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The Skeletal System
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Things to Know: Oste “bone” Art “joint” -blast “germ” or embryonic
-clast “broken” -cyte “cell” Peri- “around” Dia- “between or across” Epi- “upon” Hemat- “blood”
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The Skeletal System Parts of the skeletal system Bones (skeleton)
Joints Cartilages Ligaments Two subdivisions of the skeleton Axial skeleton Appendicular skeleton
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Functions of Bones Support the body Protect soft organs
Allow movement due to attached skeletal muscles Store minerals and fats Blood cell formation
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Support the body (internal framework) Protect soft organs (vertebrae)
Functions of Bones Support the body (internal framework) Protect soft organs (vertebrae) L Allow movement due to attached skeletal muscles Store minerals and fats (fats, clacium, phosphorus) Hematopoiesis (Blood cell formation)
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Bones of the Human Body The adult skeleton has 206 bones
Two basic types of bone tissue Compact bone Homogeneous Spongy bone Small needle-like pieces of bone Many open spaces Figure 5.2b
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Classification of Bones on the Basis of Shape
Figure 5.1
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Classification of Bones
Long bones Typically longer than they are wide Have a shaft with heads at both ends Contain mostly compact bone Example: Femur Humerus
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Classification of Bones
Figure 5.1a
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Classification of Bones by Shape
Long bones Have a shaft with heads at both ends Typically longer than they are wide Contain mostly compact bone Examples: Femur (longest bone in the body) Head Shaft Head Figure 5.1a
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Classification of Bones
Short bones Generally cube-shape Contain mostly spongy bone Example: Carpals Tarsals
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Classification of Bones
Figure 5.1b
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Classification of Bones
Flat bones Thin, flattened, and usually curved Two thin layers of compact bone surround a layer of spongy bone Example: Skull Ribs Sternum
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Classification of Bones
Figure 5.1c
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Classification of Bones
Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae Hip bones
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Classification of Bones
Figure 5.1d
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Anatomy of a Long Bone Diaphysis Shaft Composed of compact bone
Protected by periosteum (membrane) Epiphysis Ends of the bone Thin layer of compact bone But mainly spongy bone in the middle Protected by articular cartilage
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Anatomy of a Long Bone Figure 5.2a
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Anatomy of a Long Bone Periosteum Outside covering of the diaphysis
Fibrous connective tissue membrane Sharpey’s fibers Secure periosteum to underlying bone Arteries Supply bone cells with nutrients
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Anatomy of a Long Bone Figure 5.2c
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Anatomy of a Long Bone Articular cartilage
Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces
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Anatomy of a Long Bone Epiphyseal plate
Flat plate of hyaline cartilage seen in young, growing bone Epiphyseal line Remnant of the epiphyseal plate Seen in adult bones
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Anatomy of a Long Bone Figure 5.2a
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Anatomy of a Long Bone Medullary cavity Cavity inside of the shaft
Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation) in infants
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Anatomy of a Long Bone Medullary cavity Cavity inside of the diaphysis
Contains yellow marrow (mostly adipose) in adults Contains red marrow (for blood cell formation) in infants
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Anatomy of a Long Bone Figure 5.2a
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Bone Markings Surface features of bones
Sites of attachments for muscles, tendons, and ligaments Passages for nerves and blood vessels Categories of bone markings Projections or processes—grow out from the bone surface Depressions or cavities—indentations
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Bone Markings Table 5.1 (1 of 2)
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Bone Markings Table 5.1 (2 of 2)
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Microscopic Anatomy of Bone
Osteon (Haversian system) A unit of bone containing central canal and matrix rings Central (Haversian) canal Opening in the center of an osteon Carries blood vessels and nerves Perforating (Volkman’s) canal Canal perpendicular to the central canal
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Microscopic Anatomy of Bone
Figure 5.3a
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Microscopic Anatomy of Bone
Lacunae Cavities containing bone cells (osteocytes) Arranged in concentric rings Lamellae Rings around the central canal Sites of lacunae
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Microscopic Anatomy of Bone
Figure 5.3b–c
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Microscopic Anatomy of Bone
Canaliculi Tiny canals Radiate from the central canal to lacunae Form a transport system connecting all bone cells to a nutrient supply
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Microscopic Anatomy of Bone
Figure 5.3b
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Formation of the Human Skeleton
In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints
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Bone Growth (Ossification)
Epiphyseal plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Enclosed cartilage is digested away, opening up a medullary cavity Bone replaces cartilage through the action of osteoblasts
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Bone Growth (Ossification)
Bones are remodeled and lengthened until growth stops Bones are remodeled in response to two factors Blood calcium levels Pull of gravity and muscles on the skeleton Bones grow in width (called appositional growth)
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Long Bone Formation and Growth
Bone starting to replace cartilage Epiphyseal plate cartilage Articular cartilage Spongy bone In a child In a fetus In an embryo New bone forming Growth in bone width Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a
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Long Bone Formation and Growth
Bone starting to replace cartilage In an embryo Bone collar Hyaline cartilage model (a) Figure 5.4a, step 1
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Long Bone Formation and Growth
Bone starting to replace cartilage In a fetus In an embryo Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a, step 2
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Long Bone Formation and Growth
Bone starting to replace cartilage Epiphyseal plate cartilage Articular cartilage Spongy bone In a child In a fetus In an embryo New bone forming Growth in bone width Growth in bone length Blood vessels Hyaline cartilage New center of bone growth Medullary cavity Bone collar Hyaline cartilage model (a) Figure 5.4a, step 3
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Long Bone Formation and Growth
Figure 5.4b
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Types of Bone Cells Osteocytes—mature bone cells
Osteoblasts—bone-forming cells Osteoclasts—bone-destroying cells Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone Bone remodeling is performed by both osteoblasts and osteoclasts
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