The Skeletal System

1. The Skeletal System

2. The Skeletal System Parts of the skeletal system Bones (skeleton)‏ Joints Cartilages Ligaments Two subdivisions of the skeleton Axial skeleton – bones that form the longitudinal axis of the body (trunk of body) Appendicular skeleton– bones of limbs & girdles

3. 5 Functions of Bones 1. Support 2. Protection 3. Movement 4. Storage 5. Blood cell formation

4. Classification of Bones The adult skeleton has 206 bones Two basic forms of bone tissue Compact bone Dense &Homogeneous Spongy bone Small needle-like pieces of bone Many open spaces Figure 5.2b

5. Classification of Bones on the Basis of Shape Figure 5.1

6. 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

7. Classification of Bones Figure 5.1a

8. Classification of Bones Short bones Generally cube-shape Contain mostly spongy bone Bones of wrist & ankle (Sesamoid bones) Example: Carpals Tarsals Patella

9. Classification of Bones Figure 5.1b

10. 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

11. Classification of Bones Figure 5.1c

12. Classification of Bones Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae Hip bones

13. Classification of Bones Figure 5.1d

14. Anatomy of a Long Bone Diaphysis Shaft Composed of compact bone Makes up most of the bones length Covered and protected by periosteum Epiphysis Ends of the long bone Composed mostly of spongy bone

15. Anatomy of a Long Bone Figure 5.2a

16. 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

17. Anatomy of a Long Bone Figure 5.2c

18. Anatomy of a Long Bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces

19. 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

20. Anatomy of a Long Bone Figure 5.2a

21. 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

22. Anatomy of a Long Bone Figure 5.2a

23. Types of Bone Cells Osteocytes—mature bone cells– are osteoblasts that have been surrounded by a matrix 1. These cells are found within a chamber called Lacunae 2. Responsible for maintaining the mineral content of the bone. 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

24. Bone Growth (Ossification)‏-- overview 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

25. Bone development & Growth • Occurs in two ways • Intramembranous Bones – form from membranelikeconncective tissues that are found in the location of future bones ex: Flat bones of the skull (soft spots) • Connective tissue form osteoblasts which deposits a matrix around them to form haversian systems. • Those cells on the outer membranous tissue form the periosteum • Those cells on the inner membranous tissue for the spongy bone

26. Bone development & Growth B. Endochondral Bones – are developed from masses of hyaline cartilage that is later replaced by bone Process: • Hyaline cartilage cells shaped like the bone divides rapidly • Catilage breaks down and disappears as the periosteum forms from the cells that encircles the diaphysis • Osteoblasts forms spongy bone and bone tissue develops from this diaphysis region to the ends (Primary Ossification Center) • Compact bone forms around this primary ossification site and the epiphyses remain cartilage • The epiphyses are the location of the secondary ossification site which forms bone in all directions at an area called epiphyseal disk

27. Endochondral Bones (Continued) 6. Cartilage cells at the disks undergo mitosis 7. Matrix calcifies due to calcium salts and cartilage cells die. 8. Osteoclasts break down this old matrix at the epiphyseal disk and osteoblasts forms new bone. 9. When diaphysis and epiphyses meet then length of the bone ceases

28. 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

29. Marrow & Blood Cell Production (Hematopoiesis) A.. As an embryo blood cells are formed in the yolk sac and as development progresses from the liver and spleen 2 Types of marrow: 1. Yellow Marrow – found in the diaphysis and is a storage for fat 2. Red Marrow – is responsible for hemotopoiesis which forms all blood cells a. found in spongy bone b. as and adult (skull, ribs, sternum, clavicles, vertebrae, & pelvis have active red marrow)