Chapter 7
Skeletal Tissues
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 1
Types of Bones
• Structurally, there are four types of bones
(Figure 7-1):

Long bones

Short bones

Flat bones

Irregular bones
• Bones serve various needs, and their size,
shape, and appearance will vary to meet
those needs
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 2
Types of Bones
• Bones vary in their proportions 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 3
Types of Bones
• Parts of a long bone (Figure 7-2)

Diaphysis
• Main shaft of long bone
• Hollow, cylindrical shape and thick,
compact bone
• Function is to provide strong support without
cumbersome weight
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 4
Types of Bones
• Parts of a long bone (cont.)

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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 5
Types of Bones
• Parts of a long bone (cont.)

Articular cartilage
• Layer of hyaline cartilage that covers the articular surface
of epiphyses
• Function is to cushion jolts and blows
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 6
Types of Bones
• Parts of a long bone (cont.)

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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 7
Types of Bones
• Parts of a long bone (cont.)

Medullary (or marrow) cavity
• Tubelike, hollow space in diaphysis
• Filled with yellow marrow in adult

Endosteum—thin epithelial membrane that lines
medullary cavity
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 8
Types of Bones
• Short, flat, and irregular bones

Inner portion is cancellous bone, covered on the
outside with compact bone

Spaces inside cancellous bone of a few irregular
and flat bones are filled with red marrow
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 9
Bone Tissue
• Most distinctive form of connective tissue
• Extracellular components are hard and
calcified
• Rigidity of bone allows it to serve its
supportive and protective functions
• Tensile strength is nearly equal to cast iron at
less than one third the weight
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 10
Bone Tissue
• Composition of bone matrix

Inorganic salts
• Hydroxyapatite—highly specialized chemical crystals of
calcium and phosphate contribute to bone hardness
• Slender, needle-like crystals are oriented to most
effectively resist stress and mechanical deformation
• Magnesium and sodium are also found in bone
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 11
Bone Tissue
• Composition of bone matrix (cont.)

Measuring bone mineral density

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 resilience to the bone
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 12
Microscopic Structure of the Bone
(Figure 7-3)
• Compact bone

Contains many cylinder-shaped structural units called
osteons, or Haversian systems

Osteons surround canals that run lengthwise through bone
and are connected by transverse Volkmann’s 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 13
Microscopic Structure of the Bone
• Compact bone (cont.)

Four types of structures make up each osteon:
• Lamella—concentric, cylinder-shaped layers of calcified
matrix
• Lacunae—small spaces containing tissue fluid in which
bone cells are located between hard layers of the lamella
• Canaliculi—ultrasmall canals radiating in all directions
from the lacunae and connecting them to each other and
to the Haversian canal
• Haversian canal—extends lengthwise through the center
of each osteon and contains blood vessels and lymphatic
vessels
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 14
Microscopic Structure of the Bone
• Cancellous bones (Figure 7-4)

No osteons in cancellous bone; instead, it has
trabeculae

Nutrients are delivered and waste products
removed by diffusion through tiny canaliculi

Bony spicules are arranged along lines of stress,
enhancing the bone’s strength
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 15
Microscopic Structure of the Bone
• 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, penetrate
bone and then, by way of Volkmann’s canals,
connect with vessels in the Haversian canals
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 16
Microscopic Structure of the Bone
• 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 serve as a
framework for the deposition of calcium and phosphate
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 17
Microscopic Structure of the Bone
• Types of bone cells (cont.)

Osteoclasts (Figure 7-5)
• Giant multinucleate cells
• Responsible for the active erosion of bone minerals
• Contain large numbers of mitochondria and lysosomes

Osteocytes—mature, nondividing osteoblast
surrounded by matrix, lying within lacunae
(Figure 7-6)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 18
Bone Marrow
• Specialized type of soft, diffuse connective
tissue; called myeloid tissue
• Site for the production of blood cells
• Found in medullary cavities of long bones
and in the spaces of spongy bone
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 19
Bone Marrow
• Two types of marrow are present during a person’s
lifetime:

Red marrow
• Found in virtually all bones in an infant’s or child’s body
• Functions to produce 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 20
Bone Marrow
• The main bones in an adult that still contain
red marrow include the ribs, bodies of the
vertebrae, the humerus, the pelvis, and the
femur
• Yellow marrow can alter to red marrow during
times of decreased blood supply, such as with
anemia, exposure to radiation, and certain
diseases
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 21
Functions of Bone
• Support—bones form the framework of the body and
contribute to the shape, alignment, and positioning of
the body parts
• Protection—bony “boxes” protect the delicate
structures they enclose
• Movement—bones with their joints constitute levers
that move as muscles contract
• Mineral storage—bones are the major reservoir for
calcium, phosphorus, and other minerals
• Hematopoiesis—blood cell formation is carried out by
myeloid tissue
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 22
Regulation of Blood Calcium Levels
• Skeletal system serves as a storehouse for
about 98% of body calcium reserves

Helps maintain constancy of blood calcium levels
• Calcium is mobilized and moves into 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 23
Regulation of Blood Calcium Levels
• Skeletal system (cont.)

Homeostasis of calcium ion concentration
essential for the following:
• Bone formation, remodeling, and repair
• Blood clotting
• Transmission of nerve impulses
• Maintenance of skeletal and cardiac muscle contraction
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 24
Regulation of Blood Calcium Levels
• 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 25
Regulation of Blood Calcium Levels
• Mechanisms of calcium homeostasis (cont.)

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 parathyroid hormone
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 26
Development of Bone
• Osteogenesis—development of bone from small
cartilage model to an adult bone
• Intramembranous ossification

Occurs within a connective tissue membrane

Flat bones begin when groups of cells differentiate into
osteoblasts

Osteoblasts are clustered together in centers of ossification

Osteoblasts secrete matrix material and collagenous fibrils
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 27
Development of Bone
• Intramembranous ossification (cont.)

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

Apposition growth occurs by adding of osseous tissue
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 28
Development of Bone
• Endochondral ossification (Figure 7-8)

Most bones begin as a cartilage model, with bone
formation spreading essentially from the center to
the ends

Periosteum develops and enlarges, producing a
collar of bone

Primary ossification center forms

Blood vessel enters the cartilage model at the
midpoint of the diaphysis
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 29
Development of Bone
• Endochondral ossification (cont.)

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 diaphysis and
each epiphysis until bone growth in length is
complete (Figure 7-10)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 30
Development of Bone
• Endochondral ossification (cont.)

Epiphyseal plate is composed of four layers
(Figure 7-9):
• “Resting” cartilage cells—point of attachment joining the
epiphysis to the shaft
• Zone of proliferation—cartilage cells undergoing active
mitosis, causing 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 31
Bone Growth and Resorption
(Figures 7-11 and 7-12)
• Bones grow in 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 32
Repair of Bone Fractures
• Fracture—break in the continuity of a bone
• Fracture healing (Figure 7-13)

Fracture tears and destroys blood vessels that carry
nutrients to osteocytes

Vascular damage initiates repair sequence

Callus—specialized repair tissue that binds the broken ends
of the fracture together

Fracture hematoma—blood clot occurring immediately after
the fracture, is then resorbed and replaced by callus
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 33
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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 34
Cartilage
• Types of cartilage (Figure 7-14)

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 specialized cells in centers of chondrification,
which secrete matrix material
• Chondrocytes are isolated into lacunae
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 35
Cartilage
• Types of cartilage (cont.)

Elastic cartilage
• Forms external ear, epiglottis, and eustachian tubes
• Large number of elastic fibers confers elasticity and resiliency

Fibrocartilage
• Occurs in symphysis pubis and intervertebral disks
• Small quantities of matrix and abundant fibrous elements
• Strong and rigid
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 36
Cartilage
• Histophysiology of cartilage

Gristle-like 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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 37
Cartilage
• Growth of cartilage

Interstitial or endogenous growth
• Cartilage cells divide and secrete additional matrix
• Seen during childhood and early adolescence while
cartilage is still soft and capable of expansion from
within
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 38
Cartilage
• Growth of cartilage (cont.)

Appositional or exogenous growth
• Chondrocytes in the deep layer of the perichondrium
divide and secrete matrix
• New matrix is deposited on the surface, increasing its size
• Unusual in early childhood but, once initiated, continues
throughout life
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 39
Cycle of Life: Skeletal Tissues
• Skeleton fully ossified by mid-twenties

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
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 40