The Skeletal System 1 The Skeletal System Parts

The Skeletal System 1

The Skeletal System • Parts of the skeletal system – Bones – Joints – Ligaments – Cartilage • Divided into two divisions – Axial – longitudinal axis – Appendicular – limbs and girdles 2

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) 3

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. 2 b 4

Classification of Bones on the Basis of Shape • Bones are classified as: – Long – Short – Flat – Irregular Figure 5. 15

Classification of Bones on the Basis of Shape 6

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) 7

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 8

Gross Anatomy of a Long Bone • Diaphysis – shaft of bone Articular cartilage Proximal epiphysis – Compact bone – Covered by connective tissue called periosteum • Epiphysis – ends of bone Diaphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) – Compact bone surrounding spongy bone center Distal epiphysis (a Figure 5. 2 a 9

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. 2 c 10

Structures of a Long Bone • Articular cartilage – covers the epiphyses Articular cartilage Proximal epiphysis – made of hyaline cartilage – Reduces friction at joints • Medullary cavity – (yellow marrow) Diaphysis – 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 Distal epiphysis some long bones (pelvis, femur, etc. ) Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Figure 5. 2 a 11

Anatomy of a Long Bone • Epiphyseal plate Proximal epiphysis – Flat plate of hyaline cartilage seen in young, growing bone • Epiphyseal line – Remnant of the epiphyseal plate – Seen in adult bones Diaphysis Distal epiphysis (a) Articular cartilage Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) 12

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 13

Long Bone Formation and Growth Figure 5. 4 a 14

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 15

Long Bone Formation and Growth http: //www. youtube. com/watch? v=y. FJ 4 isw. Riu 4&safe=active Bone Remodeling Activity Figure 5. 4 b 16

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”

Microscopic Anatomy of Bone Figure 5. 3 18

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 – Carries blood vessels and nerves 19

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 20

Osteon Lacuna (c) Central canal Interstitial lamellae Figure 5. 4 c

Types of Bone Cells • Osteocytes – Mature bone cells • 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 – 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 22