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The Skeletal System
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Parts of the skeletal system
Bones Joints Ligaments Cartilage Divided into two divisions Axial – longitudinal axis Appendicular – limbs and girdles
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Functions of Bones Support of the body Protection of soft organs
Skull and vertebrae for brain and spinal cord Rib cage for thoracic cavity organs Movement due to attached skeletal muscles Storage of minerals (Ca+ and P) and fats Blood cell formation (hematopoiesis)
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Bones of the Human Body The adult skeleton has 206 bones
Two basic types of bone tissue Compact Bone – dense, looks smooth and homogenous - Spongy Bone – needlelike pieces of bone and open space Spongy bone Compact bone Figure 5.2b
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Classification of Bones on the Basis of Shape
Bones are classified as: Long Short Flat Irregular Figure 5.1
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Classification of Bones on the Basis of Shape
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Classification of Bones
Long bones – longer than they are wide Usually shaft w/head at ends Limb bones except wrist and ankle Mostly compound bone Example: Humerus Short bones – cube shaped Mostly spongy bone Wrist and ankle Sesamoid bones are a type of short bone which form within tendons (patella)
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Classification of Bones
Flat bones – Thin, flat and usually curved 2 thin layers of flat compound bone sandwiching spongy bone Ex. Skull, ribs and sternum Irregular bones – miscellaneous Vertebrae, hip bones
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Gross Anatomy of a Long Bone
Articular cartilage Diaphysis – shaft of bone Compact bone Covered by connective tissue called periosteum Epiphysis – ends of bone Compact bone surrounding spongy bone center Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis Figure 5.2a (a
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Structures of a Long Bone
Periosteum – connective tissue covering diaphysis Sharpey’s fibers (perforating fibers)- hold periosteum to the bone Arteries – provide nutrients to bone cells and remove wastes Figure 5.2c
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Structures of a Long Bone
Articular cartilage Articular cartilage – covers the epiphyses made of hyaline cartilage Reduces friction at joints Medullary cavity (yellow marrow) Adults – a storage area for adipose Infants have red bone marrow here ** Red bone marrow in adults is in spongy bone of flat bones and epiphyses of some long bones (pelvis, femur, etc.) Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis Figure 5.2a Figure 5.2a
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Anatomy of a Long Bone Epiphyseal plate Epiphyseal line
Articular cartilage 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 Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Distal epiphysis (a)
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Changes in the Human Skeleton
In embryos, the skeleton is primarily hyaline cartilage In a fetus the cartilage is covered over with bone and the cartilage is digested, forming the medullary cavity During development, much of this cartilage is replaced by bone - ossification Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints
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Long Bone Formation and Growth
Figure 5.4a
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Bone Growth (Ossification)
Epiphyseal plates allow for growth of long bone during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Bone replaces cartilage Bones are remodeled and lengthened until growth stops Bones change shape somewhat Bones grow in width
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Long Bone Formation and Growth
Bone Remodeling Activity Figure 5.4b
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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 Terms often begin with “T” Depressions or cavities—indentations Terms often begin with “F”
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Microscopic Anatomy of Bone
Figure 5.3
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Microscopic Anatomy of Compact Bone
Osteocyte – mature bone cells found in lacunae Osteon (Haversian System) A unit of bone 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
Lacunae – cavity containing osteocytes (bone cells) Lamellae – circles of lacunae arranged around a central (Haversian) canal Canaliculi – tiny canals off of the central canal to the lacunae, provides each osteocyte with nutrient supplies
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Osteon Lacuna (c) Central canal Interstitial lamellae Figure 5.4c
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Types of Bone Cells Osteocytes Osteoblasts
Rickets – disease where bones fail to calcify, legs bow out Caused by a lack of vitamin D Bones can also atrophy in bed ridden people Osteocytes Mature bone cells Osteoblasts Bone-forming cells Osteoclasts—giant bone-destroying cells Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone Bone remodeling is a process by both osteoblasts and osteoclasts Bones are remodeled in response to Ca+ levels in the blood and the pull of gravity and muscles
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