Bones and Skeletal
Tissues
Chapter 6-8
Skeletal Cartilages
• Initially, skeleton composed of cartilage and
fibrous membranes
• Most are then replaced by bone in the adult
skeleton
• Some places where flexibility is needed, remain
cartilage
Basic Structure, Types, and Locations
• Skeletal Cartilage – made of some variety of
cartilage tissue (mostly water)
• The water lets cartilage spring back to shape
• Perichondrium (a dense connective membrane)
surrounds blood vessels and nerves
Basic Structure, Types, and Locations
• Three types of Cartilage: hyaline, elastic, and
fibrocartilage (remember chapter 4?)
Basic Structure, Types, and Locations
• Hyaline Cartilages
• Articular – bone ends, movable ends
• Costal – connect ribs to the sternum
• Laryngeal – for the skeleton of the larynx
• Tracheal and bronchial – reinforce other passageways
of the respiratory system
• Nasal – support the external nose
Basic Structure, Types, and Locations
• Elastic Cartilages
• Looks similar to hyaline (ref. ch. 4)
• More stretchy elastic fibers – better for bending
• Supports external ear
• Forms epiglottis
Basic Structure, Types, and Locations
• Fibrocartilages
• Parallel rows of chondrocytes and thick collagen fibers
• Compressible
• High tensile strength
• Places subjected to heavy pressure and stretch
• Pad-like cartilages (menisci) of the knee
• Discs between vertebrae
Growth of Cartilage
• Two growth patterns:
• Appositional Growth – cartilage-forming cells in
perichondrium around matrix secrete new matrix
against external face of existing cartilage
• Interstitial growth – the lacunae bound chondrocytes
inside the cartilage divide and secrete new matrix
expanding from within
Functions of Bones
• 1. Support – hard framework that supports the
body and cradles soft organs
• 2. Protection – fused bones of skull enclose brain
(vertebrae surround spinal cord)
• 3. Movement – used as levers for skeletal muscles
attached by tendons
Functions of Bones
• 4. Mineral Storage – reservoir for minerals such as
calcium and phosphate
• 5. Blood Cell Formation – hematopoiesis
(formation of blood cells)
Classification of Bones
• Compact Bone – dense outer layer; appears
smooth and solid
• Spongy Bone – honeycomb of small needle-like of
flat pieces called trabeculae
Classification of Bones
• Bone Shape:
• 1. Long Bones:
• Longer than they are wide
• Shaft and two ends
• Mostly compact bone with some spongy bone
• All bones of limbs
Classification of Bones
• Bone Shape:
• 2. Short Bones:
• Roughly cube-like
• Mostly spongy bone; compact bone only forms thin
outer layer
• Bones of wrist and ankle
• Sesamoid bones – short bone embedded within tendon
- patella
Classification of Bones
• Bone Shape:
• 3. Flat Bones
• Thin, flat, and usually curved
• Two compact bone surfaces with spongy between
• Sternum, ribs, most skull bones
Classification of Bones
• Bone Shape:
• 4. Irregular Bones
• Complex shapes and mainly spongy bone
• Don’t fit the previous three categories
• Vertebrae, hip bones
Bone Structure
• Bones are organs and consist of a variety of
tissues
• Osseous tissue (the most common)
• Nervous tissue
• Articular cartilages
• Fibrous connective tissue
• Muscle and epithelial tissue in their blood vessels
Structure of Typical Long Bone
• Diaphysis – long part of compact bone that
surrounds the medullary cavity (yellow bone
marrow cavity in adults)
• Epiphyses – ends of the bones; covered in
articular cartilage; also has epiphyseal line (from
before birth)
Structure of Typical Long Bone
• Membranes – bones are covered in shiny white
membrane called periosteum composed of dense
irregular tissue
• Inner layer: osteogenic layer made of osteoblasts
(bone forming) osteoclasts (bone destroying)
Structure of Typical Long Bone
• Nutrient foramen richly vascularized; supplies
nutrients
• Sharpey’s fibers – tufts of collagen fibers that
extend from the fibrous layer; provides anchoring
points for tendons
• Endosteum – delicate connective tissue; covers
trabeculae of spongy bone in marrow cavities
• Fig. 6.3
Structure of Short, Irregular, and Flat Bones
• Thin plates of periosteum-covered compact bone
• Endosteum-covered spongy bone within
• Diploë – internal layer of spongy bone
• Fig. 6.4
Location of Hematopoietic Tissue in Bones
• Hematopoietic tissue – red marrow
• Red marrow cavities – cavities of spongy bone in
long bones and diploë of flat bones
• Sites of red marrow: diploë of flat bones
(sternum), some irregular (hip bone), long bones
(femur and humerus)
Microscopic Structure of Bone
• Compact Bone
• Appears very dense
• Has many tunnels and passageways filled with blood
vessels and nerves
• Osteon (or Haversian system) – structural part of bone
• Osteons are like pillars bearing weight
Compact Bone
• Lamella – matrix of tubes
• Compact bone called lamellar bone
• Central (Haversian) canal – runs through the core
of each osteon
• Perforating (Volkmann’s) canals – second type of
canals at right angles to long axis of bones;
connects vascular and nerve supplies
Compact Bone
• Osteocytes occupy small cavities – lacunae
• Canaliculi – hair-like canals that connect lacunae
to each other and to the central canal
• Osteoblasts secrete bone forming material into
matrix trapping cells as it hardens
Compact Bone
• Interstitial lamellae – fill gaps between osteons
• Circumferential lamellae – just deep of the
periosteum and extend around the circumference
of the shaft
• Resist twisting
Spongy Bone
• Consists of trabeculae
• Form along lines of stress and not randomly to
strengthen bone
• No osteons
• Few cell layers thick
• Irregular lamellae and osteocytes
Chemical Composition of Bone
• Organic components :
• Cells: osteoblasts, osteocytes, and osteoclasts osteoid
• Osteoid – proteoglycans, glycoproteins, and collagen
fibers
• Inorganic components:
• 65% of mass, made of hydroxyapatites (mineral salts)
• Hydroxyapatites – calcium phosphates (makes bone
hard)
Bone Markings
• Bones are rarely smooth on outside
• Display bulges, depressions, and holes
• Serve as sites for muscles, ligaments, and tendons to
attach
• Or for blood vessels and nerves to enter
Bone Markings
• Projections – spines, trochanters
• Depressions – openings, fossae, sinuses,
foramina, and grooves
• See Table 6.1
Bone Development (Osteogenesis)
• Osteogenesis (ossification) – process of bone
formation
• Formation of the skeleton, bone growth, or
remodeling
Formation of the Bony Skeleton
• Membrane bone – intramembranous ossification
• Bone formation that occurs by replacing hyaline
cartilage structure is called endochondral
ossification
• Resulting bone is cartilage (endochondral) bone
Intramembranous Ossification
• Produces all flat bones
• 1. Formation of ossification center in fibrous
membrane
• 2. Formation of bone matrix within the fibrous
membrane
• 3. Formation of woven bone and the periosteum
• 4. Formation of compact bone plates and red
marrow
-See Fig. 6.7
Endochondral Ossification
• Most bones of the skeleton formed by this process
• Late in second month of development
• Hyaline cartilage as model, later replaced by
bone
Endochondral Ossification
• 1. A bone collar forms around the diaphysis of the
hyaline cartilage model
• 2. Cartilage in the center of the diaphysis
calcifies
• 3. The periosteal bud invades the internal cavities
and spongy bone forms
• 4. the medullary cavity forms
• 5. the epiphyses ossify
-See Fig. 6.8
Postnatal Bone Growth
• Most bones stop growing during adolescence or
early adulthood
• Some facial bones (nose and jaw continue)
Growth in Length of Long Bones
• Mimics many of the events of endochondral
ossification
• Causes bone to lengthen
• Hormones also regulate bone growth
• See Fig. 6.9 and Fig. 6.10
Bone Homeostasis: Remodeling and Repair
• Architecture is constantly changing
• 5-7% of bone mass is recycled
• At least half a gram of calcium is entering and
leaving bones each day
Bone Remodeling
• Bone deposit and bone resorption occur
• Remodeling units - “packets” of osteoblasts and
osteoclasts
• Occurs at different rates if various bones
• Bone deposit – when bone is injured or added
bone strength is required
Bone Remodeling
• New matrix deposit occurs at an osteoid seam
• Controlled by osteoblasts
• Calcium salts are crystalized here
• Alkaline phosphatase is essential for
mineralization
• These are contained in matrix vesicles which
carry the phosphates
Bone Remodeling
• Bone resorption
• Accomplished by osteoclasts
• Giant multinucleate cells that are believed to arise
from hematopoietic stem cells
• Osteoclasts secrete…
• 1. lysosomal enzymes
• 2. metabolic acids
Control of Remodeling: Hormonal Mechanism
• Reflected by the interaction of parathyroid
hormone (PTH) and calcitonin
• Released when blood levels of ionic calcium
decline
• Human body contains 1200-1400g of calcium – 99%
in bones
Control of Remodeling
• Ca2+ is needed for a wide variety of physiological
processes
• Nerve impulses
• Muscle contraction
• Blood coagulation
• Secretion by glands and neurons
• Cell division
Mechanical Stress
• Wolff’s law – (not universally accepted) says that
bones remodel or strengthen in response to
where stress or force is acting upon it
• Bone anatomy reflects the common stresses it
encounters
Mechanical Stess
• 1. long bones are thickest midway along the shaft
(where bending stress is greatest)
• 2. Curved bones are thickest where they are most
likely to buckle
• 3. trabeculae of spongy bone forms trusses or struts
along compression
• 4. large, bony projections occur where heavy active
muscles attach
Mechanical Stress
• Electrical impulses are created as bones grow
• It is suggested that as stress occurs, electrical
signals direct the remodeling process