Chapter 6: Skeletal Tissues:
Bones,
Ligaments,
Cartilage
FUNCTIONS OF skeletal tissues
 SUPPORT: Bones form the FRAMEWORK of the body and contribute
to the shape, alignment, and positioning of body parts;
 LIGAMENTS
help hold bones together,
 CARTILAGE provides cushion and ‘shock-absorption ‘between
bones
 PROTECTION:
bony “boxes” protect the delicate structures they
enclose (ref; cranium, rib cage, pelvis)
 MOVEMENT: bones and their joints constitute levers that move as
muscles contract, and as sites of attachment for muscles
 MINERAL STORAGE: bones are the major reservoir for CALCIUM,
PHOSPHORUS, and other minerals
 HEMATOPOIESIS: blood cell formation is carried out by

Myeloid tissue, which is located in the bone marrow
Bones are the ‘organs’ of the
skeletal system.
All bones have:
 outer “dense” layer of compact
bone
 Inner, honeycombed region of
spongy (cancellous) bone
trabeculae
Spaces between trabeculae filled with red or
yellow marrow
TYPES OF BONES
 Five major types of structural bones





Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
develops within a tendon
( ex.: patella)
 Bones serve various needs, and their size, shape, and appearance vary to meet
those needs
 Bones vary in the proportion of compact and
cancellous (spongy) bone;
 COMPACT BONE is dense and solid in appearance,
whereas CANCELLOUS BONE is characterized by
open space partially filled with needle-like structures,
called spicules, or trabeculae
Most of the bones of the skull are ‘flat bones’
The

6
‘long’ bones:
Humerus
Upper
extremity
 Radius

Ulna
Femur
 Tibia
Fibula
Lower
extremity
Parts of a long bone
 DIAPHYSIS
 Main SHAFT of a long bone
 Hollow, cylindrical shape and thick compact bone on the
perimeter, with marrow in the middle, (MEDULLARY cavity)
 Function is to provide strong support without cumbersome
weight. (like an architechural column)
 EPIPHYSES
 Both ends of a long bone; made of CANCELLOUS
BONE filled with marrow
 Bulbous shape
 Function is to provide attachments for muscles and give stability
to joints

Long bone


diaphysis – shaft
epiphyses – bone ends
Articular cartilage covers joint surface
Epiphyseal line located between diaphysis
and each epiphysis
(in young, growing bones, this can be
seen as a METAPHYSIS - an ‘area’
of cartilage between the epiphysis
and the diaphysis)
In a youngster, this is seen as the epiphyseal plate;
Once the bone is mature, it is simply an epiphyseal
‘line’
Epiphysis
Diaphysis
Articular
cartilage
Periosteum
Medullary
cavity
Endosteum
Compact
bone
Cancellous
(spongy)bone
(Pls. remember this concept: perimysium, perineurium)

membranes
 periosteum – covers surface of bone
(attachment site for tendons &
ligaments)
 endosteum – lines marrow cavity
Both membranes contain:
•
osteogenic cells – stem cells;
which give rise to osteoblasts &
osteoclasts
•
• OSTEOBLASTS – cells that
secrete bone matrix
•
OSTEOCLASTS – cells that
break down bone matrix
More on the components of bones
 Articular cartilage
 Layer of hyaline cartilage that covers the articular
surface of epiphyses
 Function is to cushion jolts and blows
 Periosteum
 Dense, white fibrous membrane that covers bone
 Attaches tendons firmly to bones
 Contains cells that form and destroy bone
 Contains blood vessels important in growth and
repair
 Contains blood vessels that send branches into bone
 Essential for bone cell survival and bone formation
Components of bone
 Medullary (or marrow) cavity
 Tubelike, hollow space in the diaphysis
 Filled with yellow marrow in adults .
(Yellow marrow is fatty, can be called upon to
become active hematopoietic tissue if needed)
 Endosteum: thin, fibrous membrane that
lines the medullary cavity
 Short, irregular & flat bones

do NOT have shaft, epiphyses, or
medullary cavity
 thin layer of compact bone surrounds
spongy bone center (contains red
marrow)
•
•
periosteum covers
compact bone
endosteum encloses
trabeculae
Spongy bone of flat bones is
called diploe
Frontal sinuses
GLOSSARY OF TERMS: SKELETAL SYSTEM
Term: Definition (with one example):
analagous to geographic terms such as peak mount hill cape bluff isle cove

condyle a rounded process that articulates with
another bone
eg. occipital condyle

crest a narrow, ridge-like projection; eg. iliac crest

linea a narrow line-like ridge; eg. linea aspera of femur

epicondyle a projection situated above a condyle

meatus a tube-like passageway within a bone
eg. medial epicondyle of humerus

facet a small smooth surface eg. rib facet of a thoracic
vertebra

foramen an opening for the passage of b.v. &/or nerves
eg. foramen magnum

fossa a relatively deep pit or depression; eg. olecranon
fossa
eg. external auditory meatus

process a prominent projection of a bone
eg. mastoid process of temporal bone

ramus a branch-like process; eg. ramus of mandible

sinus

Spine a sharp projection; eg. spine of scapula
a cavity within a bone;
eg. frontal sinus

fovea a tiny pit or depression; eg. fovea capitis

styloid a pen-like projection; eg. styloid process of ulna

head an enlargement at the end of a bone;

suture interlocking junction between cranial bones;
eg. femoral head



eg. coronal suture
trochanter
a relatively large process;
eg. Greater trochanter of femur

tubercle a small knob-like process; eg. tubercle of rib

tuberosity a knob-like process larger than a tubercle;
eg. tibial tuberosity
 condyle
a rounded process that articulates
with another bone
eg. occipital condyle
 crest a narrow, ridge-like projection;
eg. iliac crest
 epicondyle a projection situated above a condyle
eg. medial epicondyle of humerus
 facet a small smooth surface
eg. rib facet of a thoracic vertebra
 foramen an opening for the passage
of b.v. &/or nerves
eg. foramen magnum
 fossa a relatively deep pit or depression;

eg. Olecranon fossa
 fovea
 head
a tiny pit or depression; eg. fovea capitis
an enlargement at the end of a bone;
eg. femoral head
 linea





a narrow line-like ridge;
eg. linea aspera of femur
meatus a tube-like passageway within a bone
eg. external auditory meatus
process a prominent projection of a bone
eg. mastoid process of temporal bone
ramus a branch-like process;
eg. ramus of mandible,
Pubic ramus
sinus a cavity within a bone; eg. frontal sinus
spine a sharp projection; eg. spine of scapula
 styloid a pen-like projection;
eg. styloid process of ulna
 suture interlocking junction between cranial bones;
eg. coronal suture
 TROCHANTER

a relatively large process;
eg. Greater trochanter of femur
 TUBERCLE a small knob-like process;
eg. tubercle of rib
 TUBEROSITY a knob-like process larger than a
tubercle;
eg. tibial tuberosity
Important points re: the makeup of
BONE TISSUE
 Bone is Most distinctive form of connective tissue
 Extracellular components are hard and calcified
 Rigidity of bone gives it supportive and protective
functions
 Tensile strength nearly equal to that of cast iron at
less than one third the weight:
 It takes:
 GRIT
and GLUE
TO MAKE BONE:,
 MINERAL and MATRIX >>>>>>> see next slide
BONE TISSUE , grit and glue,
calcium and collagen
 Composition of bone matrix
!!!
 INORGANIC SALTS
 Hydroxyapatite: crystals of CALCIUM AND
PHOSPHATE contribute to bone hardness
 Slender, needlelike crystals are oriented to most effectively
resist stress and mechanical deformation
 Magnesium, sodium, sulfate, and fluoride also found in bone
 ORGANIC MATRIX
 Composite of COLLAGENOUS fibers and an amorphous
mixture of protein and polysaccharides called ground
substance
 Ground substance is secreted by connective tissue cells
 Adds to overall strength of bone and gives some degree of
Collagen provides flexibility & tensile strength
(ability to endure stretching forces)
Bones break easily if collagen is inadequate
Hydroxyapatites (calcium and phosphate)
provide compression strength (ability to
endure squeezing forces)
Inadequate mineralization = “soft bones”
ie osteoporosis
MICROSCOPIC STRUCTURE
OF Compact bone -- OSTEONS
 Compact bone contains many cylinder-shaped
structural units called osteons, or haversian
systems
 Osteons surround central (osteonal or haversian)
canals that run lengthwise through bone and are
connected by transverse canals
 Living bone cells are located in these units,
which constitute the structural framework of
compact bone

Osteons permit delivery of nutrients and
removal of waste products
2. Microscopic Anatomy (compact bone)
Osteon

osteon (Haversian system) – structural unit of
compact bone; runs parallel to long axis of
bone; consists of:

concentric lamellae - rings of matrix that surround
the central canal like ‘wrappings’
Represents a single osteon
(Singular:
Lamella)
ref.:
‘ laminate ‘
 osteocytes – mature bone cells;
embedded in lacunae (cavities within
matrix)
 canaliculi – tiny channels; connect
osteocytes to central canal
Circumferential lamellae
surround diaphysis
Interstitial lamellae
Concentric
lamellae
Flat bones also have both compact and cancellous bone tissue
MICROSCOPIC STRUCTURE OF BONE (cont.)
 Structures that make up each osteon
 Lamellae
 Concentric Lamellae: cylinder-shaped layers of
calcified matrix around the central canal
 Interstitial Lamellae: layers of bone matrix between
the osteons; leftover from previous osteons
 Circumferential Lamellae: few layers of bone matrix
that surround all the osteons; run along the outer
circumference of a bone and inner circumference
(boundary of medullary cavity) of a bone
MICROSCOPIC STRUCTURE OF BONE (cont.)
 Structures that make up each osteon (cont.)
 Lacunae: small spaces containing tissue fluid in
which bone cells are located between hard
layers of the lamella
 Canaliculi: ultra-small canals radiating in all
directions from the lacunae and connecting
them to each other and to the central canal
 Central (osteonal or Haversian) canal: extends
lengthwise through the center of each osteon;
contains blood vessels and lymphatic vessels
MICROSCOPIC STRUCTURE OF BONE (cont.)
 Cancellous bone
 No osteons in cancellous bone; it has trabeculae instead
 Nutrients are delivered and waste products removed by
diffusion through tiny canaliculi
 Bony branches (trabeculae) are arranged along lines of stress
to enhance the bone’s strength
 Blood supply
 Bone cells are metabolically active and need a blood supply,
which comes from the bone marrow in the internal
medullary cavity of cancellous bone
 Compact bone, in addition to bone marrow and blood
vessels from the periosteum, penetrates the bone and then,
by way of transverse (Volkmann) canals, connects with
vessels in the central canals of osteons
MICROSCOPIC STRUCTURE
OF BONE (cont.)
 Types of bone cells
 Osteoblasts
 Bone-forming cells found in all bone surfaces
 Small cells synthesize and secrete osteoid, an
important part of the ground substance
 Collagen fibrils line up in osteoid and form a
framework for the deposition of calcium and
phosphate
MICROSCOPIC STRUCTURE OF BONE
(cont.)
 Types of bone cells
 Osteoclasts
 Giant multinucleated cells
 Responsible for the active erosion of bone minerals
 Contain large numbers of mitochondria and
lysosomes
 Osteocytes: mature, nondividing osteoblasts surrounded
by matrix and lying within lacunae
((retirees of the bone, - alive, but relativley inactive,
except for ‘maintenance’ - they maintain the
matrix surrounding them)
So,
Osteoblasts
MAKE
bone,
Osteoclasts BREAK DOWN bone,
and
Osteocytes MAINTAIN
bone.
Slide 40
Slide 41
More functions of the skeletal system,
bone tissue:
Blood formation, calcium storage /
regulation
BONE MARROW
 Type of soft, diffuse connective tissue;
called myeloid tissue
(it is the primary HEMATOPOIETIC
tissue - producing BLOOD CELLS)
 Site for the production of blood cells
 Found in the medullary cavities of long
bones and in the spaces of spongy bone
BONE MARROW (cont.)
 Two types of marrow occur during a person’s
lifetime
 RED MARROW
 Found in virtually all bones in an infant’s or child’s body
 Produces red blood cells
 YELLOW MARROW
 As an individual ages, red marrow is replaced by yellow
marrow
 Marrow cells become saturated with fat and are no
longer active in blood cell production
BONE MARROW (cont.)
 The main bones in an adult that still
contain red marrow include the ribs,
bodies of the vertebrae, humerus, pelvis,
and femur
 Yellow marrow can change to red marrow
during times of decreased blood supply,
such as anemia, exposure to radiation,
and certain diseases
REGULATION OF BLOOD CALCIUM LEVELS
 Skeletal system is a storehouse for about 98% of
body calcium reserves
 Helps maintain constancy of blood calcium levels
 Calcium is mobilized and moves in and out of blood during
bone remodeling
 During bone formation, OSTEOBLASTS REMOVE
CALCIUM from blood and lower circulating levels
 During breakdown of bone, OSTEOCLASTS
RELEASE
CALCIUM into blood and increase circulating levels
REGULATION OF BLOOD CALCIUM LEVELS (cont.)
 Homeostasis of calcium ion concentration
is essential for the following:
 Transmission of nerve impulses
 Blood clotting
 Bone formation, remodeling, and repair
 Maintenance of skeletal and cardiac muscle
contraction
REGULATION OF BLOOD CALCIUM LEVELS (cont.)
 Mechanisms of calcium homeostasis
 Parathyroid hormone
 Primary regulator of calcium homeostasis
 Stimulates osteoclasts to initiate breakdown of bone matrix
and increase blood calcium levels
 Increases renal absorption of calcium from urine
 Stimulates vitamin D synthesis
REGULATION OF BLOOD CALCIUM LEVELS (cont.)
 Mechanisms of calcium homeostasis
 CALCITONIN
 Protein hormone produced in the thyroid gland
 Produced in response to high blood calcium levels
 Stimulates bone deposition by osteoblasts
 Inhibits osteoclast activity
 Far less important in homeostasis of blood
calcium levels
than is parathyroid
hormone
CARTILAGE
CARTILAGE
 Characteristics
 Avascular connective tissue
 Fibers of cartilage are embedded in a firm gel
 Has the flexibility of firm plastic
 No canal system or blood vessels
 Chondrocytes receive oxygen and nutrients by
diffusion
 Perichondrium: fibrous covering of the cartilage
 Cartilage types differ because of the amount of matrix
present and the amounts of elastic and collagenous
fibers
CARTILAGE (cont.)
 Types of cartilage (Figure 7-21)
 HYALINE CARTILAGE
 Most common type
 Covers the articular surfaces of bones
 Forms the costal cartilages, cartilage rings in the trachea,
bronchi of the lungs, and the tip of the nose
 Forms from special cells in chondrification centers, which
secrete matrix material
 Chondrocytes are isolated into lacunae
CARTILAGE (cont.)
 Types of cartilage
 Elastic cartilage
 Forms external ear, epiglottis, and eustachian tubes
 Large number of elastic fibers confers elasticity and
resiliency
 Fibrocartilage
 Occurs in pubic symphysis and intervertebral
disks, and the meniscii of the knee joints
 Small quantities of matrix and abundant fibrous elements
 Strong and rigid
CARTILAGE (cont.)
 Functions
 Tough, rubberlike nature permits
cartilage to sustain great weight or
serve as a shock absorber
 Strong yet pliable support structure
 Permits growth in length of long
bones
Next few slides are of
INTEREST - not to be
tested upon, sit back and
relax , watch, listen.
Bone development,
fractures and repair:
DEVELOPMENT OF BONES
 Osteogenesis: development of bone from small
cartilage model to adult bone (Figure 7-11)

Intramembranous ossification, (some)

Endochondral ossification (most)
 Intramembranous ossification:
 Occurs within a connective tissue membrane
 Flat bones begin when groups of cells differentiate into
osteoblasts
 Osteoblasts are clustered together in ossification
center
 Osteoblasts secrete matrix material and collagenous
fibrils
. Bone Development (osteogenesis)
1. Formation of the skeleton
Initial embryonic skeleton made of
a. fibrous membranes (cranial bones & clavicles) &
b.
hyaline cartilage (all other bones)
At birth,
osseous
development,
(shows
Large
Areas still are
cartilagenous)
DEVELOPMENT OF BONES (cont.)
 Intramembranous ossification
 Large amounts of ground substance accumulate
around each osteoblast
 Collagenous fibers become embedded in the ground
substance and constitute the bone matrix
 Bone matrix calcifies when calcium salts are
deposited
 Trabeculae appear and join in a network to form
spongy bone
 Appositional growth occurs by adding osseous tissue

(like a tree grows in diameter)
DEVELOPMENT OF BONES (cont.)
 Endochondral ossification
 Most bones begin as a cartilage model with bone formation spreading
essentially from the center to the ends
 Periosteum develops and enlarges to produce a collar of bone
 Primary ossification center forms
 Blood vessel enters the cartilage model at the midpoint of the diaphysis
 Bone grows in length as endochondral ossification progresses from the
diaphysis toward each epiphysis
 Secondary ossification centers appear in the epiphysis, and bone growth
proceeds toward the diaphysis
 Epiphyseal plate remains between the diaphysis and each epiphysis until
bone growth in length is complete
DEVELOPMENT OF BONES (cont.)
 Epiphyseal plate is composed of four layers
 “Resting” cartilage cells: point of attachment joining
the epiphysis to the shaft
 Zone of proliferation: cartilage cells undergoing
active mitosis, which causes the layer to thicken and
the plate to increase in length
 Zone of hypertrophy: older, enlarged cells
undergoing degenerative changes associated with
calcium deposition
 Zone of calcification: dead or dying cartilage cells
undergoing rapid calcification
DEVELOPMENT OF BONES (cont.)
 Epiphyseal plate can be a site for
bone fractures in young people
 Long bones grow in both length
and diameter
BONE REMODELING
 Primary osteons develop within early woven bone
 Conelike or tubelike space is hollowed out by
osteoclasts
 Osteoblasts in the endosteum that lines the tube begin
forming layers (lamellae) that trap osteocytes between
layers
 A central canal is left for the blood and lymphatic
vessels and nerves
 Primary osteons can be replaced later by secondary
osteons in a similar manner
Bones grow in length and diameter by the
combined action of osteoclasts and
osteoblasts
Osteoclasts enlarge the diameter of the
medullary cavity
Osteoblasts from the periosteum build new
bone around the outside of the bone
Mechanical stress, such as
physical activity, strengthens bone
Fractures
and Repairs
Slid
e
76
REPAIR OF BONE FRACTURES
 Fracture: break in the continuity of a bone
 Fracture healing
 Fracture tears and destroys blood vessels that carry
nutrients to osteocytes
 Vascular damage initiates repair sequence
 Callus: special repair tissue that binds the broken ends
of the fracture together
 Fracture hematoma: blood clot occurring immediately
after the fracture, which is then resorbed and replaced
by callus
CYCLE OF LIFE: SKELETAL ISSUES
 Skeleton fully ossified by mid-20s
 Soft tissue may continue to grow; ossifies more
slowly
 Adults: changes occur from specific conditions
 Increased density and strength from exercise
 Decreased density and strength from pregnancy,
nutritional deficiencies, and illness
 Advanced adulthood: apparent degeneration
 Hard bone matrix replaced by softer connective
tissue
 Exercise can counteract degeneration