Lecture 5
Bone Tissue
Tissues and Organs of the Skeletal System
 Functions of the Skeleton
o _______________ – bones of the legs, pelvis, and vertebral column hold
up the body; jaw bones support teeth; most bones provide support for
muscles
o Movement – Skeletal muscle are useful for movement because they are
attached to bones
o __________________ – Bones enclose and protect delicate organs and
tissues such as the brain, spinal cord, lungs, heart, pelvic viscera, and
bone marrow
o Blood formation – Red bone marrow is the major producer of blood cells,
including most cells of the immune system
o Electrolyte balance – The skeleton is the body’s main mineral reservoir. It
stores calcium and phosphate and releases them when needed for other
purposes
o Acid-base balance – Bone buffers the blood against excessive pH changes
by absorbing or releasing alkaline salts such as calcium phosphate
o _______________________ – Bone tissue removes heavy metals and
other elements from the blood to reduce their toxic effects on other tissues
(It can later release these more slowly for excretion)
 Bones and Osseous Tissue
o Osseous tissue is connective tissue in which the matrix is hardened by the
deposition of calcium phosphate and other ___________________
 This hardening process is called mineralization or calcification
o Other tissues in bone include blood, bone marrow, cartilage, adipose
tissue, nervous tissue, fibrous connective tissue
o “Bone” can denote an ______________ containing all of these tissues, or
it can denote just the osseous ______________
 Shapes of Bones
o Long bones – roughly cylindrical in shape and significantly longer than
they are wide.
 Serve as _______________ to produce movement
 Femur, humerus, ulna, etc.
o Short bones - more nearly equal in length and width
 Have limited motion, but glide across one another
 Carpals (wrist bones), tarsels (ankle bones)
o Flat bones – have flat surfaces
 enclose and ____________ soft organs and provide surface for
muscle attachment
 cranial bones, ribs, sternum, scapulae, ossa coxae
o Irregular bones – have elaborate shapes that don’t fit any of the other
categories

 Vertebrae, ethmoid & sphenoid bones of the skull, etc.
General Features of Bone
 Compact bone - bone tissue that forms the surface of skeleton.
 It is dense calcified tissue, with no ____________ visible to
the naked eye
 About ¾ of the skeleton is compact bone, by weight
 Spongy bone - bone tissue that fills the heads of the long bones.
 It is made up of many long delicate slivers that give it a
spongy appearance
o Parts of a long bone
 Diaphysis – the _______________ of a long bone
 Epiphysis – the expanded head at the end of a long bone
 Filled with spongy bone
 Contains red bone marrow
 Medullary cavity – cylindrical hollow cavity inside the diaphysis
 Contains ________________ bone marrow
 Epiphyseal plate – hyaline cartilage that separates the marrow
spaces of the epiphysis and diaphysis
 It’s the zone where bones grow in ____________
 When the plate is depleted, an epiphyseal line remains
visible
 Periosteum – A sheath that covers the bone and provides strong
attachment from tendon to bone
 Perforating fibers – fibers of the periosteum that penetrate into
bone ___________
 Nutrient foramina – minute holes through the compact bone that
allow blood vessels of the periosteum to penetrate into the bone
 Endosteum – Thin layer of connective tissue lining the inside of
the diaphysis (lining the medullary cavity)
 Articular cartilage – Thin layer of hyaline cartilage covering the
ends of adjoining bones
 The cartilage, along with ______________ fluid, allows the
bones to move easily at the joint
Histology of Osseous Tissue
 Cells
o Osteogenic cells – ______________cells found in the endosteum, the
periosteum, and compact bone. They multiply continually and some of
them differentiate into osteoblasts
o Osteoblasts – bone _________________ cells that synthesize the organic
matter of the matrix and help to mineralize bone. Stress and fractures
stimulate mitosis of osteogenic cells leading to increasing numbers of
osteoblasts
o Osteocytes – mature bone cells that are essentially osteoblasts that have
become trapped in the matrix they deposited
 Lacunae are the tiny cavities that house osteocytes

Canaliculi are tiny channels that connect _______________
together
o Osteoclasts – bone-_________________ cells found on the bone surface
 They develop from the same marrow cells that produce monocytes
of the blood.
 Matrix
o By weight, the matrix is 1/3 organic matter and 2/3 inorganic matter
o Organic matter
 Collagen and large protein-carbohydrate complexes
 The collagen and minerals form a composite that gives bone
flexibility and strength
 The minerals resist compression
o When bones are deficient in calcium salts, they
become soft and _____________ easily
 The collagen fibers give it the ability to resist tension, so
that the bone can bend slightly without snapping.
o Without collagen, running would shatter the legs
 Compact Bone
o The basic structural unit of compact bone is a cylindrical unit called an
_____________
 Osteons are composed of concentric lamellae – small rings
surrounded by larger and larger rings of matrix
 The central canal is a canal that passes lengthwise through the core
of the osteon and contains blood vessels and nerves
 Lacunae lie between adjacent layers of matrix and are connected
with each other by canaliculi
 Spongy Bone
o Trabeculae – thin plates or sheets of calcified tissue
o ________________ – spines of calcified tissue
o Together they form a latticelike appearance to resemble a sponge.
 Bone Marrow
o Bone marrow is a general term for the soft tissue that occupies the
medullary cavity, the spaces within spongy bone, and larger central canals
 ______________ bone marrow
 Tissue that forms blood cells (process called hemopoiesis)
 Yellow bone marrow – replaces red bone marrow in medullary
cavity with age
 Stores __________
Bone Development
 Endochondral Ossification – process in which a bone develops from hyaline
cartilage
o Embryonic tissue condenses into a hyaline ___________________ model
that resembles the shape of the bone to come
o In the cartilage model chondrocytes near the center of the model multiply
and swell forming a primary ossification center
o Within the primary ossification center:



As the lacunae enlarge, the matrix between them is reduced to thin
walls and the model becomes weak
 Next, some cells of the perichondrium become _______________,
which produce a body collar around the model
 This bony collar (now called periosteum) cuts off the diffusion of
nutrients to the chondrocytes, killing them
 Buds of connective tissue grow into the cartilage and break down
the lacunae
 Osteogenic cells then invade and produce osteoblasts which
deposit osteoid tissue
o Around the time of birth, ___________________ ossification centers
begin to form in the epiphyses
 Chondrocytes enlarge, the walls of the matrix between them
dissolve, and chondrocytes die
 Vascular buds arise from the perichondrium and grown into the
cartilage, bringing ostegenic cells and osteoclasts with them
 The cartilage is eroded from the center of the epiphysis outward in
all directions
 Hyaline cartilage persists on the epiphyseal surfaces as articular
cartilage and at the junctions with the diaphyses, where they form
epiphyseal ___________________
Bone Growth and Remodeling
o Bone changes in size and shape to accommodate changing forces applied
to the skeleton
o The femurs grow longer, the curvature of the cranium increases, many
bones develop bumps, spines, and ridges
o Cartilage grows by two mechanisms
 Interstitial growth (adding more matrix internally)
 Occurs in the epiphyseal plate to ________________ the
bone
 Appositional growth (adding more to the surface)
 Osteogenic cells in the periosteum become osteoblasts
which deposit new bone tissue on the outside
 On the inner surface of the bone, osteoclasts dissolve bone,
enlarging the marrow cavity
 If one process outpaces the other,
______________________ can occur
Aging Skeletal System
o At age 30, osteoblasts become less active than osteoclasts
 _____________________ – the loss of bone
o At age 40, women lose about 8% of their bone mass per decade, and men
lose about 3% per decade
 Bone loss in the jaws contributes to tooth loss
 As bone density decreases, bones become brittle, and fractures
occur more easily
o Arthritis is also associated with aging
Structural Disorders of Bone
 Fractures
o ___________________ fractures – breaks caused by abnormal trauma to a
bone, such as incurred in falls, athletics, etc.
o Pathologic fractures – breaks due to bone that is weakened by disease,
such as bone cancer or osteoporosis
 Osteoporosis
o Means “porous bones”
o Involves loss of bone mass to the point that the body weight cannot be
supported
o Weight-bearing bones of the vertebrae become compressed, and people
may lose ___________________ and develop an exaggerated spinal
curvature called kyphosis
Skeletal Regions
 Axial skeleton – Skull, vertebral column, ribs, sternum
 Appendicular skeleton – Bones of the upper and lower limbs, and bones of the
pectoral and pelvic girdle
Bone Landmarks
 Articulations
o Condyle – rounded knob
o Facet – smooth, flat, slightly ________________ or convex articular
surface
o Head – prominent expanded end of a bone, sometimes rounded
 Extensions and Projections
o Crest – narrow ridge
o Epicondyle – projection superior to a condyle
o _______________ – any bony prominence
o Protuberence – a bony outgrowth or protruding part
o Spine – a sharp, slender, or narrow process
o Trochanter – Massive process unique to the femur
o Tubercle – small rounded process
o ________________________ – rough surface
 Depressions
o Alveolus – pit or socket
o Fossa – shallow, broad, or elongated basin
o Sulcus – a groove for a tendon, nerve, or blood vessel
 Passages
o Canal – tubular passage or tunnel in a bone
o Fissure - slit through a bone
o Foramen – a hole through a bone, usually round
o ______________________ – an opening into a canal