Name: ___KEY______________________________________ Period: ____ Date: ______________
Chapter 6: The Skeletal System
I. Functions of Bone and the Skeletal System
OBJ: Discuss the functions of bone and the skeletal system.
Basic functions of bone tissue and the skeletal system:
a. Support: _framework for the body, supports soft tissues, provides points of attachment for
most skeletal muscles_____________________________
b. Protection: _for internal organs; i.e. cranial bones protect brain, vertebrae protect spinal
cord, rib cage protects heart and lungs_______________
c. Assisting in movement: _skeletal muscles attach to bone-so when muscles contract they pull
on bone; bone + muscle produce movement___________
d. Mineral homeostasis: _bone tissue stores minerals; i.e. calcium and phosphorus; releases
them on demand when needed into blood stream to distribute to other body parts thus
maintaining homeostasis____________________________
e. Production of blood cells:
i. Red bone marrow: _connective tissueproduces red blood cells, white blood cells, and
platelets_______________________________________
Consists of: _developing red blood cells, adipocytes, fibroblasts, and macrophages_____
Found where: _developing bones of fetus and in some adult bones i.e. pelvis, ribs,
sternum, vertebrae, skull, and ends of arm bones and thigh bones_____________
ii. Hemopoiesis: _process by which red blood cells, white blood cells, and platelets are
produced___________________________________________________________
f. Triglyceride storage:
i. Yellow bone marrow: _stores triglycerides in its adipose cells; potential energy reserve__
Consists of: _adipose cells and a few blood cells_____________________________
Found in: _mainly adults, newborn have red bone marrow involved in hemopoiesis which
changes to yellow as they age___________________________________________
CHECKPOINT:
How do red and yellow bone marrows differ in composition, location, and function?
_Composition: RED—blood cells & platelets; YELLOW—adipose tissue and some blood cells; also
different color
_Location: RED—mainly in developing newborns and fetuses where mostly needed only in certain
bones of adults: pelvis, ribs, sternum, vertebrae, skull, and ends of arm bones and thigh bones;
YELLOW—only in adults
_Function: RED—hemopoiesis; YELLOW—triglycerides storages, possible energy reserves___
II. Types of Bones
OBJ: Classify bones on the basis of their shape and location.
Four main types of bones of the body:
a. Long bones: have greater length and width, consists of a shaft and a variable number of
ends, usually somewhat curved for strength.
Examples: thigh (femur), leg (tibia and fibula), arm (humerus), forearm (ulna and
radius), and fingers and toes (phalanges)
b. Short bones: somewhat cube-shaped and nearly equal in length and width.
Examples: most wrist and ankle bones
c. Flat bones: generally thin, offer considerable protection, have extensive surface areas
for muscle attachment.
Examples: cranial bones (protect the brain), sternum/breastbone and ribs (protect
organs in thorax), pelvis (protects digestive and reproductive organs),and scapulae
(shoulder blades)
d. Irregular bones: complex shapes
Examples: vertebrae of the backbone and some facial bones
III. Structure of Bones
OBJ: Describe the parts of a long bone.
 Describe histological features of bone tissue.
A. Macroscopic Structure of Bone
Parts as they relate to a long bone with greater length than width
1. Diaphysis: _bone’s shaft or body—long, cylindrical, main portion of bone_____________
2. Epiphyses: _distal and proximal ends of bones__________________________________
3. Metaphyses: _regions in a mature bone where diaphysis joins epiphyses; in growing
bone each metaphyses includes an epiphyseal plate, layer of hyaline cartilage that
allows the diaphysis of bone to grow in length; when bone growth in length stops,
cartilage in epiphyseal plate replaced by bone and this bony structure is noe known as
the epiphyseal line________________________________________________________
4. Articular cartilage: _thin layer of hyaline cartilage covering part of the epiphysis where
bone forms a joint (articulation) with another bone; it reduces friction and absorbs
shock; lacks a perichondrium so repair of damage is limited________________________
5. Periosteum: _tough sheath of dense irregular connective tissue surrounding a bone’s
surface wherever it lacks articular cartilage; consists of bone-forming cells enabling bone
to grow in diameter or thickness; protects the bone, assists in fracture repair, helps
nourish bone tissue, serves as attachment point for ligaments and tendons___________
6. Medullary cavity: _marrow cavity; space within diaphysis containing yellow bone
marrow in adults__________________________________________________________
7. Endosteum: _thin membrane lining medullary cavity; contains single layer of boneforming cells_____________________________________________________________
CHECKPOINT:
Which part of a bone reduces friction at joints? Produces blood cells? Lines the medullary
cavity? _REDUCE FRICTION: articular cartilage; PRODUCES BLOOD CELLS: red bone marrow;
LINES MEDULLARY CAVITY: endosteum_______________________________________________
B. Microscopic Structure of Bone
Composition of intracellular materials of the bone, or osseous tissue matrix
_25___% water
_25___% collagen fibers (protein)
_50___% crystallized mineral salts
Define calcification: _Mineral salts are deposited into a framework formed by collagen fibers
they crystallize and tissue hardens___________________________
Calcification is initiated by: _osteoblasts; bone-building cells______
Hardness of bone depends on _ crystallized inorganic mineral salts_________
Flexibility depends on _collagen fibers______________________________
Tensile strength is _provided by collagen fibers and other organic molecules that offer
resistance to being stretched or torn apart__
Three major types of cells in bone tissue are:
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(1)_Osteoblasts_______________________
_bone-building cells; do not undergo cell division; synthesize and secrete collagen fibers and
other organic components to build matrix of bone tissue. They become trapped in their
secretions and become osteocytes_
(2)_Osteocytes_______________________
_mature bone cells; main cells in bone tissue and maintain its daily metabolism, i.e. exchange of
nutrients and wastes with blood; do not undergo cell division____
(3)_Osteoclasts________________________
_huge cells derived from fusion of up to 50 monocytes (type of white blood cells)-concentrated
in endosteum; release strong lysosomal enzymes and acids to digest proteins and mineral
components of bone matrix; this breakdown of bone matrix called resorption (part of normal
growth, development, maintenance, repair of bones______
Spaces between cells and matrix are for:
(a)_channels for blood vessels (supply bone with nutrients)__
(b)_storage for red blood marrow_________________________
Composition of skeleton: BASED ON SIZE AND DISTRIBUTION OF SPACES
_80___% compact bone
_20___% spongy bone
1. Compact Bone Tissue
Contains few spaces; forms external layer of all bones; makes up bulk of diaphysis of long
bone; provides protection and support; resists stress produced by weight and movement
2. Spongy Bone Tissue
Makes up most of the bone tissue of short, flat, and irregularly shaped bones; forms most of
epiphyses of long bone and a narrow rim around the medullary cavity of the diaphysis of
long bones.
3. Complete chart below; using information found on page 89, Table 4.2 and information
on pages 120-121.
Dense or Compact Bone
Spongy or Cancellous Bone
Hardness
Mostly solid
Bony structures with spaces
filled with bone marrow
Consists of
Osteocytes in lacunae
Osteocytes in lacunae
Location
Covers all bone surfaces; except Short, flat bones, inside ends of
where they could rub
long bones
Functional units
Osteons or haversian systems
Trabeculae filled with red bone
marrow
Stress tolerance
High end to end; low from side
Not on heavy stress areas, can
take stress from any directiondisperses it
4. Osteon or haversian systems: examine the picture below and using information found on
page 120 explain on the next page how these structures provide routes for nutrients and
oxygen to reach osteocytes and for waste to diffuse away.
_Blood vessels, lymphatic vessels, and nerves from periosteum penetrate compact bone through
transverse perforating (Volkmann’s) canals; these connect with the ones in the medullary cavity,
periosteum, and central (Haversian) canals. Central canals run longitudinally through bone. Around
canals are concentric lamellae—rings of hard, calcified matrix. Between lamellae small spaces called
lacunae (contain osteocytes). Radiating from lacunae are tiny canaliculi (small channels) filled with ECF.
Inside canaliculi are slender fingerlike processes of osteocytes. Canalculi connect lacunae to one another
and with central canals=> intricate miniature canal system throughout bone = route for nutrients and
oxygen to reach osteocytes and for waste to diffuse away.______
5. What are trabeculae? _little beams; irregular latticework of thin columns of bone; spaces
between filled with red bone marrow____
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6. What is a bone scan? _diagnostic procedure that uses radioactive tracers injected
intravenously; x-ray like scan light or dark spots could be problem areas=> dark maybe
cancerous, abnormal heal spots from fracture, etc. light degenerative bone disease, fractures,
bone infections___________________________
IV. Ossification: Bone Formation
OBJ: Explain the steps involved in ossification(bone formation).
Where is the site of ossification? _loose fibrous connective tissue membranes and pieces of hyaline
cartilage, shaped like little bones in embryonic skeleton____
What is the first stage of ossification? _appearance of osteogenic cells undergoing cell division to
produce osteoblasts, which secrete matrix of bone_________
When does ossification begin and end? _sixth/seventh week of embryonic life continues through
adulthood__________________________________________
What are the two methods of bone formation (ossification)?
A. (1)_ Intramembranous Ossification___
Where? _directly on or within loose fibrous connective tissue membranes___________
B. (2) _ Endochondral Ossification______
Where? _within hyaline cartilage______________
C. Intramembranous Ossification
Simplest of two methods.
Forms what? _flat bones of skull and mandible (lower jawbone) _____
Replaces what on infants? _‘soft spot’ on fetal skull ______________
What is the sequence of events at the center of ossification?
a. _mesenchymal cells cluster together and differentiate; first into osteoblast__________
b. _osteoblasts secrete organic matrix of bone until trapped/surrounded by it__________
c. _secretion stops now osetocytes____________________________________________
d. _bone matrix forms, develops into trabeculae that fuse to one another to form spongy
bone__________________________________________________________________
e. _blood vessel grow in spaces between trabeculae along surface of new bone_______
f. _connective tissue associated with blood vessels in trabeculae develops into red bone
marrow_______________________________________________________________
g. _periphery of bone; mesenchyme condenses, develops into periosteum____________
h. _surface layer of spongy bone replaced with compact bone; remains spongy in center_
D. Endochondral Ossification
Replacement of cartilage by bone.
What is the sequence of events of endochondral ossification in long bones?
(1) _development of the cartilage model___________________________________
Explain: _mesenchymal cells crowd into shape of future bone develop into chondroblasts; these
secrete cartilage matrix consisting of hyaline cartilage; perichondrium membrane develops
around cartilage model_______
(2) _growth of the cartilage model_________________________________________
Explain: _chrondoblasts become chrondrocytes; cartilage model continues to grow; cells grow
some bursts release contents increasing pH of surrounding matrix; change in pH triggers
calcification; other cells die and lacunae form and slowly merge into cavities_______
(3) _development of the primary ossification center___________________________
Explain: _proceeds inward from external surface of bone; nutrient artery penetrates
perichondrium simulating osteogenic cells to differentiate into osteoblasts; perichondrium
starts to form bone now known as periosteum; periosteal capillaries grow into disintegrating
calcified cartilage; primary ossification center forms from capillaries now bone tissue will replace
most cartilage; osteoblasts deposit bone matrix forming spongy bone trabeculae then
osteoblasts break down trabeculae at bone ends leaving a cavity; medullary cavity fills with red
bone marrow___________________________________________
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(4) _development of the secondary ossification centers________________________
Explain: _branches of epiphyseal artery enter epiphyses secondary ossification centers develop;
around time of birth; spongy bone remains in the interior of epiphyses no medullary cavities
formed; proceeds outward from center of epiphyses toward surface of bone________
(5) _formation of articular cartilage and the epiphyseal plate___________________
Explain: _hylaine cartilage covering epiphyses becomes articular cartilage; prior to adulthood
hyaline cartilage remains between diaphysis and epiphyses as epiphyseal plate = lengthwise
growth of bones; stops between ages 18-25 cartilage replaced by bone = epiphyseal line bone
length growth stops. Damage to epiphyseal plate may result with shorter bone in adulthood__
V. Homeostasis of Bone
OBJ: Describe the factors involved in bone growth and maintenance and how hormones regulate
calcium homeostasis.
A. Bone Growth and Maintenance
1. Define bone remodeling: _ongoing replacement of old bone tissue by new bone tissue____
2. What is the job of osteoclasts in this process?
_responsible for the resorption of bone tissue_
a. What happens if too much mineral is deposited? _surplus bone tissue may form thick
bumps, called spurs which can interfere with joint movement______________________
b. What happens if there is excessive loss of calcium? _bone is weakened becomes overly
flexible and vulnerable to fracture______________________________
3. Factors that control bone metabolism:
a. Minerals: _Ca, P, Mg need adequate amounts of each____________________
b. Vitamins: _A, C, D___________________________________________
c. Hormones: _hGH, IGFs (insulin-like growth factors; produced locally by bone and by the
liver when stimulated by hGH ), insulin, thyroid hormones, parathyroid hormones,
calcitonin_______________
hGH: _main hormone before puberty that stimulates bone growth; produced by
anterior lobe of pituitary gland_______________
over secretion of hGH: _produces giantism, person becomes taller and heavier than
normal____________________________________________________
under secretion of hGH: _produces dwarfism, short stature___________________
d. Stress (weight bearing exercise):
Mineral crystals generate _production of collagen fibers, bone mass_________
Osteoblasts are _bone-forming cells________________________________
Heavily stressed bones are _notably thicker; builds & retains bone mass____________
Unstressed bones become _lose strength; loss of bone mass_________________
Example: leg in cast up to ~30% of bone mass
Examples of serious bone health risks: _bedridden or paralyzed patients; people in
weightless environments_________________________________
B. Bone’s Role in Calcium Homeostasis
1. Bone stores _99__% of the total amount of calcium in the body.
2. How does calcium become available to other tissues? _when broken down during
remodeling (replacement of old bone with new bone)_______________________
3. Effects of small changes in blood calcium levels:
a. Too high: _heart may stop________________________________________
b. Too low: _breathing may cease___________________________________
4. Nerve cell functions depend on the right levels of _Ca2+____.
5. Enzymes require _ Ca2+__, as a cofactor.
6. Blood clotting requires _ Ca2+____.
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7. What is the function the bone in calcium homeostasis in blood calcium levels? _to “buffer”
the blood calcium level, releasing Ca2+ to the blood when blood calcium levels falls and
depositing Ca2+ back in bone when blood level rises________________________
8. What hormone regulates Ca2+? _parathyroid hormone (PTH)____________________
Produced by? _parathyroid glands________________________________________
9. What other hormone is involved in calcium homeostasis? _calcitonin (CT)___________
Produced by? _thyroid gland_____________________________________
VI. Aging and the Skeletal System—page 150
CHECKPOINT:
How does aging affect the brittleness of bone and the loss of bone mass?
_brittleness result of decrease in rate of protein synthesis and in the production of growth hormone,
which lowers production of collagen fibers that give bones strength and flexibility; thus inorganic
minerals slowly become greater proportion of bone matrix = loss of bone mass_______________
VII. COMMON DISORDERS---PAGE 152
A. FRACTURES
Define fracture: _any break in a bone____________________________________
List and define the four different types of fractures below:
(1) _partial: incomplete break across the bone; i.e. a crack_________________________
(2) _complete: complete break across the bone; bone broken in two or more pieces____
(3) _closed (simple): fractured bone does not break through skin____________________
(4) _open (compound): broken ends of bone protrude through skin__________________
Obtain and read “Devil’s Pulpit Incident” and do the activity attached to it.
Chapter 4: Tissues—page 84
I. Connective Tissue Matrix
Matrix consists of: _fluid, gel, or solid ground substances plus protein fiber_____________
What is ground substance? _component of connective tissue between cells and fibers, supports
cells, binds them together, and provides a medium through which substances are exchanged
between blood and cells________________________
What are fibers? _strengthen and support connective tissues; three types embedded in matrix
between cells: collagen fibers, elastic fibers, and reticular fibers_____________
II. Types of Connective Tissue
A. Cartilage- page 90
Consists of: _dense network of collagen fibers and elastic fibers embedded in a rubbery
component of ground substance (chrondroitin sulfate)____________________________
Strength is due to: _collagen fibers_________________________
Resilience due to: _chrondroitin sulfate______________________
Cells called _chrondrocytes__ which are found in _lacunae__
What are lacunae? _spaces in the bone matrix where osteocytes lie__________
What surrounds the surface of cartilage? _membrane of dense irregular connective tissue
called perichondrium____________
How is cartilage different from other types of connective tissue? _has no blood vessels or
nerves, except in perichondrium__________
What are the three types of cartilage?
(1)_hyaline cartilage_ (most common; weakest)
Consists of: _resilient gel as its ground substance; appears in body as bluish-white shiny
substance__________
Properties: _compressible, flexible, insensitive____
Locations: ribs to sternum; supporting larynx, trachea, and bronchia; bone ends at synovial
joints; part of large septum
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(2) _fibrocartilage____ (strongest)
Consists of: _chondrocytes scattered among bundles of collagen fibers_____
Lacks: _perichondrium________
Properties: _strength and rigidity____
Location: _discs between vertebrae, pads of knee joints_______
(3) _elastic cartilage____
Consists of: _chondrocytes within threadlike network of elastic fibers_______
Properties: _strength and elasticity; maintains shape of certain structures; i.e. external ear__
Locations: auricle of external ear; epiglottis and part of larynx; auditory canal
EXTRA CREDIT: Sharks, whose skeletons are entirely made of cartilage, are being used in cancer
research. Investigate the connection and write a small report. Be sure to include all references in MLA
format….10 points
B. Bone Tissue- page 91
List the types of bone tissue: SHOULD READ COMPOSED OF…
a. _bone or osseous tissue____________
b. _periosteum_____________________
c. _red and yellow bone marrow______
d. _endosteum____________________
Main component of compact bone: _Osteon of Haversian system_______________
Main component of spongy bone: _Trabeculae_______________________________________
Critical thinking applications:
1. While investigating her new baby brother, a 4-year-old girl discovers a soft spot on the baby’s
skull and announces that the baby needs to go back because “it’s not finished yet.” Explain the
presence of the soft spots in the infant’s skull and the lack of soft spots in yours.
The soft spots are fibrous connective tissue membranes that fill the spaces between the skull
bones. The fontanels ossify by intramembranous ossification.
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