Skeletal System
Structure and Function of Bone
• 1. Support—The skeleton forms a rigid framework to which
are attached the softer tissues and organs of the body.
• 2. Protection—The skull, vertebral column, rib cage, and
pelvic girdle enclose and protect vital organs; sites for
blood cell production are protected within the hollow
centers of certain bones.
• 3. Movement—Bones act as levers when attached muscles
contract, causing movement about joints.
• 4. Hemopoiesis—Red bone marrow of an adult produces
white and red blood cells and platelets.
• 5. Mineral and energy storage—The matrix of bone is
compose of calcium and phosphorus which can be
withdrawn in small amounts if needed elsewhere in the
body. Lipids stored in adipose cells of yellow bone marrow
store energy.
Bones can be Compact or Spongy
• Compact bone is dense and looks smooth and
homogeneous.
• Spongy bone is composed of small needlelike
pieces of bone and lots of open space.
Categorization of Bones
• Long Bones: Longer than wide; Found in
appendages.
• Short Bones: More or less cubical; found in
confined spaces.
• Flat Bones: Protection; bones of the skull, ribs.
• Irregular Bones: Odd shaped; vertebrae,
certain skull bones.
Structure determines function
• The shape of a bone is consistent with its
functions. The femur, for instance, withstands
great weight and pressure as it provides
support for the body and attachment points
form many muscles. The hollow cylindrical
design provides maximum strength with
minimal weight.
Types of Bones
Structure of Long Bones
• The diaphysis, or shaft, makes up most of the bone’s
length and in made of compact bone.
• It is covered and protected by a fibrous connective
tissue membrane, the periosteum, which is secured to
the bone by hundreds perforating or Sharpey’s fibers.
• Epiphysis are the ends of long bones, consisting of a
thin layer of compact bone enclosing an area filled with
spongy bone. It is covered by articular cartilage, a
glassy hyaline cartilage, providing a smooth slippery
surface that decreases friction at joins.
• The epiphyseal line is a remant of the plates that fuse
together from growing bone.
Parts of the Bone
Inside a long bone.
• The yellow marrow is the cavity of the shaft
and is used for storage of fat tissue.
• Red marrow is in cavities of the spongy bone
of flat bones and the epiphyses of some long
bones.
Major Parts of Bone--Summary
•
1. EPIPHYSIS - expanded ends of bone. ARTICULATES (forms a joint)
with another bone.
2. DIAPHYSIS - shaft of the bone
3. ARTICULAR CARTILAGE - hyaline cartilage covering the ends of
bones
4. PERIOSTEUM - tough membrane-like covering over entire bone,
except for articular cartilage. Connects with tendons and ligaments.
Forms bone tissue.
•
MEDULLARY CAVITY - hollow chamber within the diaphysis
connects to spaces in spongy bone. Filled with soft specialized
tissue called bone marrow.
• " Red Marrow - mainly in spongy bone in adults. Produces blood
cells
" Yellow Marrow - fat storage. Replaces much of the red marrow in
diaphysis through childhood
• ENDOSTEUM - lining of the medullary cavity
Long Bone
Compact bone through a microscope
has a very complex structure.
Microscopic Structure of Bone
• - MATRIX composed of collagen and inorganic salts
- OSTEOCYTES (mature bone cells) are enclosed in tiny
chambers called LACUNAE and form concentric "ring"
(layers) around a passageway called the HAVERSION CANAL
- The osteocytes are connected by minute passages called
CANALICULI (canaliculus) through which tiny "branches" or
processes pass
- The circular layers of matrix material and osteocytes,
along with the haversian canal, forms a unit called a
HAVERSIAN SYSTEM. Compact bone tissue is formed in this
way
- The haversian canals are interconnected by passages
called VOLKMANN'S CANALS. All of these canals contain
blood vessels and nerve fibers
• Mature bone cells, osteocytes, are found within
the matrix in tiny cavities called lacunae. The
lacunae are arranged in concentric circles called
lamellae around central (Haversian) canals. Each
complex consisting of central canal and matrix
rings is called an osteon, or Haversian system.
They run lengthwise through bony matrix,
carrying blood vessels and nerves to all areas of
the bone. Tiny canals, canaliculi, radiate outward
to all lacunae and form a transportation system
that connects all the bone cells tot the nutrient
supply through the hard bone matrix. Volkmann’s
canals are their communication network.
Microscopic structure of the bone
Bone Formation
•
Bone Development and Growth:
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There are two types of bone based on the way the bones form
1. INTRAMEMBRANOUS BONES = broad, flat bones of the skull. These bones form from membrane-like sheets of
connective tissue
2. ENDOCHONDRAL BONES = all other bones.
Bones first form as hyaline cartilage. The cartilage then gradually changes into bone tissue - a process called
OSSIFICATION, which begins near the middle of the diaphysis in an area called the PRIMARY OSSIFICATION
CENTER. Later the bone begins to ossify in the epiphysis - these areas are called the SECONDARY OSSIFICATION
CENTERS.
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As long as growth is occurring, a "band" of cartilage (called an epiphyseal disk, growth plate) remains between the
diaphysis and the epiphysis.
Bones increase in length as these cartilage cells continue to reproduce and ossify
Cartilage cells form cells called OSTEOBLASTS. These cells produce bone matrix and once the cell is enclosed in
bone matrix it is considered to be a mature bone cell and called an OSTEOCYTE
Growth in thickness of bone occurs as osteoblasts from beneath the periosteum produce bone matrix and build
compact bone just underneath the periosteum
Bone tissue is constantly being replaced as special cells called OSTEOCLASTS dissolve bone tissue from within the
medullary cavity - a process called RESORPTION. At the same time new bone tissue is being added to the outside
of the bone.
3 Types of Joints
• 3 Basic Types of Joints (articulations):
• 1. SYNARTHROTIC - immoveable joint, such as bones in the skull,
these junctions are called SUTURES. - Fibrous Joints
• 2. AMPHIARTHROTIC - slightly moveable joint, vertebrae Cartilaginous Joints
• 3. DIARTHROTIC - freely moveable joint, such as shoulders, hips,
knees, elbows, wrists, fingers…
--these joints are enclosed within a fibrous capsule which contains a
lubricating fluid called SYNOVIAL fluid. These are called SYNOVIAL
JOINTS.
• Ball & Socket
Hinge
Pivot
Saddle
Bones of the Skull
• 1. Frontal - anterior portion above eyes
2. Parietal - one on each side of the skull, just
behind frontal bone
3. Occipital - forms the back of the skull and base
of the cranium
4. Temporal - forms parts of the sides and base of
cranium
5. Sphenoid - wedged between several other
bones in anterior portion of the cranium
6. Maxilla - forms upper jaws
7. Mandible - lower jaws, only moveable bone of
the skull
Sutures
• 1. Coronal - between frontal and parietal bones
2. Lambdoidal - between occipital and parietal
bones
3. Squamosal - between temporal and parietal
bones
4. Sagittal - between parietal bones
• Fontanels - "soft spots" of an infant's skull:
- anterior fontanel, posterior fontanel, sphenoid
fontanel, mastoid fontanel
• Foramen Magnum - Large opening through the
underside of the skull, spinal cord enters skull
Cranial and Facial Bones
Label:
The Rest of the Bones
• Ribs - Thoracic Cage, 12 pairs
- True Ribs - first seven pairs, attach directly to STERNUM by costal
cartilage (Vertebralsternal)
- False Ribs - last five pairs (Vertebralchondral)
- Floating ribs - last two pairs (Vertebral)
• Pectoral Girdle: Shoulder. Two clavicles
• (collar bones) and two scapula (shoulder
blade)
• Arms: Upper arm - humerus. Lower arm
- radius and ulna.
Wrist - 8 small bones called carpals
Fingers - Metacarpals, Phalanges
• Pelvic Girdle: Hips. Two large bones called
COXAL BONES
• Legs: Upper leg (thigh) - FEMUR. Lower leg - tibia & fibula.
Ankle and Upper foot - 7 bones called TARSALS,
Largest is the heel bone called the CALCANEOUS
Toes - Metatarsals, Phalanges
The Bones for “Chunk #1”
Wrist Bones
Ankle Bones
What About Broken Bones?
• A complete fracture (or closed) is when the bone has broken into
two pieces.
• A greenstick fracture is when the bone cracks on one side only, not
all the way through.
• A single fracture is when the bone is broken in one place.
• A comminuted (say: kah-muh-noot-ed) fracture is when the bone is
broken into more than two pieces or crushed
• A bowing fracture, which only happens in kids, is when the bone
bends but doesn't break
• An open fracture is when the bone is sticking through the skin.