Bone &
Skeletal
Tissue
Chapter 6
Functions of the Skeletal system
1.
2.
3.
4.
5.
Support
Protection
Movement
Mineral storage
Hematopoiesis (blood cell formation)
Skeletal
Cartilages
Cartilages
of the
respiratory
tract
Classification of Bones
• Bone are identified by:
– shape
– internal tissues
– bone markings
Bone Shapes
1.
2.
3.
4.
5.
6.
Long bones
Flat bones
Sutural bones
Irregular bones
Short bones
Sesamoid bones
Long Bones
Figure 6–1a
Long Bones
• Are long and thin
• Are found in arms, legs, hands, feet,
fingers, and toes
Flat
Bones
Figure 6–1b
Flat Bones
• Are thin with parallel surfaces
• Are found in the skull, sternum, ribs, and
scapula
Sutural
Bones
Figure 6–1c
Sutural Bones
• Are small, irregular bones
• Are found between the flat bones of the
skull
Irregular Bones
Figure 6–1d
Irregular Bones
• Have complex shapes
• Examples:
– spinal vertebrae
– pelvic bones
Short
Bones
Figure 6–1e
Short Bones
• Are small and thick
• Examples:
– ankle
– wrist bones
Sesamoid Bones
Figure 6–1f
Sesamoid Bones
• Are small and flat
• Develop inside tendons near joints of
knees, hands, and feet
Bone Markings
• Depressions or grooves:
– along bone surface
• Projections:
– where tendons and ligaments attach
– at articulations with other bones
• Tunnels:
– where blood and nerves enter bone
Bone Markings
Bone Markings
Table 6–1 (2 of 2)
• The femur
Long Bones
Figure 6–2a
Structure
of a long
bone
The Humerus
Long Bones
• Diaphysis:
– the shaft
• Epiphysis:
– wide part at each end
– articulation with other bones
• Metaphysis:
– where diaphysis and epiphysis meet
Flat Bones
• The parietal bone of the skull
Figure 6–2b
Compact Bone Structure
Spongy Bone
Figure 6–6
Spongy Bone Structure
Bone Cells
• Make up only 2% of bone mass:
– osteocytes
– osteoblasts
– osteoprogenitor cells
– osteoclasts
Bone Cells:
Osteoblasts, Osteocytes & Osteoclasts
Periosteum
Figure 6–8a
Endosteum
Figure 6–8b
Bone Development
• Human bones grow until about age 25
• Osteogenesis:
– bone formation
• Ossification:
– the process of replacing other tissues with
bone
Intramembranous Ossification
• Also called dermal ossification:
– because it occurs in the dermis
– produces dermal bones such as mandible and
clavicle
• There are 3 main steps in
intramembranous ossification
Intramembranous
Ossification:
Step 1
Figure 6–11 (Step 1)
Intramembranous
Ossification: Step 1
• Mesenchymal cells aggregate:
– differentiate into osteoblasts
– begin ossification at the ossification center
– develop projections called spicules
Step 2
Intramembranous
Ossification: Step 2
• Blood vessels grow into the area:
– to supply the osteoblasts
• Spicules connect:
– trapping blood vessels inside bone
Step 3
Figure 6–11 (Step 3)
Intramembranous
Ossification: Step 3
• Spongy bone develops and is remodeled
into:
– osteons of compact bone
– periosteum
– or marrow cavities
Endochondral Ossification
• Ossifies bones that originate as hyaline
cartilage
• Most bones originate as hyaline cartilage
Endochondral
Ossification:
Step 1
• Chondrocytes in the
center of hyaline
cartilage:
– enlarge
– form struts and calcify
– die, leaving cavities in
cartilage
Figure 6–9 (Step 1)
Step 2
Endochondral
Ossification: Step 2
• Blood vessels grow around the edges of
the cartilage
• Cells in the perichondrium change to
osteoblasts:
– producing a layer of superficial bone around
the shaft which will continue to grow and
become compact bone (appositional growth)
Step 3
• Blood vessels enter
the cartilage:
– bringing fibroblasts
that become
osteoblasts
– spongy bone
develops at the
primary ossification
center
Step 4
• Remodeling creates a
marrow cavity:
– bone replaces cartilage
at the metaphyses
Step 5
• Capillaries and
osteoblasts enter
the epiphyses:
– creating
secondary
ossification
centers
Step 6
Endochondral
Ossification: Step 6
• Epiphyses fill with spongy bone:
– cartilage within the joint cavity is articulation
cartilage
– cartilage at the metaphysis is epiphyseal
cartilage
Endochondral Ossification
• Appositional growth:
– compact bone thickens and
strengthens long bone with
layers of circumferential
lamellae
PLAY
Endochondral Ossification
Figure 6–9 (Step 2)
Appostional Growth
Blood Supply
of Mature
Bones
• 3 major sets of
blood vessels
develop
Figure 6–12
Blood Vessels of Mature Bones
• Nutrient artery and vein:
– a single pair of large blood vessels
– enter the diaphysis through the nutrient
foramen
– femur has more than 1 pair
• Metaphyseal vessels:
– supply the epiphyseal cartilage
– where bone growth occurs
Blood Vessels of Mature Bones
• Periosteal vessels provide:
– blood to superficial osteons
– secondary ossification centers
Mature Bones
• As long bone matures:
– osteoclasts enlarge marrow cavity
– osteons form around blood vessels in
compact bone
Effects of Exercise on Bone
• Mineral recycling allows bones to adapt to
stress
• Heavily stressed bones become thicker
and stronger
Bone Degeneration
• Bone degenerates quickly
• Up to 1/3 of bone mass can be lost in a
few weeks of inactivity
Wolff’s Law
Tension and compression
cycles create a small
electrical potential that
stimulates bone deposition
and increased density at
points of stress.
Effects of Hormones
and Nutrition on Bone
• Normal bone growth and maintenance
requires nutritional and hormonal factors
Minerals
• A dietary source of calcium and phosphate
salts:
– plus small amounts of magnesium, fluoride,
iron, and manganese
Calcitriol
• The hormone calcitriol:
– is made in the kidneys
– helps absorb calcium and phosphorus from
digestive tract
– synthesis requires vitamin D3 (cholecalciferol)
Vitamins
• Vitamin C is required for collagen
synthesis, and stimulates osteoblast
differentiation
• Vitamin A stimulates osteoblast activity
• Vitamins K and B12 help synthesize bone
proteins
Other Hormones
• Growth hormone and thyroxine stimulate
bone growth
• Estrogens and androgens stimulate
osteoblasts
• Calcitonin and parathyroid hormone
regulate calcium and phosphate levels
Hormones for Bone Growth
and Maintenance
Chemical Composition of Bone
Figure 6–13
Bone
homeostasis
Calcitonin and Parathyroid
Hormone Control
• Bones:
– where calcium is stored
• Digestive tract:
– where calcium is absorbed
• Kidneys:
– where calcium is excreted
Parathyroid Hormone (PTH)
• Produced by parathyroid glands in neck
• Increases calcium ion levels by:
– stimulating osteoclasts
– increasing intestinal absorption of calcium
– decreases calcium excretion at kidneys
Parathyroid Hormone (PTH)
Figure 6–14a
Calcitonin
Figure 6–14b
Calcitonin
• Secreted by C cells (parafollicular cells) in
thyroid
• Decreases calcium ion levels by:
– inhibiting osteoclast activity
– increasing calcium excretion at kidneys
A misleading view of bone
homeostasis
Calcitonin does not play a central role
in maintaining blood plasma Ca++
levels in adults.
It is important to maintaining bone
density, though.
Fracture
Repair:
Step 1
Figure 6–15 (Step 1)
Fracture Repair: Step 1
• Bleeding:
– produces a clot (fracture hematoma)
– establishes a fibrous network
• Bone cells in the area die
Fracture
Repair: Step 2
Figure 6–15 (Step 2)
Fracture Repair: Step 2
• Cells of the endosteum and periosteum:
– Divide and migrate into fracture zone
• Calluses stabilize the break:
– external callus of cartilage and bone
surrounds break
– internal callus develops in marrow cavity
Fracture Repair:
Step 3
Figure 6–15 (Step 3)
Fracture Repair: Step 3
• Osteoblasts:
– replace central cartilage of external callus
with spongy bone
Fracture
Repair:
Step 4
Figure 6–15 (Step 4)
Fracture Repair: Step 4
• Osteoblasts and osteocytes remodel the
fracture for up to a year:
– reducing bone calluses
Common
fracture types
The Major Types of Fractures
• Pott’s fracture
Figure 6–16 (1 of 9)
• Comminuted fractures
• Transverse fractures
Figure 6–16 (3 of 9)
• Spiral fractures
Figure 6–16 (4 of 9)
• Displaced fractures
Figure 6–16 (5 of 9)
• Colles’ fracture
Figure 6–16 (6 of 9)
• Greenstick fracture
Figure 6–16 (7 of 9)
• Epiphyseal fractures
• Compression
fractures
Figure 6–16 (9 of 9)
Depression fracture of the skull
Age and Bones
• Bones become thinner and weaker with age
• Osteopenia begins between ages 30 and 40
• Women lose 8% of bone mass per decade,
men 3%
Effects of Bone Loss
• The epiphyses, vertebrae, and jaws are
most affected:
– resulting in fragile limbs
– reduction in height
– tooth loss
Osteoporosis
• Severe bone loss
• Affects normal function
• Over age 45, occurs in:
– 29% of women
– 18% of men
Hormones and Bone Loss
• Estrogens and androgens help maintain
bone mass
• Bone loss in women accelerates after
menopause
Cancer and Bone Loss
• Cancerous tissues release osteoclastactivating factor:
– that stimulates osteoclasts
– and produces severe osteoporosis
Some
decorative
arrangements
I dare not
Jim!