Chapter 6

1. Chapter 6 Osseous Tissue & Bone Structure

2. Objectives • Describe the primary functions to the skeletal system • Classify bones according to shape and internal organization • Be able to give examples of each type, and explain the functional significance of each of the major type of bone markings • Identify cell types in bone, and list their major functions. • Compare the structures and functions of compact bone and spongy bone • Describe the remodeling and homeostatic mechansims of the skeletal system

3. Introduction to the Skeletal System • Functions - Support - Storage of Minerals and Lipids - Blood Cell Production - Protection - Leverage

4. Bone Classifications - a bone may be classified by its general shape or by its internal tissue organization. • Shapes • typical adult skeleton contains 206 major bones - divided into six broad categories according to their individual shapes Long Bones: - relatively long and slender - located in the arm, forarms, thigh, leg, palms, soles, fingers, and toes

5. Bone Classification Cont. Flat Bones: - have thin roughly parallel surfaces - provide protection for underlying soft tissues - offer an extensive surface area for attachment of skeletal muscles ex., sternum, ribs, scapulae, form the roof of the skull Sutural Bones: - small, flat, irregular shaped bones - vary in number, shape, size, and position - located between the flat bones of the skull

6. Bone Classification Cont. Irregular: - have complex shapes with short, flat, notched, or ridged surfaces ex. bones of the pelvis, spinal vertebrae, and several skull bones Short Bones: - small and boxy ex. carpals and tarsals Sesamoid Bones: - general small, flat, and shaped somewhat like a sesame seed - develop inside tendons, most commonly located near joints at the knees, hands, and feet - individuals vary in the location and abundance (form in at least 26 locations)

7. Bone Classification Cont.

8. Bone Markings/Surface Features • external and internal characteristics - elevations or projections form where tendons and ligaments attach - depressions, grooves, and tunnels in bone indicate cites where blood vessels or nerves lie alongside/penetrate bone Uses - determine size, age, sex and general appearance

9. Anatomical Terms: Bone Surfaces Elevations and Projections - Process: projection or bump - Ramus: extension of a bone making an angle with the rest of the structure Processes formed where tendons or ligaments attach - Trochanter: large, rough projection - Tuberosity: smaller, rough projection - Tubercle: small, rounded projection - Crest: prominent ridge - Line: low ridge - Spine: pointed or narrow process

10. Anatomical Terms: Bone Surfaces Processes formed for articulation with adjacent bones - Head: expanded articular end of an epiphysis, separated form the shaft by a neck - Neck: narrow connection between the epiphysis and the diaphysis - Condyle: smooth, rounded articular process - Trochlea: smooth, grooved articular process shaped like a pulley - Facet: small, flat articular surface Depressions: - Fossa: shallow depression - Sulcus: narrow groove

11. Anatomical Terms: Bone Surfaces Openings - Foramen: rounded passageway for blood vessels or nerves - Canal: passageway through the substance of a bone - Fissure: elongated cleft - Sinus: chamber within a bone, normally filled with air

12. Structure of a Long Bone • Diaphysis: shaft, makes up up of the bone’s length - wall consists of a layer of compact bone (dense bone) - relatively solid, forms a sturdy protective layer that surrounds a central space, medullary cavity - covered and protected by a fibrous connective tissue membrane called the periosteum, attached to bone by Sharpey’s fibers • Epiphysis: at end end of the long bone - thin layer of compact bone composed largely of spongy bone - open network of struts and plates, like a lattice - glassy hyaline cartilage known as an articular cartilage covers it’s external surface provides slippery surface that decreases friction - epiphyseal line : remnant of epiphyseal plate with growth occurs

13. Bone Structure Cont. • Metaphysis: narrow zone connecting the epiphysis and diaphysis • Medullary cavity: central space in bone primarily a storage area for adipose tissue - in infants formation of blood cells and red marrow can be found

15. Structure of Compact Bone • Osteon (Haversian system) - basic unit of mature compact bone - osteocytes are arranged in concentric layers around a central canal -canal contain blood vessels that carry blood to and from the osteon - central canals general parallel to the surface of the bone - perforating canals extend perpendicular to the surface - lamellae of each osteon form a series of nestled cylinders around the central canal (target/bullseye) - canaliculi radiating through the lamellae interconnect the lacunae with one another and the central canal

16. Structure of Spongy Bone • Matrix - forms struts and plates called trabeculae - branch to create an open network - no capillaries or venules - nutrients reach the osteocytes by diffusion along the canaliculi • Characteristics - lighter than compact bone - able to withstand stress from multiple directions • Locations - short bones (carpal of wrist) - inner layer of flat bones - sesamoid

17. Bone Composition • Specialized cells ex. osteblasts, osteocytes • Matrix consisting of extracellular protein fibers and ground substance - very dense and contains calcium deposits - bone cells (ostecytes) inside of lacunae - canaliculi

18. Cells of the Bone • 4 types of cells - osteocysts - osteoblasts - osteoprogenitors - osteoclasts

19. Cells of Bone Cont. • Osteocytes - mature bone cells, cannot divide - most abundant - occupies a lacunae (tiny cavities) arranged in concentric circles called lamellae around central (Haversian) canals - a central canal, and matrix rings is called an osteon or Haversian system - lamellae are penetrated by canaliculi (narrow passageways) radiating through matrix connecting lacunae and sources of nutrients, such as a central canal • Functions: - maintain the protein and mineral content of the surrounding matrix - participate in the repair of damaged bone

20. Cells of Bone Cont. • Osteoblasts - produce new bone matrix by osteogenesis - make and release proteins and other organic components of the matrix before calcium salts are deposits - assist in elevating local concentrations of calcium phosphate above its solubility limit triggering the deposition of calcium salts in the organic matrix converting matrix to bone - become osteocytes once completely surrounded by bone matrix

21. Cells of Bone Cont. • Osteoprogenitor - small numbers of mesenchymal cells - squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts - maintain populations of osteoblasts - important in the role of fractures - located in the endosteum

22. Cells of Bone Cont. • Osteoclasts - giant cells with more than 50 nuclei - remove and recycle bone matrix by secreting enzymes that dissolve and release stored minerals (osteolysis)

23. Bone Formation, Growth • Two types • Ossification - process of bone formation by replacing other tissues - hyaline cartilage is completely covered with bone matrix by osteoblasts - hyaline cartilage is digested away opening up a medullary cavity - epiphyses fill with spongy bone, except at the center where calcification occurs. - articular cartilage becomes a thin superficial layer - at puberty rising levels of sex, growth, and thyroid hormones stimulate bone growth; osteoblasts produce bone faster than chondrocytes at producing new cartilage

24. Bone Formations and Growth Cont. Bone growth length osteoblasts at the shaft end remove cartilage at the same rate as cartilage is forming on the epiphyseal side * As long as the epiphyseal cartilage (plate) continues to grow the bone will continue to increase in length Appositional Bone growth (width/diameter) - osteoblasts in periosteum add bone tissue to the external face of the diaphysis - osteoclasts in the endosteum remove bone from the inner face of the diaphysis wall • Calcification - deposition of calcium deposits, occurs during ossification

25. Bone Remodeling • Remodeling - components of bone continuously recycle and renew - occurs through out, as normal bone maintance - older minerals deposits are removed from bone and released in to the circulation at the same time that circulating minerals are being absorbed and deposited - “game” between osetocytes, blasts, and clasts - osteocyts create osteon, at the same rate osteoclasts remove one by ostelysis - 1/5th of the adult skeleton is replaced every year - depends on location, and abuse - femur spongy bone replaced 2-3 times a year

26. Bone Fractures • General Categories - Closed (simple) - Open (compound) • Closed - completely internal - no break of the skin, so they can only be seen in x-rays - usually easy to treat • Open - project through the skin - more dangerous due to possibility of infection

27. Types of fractures • Pott - occurs at the ankle and affects both bones of the leg • Comminuted - shatter bone into multiple fragments • Transverse - break bone shaft across its axis • Spiral - twisting up/down the length of the bone • Displaced/Nondisplaced - produce new and abnormal bone arrangements - retain normal alignment

28. Type of Fractures • Colles - break in the distal portion of the radius • Greenstick - only one side of the shaft is bone, and the other is bent • Epiphyseal - occur where bone matrix is undergoing calcification - can permanently stop growth • Compression - occur in the vertebrae • Avulsion - tendon or ligament is injured in such a manner that it pulls off a piece of bone

29. Fractures

30. Repair of a Fracture • Step 1 - extensive bleeding leading to a hematoma or large blood clot • Step2 - internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges • Step 3 - cartilage of external callus replaced with bone, struts of spongy bone now unite the broken ends - fragments or dead bone is removed • Step 4 - swelling over fracture until remodeling occurs

31. Skeleton • 2 parts - axial - appendicular • Axial - forms the longitudinal axis of the body - 80 bones - 40% of the bones in human body - Includes - Skull & associated bones - Vertebral column - Thoracic cage • provide framework that supports and protects the brain, spinal cord, and organs in the ventral cavities • extensive surface areas for attachment of muscles • joints have limited movement

32. Skull • Contains 22 bones - 8 from the cranium - occipital - ethmoid - parietal (2) - frontal - spheniod - temporal (2) - enclose the cranial cavity, a fluid filled chamber that cushions and supports the brain - occipital, parietal, and frontal bones form the calvaria - blood vessels, nerves, and membranes that stabilize the position of the brain are attached to the inner surface of the cranium - outer surface provides areas of attachment for muscles of the eyes, jaws, and head - joint between occipital bone and 1st vertebrae of neck stabilize the positions of the brain and spinal cord

33. Skull Cont. - 14 associated with the face - superficial bones - paired maxillae, lacrimal, nasal, zygomatic, mandible - provide areas for the attachment of muscles that control facial features and assist in the manipulating of food - deep bones - paired palatine inferior nasal conchae, median vomer - separate the oral and nasal cavities - increase surface area of cavities - help form the nasal septum which divides the nasal cavities

34. Skull Cont. • Sinuses - air-filled chambers - two major functions - make bone lighter - mucous membrane lining produces mucus that moistens and cleans air • Joints or Articulations - form where two bones interconnect - exception between mandible and cranium contact - sutures are located between immovable joints of the skull bones in adults - bones are tied together via dense fibrous connective tissue - 4 major sutures

35. Skull Cont. • Lambdoid - arches across the posterior surface of the skull - seperates the occipital bone from the two parietal bones • Coronal - attaches the frontal bone to the parietal bones of either side • Sagital - extends from lambdoid suture to the coronal suture, between the parietal bones • Squamous - one each side of the skull forms the boundary between the temporal bone and the parietal bone of that side

36. Orbital Complexes • cranial bones and facial bones which surrounds each eye, and the nasal complex surrounding the cavities • protect and support openings of the digestive and respiratory systems and sense organs responsible for vision and smell • Orbits - bony recesses that contain the eyes - each orbit is formed by 7 bones of the orbital complex - frontal - maxilla - ethmoid - zygomatic - palatine - spheniod - lacrimal

37. Nasal Complexes • bones that enclose the nasal cavities and the paranasal sinuses - superoir wall: - frontal - sphenoid - ethmoid - lateral walls: - maxilla - lacrimals - ethmoid - nasal conchae - nasal bones • Paranasal Sinuses - sphenoid - ethmoid - frontal bone - maxillia - palatine bone - lighten the skull bones and provide an extensive area of mucous epithelium - as mucous secretions are released ciliated epithelium pass it back toward the throat to be swallowed or expelled by coughing - incoming air is humidified was warmed - foreign particles are trapped swallowed or expelled by coughing

38. Fontanelles - Largest fibrous areas between the cranial bones • Anterior fontanelle (exists about 2 years after birth) - largest - located at the intersection of the frontal, sagittal, and coronal sutures in the anterior portion of the skull - often referred to as the “soft spot” • Occiptial fontanelle (disappear 1-2 months after birth) - junction between the lambdoid and sagittal sutures • Sphenoidal fontanelles - junctions between the squamous and coronal sutures • Mastoid fontanelles (disappear 1-2 months after birth) - junctions between the squamous and lambdoid suture

39. Vertebral Column • consists of 26 bones - vertebrae (24) – sacrum - coccyx • provides a column of support • bears the weight of the head, neck, and trunk • protects the spinal cord • helps maintain an upright body position • averages 71 cm or 28 in in adults • several curves

40. Spinal Curvature • 4 curves • Cervial - neck • Thoracic - upper back • Lumbar - lower back • Sacral - gluteal reigon

41. Vertebral Anatomy • 3 basic parts - vertebral body - vertebral arch - articular process • Vertebral Body - transfers weight along the axis of the vertebral column - interconnected by ligaments - separated by fibrous cartilage (intervertebral discs) • Vertebral Arch - forms the posterior margin of each vertebral foreman - pedicles (walls) arise along the posterior and lateral margins of body - roof called laminae, extend dorsally and medially - successive vertebrae form the vertebral canal, enclosing spinal cord

42. Vertebral Anatomy Cont. - intervertebral disc separate adjacent vertebral bodies - intervertibral formina (gaps) separate successive pedicles, permitting passage of nerves - spinous process projects posteriorly where vertebral laminae fuse to complete arch (feel through skin when back is flexed) - transverse processes project laterally on both sides where laminae join pedicles - sites for muscle attachments - some articulate with ribs • Articular processes - arise at the junction between the pedicles and the laminae - superior articulate with inferior on each side - each articulation has a smooth concave surface called an articular facet

43. Vertebral Regions • Cervical - C1-C7, create the neck - extend from occipital bone to the thorax - smallest of the vertebral column - small body compared to foramen - support only the weight of the head • General Characteristics C3-C6 - superior surface of body is concave side to side - slopes with the anterior edge inferior to posterior edge - stumpy spinous process, shorter than the diameter of foramen, with prominent notch (bifid) - laterally transverse processes are fused to costal processes - encircle round transverse foramina - provide more flexibility than other regions

44. Vertebral Regions Cont. • Atlas: C1 (after Atlas who holds the world on his shoulders) - holds up the head - articulates superiorly with occipital condyles, allowing us to nod yes - articulates with the axis, allowing us rotation for no - no spinous process - large, round vertebral foramen bounded by anterior and posterior arches • Axis: C2 - during development fuses with atlas creating the prominent dens (adontoid) - a transverse ligament binds the dens to the inner surface of the atlas - strong spinous process for muscle attachment - incomplete in children

45. Vertebral Regions Cont. • Vertebra Prominens (C7) - has a long, slender spinous process - ends in a broad tubercle (you can feel this - transverse process are large, for muscle processes - beginning of the ligamentum nuchae - extends to an insertion along the occipital crest - attaches to the spinous processes of other cervical vertebrae - acts like a string on a bow

46. Vertebral Regions Cont. • Thoracic - 12 vertebrae • General Characteristics - heart shaped body more massive than cervical - smaller foramen than cervical - long slender spinous processes projecting posterior and inferiorly - T 10-12 increasingly resemble lumbar region - compression injuries often occur here - articulate with ribs along dorsolateral surfaces of body - costal facets on bodies articulate with heads of ribs - transverse process T1-10 ,thick, contain transverse costal facets for ribs

47. Vertebral Regions Cont. • Lumbar - 5 vertebra • General Characteristics - large, thick bodies - oval superior and inferior surfaces - no costal facets - slender transverse processes projecting dorsolaterally - vertebral foramen is triangular - stumpy spinous processes projecting dorsally - superior spinous processes face medially (up and in) - inferior articular processes face laterally (down and out) - bear the majority of weight - massive spinous processes provided surface area for muscles of lower back

48. Vertebral Regions Cont. • Sacrum- fused components of five sacral vertebrae, marked by transverse lines - begin fusing after puberty end between 25-30yrs old - protect the reproductive, digestive and urinary organs - superior articular processes of the first sacral vertebrae articulate with the last lumber vertebrae - attaches the axial skeleton to the pelvic girdle of the appendicular skeleton - sacrum is curved, convex posterior surface - sacral canal is a passageway that begins between the articular processes and extends the length of the sacrum - nerves & membranes of spinal cord continue into canal - fused spinous processes form a ridge, median sacral crest - laminae at the 5th vertebrae do not contact one another at the midline forming the sacral cornua

49. Vertebral Regions Cont. - sacral hiatus: opening at the inferior end of canal - sacral foramina: opening on each side of the median sacral crest (4 pairs) - fused transverse processes create lateral sacral crests - site of muscle attachments - sacrum is curved (degree varies with sex and individual) - auricular surface: thick flattened area lateral and anterior to the superior portion of the lateral sacral crest - site of articulation with the pelvic girdle - sacral tuberosity: roughened area between the lateral sacral crest and the auricular surface - apex: narrow, inferior portion - base: broad superior surface - sacral promontory, prominent bulge at anterior tip of base - sacral ala: wings

50. Vertebral Regions Cont. • Coccyx - consist of 3-5 coccygeal vertebrae - begin fusing around 25 but do not fuse completely until late adulthood - provided attachment sites for ligaments and muscle -1st and 2nd vertebrae have transverse processes and unfused arches - prominent laminae of the 1st coccygeal vertebrae are known as the coccygeal cornua, curve to meet with sacral cornua