ch5
TRANSCRIPT
The Skeletal System
Chapter Five
Classifications of Bones
• Two basic types of bone (osseous) tissue– Compact bone
• Dense• Smooth• Homogenous
– Spongy bone
• Small pieces of
bone• Lots of open space
Four Basic Shapes
• Long bones – Mostly compact bones– Examples:
• Femur • Tibia• Fibula• Humerus• Metacarpal• Radius• Ulna• See p. 125 for locations
Four Basic Shapes
• Short bones – Mostly spongy bones– Examples:
• Calcaneus (heel)• Patella• Carpals• Tarsals • See p. 125 for locations
Four Basic Shapes
• Flat bones – Usually thin and curved– 2 thin layers of compact bone
with spongy bone in the middle– Examples:
• Ribs• Sternum• Skull • See p. 125 - 127 for locations
Four Basic Shapes
• Irregular bones – Bones that don’t fit into any of
the three previous shapes– Examples:
• Vertebrae• Pelvis (hip)• See p.117, 125 - 127 for locations
Structure of a Long Bone
• Diaphysis – Shaft of the bone– Made up of compact
bone in adults
Periosteum
Structure of a Long Bone
• Diaphysis – Covered with periosteum
• Connective tissue membrane• Connected to the bone with
Sharpey’s fibers (p.120)
Sharpey’s fibers
Structure of a Long Bone
• Diaphysis – Inside the shaft is the Medullary
cavity– In Infants
• Blood cells are formed here
(hematopoiesis) • Red marrow found here
Structure of a Long Bone
• Diaphysis – Inside the shaft is the Medullary
cavity– In Adults
• Area to store adipose tissue
• Yellow marrow found here • Around yellow marrow
is a membrane called the
endosteum (see p. 118)
Structure of a Long Bone
• Diaphysis, cross-section
Endosteum
Periosteum
Medullary Cavity
Compact bone
Structure of a Long Bone
• Epiphyses – The ends of the long bones– Thin layer of
compact bone
with spongy
bone inside
Structure of a Long Bone
• Epiphyses – Covered with articular
cartilage• Smooth surface• Decreases friction
– In Adults • Blood cells are formed • Red marrow found here
Structure of a Long Bone
• Epiphyses – Epiphyseal plate
• Flat plate of hyaline
cartilage in young,
growing bone• Causes the lengthwise
growth of a long bone
– Epiphyseal line• Plates will be replaced
by bone after puberty
Microscopic Anatomy
• Osteocytes see p. 120– Mature bone cells
• Lacunae– Tiny cavities in matrix – Osteocytes are inside
• Lamella – concentric circles lacunae are
arranged in. It is formed from layers of calcified matrix (nonliving, structural part of bone).
Microscopic Anatomy
• Central / Haversian canal – longitudinal canal that carries
blood vessels and nerves
• Canaliculi – tiny canals from the central canal
that forma a transportation system to the lacunae
• Perforating / Volkmann’s canals– run perpendicularly to the central
or Haversian canal
Bone Formation, Growth, Remodeling
• Skeleton is made from cartilage and bone
– Embryos, the skeleton is mostly hyaline cartilage
– Young children, the cartilage is being replace by bone
– Adults, cartilage still remains in nose, ears, parts of ribs, joints
• See Figure 5.4 on p. 121
Ossification
• Process of bone formation– First the hyaline cartilage is
covered with bone matrix by osteoblasts (immature, bone-forming cells)• Osteocytes are mature bone cells
– Then, the cartilage is digested away (forming medullary cavity)
Growth
• Appositional growth– increase in diameter as
osteoblasts add bone tissue
Bone Remodeling
• Remodeling is done in responses to changes in:
– Calcium levels in the blood• Too little calcium, parathyroid
hormone is released and then osteoclasts (bone-destroying cells in bone) will break down bone matrix and release calcium into the blood
• Too much calcium, then calcitonin will cause calcium to be deposited into bone matrix
Bone Remodeling
• Remodeling is done in responses to changes in:
– Pull of gravity and muscles on the skeleton• Bedridden or physically inactive
people lose mass and their bones can atrophy
• Astronauts must do special exercises if they are without gravity to counteract atrophy also.
• Bones that are stressed or under tension will have more bony matrix deposits