The Skeleton
0 The skeletal system supports the body, protects
internal organs, provides for movement, stores
mineral reserves, and provides a site for blood cell
formation.
0 206 bones in the human body
0 Divided into 2 subgroups
0 Axial – skull, vertebral column, and rib cage
0 Appendicular – arms, legs, pelvis, shoulders
Structure of Bones
0 Bones – solid network of living cells and protein fibers
that are surrounded by calcium salts
0 Periosteum – tough layer of connective tissue
surrounding the bone
0 Blood vessels pass through this region carrying
oxygen and nutrients to the bone
0 Below Periosteum is compact bone
0 Running through this compact bone are Haversian
Canals which contain blood vessels and nerves
0 Spongy bone is found inside compact bone
0 Lattice work in spongy bone gives the bone
strength
Bones Cont.
0 Bones are composed of bone cells called osteocytes –
mature bone cells
0 2 other types of bone cells:
0 Osteoclasts – break down bone
0 Osteoblasts – produce bone
0 Bones are continually remodeled through the
work of these two cells
Bones Cont.
0 Deep within bone is a soft tissue called bone marrow
0 2 types of bone marrow
0 Yellow – made up of fat cells
0 Red – produces red blood cells, white blood cells,
cell fragments, and platelets.
Development of Bones
0 The skeleton of an embryo is primarily cartilage.
Cartilage is made of protein fibers including collagen
and elastin
0 Cartilage contains no blood vessels
0 Cartilage is replaced by bone during ossification.
0 Occurs 7 months before birth
0 Bone tissue forms as osteoblasts secrete mineral
deposits replacing cartilage
0 When osteoblasts are surrounded by connective
tissue, they become osteocytes.
Cont. Bone Formation
0 Many long bones have growth plates at each end
0 Growth of cartilage at these locations cause bones to
lengthen and cartilage eventually is turned into
ossified bone and the bone stops growing. (usually in
adolescence/adulthood)
0 Cartilage is found in adults in the following places:
0
0
0
0
Nose
Ears
Ribs
Some joints
Types of Joints
0 Joint – place where one bone attaches to another
0 Depending on its type of movement, joints are
classified as immovable, slightly moveable, or freely
moveable.
3 Types of Joints
0 Immovable
0 Called fixed joints – held together by connective tissue
0 Where bones in the skull meet
0 Slightly Moveable
0 These bones are separated from each other
0 Vertebrae, tibia/fibula
0 Freely Moveable
0 Can move in more than one direction
0 Several types of these joints
0 Ball and socket - Shoulder
0 Hinge joints - Knee
0 Pivot joints - elbow
0 Saddle joints - hand
Structure of Joints
0 In freely movable joints, cartilage covers the surfaces
where bones come together
0 This capsule is composed of two layers
0 Ligaments – connective tissue that holds bones together
in a joint
0 Synovial Fluid – enables the surfaces of the joint to slide
over each other smoothly
0 In some joints, small sacs of fluid form called “bursae”
0 Acts as shock absorber and reduces friction
Skeletal System Disorders
0 May be damaged just like any other tissue
0 Excessive strain can result in inflammation
0 Ex: bursitis
0 arthritis
0 Loss of calcium as people age can lead to osteoporosis
0 Weakening of the bone causing fractures