cells) form new bones
- Osteoclasts reabsorb bone
- The combined action of these two sculpt the bone into its adult shape
- This allows the bones to respond to stress, or injury by changing size, shape, & density - EXERCISE MAKES BONES DENSER!!!
How do we get new bone?
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I. Bones – 2 basic types of osseous (bone) tissue
A. Compact Bone – outer layer, hard & dense also has different appearance & texture according to the location of the bone – looks smooth & homogeneous
- compact bone doesn’t contain a network of open spaces – instead their structural unit is the Haversian System or osteon (composed of multiple layers of calcified matrix arranged in 3 types of rings)
Skeletal System contains 2 major types of connective tissue: Bones & Cartilage
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- osteocytes are found in the lacunae which are arranged in concentric circles called lamella around the central (Haversian) canals
- canaliculi – tiny canals that radiate outward from central canals to all lacunae – these canals provide the transportation system that connects all bone cells to the nutrient supply
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- blood vessels & nerves run lengthwise through the bony matrix
- perforating (Volkmann’s) canals – provides routes from the outside of the bone to the interior
- all of the rings are covered by periosteum (double-layered connective tissue that covers & nourishes bone)
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B. Spongy Bone – porous with small needle-like pieces
- contains many spaces that may be filled with red marrow
- the needle-like threads of spongy bone that surround a network of spaces are called trabeculae
II. Cartilage – resembles & differs from bone
- fibers are embedded in a firm gel instead of calcified to allow for flexibility
- cartilage cells - Chondrocytes
- no blood vessels in cartilage
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1.) Long – longer than wide – have a shaft w/ a head at both ends - ex. humerus, femur
2.) Short – generally cube shaped & contain mostly spongy bone – ex. carpals, tarsals
3.) Flat –thin, flatted & usually curved – have 2 thin layers of compact bone sandwiching a layer of spongy bone – ex. frontal bone of skull, ribs, sternum
4.) Irregular – don’t fit any of the other 3 – ex. Vertebrae
Types of Bones:
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- contains cells, fibers & calcified extracellular matrix
- the matrix is more abundant in bone – divided into 2 chemical components
1.) Inorganic salts – Ca2+, PO42-,Mg, Na,
SO42-, F - 2.) Organic Matrix –
collagenous fibers & ground substances (proteins & polysaccharrides)
- chondroitin sulfate – along with glucosamine are req for repair & maintenance of bone & cartilage
Bone Tissue: or Osseous Tissue
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1. Osteoblasts – small cells that synthesize & secrete osteoid
- collagen fibrils line up in the osteoid where Ca & PO4 are deposited
- results in accumulation of mineralized bone
- made from osteogenic stem cells found in the endosteum & Haversian canal lining that undergo cell division
Bone Cells:
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2. Osteoclasts – large multinucleated cells that are responsible for the erosion of bone minerals
- formed from fusion of precursor cells
- contain lots of mitochondria & lysosomes
3. Osteocytes – mature, non-dividing osteoblasts that are surrounded by matrix & now lie w/in lucunae
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- functions in blood cell production (Hematopoiesis)
- found in medullary cavities of long bones, & in spaces of spongy bone
- 2 types of marrow:
A.) Red Marrow – produces RBCs
B.) Yellow Marrow – marrow cells are saturated w/ fat – no blood cell production- found in older people – is inactive adipose (fatty) tissue that is converted from Red Bone Marrow
*****During anemic conditions, yellow marrow can alter to become red marrow
Bone Marrow – myeloid tissue
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2 Hormones are responsible:
1.) Parathyroid Hormone – produced by parathyroid gland
- when Ca levels dec, it stimulates osteoclasts to break down bone matrix
- also increases renal absorption of Ca from urine
- stimulates vitamin D synthesis, helps intestinal absorption of Ca
2.) Calcitonin – produced by thyroid gland
- when Ca levels inc, it stimulates osteoblasts to deposit bone
Regulation of Blood Calcium Levels:
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- in embryos the skeleton is made mostly of hyaline cartilage
- as the child grows ossification (bone forming) occurs in 2 steps:
1.) hyaline cartilage is completely covered w/ bone matrix by osteoblasts
2.) then the hyaline cartilage is digested away opening up a medullary cavity
- by birth or shortly after most of the hyaline cartilage is converted to bone
- bone remodeling retains the bones normal proportions & strength as the body increases in weight & size
Bone Formation, Growth, & Remodeling:
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- every bone in the body connects to at least 1 other except the hyoid bone
- Purpose - hold bones together & allow for movement
-classified in 2 ways:
1.) structurally – based on the material that separates the bony regions
a.) fibrous joints – united by fibrous tissue -usually immovable - ex.) sutures in skull
b.) cartilaginous joints – united by cartilage - slightly movable - ex.) intervertebral joints
c.) synovial joints – bone ends are separated by a joint cavity containing synovial fluid
- very movable but flexibility varies
- nonaxial joints only allow slipping movement – wrist joints
- uniaxial joints only allow movement in 1 plane – elbow joint
- biaxial joints allow movement in 2 planes – knuckles & thumb
- multiaxial joints move in all planes – shoulder joint
Joints (Articulations) –
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2.) functionally – based on the amount of movement allowed – 3 types:
a.) synarthroses - no movement – ex.) skull sutures
b.) amphiarthroses – slight movement – ex.) intervertebral disc
c.) diarthroses – free movement – most joints are this type
- types of diarthroses:
a.) ball & socket – ex.) shoulder & hip
b.) hinge – flexing & extending – ex.) elbows & knees
c.) pivot – atlas & axis – neck & head
d.) saddle – only 1 pair in the body located between the thumb & wrist – extreme range of motion
e.) gliding – least movable – ex.) vertebrae
f.) condyloid – ones in which a condyle fits into an elliptical socket – ex.) knuckles
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Osteomalacia
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Paget Disease
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OSTEOMYELITIS
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Osteoarthritis
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Gout
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