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Chapter 4-9

ANAT100 Chapter 4-9: Module02: Skeletal systems


Department
Anatomy and Cell Biology
Course Code
ANAT 100
Professor
Leslie W Mac Kenzie
Chapter
4-9

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Module 2: Skeletal System 2.1 Cartilage and Bone
Cartilage (supportive connective tissue)
Cartilage is an important structural component of the body. It is a firm tissue but is softer and much more
flexible than bone. Cartilage is a connective tissue found in many areas of the body including: Joints
between bones e.g. the elbows, knees and ankles, Ends of the ribs, between the vertebrae in the spine, ears
and nose, bronchial tubes or airways.
Unique connective tissue
Cells, fibers, ground substance
Ground substance is like a firm gel that makes cartilage solid but flexible cells called
chondrocytes are located throughout the intercellular substance in small spaces called lacunae,
which contain one or more cells
Functions
1. supports soft tissue
2. provides gliding surface at articulations, where two bones meet
3. (provide model for formation of most bones in the body)
Cartilage is categorized into three types:
1. Hyaline: This is a low-friction, wear-resistant tissue present within joints that is designed to bear
and distribute weight. It is a strong, rubbery, flexible tissue but has a poor regenerative capacity
2. Fibrous: Fibrous cartilage is a tough and inflexible form of cartilage found in the knee and
between vertebrae
3. Elastic: Elastic cartilage is more flexible than hyaline cartilage and is present in the ear, larynx
and epiglottis
Histology of Hyaline Cartilage:
Cells, fibers (not easily seen), ground substance
Most common cartilage
Strong, flexible and found at the joint surface of moveable joints, walls of the nose, larynx,
trachea, bronchi (upper respiratory tract), anterior end of ribs, and forms the skeleton in early life
Avascular
Perichondrium (dense irregular connective tissue):
Cellular and fibrous layer
Histology of Fibrous Cartilage:
Lots of collagen fibers
Little ground substance
Appears very similar to dense connective tissue with
Scattered rows of lacunae containing chondrocytes
Very tough, resistant to compression, durable
No perichondrium
Found in intervertebral discs, symphysis pubis, some joints and tendons
Histology of Elastic Cartilage:
Presence of elastic fibers that are easily seen
Flexible
Found in external ear, eustachian tubes, epiglottis, larynx
Perichondrium

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Appears similar to hyaline cartilage
Bone (supportive connective tissue):
Bone has many functions which include support, locomotion, protection, blood cells production and
mineral metabolism. Each bone is composed of two layers: the outer layer is made up of compact bone
which is hard and strong; the inner layer of bone is made up of spongy bone. Inside the bone is a cavity
called the marrow or medullary cavity that contains the blood forming tissue.
Functions:
1. Support: provides framework that supports and anchors all soft organs. Leg bones act as pillars to
support the body trunk, and the ribs support the thorax wall.
2. Protection: skull and vertebrae surround soft tissue of the nervous system, and the rib cage
protects vital thoracic organs.
3. Movement: skeletal muscles use the bones as levers to move the body.
4. Storage: fat stored in the interior of the bones. Bone matrix serves as a storehouse for various
minerals.
5. Blood Cell Formation: hematopoiesis occurs within the marrow cavities of the bones.
Bone is composed of Organic (40% dry weight) and Inorganic (60% dry weight) components:
Organic Components:
Cells, fibers, ground
Inorganic Components
Mineralized salts
Hydroxyapatite (calcium phosphate, calcium
hydroxide)
Calcium carbonate, sodium, magnesium, fluoride
Microscopic structure:
Osteon (Haversian System): basic structural
unit of bone
Lamella: concentric rings of bone, encircle a
central canal = Haversian canal
Lacunae: house bone cells
Canaliculi: small passageway through which
osteocytes communicate
Osteocyte: bone cell
Haversian canal: canal through which blood
vessels and nerves pass through
Volkman’s canal (perforating canal):
interconnect Haversian canals w/periosteum
(perpendicular to main canals)
Interstitial lamellae: one of the lamellae of
partially resorbed osteons occurring between
newer, complete osteons
Cement lines: boundary of an osteon
Macroscopic structure:

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Forms:
Compact bone: appears solid (actually perforated), forms hard outer shell
Spongy bone: inside bone, contains spaces - bone connective tissue forms latticework structure
-> strong and lightweight
Types:
Long: greater length than width, most common; occur in upper and lower limb
Short: length nearly equal to width, external surfaces covered by compact bone, inside = spongy;
ex: carpals, tarsals
Flat: flat thin surfaces, parallel surface of compact bone with layer of spongy bone, provide
extensive surface for muscle attachment; ex: sternum, scapulae (shoulder blades), ribs
Irregular: elaborate complex shapes, do not fit into any preceding categories; ex: vertebrae, ossa
coxae (hip bones)
Structure:
1. Long Bone:
Diaphysis: shaft
Epiphysis: knobby end region
Epiphyseal line: mature bone = between dia and epi-physis, growing bone = contains hyaline
cartilage to provide continued lengthwise growth
Articular cartilage: thin layer of hyaline cartilage covering epiphysis at a joint surface
Medullary or marrow cavity: hollow cylindrical space w/in diaphysis
Endosteum: layer of cells that covers all internal surfaces
Periosteum: covers outer surface of bone
2. Short, Flat, Irregular Bones:
Sandwich of spongy bone
Bone cells: There are two categories of bone cells. Osteoclasts are in the first category. They resorb
(dissolve) the bone. The other category is the osteoblast family, which consists of osteoblasts that form
bone, osteocytes that help maintain bone, and lining cells that cover the surface of the bone.
Osteoprogenitor: osteoblast stem cells
Osteoblast: secrete semisolid organic form of bone matrix = osteoid
later calcifies and hardens w/ Ca deposition
produce new bone
once entrapped differentiate into osteocytes
Osteocyte: mature bone cells, reside in lacunae, maintain bone matrix and detect mechanical
stress on a bone -> communicate this to osteoblasts
Osteoclast: involved in bone resorption - dissolve matrix releasing stored calcium and
phosphate
osteolysis: HCl: dissolves mineral parts of matrix AND enzymes: dissolve organic part of
matrix
large multinuclear phagocytic cells, ruffled border where in contact w/ bone
Bone Markings
distinctive bone markings characterize each bone in the body
projections from bone surface mark point where tendons and ligaments attach
sites of articulation between adjacent bones are smooth and flat
depressions, grooves, and tunnels through bones indicate sites where blood vessels and
nerves either lie alongside or penetrate the bone
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