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Functions and Structure of Bones

This text explores the five functions of bones (support, protection, movement, storage, blood cell formation), the classification of bones by shape, bone textures, and the chemical composition of bone. It also covers bone formation, growth, and remodeling, including hormonal control and the response to mechanical stress. Additionally, it discusses homeostatic imbalances, such as osteoporosis. The text concludes with an overview of the axial and appendicular skeleton.

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Functions and Structure of Bones

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  1. Ch. 5 The skeletal system

  2. Five Functions of Bones • Support • For the body and soft organs • Protection • For brain, spinal cord, and vital organs • Movement • Levers for muscle action

  3. Functions of Bones • Storage • Minerals (calcium and phosphorus) and growth factors; Triglyceride (energy) storage in bone cavities • Blood cell formation (hematopoiesis) in marrow cavities

  4. Classification of Bones by Shape • Long bones • Longer than they are wide • All limb bones except carpals and tarsals, patella • Short bones • Cube-shaped bones (in wrist and ankle) • Sesamoid bones (within tendons, e.g., patella)

  5. Classification of Bones by Shape • Flat bones • Thin, flat, slightly curved • Examples: Sternum, scapulae, ribs most skull bones • Irregular bones • Complicated shapes • Examples: coxal, vertebrae

  6. Figure 6.2

  7. Bone Textures • Compact bone • Dense outer layer of bone • Composed of osteons • Spongy bone • Internal to compact bone & composed of trabeculae • No osteons • Spaces between trabeculae are filled with bone marrow

  8. Membranes of Bone • Periosteum • Surrounds entire outer surface of compact bone, except joint surfaces • Contains: Osteoblasts and osteoclasts • Secured to compact bone by Sharpey’s fibers • Endosteum • Lines internal surfaces of bone and also contains osteoblasts and osteoclasts

  9. Structure of a Long Bone • Diaphysis (shaft) • Compact bone collar surrounds medullary (marrow) cavity

  10. Structure of a Long Bone • Epiphyses • Expanded ends • Spongy bone interior • Epiphyseal line (remnant of growth plate) • Articular (hyaline) cartilage on joint surfaces

  11. Articular cartilage Compact bone Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) (b) Diaphysis Distal epiphysis (a) Figure 6.3a-b

  12. Structure of Short, Irregular, and Flat Bones • Endosteum covered spongy bone surrounded/sandwiched by compact bone covered in periosteum

  13. Spongy bone (diploë) Compact bone Trabeculae Figure 6.5

  14. Chemical Composition of Bone: Organic • Bone cells (osteoblasts, osteocytes, osteoclasts) • Osteoid—organic bone matrix secreted by osteoblasts

  15. Chemical Composition of Bone: Inorganic • Hydroxyapatites (mineral salts) • 65% of bone by mass • Mainly calcium phosphate crystals • Responsible for hardness and resistance to compression

  16. Bone Formation, Growth and Remodeling • Ossification- bone tissue formation • Stages • Bone formation—begins in the 2nd month of development • Postnatal bone growth—until early adulthood • Interstitial ( in length of long bones)and appositional ( in bone width & continues after adulthood) • Bone remodeling and repair—lifelong

  17. Month 3 Birth Childhood toadolescence Week 9 Articularcartilage Secondaryossificationcenter Spongybone Epiphysealblood vessel Area ofdeterioratingcartilage matrix Epiphysealplatecartilage Hyalinecartilage Medullarycavity Spongyboneformation Bonecollar Bloodvessel ofperiostealbud Primaryossificationcenter 1 2 3 4 5 Bone collarforms aroundhyaline cartilagemodel. Cartilage in thecenter of thediaphysis calcifiesand then developscavities. The periostealbud inavades theinternal cavitiesand spongy bonebegins to form. The diaphysis elongatesand a medullary cavityforms as ossificationcontinues. Secondaryossification centers appearin the epiphyses inpreparation for stage 5. The epiphysesossify. Whencompleted, hyalinecartilage remains onlyin the epiphysealplates and articularcartilages.

  18. Control of Remodeling • What controls continual remodeling of bone? • Hormonal mechanisms that maintain calcium homeostasis in the blood • Mechanical and gravitational forces

  19. Hormonal Control of Blood Ca2+ • Primarily controlled by parathyroid hormone (PTH)  Blood Ca2+ levels  Parathyroid glands release PTH  PTH stimulates osteoclasts to degrade bone matrix and release Ca2+   Blood Ca2+ levels

  20. Calcium homeostasis of blood: 9–11 mg/100 ml BALANCE BALANCE Stimulus Falling blood Ca2+ levels Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into blood. Parathyroid glands Parathyroid glands release parathyroid hormone (PTH). PTH

  21. Response to Mechanical Stress • Curved bones are thickest where they are most likely to buckle • Trabeculae form along lines of stress • Large, bony projections occur where heavy, active muscles attach

  22. Load here (body weight) Head of femur Tension here Compression here Point of no stress Figure 6.13

  23. Homeostatic Imbalances • Read about Osteoporosis and focus on its risk factors, symptoms and characteristics

  24. Figure 6.16

  25. The skeleton

  26. The Skeleton • Two Major Divisions of the Skeletal System: Axial and Appendicular • The Axial Skeleton Includes Three Regions: • Skull and associated bones (aud. ossicles and hyoid) • Vertebral column • Thoracic cage

  27. Cranium Skull Facial bones Clavicle Thoracic cage (ribs and sternum) Scapula Sternum Rib Humerus Vertebra Vertebral column Radius Ulna Sacrum Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals (a) Anterior view Phalanges Figure 7.1a

  28. The Skull • Two sets of bones • Cranial bones (8) • Enclose the brain in the cranial cavity • Calvaria: • Cranial base: anterior, middle, and posterior cranial fossae

  29. The Skull • Facial bones • Cavities for: special sense organs for sight, taste, and smell • Provide sites of attachment for: teeth and muscles of facial expression • All skull bones are joined by: sutures except temperomandibular joint(TMJ)

  30. Bones of cranium (cranial vault) Coronal suture Squamous suture Facial bones Lambdoid suture

  31. Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (b) Superior view of the cranial fossae

  32. Frontal Bone • Forms most of forehead • Superior wall of orbits

  33. Frontal bone Parietal bone Frontonasal suture Supraorbital foramen (notch) Squamous part of frontal bone Supraorbital margin (a) Anterior view Figure 7.4a

  34. Parietal Bones and Major Associated Sutures • Superior and lateral aspects of craniaum • Four sutures mark the articulations of parietal bones with frontal, occipital, and temporal bones: • Coronal suture—between parietal bones and frontal bone • Sagittal suture—between right and left parietal bones • Lambdoid suture—between parietal bones and occipital bone • Squamous (squamosal) sutures—between parietal and temporal bones on each side of skull

  35. Frontal bone Coronal suture Sphenoid bone (greater wing) Parietal bone Temporal bone Lambdoid suture Squamous suture Occipital bone (a) External anatomy of the right side of the skull Figure 7.5a

  36. Occipital Bone • Most of skull’s posterior wall and posterior cranial fossa • Articulates with 1st vertebra at occipital condyles • Contains the foramen magnum

  37. Sagittal suture Parietal bone Lambdoid suture Occipital bone Superior nuchal line External occipital protuberance Occipital condyle (b) Posterior view Figure 7.4b

  38. Occipital Condyles Foramen Magnum (a) Inferior view of the skull (mandible removed) Figure 7.6a

  39. Temporal Bones • Inferior to parietal bones • External acoustic canal leads to eardrum • Zygomatic process joins with cheek bone • Mandibular fossa for mandible

  40. External acoustic meatus Zygomatic process Mandibular fossa Mastoid process Styloid process Figure 7.8

  41. Sphenoid Bone • Complex, bat-shaped bone • Processes : greater & lesser wings • Contains the: sella turcica (for pituitary)

  42. Frontal bone Olfactory foramina Lesser wing Sphenoid Foramen rotundum Greater wing Foramen ovale Foramen spinosum Foramen lacerum Temporal bone (petrous part) Foramen magnum View Parietal bone Occipital bone (a) Superior view of the skull, calvaria removed Figure 7.7a

  43. Lesser wing Body of sphenoid Superior orbital fissure Greater wing Pterygoid process (b) Posterior view

  44. Ethmoid Bone • Helps form the nasal septum • Contains crista galli and cribriform plate for olfactory fibers to pass

  45. Frontal bone Parietal bone Nasal bone Sphenoid bone Temporal bone Ethmoid bone Lacrimal bone Middle nasal concha Zygomatic bone Ethmoid bone Perpendicular plate Inferior nasal concha Vomer (a) Anterior view Figure 7.4a

  46. Cribriform plate Frontal bone Ethmoid bone Crista galli Olfactory foramina Anterior cranial fossa Optic canal Lesser wing Sphenoid Foramen rotundum Greater wing Foramen ovale Foramen spinosum Hypophyseal fossa of sella turcica Foramen lacerum Middle cranial fossa Internal acoustic meatus Temporal bone (petrous part) Jugular foramen Hypoglossal canal Foramen magnum Posterior cranial fossa View Parietal bone Occipital bone (a) Superior view of the skull, calvaria removed

  47. Mandible • Lower jaw • Temporomandibular joint: only freely movable joint in skull

  48. Mandibular fossa of temporal bone Temporomandibular joint Mandibular condyle Figure 7.11a

  49. Maxillary Bones • Medially fused to form upper jaw • Carry teeth in the alveolar margin

  50. Articulates with frontal bone Alveolar margin (b) Maxilla, right lateral view Figure 7.11b

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