Download Skeletal System: Bones and Bone Tissue

Chapter 6
Skeletal System:
Bones and Bone Tissue
6-1
Skeletal System
• Consists of bones, cartilage,
tendons, ligaments
• Functions:
–
–
–
–
–
Support
Protection
Movement
Storage
Blood cell production
6-2
Hyaline Cartilage
•Most bones develop from it
• Chondroblasts produce
matrix; become
chondrocytes
• Matrix contains collagen
fibers (strength) and
proteoglycans (trap water)
• Contains no blood vessels
or nerves
• Perichondrium
– Dense connective tissue
membrane that surrounds
cartilage
Cartilage most intimately associated with bone
6-3
Hyaline Cartilage (cont’d)
• Articular Cartilage:
thin layer of hyaline cartilage
covering ends of bones at moveable joints
•Has no perichondrium, no blood vessels, no nerves
•Growth:
•Appositional: chondroblasts in perichondrium
secrete new matrix; add new chondrocytes to
outside of tissue
•Interstitial: chondrocytes within cartilage divide;
add more matrix from inside existing cartilage
6-4
Bone Shapes
• Long
– Upper and lower limbs
• Short
– Carpals and tarsals
• Flat
– Ribs, sternum, skull,
scapulae
• Irregular
– Vertebrae, facial, hip
6-5
Long Bone Structure
• Diaphysis
– Shaft
– Compact bone
• Epiphysis
– End of the bone
– Cancellous bone
• Epiphyseal plate
– Hyaline cartilage
– Bone growth in length
• Epiphyseal line
– When bone stops
growing in length,
becomes ossified
6-6
Long Bone Structure
• Medullary cavity
– Red marrow: site of
blood cell formation
– Yellow marrow:
adipose tissue
• Periosteum
– Glistening, white outer
surface of bone
– Bone growth in
diameter
• Endosteum
– Lines bone cavities
6-7
6-8
6-9
Flat, Short, Irregular Bones
• Flat Bones
– No diaphyses, epiphyses
– Outer covering of
compact bone that
surrounds cancellous
bone
• Short and Irregular Bone
– Compact bone that
surrounds cancellous
bone center
– No diaphyses and not
elongated
6-10
Bone Histology
• Bone matrix
– Organic: Collagen (flexibility) and proteoglycans (traps water)
– Inorganic: Hydroxapatite: calcium phosphate (compression)
• Bone cells
– Osteoblasts-produce collagen and proteoglycans in matrix
» Bone-forming cells (ossification or osteogenesis)
– Osteocytes- mature cells
» Produce substances needed to maintain bone matrix
– Osteoclasts-responsible for resorption (breakdown) of bone
– Stem cells or osteochondral progenitor cells: become osteoblasts or
chondroblasts
• Woven bone: Collagen fibers randomly oriented
• Lamellar bone: Mature bone in thin layers, called lamellae
• Cancellous(spongy) bone: Trabeculae
• Compact bone: Denser: fewer spaces than cancellous bone
6-11
Bone Matrix
•Mineral gives weight-bearing
strength
•Collagen gives
flexible strength
6-12
Bone Cells
• Osteoblasts
– Formation of bone
through ossification or
osteogenesis
• Osteocytes
– Mature bone cells
– Lacunae: Spaces
– Canaliculi: Cell
processes
• Osteoclasts
– Responsible for bone
resorption (breakdown)
6-13
Woven and Lamellar Bone
• Woven bone
– Collagen fibers randomly oriented in many direction
– Formed:
• During fetal development
• During fracture repair
• Remodeling
– Removing old bone (osteoclasts) and adding new
(osteoblasts)
• Lamellar bone
– Mature bone in sheets called lamellae
6-14
Cancellous Bone
•Consists of trabeculae: interconnecting rods or plates of bone;
spaces filled with bone marrow, blood vessels
•Oriented along lines of stress; provide structural strength
6-15
Compact Bone
•Blood vessels enter bone
itself
•Lamellae oriented around
blood vessels
• Central or haversian canals: Parallel to long axis
• Lamellae: Concentric, circumferential, interstitial
• Osteon or haversian system: Central canal, contents, associated
concentric lamellae and osteocytes
• Perforating or Volkmann’s canal: Perpendicular to long axis
6-16
Bone Development
• Intramembranous ossification
– Takes place in connective tissue membrane
– Some skull bones, part of mandible, diaphysis of
clavicles
– Begins at 8 weeks, ends at 2 years
• Endochondral ossification
– Takes place in cartilage
– Most bones develop from cartilage
– Begins at 8 weeks; some begins at 18-20 years
• Both methods of ossification
– Produce woven bone that is remodeled
– After remodeling, formation cannot be distinguished as
one or other
6-17
Intramembranous Ossification
6-18
Endochondral Ossification
6-19
Endochondral Ossification
6-20
Endochondral Ossification
6-21
6-22
Growth in Bone Length
• Appositional growth
– New bone on old bone
or cartilage surface
• Epiphyseal plate zones
–
–
–
–
Resting cartilage
Proliferation
Hypertrophy
Calcification
6-23
Growth in Bone Length
•Epiphyseal plate closure occurs between 12 and 25 years of age
6-24
Growth in Bone Width
6-25
Factors Affecting Bone Growth
• Nutrition
– Vitamin D
• Necessary for absorption of calcium from intestines
• Insufficient causes rickets and osteomalacia
– Vitamin C
• Necessary for collagen synthesis by osteoblasts
• Deficiency results in scurvy
• Hormones
– Growth hormone from anterior pituitary
– Thyroid hormone required for growth of all tissues
– Sex hormones as estrogen and testosterone
• Females stop growing earlier than males: estrogen causes
quicker closure of epiphyseal plate than testosterone
6-26
Bone Remodeling
• Converts woven bone into lamellar bone
• Old bone constantly removed by osteoclasts and new bone formed by
osteoblasts
• Involved in bone growth, changes in bone shape, adjustment of bone to
stress, bone repair, calcium regulation
6-27
Bone Repair
•4 Steps:
6-28
Calcium Homeostasis
• Bone is the major storage site for calcium in
the body
– Calcium moves into bone as osteoblasts build
new bone
– Calcium moves out of bone as osteoclasts break
down bone
• Osteoclast activity increases when blood calcium
levels are too low; decreases when blood calcium
too high
– When osteoclast and osteoblast activity is
balanced, the movement of calcium in and out
is equal
6-29
Calcium Homeostasis Cont’d
• Parathyroid hormone (PTH) from
parathyroid glands is the major regulator of
blood calcium levels
• PTH increases blood calcium levels by:
– Increasing bone breakdown (increased numbers of
osteoclasts)
– Increasing calcium absorption from small intestine (by
promoting formation of Vitamin D)
– Reabsorption of calcium from urine
• Tumors that secrete large amounts of PTH cause so much
bone breakdown that bones become weak and fracture
easily
• Calcitonin from thyroid gland decreases blood calcium by
decreasing bone breakdown (decreasing osteoclast activity)
6-30
Calcium Homeostasis
6-31
Effects of Aging on
Skeletal System
• Bone Matrix decreases (less collagen; matrix
formation by osteoblasts slower than matrix breakdown by
osteoclasts) and
becomes more brittle
• Bone Mass decreases (after age 35)
• Increased bone fractures
• Bone loss causes deformity, loss of height,
pain, stiffness
– Stooped posture
– Loss of teeth
6-32
Bone Fractures
6-33