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Bones include these active, living tissues
- Bone tissue
- Cartilage
- Dense connective tissue
- Blood
- Nervous tissue
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Bones support and protect
Softer tissues
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Bones provide points of
attachment for muscles
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Bones house
blood-producing cells
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Bones store
inorganic salts
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The 4 classes of bone according to shape are
long, short, flat, or irregular
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Short bones are shaped like
cubes
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Examples of short bones are
the bones of the wrists and ankles; patella
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Flat bones are ________ structures
plate-like
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Examples of flat bones are
ribs, the scapulae, and some bones of the skull
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Irregular bones have a variety of
shapes
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Examples of irregular bones are
the vertebrae that compose the backbone, and many facial bones
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Round bones are also called
sesamoid bones
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Sesamoid bones are ______ and ____
small, nodular
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Sesamoid bones are embedded within
in a tendon adjacent to a joint, where the tendon is compressed
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An example of a sesamoid bone is the
patella
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An expanded end of a long bone is called an
epiphysis
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An epiphysis articulates with
another bone (forms a joint)
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Articular cartilage is located
on the outer surface of teh articulating portion of the epiphysis
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The shaft of a long bone is called a
diaphysis
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The ___ is the widening part of the bone between the diaphysis and the epiphysis
metaphysis
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What is periosteum?
a tough, vascular covering of dense connective tissue that encloses the bone everywhere but the articular cartilage on its ends
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Periosteum functions to___
help form and repair bone tissue
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Processes provide sites for
attachment of ligaments and tendons
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The wall of the diaphysis is composed of _____ bone.
compact/cortical
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Compact bone has
a continuous extracellular matrix with no gaps
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The epiphyses are largely composed of ______ bone
spongy/cancellous
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Spongy bone consists of bony plates called
trabeculae
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A bone usually has
compact and spongy bone?
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What is the name of the semi-rigid tube with a hollow chamber that runs through the diaphysis?
the medullary cavity
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What does endosteum line?
the spaces of the spongy bone
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What kind of cells does endosteum contain?
bone-forming cells
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What is the tissue that fills the spaces of bone?
Marrow
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What are the two forms of marrow?
red and yellow
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What are bone cells called?
osteocytes
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What are lacunae?
tiny, bony chambers
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What do lacunae form?
concentric circles around central/Haversian canals
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Osteocytes transport
nutrients and wastes to and from nearby cells
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What do cellular processes of osteocytes pass through?
canaliculi
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What is the extracellular matrix of bone composed of?
collagen and inorganic salts
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What is an osteon?
a cylinder-shaped unit containing bone cells that surround a central canal
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What is the substance of compact bone formed from?
many osteons cemented together
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Each central canal contains what?
blood vessels and nerve fibers surrounded by loose connective tissue
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What do perforating canals contain?
larger blood vessels and nerves by which the smaller blood vessels and nerve fibers in central canals communicate with the surface of the bone and the medullary cavity
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what is spongy bone composed of?
osteocytes and extracellular matrix
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Unlike compact bone, the bone cells do not:
aggregate around central canals
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What lie within spongy bone cells?
the trabeculae
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Where do osteocytes get nutrients from?
substances diffusing into the canaliculi that lead to the surfaces of these thin, bony plates
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When do parts of the skeleton begin to form?
During the first few weeks of prenatal development
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When do bony structures stop growing?
adulthood
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How do bones form?
by replacing existing connective tissue
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Where do intramembranous bones originate?
within sheetlike layers of connective tissues
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Where do endochondral bones originate
As masses of cartilage later replaced by bone tissue
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What are examples of intramembranous bones?
- skull
- clavicles
- sternum
- some facial bones (mandible, maxillae, and zygomatic bones)
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What appear at the sites of their future bones during the development of intramembranous bones?
membranelike layers of unspecialized connective tissues
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What supplies the connective tissue layers?
dense networks of blood vessels
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What are osteoblasts?
bone-forming cells
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What do osteoblasts deposit?
bony matrix around themselves
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What can spongy bone become?
compact bone as spaces fill with bone matrix
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as development continues, what can osteoblasts become surrounded by?
extracellular matrix; become secluded within lacunae
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extracellular matrix enclosing the processes of osteoblasts give rise to what?
canaliculi
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what happens when osteoblasts are isolated?
they become osteocytes
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where does periosteum come from?
cells of the connective tissue of the developing bone
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what is compact bone formed by?
osteoblasts on the inside of the periosteum forming a layer of compact bone over the surface of the newly formed spongy bone
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what is intramembranous ossification?
the process of replacing connective tissue to form an intramembranous bone
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what are most of the bones of the skeleton?
endochonral bones
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what do endochondral bones develop as?
masses of hyaline cartilage shaped like future bony structures
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eventually, what happens to hyaline cartilage?
dies and degenerates
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as the cartilage decomposes, _________ forms
a periosteum
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What does periosteum form from?
connective tissue that encircles the developing structure
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as cartilage tissue disintegrates, what invades it?
blood vessels and partially differentiated connective tissue cells
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what do some of the cells differentiate into?
osteoblasts. the begin to form spongy bone in the spaces previously housing the cartilage
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What do osteoblasts form?
osteocytes
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What is endochondral ossification?
the process of forming an endochondral bone by the replacement of hyaline cartilage
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What is the epiphyseal plate?
a cartilaginous layer in the long bone epiphysis that grows and lengthens the bone
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In a long bone, what separates the diaphysis from the epiphysis?
epiphyseal plate
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What do osteoclasts break down?
the calcified matrix
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what do osteoclasts phagocytize?
components of the bony matrix
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after osteoclasts remove the extracellular matrix, what invades the region and what does it do?
- bone-building osteoblasts
- deposit bone tissue in place of the calcified cartilage
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a long bone continues to lengthen while ____
the cartilaginous cells of the epiphyseal plates are active
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when is lengthening of the bone no longer possible?
the ossification centers of the diaphysis and epiphyses meet and the epiphyseal plates ossify
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when does the medullary cavity form?
when osteoclasts erode other bone tissue on the inside of the compact bone
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bone in what regino remains spongy?
central regions of the epiphyses and diaphysis
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what does hyaline cartilage on the ends persists as?
articular cartilage
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throughout life, osteoclast _______ and osteoblasts _____________
- resorb bone tissue
- replace the bone
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what percentage of bone calcium is exchanged each year?
10-20%
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what factors affect bone development, growth, and repair?
- nutrition
- exposure to sunlight
- hormonal secretions
- physical exercise
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what is vitamin d necessary for?
proper absorption of calcium in the small intestine
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what can result from a lack of vitamin d?
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what is vitamin a necessary for?
osteoblast and osteoclast activity during normal development
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what is vitamin c required for?
collagen synthesis
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what does growth hormone stimulate?
division of cartilage cells in the epiphyseal plates
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in children, what does the absence of growth hormone lead to?
pituitary dwarfism
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an excess of growth hormone before the epiphyseal plates ossify leads to _______
pituitary gigantism
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in adults, what does an excess of growth hormone lead to?
acromegaly, in which the hands, feet, and jaw enlarge
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what can thyroxine halt and how?
replacement of cartilage in the epiphyseal plates by causing an increase in cellular metabolism
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what does parathyroid hormone stimulate?
an increase in the number and activity of osteoclasts, which break down bone
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what do sex hormones promote?
formation of bone tissue
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what do sex hormones stimulate?
ossification of the epiphyseal plates, and stop bone lengthening at a relatively early age
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why do females typically reach their maximum heights earlier than males?
effect of estrogens on the epiphyseal plates is somewhat stronger than that of testosterone
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what does physical stress stimulate?
bone growth
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bones give shape to what?
structures such as the head, face, thorax, and limbs
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what bones support the body's weight?
- lower limbs
- pelvis
- vertebral column
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what do the bones of the skull protect?
the eyes, ears, and brain
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what bones protect the heart and lungs?
rib cage and shoulder girdle
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what do bones of the pelvic girdle protect?
lower abdominal and internal reproductive organs
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whas is hematopoiesis?
process of cell formation
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where does blood cell formation begin?
in the yolk
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later in development, where are blood cells made?
marrow
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what is marrow and where is it?
- soft, netlike mass of connective tissue
- within the medullary cavities of long bones
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where does red marrow function?
spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and hip bones
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where is red marrow found?
spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and hip bones
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with increasing age, what happens to red marrow?
it is replaced by yellow marrow
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what does yellow marrow store?
fat
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in an adult, where is red marrow primarily found?
spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and hip bones
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what makes up the extracellular matrix of bone tissue?
- collagen
- inorganic mineral salts
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inorganic mineral salts account for what percentage by weight?
70%
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what are hydroxyapatities?
small crystals of a type of calcium phosphate
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why does the body require calcium?
- muscle cell contraction
- nerve impulse conduction
- blood clot formation
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when blood calcium is low, what happens?
parathyroid hormone stimulates osteoclasts to break down bone tissue releasing calcium salts from the extracellular matrix into the blood
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very high blood calcium levels inhibit what?
osteoclast activity
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bone tissue contains lesser amounts of what?
magnesium, sodium, potassiu, and carbonate ions
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how many bones are in a human skeleton?
206
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flat bones of the skull are tightly joined by what?
sutures
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what are the two major portions of the skeleton?
axial skeleton and appendicular skeleton
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what does the axial skeleton contain?
bony and cartilaginous parts that support and protect the organs of the head, neck, trunk
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what is the skull composed of?
the cranium and the facial bones
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how many bones does a human skull usually consist of?
22 bones
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what is the moveable bone in the skull?
mandible
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some cranial and skull bones together form the ____ of the eye.
orbit
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what does the cranium enclose and protect?
the brain
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what are the eight major bones that make up the cranium?
- frontal bone
- parietal bone
- occipital bone
- temporal bone
- sphenoid bone
- ethmoid bone
- superior nasal concha
- middle nasal concha
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the facial skeleton consists of how many immovable bones?
13
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the facial bones provide sites of attachment for _______
muscles that move the jaw and control facial expressions
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at birth, the skill is _____ developed with ________ connecting the cranial bones
incompletely; fibrous membranes
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what are fontanels?
soft spots
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what do fontanels permit?
some mvmt. between the bones so that the developing skull is partially compressible and can slightly change shape
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what happens to fontanels eventually?
they close and cranial bones grow together
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