1 The Skeletal System

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

3 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)

4 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 Figure 5.2b Spongy bone Compact bone

5 Classification of Bones on the Basis of Shape Figure 5.1 Bones are classified as: –Long –Short –Flat –Irregular

6 Classification of Bones on the Basis of Shape

7 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)

8 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

9 Gross Anatomy of a Long Bone Diaphysis – shaft of bone – Compact bone – Covered by connective tissue called periosteum Epiphysis – ends of bone – Compact bone surrounding spongy bone center Figure 5.2a Distal epiphysis Diaphysis Proximal epiphysis Articular cartilage Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) (a

10 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

11 Structures of a Long Bone 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.) Figure 5.2a Distal epiphysis Diaphysis Proximal epiphysis Articular cartilage Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum)

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

13 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

14 Long Bone Formation and Growth Figure 5.4a

15 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

16 Long Bone Formation and Growth Figure 5.4b Bone Remodeling Activity 4&safe=active

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”

18 Microscopic Anatomy of Bone Figure 5.3

19 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

20 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

Figure 5.4c Osteon Lacuna Central canal Interstitial lamellae (c)

22 Types of Bone Cells 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 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