Bones and Skeletal Tissues Part A

1. Bones and Skeletal Tissues Part A 6

2. Skeletal Cartilage • Although the human skeleton is initially made up of cartilages and fibrous membranes most of these early supports are soon replaced by bone. The few cartilage that remain in adults are found mainly in regions where flexible skeletal tissue is needed. • Skeletal cartilage is made of some variety of cartilage tissue, which consists primarily of water. This characteristic give to the cartilage the ability to spring back to its original shape after been compressed.

3. Skeletal Cartilage • Contains no blood vessels or nerves. • Surrounded by the perichondrium (dense irregular connective tissue) that resists outward expansion. • Three types – hyaline, elastic, and fibrocartilage (all have the same basic components- cells called chondrocytes.

4. Hyaline Cartilage • Provides support, flexibility, and resilience • Is the most abundant skeletal cartilage. When new under microscope, their chondrocytes appear spherical. • Is present in these cartilages: • Articular – covers the ends of long bones • Costal – connects the ribs to the sternum • Respiratory – makes up the larynx and reinforces air passages • Nasal – supports the external nose

5. Elastic Cartilage • Similar to hyaline cartilage but contains elastic fibers • Found in the external ear and the epiglottis (the flap that bends to cover the opening of pharynx each time we swallow)

6. Fibrocartilage • Highly compressed with great tensile strength • Contains collagen fibers • Found in sites that are subjected to both heavy pressure and stretch such as: menisci of the knee and in intervertebral discs

7. Growth of Cartilage: Two ways: • Appositional – cells in the perichondrium secrete matrix against the external face of existing cartilage • Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within • Calcification of cartilage (is not bone) occurs • During normal bone growth • During old age

8. Bones and Cartilages of the Human Body Figure 6.1

9. Classification of Bones Human body consists in 206 bones. They are divided in two groups: • Axial skeleton (form the long axis of the body) includes – bones of the skull, vertebral column, and rib cage. Functions:protecting,supporting or cary other body parts. • Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip. Function:locomotion and manipulation of our enviroment

10. Classification of Bones: By Shape Bones come in many sizes and shapes. For most part , bones are classified by their shape as: long, short flat and irregular • Long bones – longer than they are wide (e.g., humerus) • Has a shaft plus two ends Ex: All limb bones except patella and wrist and ankle bones are long bone Figure 6.2a

11. Classification of Bones: By Shape • Short bones • Cube-shaped bones of the wrist and ankle • Sesamoid bones “shaped like a sesame seed” that form within tendons (e.g., patella). They vary in size and number in different individual. Some sesamoid bones act to atter the direction of pull of a tendon Figure 6.2b

12. Classification of Bones: By Shape • Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones) Figure 6.2c

13. Classification of Bones: By Shape • Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones) Figure 6.2d

14. Function of Bones • Support – form the framework that supports the body and cradles soft organs. Ex: Lower limb • Protection – provide a protective case for: the brain (bones of skull), spinal cord (vertebrae), and vital organs (rib cage) • Movement – provide levers for muscles • Mineral storage – bone is a reservoir for minerals, especially calcium and phosphorus • Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

15. Bone Structure • Because they contain various types of tissue bones are organs. • Although bone (osseum) tissue dominantes bones, they also contains: nervous, cartilage, muscle, epithelial tissues and blood vessels. • Structure can be study :Gross, microscopic and chemically

16. Bone Markings • Bulges, depressions, and holes that serve as: • Sites of attachment for muscles, ligaments, and tendons. Ex: Tuberosity, chest, line, tubercule • Joint surfaces. Ex: Heat, facet, condyle • Conduits for blood vessels and nerves. Ex: Meatus, sinus, groove

17. Bone Markings: Projections – Sites of Muscle and Ligament Attachment • Tuberosity – rounded projection • Crest – narrow, prominent ridge of bone • Trochanter – large, blunt, irregular surface • Line – narrow ridge of bone

18. Bone Markings: Projections – Sites of Muscle and Ligament Attachment • Tubercle – small rounded projection • Epicondyle – raised area above a condyle • Spine – sharp, slender projection • Process – any bony prominence

19. Bone Markings: Projections – Projections That Help to Form Joints • Head – bony expansion carried on a narrow neck • Facet – smooth, nearly flat articular surface • Condyle – rounded articular projection • Ramus – armlike bar of bone

20. Bone Markings: Depressions and Openings • Meatus – canal-like passageway • Sinus – cavity within a bone • Fossa – shallow, basinlike depression • Groove – furrow • Fissure – narrow, slitlike opening • Foramen – round or oval opening through a bone

21. Gross Anatomy of Bones: Bone Textures Every bone has two textures: • Compact bone (also called cancellous bone) – dense outer layer • Spongy bone - (internal) honeycomb of trabeculae filled with red or yellow bone marrow

22. Structure of Long Bone Figure 6.3

23. Structure of Long Bone • Long bones consist of a diaphysis and an epiphysis and membranes. • Diaphysis • Tubular shaft that forms the axis of long bones • Composed of compact bone that surrounds the medullary cavity • Yellow bone marrow (fat) is contained in the medullary cavity

24. Structure of Long Bone • Epiphyses • Expanded ends of long bones • Exterior is compact bone, and the interior is spongy bone • Joint surface is covered with articular (hyaline) cartilage • Epiphyseal line (remnant of the epiphyseal plate) separates the diaphysis from the epiphyses

25. Bone Membranes: • Periosteum – double-layered protective membrane • Outer fibrous layer is dense regular connective tissue • Inner osteogenic layer is composed of osteoblasts (“bone germinators”) and osteoclasts (“bone breakers”) • Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina • Secured to underlying bone by Sharpey’s fibers • Endosteum – delicate membrane covering internal surfaces of bone

26. Structure of Short, Irregular, and Flat Bones • Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside (resembles a sandwich). • Have no diaphysis or epiphyses • Contain bone marrow between the trabeculae, but no marrow cavity is present.

27. Structure of a Flat Bone Figure 6.4

28. Location of Hematopoietic Tissue (Red Marrow) • In infants • Found in the medullary cavity and all areas of spongy bone • In adults • Found in the diploë of flat bones, and the head of the femur and humerus

29. Microscopic Structure of Bone: Compact Bone • Haversian system, or osteon – the structural unit of compact bone. Functionally, osteons are tiny weight-bearing pillars • Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen • Haversian, or central canal – central channel containing blood vessels and nerves • Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

30. Microscopic Structure of Bone: Compact Bone • Osteocytes – mature bone cells • Lacunae – small cavities in bone that contain osteocytes • Canaliculi – hairlike canals that connect lacunae to each other and the central canal. The canaliculi tie all the osteocytes in an osteon together, permitting nutrients and wastes to be relayed from one osteocyte to the next throughout the osteon.

31. Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

32. Chemical Composition of Bone: Organic • Bone has both organic and inorganic components. Organic components: 1.-Cells: • Osteoblasts – bone-forming cells • Osteocytes – mature bone cells • Osteoclasts – large cells that resorb or break down bone matrix 2.- Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen

33. Chemical Composition of Bone: Inorganic • The balance of the bone tissue (65% by mass) consists of inorganic mineral salts: • Hydroxyapatites, or mineral salts • Mainly calcium phosphates • Responsible for bone hardness and its resistance to compression

34. Bone Development • Osteogenesis and ossification – the process of bone tissue formation, which leads to: • The formation of the bony skeleton in embryos • Bone growth until early adulthood • Bone thickness, remodeling, and repair

35. Formation of the Bony Skeleton • Begins at week 8 of embryo development • Intramembranous ossification – bone develops from a fibrous membrane • Endochondral ossification – bone forms by replacing hyaline cartilage

36. Intramembranous Ossification • Formation of most of the flat bones of the skull and the clavicles • Fibrous connective tissue membranes are formed by mesenchymal cells. They are the supporting structures on which ossification begins at about week 8 of development. • Essentially the process involves 4 major steps

37. Intravenous Ossification. Steps • 1.- An ossification center appears in the fibrous connective tissue membrane • 2.- Bone matrix (osteoid) is secreted within the fibrous membrane • 3.- Woven bone and periosteum form • 4.- Bone collar of compact bone forms and red marrow appears