1. Bone Tissue and The Skeletal System

2. The Skeletal System Functions of the Skeletal System Support against gravity Leverage for muscle action - movement Protection of soft internal organs Blood cell production Storage - calcium, phosphorous, fat

3. The Skeletal System The skeletal system includes: Bones Cartilages Joints Ligaments Other connective tissues

4. Tissues in Bone Bones contain several types of tissues Dominated by bone CT Contain nervous tissue and Blood CT Contain cartilage in articular cartilages Contain ET lining blood vessels

5. Bone (Osseous Tissue) Specialized cells - 2% of bone weight Strong flexible matrix Calcium phosphate crystals - two-thirds of bone weight Collagen fibers

6. Types of Cartilage Hyaline cartilage – (glassy) Most abundant cartilage Provides support through flexibility Articular cartilages and costal cartilage, larynx, trachea, and nose Elastic cartilage – contains many elastic fibers Able to tolerate repeated bending Ear and epiglottis Fibrocartilage – resists strong compression and strong tension An intermediate between hyaline and elastic cartilage Intervertebral discs and pubic symphysis

7. General Shapes Of Bones Long bones (e.g., humerus, femur) Short bones (e.g., carpals, tarsals, patella Flat bones (e.g., parietal bone, scapula, sternum) Irregular bones (e.g., vertebrae, hip bones)

8. Structure of Typical Long Bone Diaphysis - tubular shaft forming the axis of long bones. Composed of compact bone Central medullary cavity Contains bone marrow Epiphysis – expanded end of long bones. Composed mostly of spongy bone Joint surface is covered with articular (hyaline) cartilage Epiphyseal lines separate the diaphysis from the epiphyses Metaphysis – where epiphysis and diaphysis meet

9. Bone Membranes Periosteum Provides anchoring points for tendons and ligaments Double-layered protective membrane, supplied with nerve fibers, blood, and lymphatic vessels entering the bone via nutrient foramina. Inner osteogenic layer is composed of osteoblasts and osteoclasts Endosteum Delicate CT membrane covering internal surfaces of bone Covers trabeculae of spongy bone Lines canals in compact bone Also contains both osteoblasts and osteoclasts

10. Gross Anatomy of Bones External Features of Bones – projections, depressions, and openings that serve as sites of muscle, ligament, and tendon attachment, as joint surfaces, or conduits for blood vessels and nerves Compact Bone – dense outer layer Spongy Bone – (cancellous bone) honeycomb of trabeculae (needle-like or flat pieces) filled with bone marrow

11. Gross Anatomy - Bone Markings Table 6.1 Superficial surfaces of bones reflect stresses on them There are three broad categories of bone markings Projections for muscle attachment Surfaces that form joints Depressions and openings

12. Histology of Compact Bone Osteon – the structural unit of compact bone Lamellae – column-like matrix tubes composed of collagen and crystals of bone salts Central canal - (Haversian canal) canal containing blood vessels and nerves

13. Histology of Compact Bone Lacunae - cavities in bone containing osteocytes Canaliculi - hairlike canals that connect lacunae to each other and the central canal Perforating canal (Volkmann’s) – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to the central canal

14. Cells in Bone Osteoprogenitor cells – precursors to osteoblasts Osteocytes - mature bone cells between lamellae Osteoclasts - bone-destroying cells, break down bone matrix for remodeling and release of calcium Source of acid, enzymes for osteolysis Calcium homeostasis Osteoblasts - bone-forming cells Responsible for osteogenesis (new bone) Source of collagen, calcium salts

15. The Structure of Spongy Bone No osteons Lamellae as trabeculae Arches, rods, plates of bone Branching network of bony tissue Strong in many directions Red marrow (blood forming) spaces

16. Short, Irregular, and Flat Bones Plates of periosteum- covered compact bone on the outside with endosteum-covered spongy bone, diploë, on the inside Have no diaphysis or epiphyses Contain bone marrow between the trabeculae

17. Bone Development Osteogenesis or Ossification – the process of bone tissue formation that leads to: The formation of the skeleton in embryos Bone growth until early adulthood Bone thickness, remodeling, and repair

18. Formation of the Skeleton Before week 8, the skeleton of a human embryo consists of fibrous membanes and hyaline cartilage Intramembranous ossification – bone develops from a fibrous connective tissue membrane. The flat bones of the skull (frontal, parietal, temporal, occipital) and the clavicles are formed this way. Endochondral ossification – bone forms by replacing hyaline cartilage, uses hyaline cartilage “bones” as patterns Bone Formation in 16-Week-Old Fetus

19. Bone Formation and Growth Intramembranous Ossification Ossification—Process of converting other tissues to bone Forms flat bones of skull, mandible, clavicle Stem cells differentiate to osteoblasts Produces spongy bone, then compact bone Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

20. Intramembranous Ossification An ossification center appears in the fibrous connective tissue membrane Osteoblasts secrete bone matrix within the fibrous membrane Osteoblasts mature into osteocytes

21. Intramembranous Ossification The bone matrix develops into trabeculae. The trabeculae formed from various ossification centers fuse with one another to create spongy bone. Eventually the spaces between trabeculae fill with red bone marrow.

22. Bone Formation and Growth Endochondral Ossification Most bones formed this way Cartilage model replaced by bone Replacement begins in middle (diaphysis) Replacement follows in ends (epiphyses) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

23. Enlarging chondrocytes within calcifying matrix Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone. Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center. The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone. Blood vessels invade the epiphyses and osteo- blasts form secondary centers of ossification. Cartilage model Bone formation Epiphysis Diaphysis Marrow cavity Primary ossification center Blood vessel Marrow cavity Blood vessel Secondary ossification center Epiphyseal cartilage Articular cartilage Figure 6-5 1 of 6 Endochondral Ossification

24. Longitudinal Bone Growth Longitudinal Growth (interstitial) – cartilage continually grows and is replaced by bone Bones lengthen entirely by growth of the epiphyseal plates Cartilage is replaced with bone CT as quickly as it grows Epiphyseal plate maintains constant thickness

25. Epiphyseal Plate Cartilage is organized for quick, efficient growth Cartilage cells form tall stacks Chondroblasts at the top of stacks divide quickly Pushes the epiphysis away from the diaphysis Lengthens entire long bone Older chondrocytes signal surrounding matrix to calcify, then die and disintegrate Leaves long trabeculae (spicules) of calcified cartilage on diaphysis side Trabeculae are partly eroded by osteoclasts Osteoblasts then cover trabeculae with bone tissue Trabeculae finally eaten away from their tips by osteoclasts

26. Appositional Bone Growth Growing bones widen as they lengthen Appositional growth – growth of a bone by addition of bone tissue to its surface Bone is resorbed at endosteal surface and added at periosteal surface Osteoblasts – add bone tissue to the external surface of the diaphysis Osteoclasts – remove bone from the internal surface of the diaphysis Figure 6-6

27. Bone - Remodeling/Homeostasis Role of Remodeling in Support Remodeling—Continuous breakdown and reforming of bone tissue Shapes reflect applied loads Mineral turnover enables adapting to new stresses What you don’t use, you lose. The stresses applied to bones during exercise are essential to maintaining bone strength and bone mass

28. Bone Remodeling Bone is active tissue – small changes in bone architecture occur continuously – 5 to 7% of bone mass is recycled weekly – spongy bone is replaced every 3-4 years and compact bone approximately every 10 years Remodeling Units – adjacent osteoblasts and osteoclasts deposit and reabsorb bone at periosteal and endosteal surfaces

29. Bone Remodeling Bone Depostition Occurs when bone is injured or extra strength is needed Requires a healthy diet - protein, vitamins C, D, and A, and minerals (calcium, phosphorus, magnesium, manganese, etc.) Bone Resorption Accomplished by Osteoclasts (multinucleate phagocytic cells) Resorption involves osteoclast secretion of: Lysosomal enzymes that digest organic matrix HCl that converts calcium salts into soluble forms Dissolved matrix is endocytosed and transcytosed into the interstitial fluid → the blood

30. Bone - Remodeling/Homeostasis Homeostasis and Mineral Storage Bones store calcium Contain 99% of body calcium Store up to two kg calcium Hormones control storage/release PTH, calcitriol release bone calcium Calcitonin stores bone calcium Blood levels kept constant

31. Joints Rigid elements of the skeleton meet at joints or articulations Greek root “arthro” means joint Functions of joints Hold bones together Allow for mobility Articulations can be Bone to bone Bone to cartilage Teeth in bony sockets

32. Classification of Joints Joints can be classified by function or structure Functional Synarthroses – immovable joints Amphiarthroses – slightly moveable joints Diarthroses – freely moveable joints Structural Fibrous joints - generally immovable Cartilaginous joints - immovable or slightly moveable Synovial joints - freely moveable Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

33. Functional Classification Functional classification – based on amount of movement Synarthroses – immovable joints Suture – very short CT fibers, e.g. between cranial bones Gomphosis – teeth in sockets Synchondrosis – hyaline cartilage unites bones, e.g. epiphyseal plate, costal cartilage of 1 st rib and manubrium Amphiarthroses – slightly moveable joints Syndesmosis – bones connected by ligaments, e.g. between tibia and fibula Symphysis - bones are covered by hyaline cartilage fused with fibrocartilage, e.g. between vertebrae, pubic bones of the hip Diarthroses - freely moveable Synovial joints – knee, elbow, etc

34. Classifications of Joints Structural classification based on Material that binds bones together Presence or absence of a joint cavity Structural classifications include Fibrous Cartilaginous Synovial

35. Fibrous Joints Bones are connected by fibrous connective tissue Primarily dense regular CT Do not have a joint cavity Most are immovable or slightly movable Types Sutures Syndesmoses Gomphoses

36. Sutures Bones are tightly bound by a minimal amount of fibrous tissue Only occur between the bones of the skull Allow bone growth so the skull can expand with brain during childhood Fibrous tissue ossifies in middle age Synostoses – closed sutures

37. Syndesmoses Bones are connected exclusively by ligaments Amount of movement depends on length of fibers Tibiofibular joint –immovable synarthrosis Interosseous membrane between radius and ulna Freely movable diarthrosis

38. Gomphoses Tooth in a socket Connecting ligament – the periodontal ligament Figure 9.1c

39. Cartilaginous Joints Bones are united by cartilage Lack a joint cavity Two types Synchondroses - hyaline cartilage unites bones Epiphyseal plates Rib and sternum Symphyses

40. Fibrocartilage unites bones – resists tension and compression Hyaline cartilage – also present as articular cartilage Slightly movable joints that provide strength with flexibility Intervertebral discs Pubic symphysis

41. Synovial Joints Most movable type of joint All are diarthroses Each contains a fluid-filled joint cavity

42. General Structure of Synovial Joints Articular cartilage Ends of opposing bones are covered with hyaline cartilage Absorbs compression Joint cavity (synovial cavity) Unique to synovial joints Cavity is a potential space that holds a small amount of synovial fluid

43. General Structure of Synovial Joints Articular capsule – joint cavity is enclosed in a two- layered capsule Fibrous capsule – dense irregular connective tissue, which strengthens joint Synovial membrane – loose connective tissue Lines joint capsule and covers internal joint surfaces Functions to make synovial fluid

44. General Structure of Synovial Joints Synovial fluid A viscous fluid similar to raw egg white A filtrate of blood Arises from capillaries in synovial membrane Contains glycoprotein molecules secreted by fibroblasts

45. General Structure of Synovial Joints Reinforcing ligaments Often are thickened parts of the fibrous capsule Sometimes are extracapsular ligaments – located outside the capsule Sometimes are intracapsular ligaments – located internal to the capsule

46. Structures Associated with the Synovial Joint Tendon sheath - elongated bursa that wraps around a tendon Bursae – flattened fibrous sacs Lined with synovial membranes Filled with synovial fluid Not actually part of the joint Menisci Fat pads Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

47. Structural Classification of Synovial Joints Gliding (plane joint, e.g., vertebra–vertebra) Hinge (e.g., knee) Pivot (e.g., atlas–axis) Ellipsoidal (condyloid plant, e.g., distal radius) Saddle (e.g., thumb) Ball-and-Socket (e.g., hip)

48. Types of Synovial Joints Based on Shape Slide 5.52a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.29a–c (Gliding)

49. Types of Synovial Joints Based on Shape Slide 5.52b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.29d–f (Ellipsoidal)

50. Summary of Joint Classes