Skeletal Tissue & The Axial Skeleton Human Anatomy Sonya Schuh-Huerta, Ph.D.

1. Skeletal Tissue & The Axial Skeleton Human Anatomy Sonya Schuh-Huerta, Ph.D.

2. Skeletal Tissue, Ch 6

3. The Skeletal System • Composed of bones, cartilages, & joints • that form the internal framework of body • -We’ll explore the microscopic & gross structure • of the skeletal tissues & system

4. Cartilage • Location & basic structure • Found throughout adult body • Ear & epiglottis • Articular cartilages & costal cartilage • Larynx, trachea, & nose • Intervertebral discs, pubic symphysis, & articular discs

5. Cartilage Cartilage in external ear Cartilages in nose Articular cartilage of a joint Epiglottis Larynx Thyroid cartilage Costal cartilage Cartilage in intervertebral disc Cricoid cartilage Trachea Lung Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Cartilages Hyaline cartilages Respiratory tube cartilages in neck and thorax Elastic cartilages Fibrocartilages

6. Cartilage • Is surrounded by perichondrium • Consists primarily of water • Resilient tissue it springs back to original shape

7. Types of Cartilage – Review! • Hyaline cartilage (glassy) • Most abundant cartilage • Provides support through flexibility • Elastic cartilage contains many elastic fibers • Able to tolerate repeated bending • Fibrocartilage resists strong compression & strong tension • An intermediate between hyaline & elastic

8. Cartilages in the Adult Body(remember these?…) Chondrocyte in a lacuna Chondrocyte in a lacuna Matrix Elastic fibers Lacuna Gelatinous ground substance Perichondrium (a) Hyaline cartilage (180) (b) Elastic cartilage (470) Chondrocyte in a lacuna Collagen fibers (c) Fibrocartilage (285)

9. Growth of Cartilage • Appositional growth • Chondroblasts in surrounding perichondrium produce new cartilage • Interstitial growth • Chondrocytes within cartilage divide & secrete new matrix • Cartilage stops growing when the skeleton stops growing

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

11. Function of Bones • Support – provides hard framework • Movement – skeletal muscles use • bones as levers • Protection of underlying organs • Mineral storage – reservoir for important minerals •  Ca2+ • Blood-cell formation – bone contains red marrow • Energy metabolism – osteoblasts secrete osteocalcin; & yellow marrow stores fat

12. Bone Tissue • Bone tissue • Organic components  cells, fibers, & ground substance • Inorganic components  mineral salts that invade bony matrix (calcium phosphate)

13. Extracellular Matrix • Unique composition of matrix • Gives bone exceptional properties • 35%  organic components • Contributes to flexibility & tensile strength • 65%  inorganic components • Provides exceptional • hardness, & • resists compression!

14. Cells in Bone • 3 types of cells in bone produce or maintain bone: • Osteogenic cells stem cells that differentiate into osteoblasts • Osteoblasts actively produce & secrete bone matrix • Bone matrix = osteoid • Osteocytes housed within lacunae, keep bone matrix healthy

15. Cells in Bone • Osteoclasts – 4th type of cell • Responsible for resorption of bone • Secrete hydrochloric acid (HCl) & lysosomal enzymes to break down bone • The “Grim Reaper” • of bone http://faculty.une.edu/com/abell/histo/histolab3.htm

16. Classification of Bones • Long bones longer than wide; a shaft plus ends • Short bones  roughly cube-shaped • Flat bones thin and flattened, usually curved • Irregular bones various shapes, do not fit into other categories

17. Classification of Bones

18. Gross Anatomy of Bones • Compact bone dense outer layer of bone • Spongy bone  internal network of bone

19. Structure of a Typical Long Bone • Diaphysis = “shaft” of a bone • Epiphysis = ends of a bone • Blood vessels well vascularized • Medullary cavity = hollow cavity filled • with yellow marrow • Membranes • Periosteum, perforating fibers, & • endosteum

20. Structure of a Long Bone Articular cartilage Compact bone Proximal epiphysis Spongy bone Endosteum Epiphyseal line Endosteum Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries Distal epiphysis

21. Microscopic Structure of Compact Bone • Compact Bone • Contains passage ways for blood vessels, lymph vessels, & nerves • Osteons long cylindrical structures • Function in support • Structurally – resembles rings of a tree in c.s.

22. Microscopic Structure of Compact Bone Spongy bone Compact bone Central (Haversian) canal Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Osteon (Haversian system) Circumferential lamellae Perforating (Sharpey’s) fibers Periosteal blood vessel Lamellae Periosteum Nerve Vein Lamellae Lamellae Artery Central canal Central canal Canaliculi Lacunae Lacunae Osteocyte in a lacuna Lacuna (with osteocyte) Interstitial lamellae

23. Microscopic Structure of Compact Bone • Osteons contain: • Lamellae • Central canal • Perforating canals • Canaliculi Lacuna (with osteocyte) Interstitial lamellae Lamellae Central canal Lacunae

24. Microscopic Structure of Compact Bone Artery with capillaries Structures in the central canal Vein Nerve fiber Lamellae Collagen fibers run in different directions Twisting force

25. Microscopic Structure of Spongy Bone • Spongy Bone • Is less complex than compact bone • Trabeculae contain layers of lamellae & osteocytes • Are too small to contain osteons (no “tree rings”)

26. Microscopic Structure of Spongy Bone Marrow space Trabecula Osteocytes Endosteum Osteoblasts

27. Structure of Short, Irregular, & Flat Bones • Contain bone marrow but no marrow cavity • Diploë • = Internal spongy bone of flat bones Spongy bone (diploë) Compact bone Trabeculae

28. Gross Anatomy of Bones Load here (body weight) • Bone design & stress • Anatomy of a bone reflects stresses • Compression & tension greatest at external surfaces Head of femur Compression here Tension here Point of no stress

29. Bone Markings • Superficial surfaces of bones reflect stresses on them • 3 broad categories of bone markings: • Projections for muscle attachment • Surfaces that form joints • Depressions & openings

30. Bone Markings

32. Bone Development • Ossification (osteogenesis) = bone-tissue formation • Membrane bones formed directly from mesenchyme (during embryonic period) • Intramembranous ossification • Other bones  develop initially from hyaline cartilage • Endochondral ossification

33. Intramembranous Ossification Mesenchymal cell Osteoblast Osteoid Collagen fiber Osteocyte Ossification center Newly calcified bone matrix Osteoid Osteoblast 2 1 Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to secrete osteoid, which is calcified within a few days. • Trapped osteoblasts become osteocytes. Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center.

34. Intramembranous Ossification Fibrous periosteum Mesenchyme condensing to form the periosteum Osteoblast Plate of compact bone Trabeculae of woven bone Diploë (spongy bone) cavities contain red marrow Blood vessel 4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken and are later replaced with mature lamellar bone, forming compact bone plates. • Spongy bone (diploë), consisting of distinct trabeculae, persists internally, and its vascular tissue becomes red marrow. 3 Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae called woven bone. • Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.

35. Endochondral Ossification • All bones except some bones of the skull & clavicles • Bones are 1st modeled in hyaline cartilage • Begins forming late in the 2nd month of embryonic development • Continues forming until early adulthood

36. Primary ossification centers in the skeleton of a 12-week fetus Parietal bone Occipital bone Frontal bone of skull Mandible Clavicle Scapula Radius Ulna Humerus Ribs Vertebra Ilium Tibia Femur

37. Stages in Endochondral Ossification Childhood to adolescence Month 3 Week 9 Birth Articular cartilage Secondary ossification center Spongy bone Epiphyseal blood vessel Area of deteriorating cartilage matrix Epiphyseal plate cartilage Hyaline cartilage Medullary cavity Spongy bone formation Bone collar Blood vessel of periosteal bud Primary ossification center 4 3 5 1 2 Bone collar forms around hyaline cartilage model. Cartilage in the center of the diaphysis calcifies and then develops cavities. The periosteal bud invades the internal cavities, and spongy bone begins to form. The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5. The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

38. Anatomy of Epiphyseal Growth Areas • In epiphyseal plates of growing bones: • 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 • As chondrocytes die, osteoblasts replace them & secrete bone matrix  lengthens bone

39. Anatomy of Epiphyseal Growth Areas • Older chondrocytes signal surrounding matrix to calcify • Older chondrocytes then die & 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

40. Organization of Cartilage within Epiphyseal Plate of Growing Long Bone Resting zone Proliferation zone Cartilage cells undergo mitosis. 1 Hypertrophic zone Older cartilage cells enlarge. 2 Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. 3 Calcified cartilage spicule Osseous tissue Ossification zone New bone formation is occurring. 4

41. Postnatal Growth of Endochondral Bones • During childhood & adolescence: • Bones lengthen entirely by growth of theepiphyseal plates • Cartilage is replaced with bone CT as quickly as it grows • Epiphyseal plate maintains constant thickness • Whole bone lengthens

42. Hormonal Regulation of Bone Growth • Growth hormone produced by the pituitary gland • Stimulates epiphyseal plates (lengthens bones) • Thyroid hormone ensures that the skeleton retains proper proportions • Sex hormones (estrogen & testosterone) • Promote bone growth • But also later induces closure of epiphyseal plates (~stop growing shortly after puberty!)

43. Postnatal Growth of Endochondral Bones • As adolescence draws to an end: • Chondroblasts divide less often • Epiphyseal plates become thinner • Cartilage stops growing • Replaced by bone tissue  no more addition • Long bones stop lengthening when diaphysis & epiphysis fuse

44. Postnatal Growth of Endochondral Bones • Growing bones widen as they lengthen • Osteoblasts add bone tissue to the external surface of the diaphysis • Osteoclasts remove bone from the internal surface of the diaphysis • Appositional growth growth of a bone by addition of bone tissue to its surface

45. Bone Remodeling • Bone is dynamic living tissue • 500 mg of calcium may enter or leave the adult skeleton each day!!! • Some bone of the skeleton is replaced every 3–4 years • Compact bone is replaced every 10 years

46. Bone Remodeling • Bone deposit & removal • Occurs at periosteal & endosteal surfaces • Bone remodeling • Bone deposition accomplished by osteoblasts • Bone reabsorption accomplished by osteoclasts

47. Osteoclast: A Bone-Degrading Cell • A giant cell with many nuclei • Crawls along bone surfaces • Breaks down bone tissue (reabsorption) • Secretes concentrated HCl • Lysosomal enzymes are released • Derived from blood stem cells Bone matrix Osteocyte within a lacuna Ruffled border of osteoclast Nuclei

48. Injuries to Bone: Common Types of Fractures

49. Common Types of Fractures

50. Common Types of Fractures