CH5

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