Skeletal System
I.
II.
Skeletal Cartilage
a. High water content
i. Helps the cartilage be resilient, ability to spring back to original shape
b. No nerves
c. No blood vessels
d. Surrounded by perichondrium – acts as a girdle to hold the outside in place when
compressed
e. All three types have chondrocytes encased in small cavities within an
extracellular matrix
f. Hyaline cartilage
i. Collagen fibers
ii. Looks like frosted glass when exposed
iii. Provides support with flexibility and resilience
iv. Most abundant of all skeletal cartilages
v. Found in many areas
1. Articular cartilage – covers the ends of bones at moveable joints
2. Costal cartilage – connects the ribs to the sternum
3. Laryngeal cartilage – forms the skeleton of the larynx
4. Trachial (bronchial) cartilage – reinforces other respiratory passages
5. Nasal cartilage – supports the external nose
g. Elastic cartilage
i. Looks similar to the hyaline but has elastic fibers
ii. Stands up to repeated bending
iii. Two locations
1. External ear
2. Epiglottis
h. Fibrocartilage
i. Parallel rows of chondrocytes alternating with thick collagen fibers
ii. Highly compressible and high tensile strength
iii. Found in areas of high pressure and stretch
1. Cartilage disks in knee – meniscus
2. Intervertebral disks in the back
i. Cartilage growth
i. Appositional growth
1. Cartilage forming cells in the surrounding perichondrium secrete the
new matrix against the existing cartilage
ii. Interstitial growth
1. Chondrocytes inside the cartilage divide and secrete new matrix
2. Expands the cartilage from within
iii. Typically cartilage stops growing during adolescence
Functions of bone
a. Support
i. Provide a hard framework that supports soft organs
ii. Supports the body – lower extremities act as pillars when standing
b. Protection
i. Fused bones in the skull provides protection for the brain
III.
IV.
ii. The vertebrae in the back protect the spinal cord
iii. Rib cage protects the heart & lungs
c. Movement
i. Serve as attachment sites for muscles
ii. The bones are used as levers to move the body and its parts
iii. The arrangement of bones and joints determines movement
d. Mineral storage
i. Reservoir for calcium & phosphate
ii. Can be released into the blood stream as needed
e. Blood cell formation
i. Hematopoiesis
ii. Occurs within the marrow of the bones
Classification of bones
a. Shape fulfills a function
b. Different shapes have different amounts of the two types of bone
i. Compact – dense bone
1. Smooth and homogeneous
ii. Spongy – cancellous bone
1. Small needlelike or flat pieces called trabecluae
2. Has large amounts of open space
3. Forms a network where the open spaces are filled with red or yellow
marrow
c. Classified by shape
i. Long bones
1. Longer than they are wide
2. Name reflects shape not necessarily size
3. Consists of a shaft with two ends
4. Primarily compact bone, but may have spongy bone in the interior
ii. Short bones
1. Nearly cubelike
2. Contain mostly spongy bone
3. Has compact bone as a thin outer layer
4. Sesamoid bones – type of short bone imbedded in a tendon
a. Patella (knee cap)
iii. Flat bones
1. Thin, flattened, usually curved
2. Two parallel compact bone surfaces
3. Layer of spongy bone between the compact
4. Sternum, ribs, skull
iv. Irregular bones
1. Bones that do not fit in any of the other categories
2. Vertebrae, pelvis
3. Consist mainly of spongy bone enclosed by thin layers of compact
Gross Bone structure
a. Long bones
i. Diaphysis
1. Shaft, the long axis of the bone
2. Thick layer of compact bone that surrounds the medullary cavity
a. Contains fat and is known as the yellow bone marrow cavity
V.
ii. Epiphyses
1. The bone ends
2. The exterior is compact bone, interior is spongy bone
3. The joint surface is covered by a layer of articular cartilage (hyaline)
a. Cushions the opposing bone ends during joint movement
4. Epiphyseal line
a. Growth plate
b. Between the diaphysis and the epiphyses
c. The area where bone lengthens
iii. Membranes
1. Periosteum
a. Covers the outer layer of the diaphysis
b. Two layers
i. Outer – fibrous layer of dense irregular CT
ii. Inner – osteogenic layer consisting of osteoblasts (bone
forming cells) and osteoclasts (bone destroying cells)
c. Rich supply of blood vessels, nerves, and lymphatic vessels
d. Secured to underlying bone by Sharpey’s fibers – bundles of
collagen
e. Serves as an anchoring point for tendons and ligaments
2. Endosteum
a. Internal membrane, CT
b. Covers the trabeculae of spongy bone in the marrow cavities
c. Contains both osteoblasts & osteoclasts
b. Short, Irregular, Flat bones
i. Thin plates of periosteoum-covered compact bone on the outside
ii. Endosteoum covered spongy bone inside
iii. Not cylindrical
iv. No shaft or epiphyses
v. Contain no cavity, but marrow is present in the spongy bone
vi. Diploe – internal layer of spongy bone
c. Hematopoietic Tissues
i. Red marrow
1. Found within the cavities of spongy bone of long bones
2. Blood cell formation occurs most in the head of the femur & humerus,
and the diploe of flat & irregular bones
Microscopic Structure of Bone
a. Compact Bone
i. The unaided eye - appears very dense
ii. Microscopic view – detailed with canals & passageways
1. Structural unit of compact bone is the Haversian system (osteon)
2. Each system is an elongated cylinder oriented parallel to the long axis
of the bone
3. Hollow tubes of bone matrix, looks like the rings in a tree
4. Each matrix tube is a lamellae
a. Collagen fibers in a particular lamella run in single directions
b. Adjacent lamella have different directions
c. This alternating pattern increases strength against twisting
5. Haversian canal
VI.
a. A canal that contains blood vessels and nerve fibers that serve
the cells
b. Runs through the core of the each system
6. Volkmann’s canal
a. Runs perpendicular to the long axis of the bone
b. Connects the periosteum to the central canals and medullary
cavity
7. Osteocytes – mature bone cells
a. Spider-shaped
b. Found in the lacunae
8. Lacunae
a. Small cavities at the junctions of the lamellae
b. House osteocytes
9. Canaliculi
a. Small canals that connect the lacunae to each other and to the
central canal
b. Allows nutrients to be transmitted between each osteocyte in the
system
10. Circumferential lamellae
a. Located under the periosteum
b. Run around the circumference of the bone shaft
b. Spongy bone
i. Trabeculae looks poorly organized, but actually they follow lines of stress
1. Only a few cell layers thick
2. Contain irregularly arranged lamellae and osteoctyes
3. Connected by canaliculi
4. Nutrients reach the osteocytes by diffusing through the canaliculi from
the marrow spaces
c. Bone Markings
i. Bone commonly has bulges, depressions, holes
ii. Serve as sites for muscle attachment, ligaments & tendons, area of
articulations, conduits for blood vessels and nerves
iii. Names
1. Projections that grow outward from the bone surface
a. Heads
b. Trochanters
c. Spines
d. Condyles
2. Depressions and openings
a. Fossae
b. Sinuses
c. Foramina
d. Grooves
Bone Development
a. Osteogenesis & ossification
i. The process of bone formation
b. Formation of bony skeleton
c. Bone Growth