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Chapter 6 Skeletal System (j (functional joint synarthrosis= immovable…
Chapter 6 Skeletal System
6.1 skeletal primary functions
support
storage
calcium salts and fat (yellow marrow)
blood cell production
RBC's and WBC (red marrow)
protection
ribs and pelvic bones
of soft tissues and organs
leverage
change magnitude and direction
6.2 Bones are classified according to shape and structure
bones are connective tissue
calcium phosphate accounts for almost two thirds of the weight of bone
remaining third is dominated by collagen fibers
macroscopic features of bones
4 shapes
long bones(longer than they are wide) ex. humerus
short bones(dimensions are roughly equal) ex. carpal bones
flat bones( thin and relatively broad) ex. ribs, shoulder blades
irregular bones( complex shapes) ex. vertebra
diaphysis- a long bones shaft
surrounds central marrow cavity containing bone marrow
bone marrow- loose connective tissue
compact bone-relatively solid
spongy bone-resembles a network of bony rods separated by spaces
both are in the humerus. compact forms the diaphysis and spongy bone fills the epiphyses
periosteum- the outer surface of a bone is covered with
endosteum- lines the marrow cavity and other inner surfaces
microscopic features of bone
containts
osteocytes
lacunae(small pockets)
lamellae(found between narrow sheets of calcified matrix)
canalaiculi(small channels radiate through the matrix, interconnecting lacunae and linking them to nearby blood vessels)
basic functional unit
osteon
central canal(contains one or more blood vessels)
perforating canals(provide passageways for linking the blood vessels of the central canals with those of the periosteum and the marrow cavity)
spongy bone has no osteons
trabeculae(frequent branching of the thin trabeculae create an open network)
cells in bone
osteocytes- are mature bone cells. Osteocytes maintain normal bone structure by recycling the calcium slats in the bony matrix around themselves and by assisting in repairs
osteoclasts- giant cells with 50 or more nuclei. Acids and enzymes secreted by osteoclasts dissolve the bony matrix and release the stored minerals through osteolysis. This process helps regulate calcium and phosphate concentrations in body fluid
osteoblasts- are the cells responsible for the porduction of new bone, a process called osteogenesis. Osteblasts produce new bone matrix and promote the deposition of calcium salts in the organic matrix
6.3 Ossification and appositional growth are mechanisms of bone formation and enlargement
during development, cartilage or other connective tissues are replaced by bone
Ossification- the process of replacing other tissues with bone
endochondral ossification- bone replaces existing cartilage
step 1. condrocytes within the cartilage model enlarge and the surrounding matrix begins to calcify
step 2- bone formation first occurs at the shaft surface
step 3- blood vessels invade the inner region of the cartilage and newly differentiated osteoblasts form spongy bone within the center of the shaft at a primary ossification center
step 4- as the bone enlarges, osteoclasts break down some of the spongy bone and create a marrow cavity
step 5- the ceners of the epiphyses begin to calcify
intramembranous ossification- bone develops within sheets or membranes of connective tissue
calcification- the deposition of calcium salts, occurs during ossification, but it can also occur in tissues other than bone
intamembranous
normally occurs in the deeper layers of the dermis
first occurs in ossification center
bone growth is an active process, and osteoblasts require oxygen and a reliable supply of nutrients
begins when osteoblasts differentiate within embryotic or fetal fibrous connective tissue
first resembles spongy bones
Endochondrial Ossification
step 1- endochondral ossification starts when chondrocytes within the cartilage model enlarge and the surrounding matrix begins to calcify
step 2- bone formation first occurs at the shaft surface. Blood vessels invade the perichondrium, and cells of its inner layer differentiate into osteoblast that begin producing bone matrix
step 3- blood vessels invade the inner region of the cartilage, and newly differentiated osteoblasts form spongy bone within the center of the shaft at a primary ossification center
step 4- as the bone enlarges, osteoclasts break down some of the spongy bone and create a marrow cavity.
step 5- the centers of the epiphyses begin to calcify. As blood vessels and osteoblsts enter these areas.
hyaline cartilage
normal bone growth and maintenance cannot occur without a reliable source of minerals, especially calcium salts
6.4 Bone growth and development depend on a balance between bone formation and resorption, and on calcium availability
the role of remodeling in support
degenerative changes occur in the skeleton after even brief periods of inactivity
The skeleton as a calcium reserve
99 percent of calcium is deposited in the skeleton
parathyroid hormone from the parathyroid glands and calcitriol from the kidneys work together to elevate calcium levels in body fluids
repair of fractures
small fracures many blood vessels are broken and extensive bleeding occurs. A large blood clot, called a fracture hematoma forms
cells of the periosteum and endosteum undergo mitosis, and the daughter cells migrate into the fracture zone
osteoblasts replace the new central cartilage of the external callus with spongy bone
the remodeling of spongy bone at the fracture site may continue over a period of 4 months to well over a year
6.5 Osteopenia has a widespread effect on aging skeletal tissue
bones become thinner and relatively weaker as a normal part of the aging process
inadequate ossiication is called osteopenia
the reduction in bone mass begins to decline while osteoclast activity continues at normal levels
not all parts of the skeleton are equally affected
j
functional joint
synarthrosis= immovable joints ex. sutures of skull amphiarthrosis =slightly movable joints ex. intervertebral discs,
DIarthrosis=freely movable joints ex joints of appendicular skeletons
structural fibrous joints= composed of fibrous tissue no joint cavity is present ex sutures, syndesmosis=cord of fibrous tissue called ligament
gomphosis=tooth within its bony socket(alveolar fossa_q
structural fibrous, cartilaginous, synovial synchondrosis= a plate of hyaline cartilage, sites of bone growth during youth ex. joints, the epiphyseal plate synphysis=pad or plate of fibrocartiage compressible "shock absorber" intervertebral discs
articular cartilage= hyaline cartilage covers the surface of each bone
joint cavity= potential space between the two bones, filled with synovial fluid
articular capsule= double layered capsule surrounding cavity, external tough, flexible fibrous capsule, synovial membrane=loose CT lining of fibrous capsule, that also covers all internal hoint surfaces excluding hyaline cartilage
synovial fluid=
gliding joints=cartilagionus joints hinge joints=permit felxion and extention only
gliding movements=when flat bone surfaces glide or slide over one another
shoulder joint= ball and socket gle
the styloid process of the radium assists in the stabilization of the wrist joint
the trochlea is a part of the humerous
the socket that receives the head of the femur is the acetabulum
the structure that surrounds a diarthrocic joint is called a joint capsule
an acessory structure of a joint that subdivides a synovial cavity, channels the flow of synovial fluid, or allows for cariations in the shape of the articular surfaces is a meniscus
a small, synovial-fluid filled pocket in connective tissue, which may be connected to a jont cavity , is bursa