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 Endosteum
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
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
Table 6.1

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
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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)
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23. Endochondral Ossification
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.
Articular
cartilage
Enlarging
chondrocytes within
calcifying matrix
Epiphysis
Epiphyseal
cartilage
Marrow
cavity
Diaphysis
Marrow
cavity
Primary
ossification
center
Secondary
ossification
center
Blood
vessel
Bone
formation
Blood
vessel
Cartilage
model
Figure 6-5
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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 Bone Resorption
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
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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 1st 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. Symphyses
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
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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
(Gliding)
Figure 5.29a–c
Slide 5.52a
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49. Types of Synovial Joints Based on Shape
(Ellipsoidal)
Figure 5.29d–f
Slide 5.52b
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50. Summary of Joint Classes