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Anatomy & Physiology I Lecture 5 Chapter 6: Bones and Skeletal Tissues.

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1 Anatomy & Physiology I Lecture 5 Chapter 6: Bones and Skeletal Tissues

2 Human Skeleton Initially made up of cartilages and fibrous membranes before becoming bone. Remaining cartilage found where flexible skeletal tissue is needed

3 Skeletal Cartilage Hyaline cartilage – Provides support, flexibility, and resilience – Collagen fibers only Elastic cartilage – Similar to hyaline cartilage, but contains elastic fibers Fibrocartilage – Thick collagen fibers—has great tensile strength

4 Hyaline Cartilages Articular – covers the ends of most bones at movable joints Costal – connects ribs to sternum Respiratory – form the skeleton of the larynx, reinforce respiratory passageway Nasal – support the external nose

5 © 2013 Pearson Education, Inc. Figure 6.1 The bones and cartilages of the human skeleton. Cartilage in external ear Cartilage in intervertebral disc Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Costal cartilage Articular cartilage of a joint Cartilages in nose Epiglottis Thyroid cartilage Cricoid cartilage Larynx Trachea Lung Bones of skeleton Axial skeleton Appendicular skeleton Hyaline cartilages Elastic cartilages Fibrocartilages Cartilages Respiratory tube cartilages in neck and thorax

6 Cartilage Growth??

7 Classification of Bones 206 named bones in skeleton Divided into two groups Axial skeleton – Long axis of body – Skull, vertebral column, rib cage Appendicular skeleton – Bones of upper and lower limbs – Girdles attaching limbs to axial skeleton

8 © 2013 Pearson Education, Inc. Figure 6.1 The bones and cartilages of the human skeleton. Cartilage in external ear Cartilage in intervertebral disc Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Costal cartilage Articular cartilage of a joint Cartilages in nose Epiglottis Thyroid cartilage Cricoid cartilage Larynx Trachea Lung Bones of skeleton Axial skeleton Appendicular skeleton Hyaline cartilages Elastic cartilages Fibrocartilages Cartilages Respiratory tube cartilages in neck and thorax

9 Classification of Bones by Shape Long bones Short bones Flat bones Irregular bones

10 Long Bones Longer than they are wide All bones but the patella, wrist and ankle

11 Short Bones Cube-shaped bones – wrist and ankle Sesamoid bones (within tendons) – Patella Vary in size and number in different individuals

12 Flat Bones Thin, flat, slightly curved Sternum, scapulae, ribs, most skull bones

13 Irregular Bones Complicated shapes Vertebrae, coxal bones

14 © 2013 Pearson Education, Inc. Figure 6.2 Classification of bones on the basis of shape. Long bone (humerus) Flat bone (sternum) Irregular bone (vertebra), right lateral view Short bone (talus)

15 Important Functions of Bones Support – for body and soft organs Protection – for brain, spinal cord, and vital organs Movement – Levers for muscle action

16 Important Functions of Bones Mineral and growth factor storage – Calcium and phosphorus, and growth factors reservoir Blood cell formation (Hematopoiesis) – red marrow cavities of certain bones Triglyceride (fat) storage – Energy source when needed

17 Important Functions of Bones Hormone production: Osteocalcin – Regulates bone formation – Protects against obesity, glucose intolerance, diabetes mellitus

18 Bones are Organs Contain different types of tissues – Bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells in its blood vessels Three levels of structure – Gross anatomy – Microscopic – Chemical

19 Gross Anatomy Bone textures – Compact and spongy bone Compact – Dense outer layer; smooth and solid Spongy (cancellous or trabecular) – Honeycomb of flat pieces of bone deep to compact called trabeculae – open spaces filled with red or yellow bone marrow

20 © 2013 Pearson Education, Inc. Figure 6.3 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone. Spongy bone (diploë) Compact bone Trabeculae of spongy bone

21 Membranes of Bone Bones are covered inside and outside by connective tissue membranes Periosteum – outside Endosteum – inside

22 © 2013 Pearson Education, Inc. Figure 6.4a The structure of a long bone (humerus of arm). Articular cartilage Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Proximal epiphysis Diaphysis Distal epiphysis

23 Structure of Long Bone Diaphysis – Tubular shaft forms long axis – Compact bone surrounding medullary cavity Epiphyses – Bone ends – External compact bone; internal spongy bone Between is epiphyseal line – Remnant of childhood bone growth at epiphyseal plate

24 Periosteum Membrane White, double-layered membrane that covers external surfaces except joint surfaces – Many nerve fibers and blood vessels Outer fibrous layer of dense irregular connective tissue – secure to bone matrix Inner layer abuts contains osteogenic cells gives rise to bone cells Anchoring points for tendons and ligaments

25 Endosteum Membrane Delicate connective tissue membrane covering internal bone surface Covers trabeculae of spongy bone Lines canals that pass through compact bone Contains osteogenic cells that can differentiate into other bone cells

26 © 2013 Pearson Education, Inc. Figure 6.4c The structure of a long bone (humerus of arm). Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey ’ s) fibers Nutrient arteries

27 Marrow Yellow – hollow interior of long – made up of fat cells – can convert itself into red bone marrow Red – within trabecular cavities of spongy bone – hematopoietic tissue

28 Bone Markings Sites of muscle, ligament, and tendon attachment on external surfaces Joint surfaces Conduits for blood vessels and nerves Three types – Projections – Depressions – Openings

29 Bone Markings Projections – Most indicate stresses created by muscle pull or joint modifications Depressions and openings – Usually allow nerves and blood vessels to pass

30 © 2013 Pearson Education, Inc. Table 6.1 Bone Markings (1 of 2)

31 © 2013 Pearson Education, Inc. Table 6.1 Bone Markings (2 of 2)

32 Cells of Bone Tissue Five major cell types Each specialized form of same basic cell type – Osteogenic cells – Osteoblasts – Osteocytes – Bone lining cells – Osteoclasts

33 Osteogenic Cells Also called osteoprogenitor cells Mitotically active stem cells in periosteum and endosteum When stimulated differentiate into osteoblasts or bone lining cells Some persist as osteogenic cells

34 Osteoblasts Bone-forming cells Secrete unmineralized bone matrix or osteoid – Includes collagen and calcium-binding proteins – Collagen = 90% of bone protein Actively mitotic

35 Osteocytes Mature bone cells in lacunae Monitor and maintain bone matrix Act as stress or strain sensors Respond to and communicate mechanical stimuli to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur

36 Bone Lining Cells Flat cells on bone surfaces believed to help maintain matrix On external bone surface called periosteal cells Lining internal surfaces called endosteal cells

37 Osteoclasts Derived from hematopoietic stem cells that become macrophages Giant, multinucleate cells for bone resorption

38 Compact Bone Also called lamellar bone Withstands stress – resist twisting Osteon or Haversian system – Structural unit of compact bone – Elongated cylinder parallel to long axis of bone – Hollow tubes of bone matrix called lamellae – Collagen fibers in adjacent rings run in different directions

39 © 2013 Pearson Education, Inc. Figure 6.6 A single osteon. Structures in the central canal Artery with capillaries Vein Nerve fiber Collagen fibers run in different directions Twisting force Lamellae

40 © 2013 Pearson Education, Inc. Figure 6.7 Microscopic anatomy of compact bone. Compact boneSpongy bone Central (Haversian) canal Osteon (Haversian system) Circumferential lamellae Perforating (Volkmann ’ s) canal Endosteum lining bony canals and covering trabeculae Perforating (Sharpey ’ s) fibers Periosteal blood vessel Periosteum Lamellae Nerve Vein Artery Canaliculi Osteocyte in a lacuna Lamellae Central canal Lacunae Interstitial lamella Lacuna (with osteocyte)

41 Canals and canaliculi Central (Haversian) canal runs through core of osteon Contains blood vessels and nerve fibers Lacunae—small cavities that contain osteocytes Canaliculi—hairlike canals that connect lacunae to each other and central canal

42 Interstitial and Circumferential Lamellae Interstitial lamellae – Incomplete lamellae not part of complete osteon – Fill gaps between forming osteons – Remnants of osteons cut by bone remodeling Circumferential lamellae – Just deep to periosteum – Superficial to endosteum – Extend around entire surface of diaphysis – Resist twisting of long bone

43 Making up the Osteoid Osteoid—1/3 of organic bone matrix secreted by osteoblasts – Made of ground substance (proteoglycans and glycoproteins) – Collagen fibers – Contributes to structure; provides tensile strength and flexibility

44 Sacrificial Bonds Resilience of bone due to sacrificial bonds in or between collagen molecules Stretch and break easily on impact to dissipate energy and prevent fracture If no addition trauma, bonds re-form

45 Inorganic Components Hydroxyapatites (mineral salts) – 65% of bone by mass – Mainly of tiny calcium phosphate crystals in and around collagen fibers – Responsible for hardness and resistance to compression

46 Bone Summary Half as strong as steel in resisting compression As strong as steel in resisting tension Last long after death because of mineral composition Reveal information about ancient people Can display growth arrest lines – Horizontal lines on bones – Proof of illness - when bones stop growing so nutrients can help fight disease

47 Bone Development Ossification (osteogenesis) – Process of bone tissue formation – Formation of bony skeleton – Begins in 2nd month of development Postnatal bone growth – Until early adulthood Bone remodeling and repair – Lifelong

48 Two Types of Ossification Endochondral ossification – Bone forms by replacing hyaline cartilage – Bones called cartilage (endochondral) bones – Forms most of skeleton Intramembranous ossification – Bone develops from fibrous membrane – Bones called membrane bones – Forms flat bones (clavicles and cranial bones)

49 Endochondral ossification Primary ossification center in center of shaft Blood vessel infiltration Bone collar forms around diaphysis of cartilage model Central cartilage in diaphysis calcifies, then develops cavities Periosteal bud invades cavities Diaphysis elongates & medullary cavity forms Epiphyses ossify

50 © 2013 Pearson Education, Inc. Figure 6.8 Endochondral ossification in a long bone. Week 9Month 3Birth Childhood to adolescence Hyaline cartilage Bone collar Primary ossification center Area of deteriorating cartilage matrix Spongy bone formation Blood vessel of periosteal bud Epiphyseal blood vessel Secondary ossification center Articular cartilage Spongy bone Epiphyseal plate cartilage Medullary cavity Bone collar forms around the diaphysis of the 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 forms. The diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses. The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages Slide 1

51 Intramembrane Ossification Forms frontal, parietal, occipital, temporal bones, and clavicles Begins within fibrous connective tissue membranes formed by mesenchymal cells – Ossification centers appear – Osteoid is secreted – Woven bone and periosteum form – Lamellar bone replaces woven bone & red marrow appears

52 © 2013 Pearson Education, Inc. Figure 6.9 Intramembranous ossification. Mesenchymal cell Collagen fibril Ossification center Osteoid Osteoblast 1 Ossification centers appear in the fibrous connective tissue membrane. Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center that produces the first trabeculae of spongy bone. Slide 2

53 © 2013 Pearson Education, Inc. Figure 6.9 Intramembranous ossification. Osteoblast Osteoid Osteocyte Newly calcified bone matrix 2 Osteoid is secreted within the fibrous membrane and calcifies. Osteoblasts begin to secrete osteoid, which calcifies in a few days. Trapped osteoblasts become osteocytes. Slide 3

54 © 2013 Pearson Education, Inc. Figure 6.9 Intramembranous ossification. Trabeculae of woven bone Blood vessel 3 Woven bone and periosteum form. Accumulating osteoid is laid down between embryonic blood vessels in a manner that results in a network (instead of concentric lamellae) of trabeculae called woven bone. Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum. Mesenchyme condensing to form the periosteum Slide 4

55 © 2013 Pearson Education, Inc. Figure 6.9 Intramembranous ossification. Fibrous periosteum Osteoblast Plate of compact bone Diploë (spongy bone) cavities contain red marrow 4 Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Trabeculae just deep to the periosteum thicken. Mature lamellar bone replaces them, forming compact bone plates. Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow. Slide 5

56 Bone Growth Interstitial (longitudinal) growth – Increase in length of long bones Appositional growth – Increase in bone thickness

57 Interstitial (longitudinal) growth Requires presence of epiphyseal cartilage Epiphyseal plate maintains constant thickness Rate of cartilage growth on one side balanced by bone replacement on other Concurrent remodeling of epiphyseal ends to maintain proportion

58 © 2013 Pearson Education, Inc. Figure 6.11 Long bone growth and remodeling during youth. Bone growth Bone remodeling Cartilage grows here. Bone replaces cartilage here. Cartilage grows here. Bone replaces cartilage here. Articular cartilage Epiphyseal plate Bone that was here has been resorbed. Appositional growth adds bone here. Bone that was here has been resorbed.

59 © 2013 Pearson Education, Inc. Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. 4 Ossification zone New bone forms. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules

60 Appositional Growth Allows lengthening bone to widen Occurs throughout life – Osteoblasts beneath periosteum secrete bone matrix on external bone – Osteoclasts remove bone on endosteal surface Usually more building up than breaking down – Thicker, stronger bone but not too heavy

61 © 2013 Pearson Education, Inc. Figure 6.11 Long bone growth and remodeling during youth. Bone growth Bone remodeling Cartilage grows here. Bone replaces cartilage here. Cartilage grows here. Bone replaces cartilage here. Articular cartilage Epiphyseal plate Bone that was here has been resorbed. Appositional growth adds bone here. Bone that was here has been resorbed.

62 Hormone Regulation of Bone Growth Growth hormone – Most important in stimulating epiphyseal plate activity in infancy and childhood Thyroid hormone – Modulates activity of growth hormone – Ensures proper proportions Testosterone (males) and estrogens (females) at puberty – Promote adolescent growth spurts – End growth by inducing epiphyseal plate closure

63 Bone Homeostasis Recycle 5-7% of bone mass each week Spongy bone replaced ~ every 3-4 years Compact bone replaced ~ every 10 years Older bone becomes more brittle – Calcium salts crystallize – Fractures more easily Consists of bone remodeling and bone repair

64 © 2013 Pearson Education, Inc. Figure 6.11 Long bone growth and remodeling during youth. Bone growth Bone remodeling Cartilage grows here. Bone replaces cartilage here. Cartilage grows here. Bone replaces cartilage here. Articular cartilage Epiphyseal plate Bone that was here has been resorbed. Appositional growth adds bone here. Bone that was here has been resorbed.

65 Control of Remodeling Occurs continuously but regulated by genetic factors and two control loops 1.Negative feedback hormonal loop for Ca2+ homeostasis – Controls blood Ca2+ levels; Not bone integrity 2.Responses to mechanical and gravitational forces

66 Calcium Functions in – Nerve impulse transmission – Muscle contraction – Blood coagulation 1200 – 1400 grams of calcium in body – 99% as bone minerals – Amount in blood tightly regulated (9-11 mg/dl) – Intestinal absorption from diet

67 Hormones for Calcium Parathyroid hormone (PTH) – Produced by parathyroid glands – Removes calcium from bone regardless of bone integrity Acts to control blood Ca 2+ levels, not bone integrity

68 Response to Mechanical Stress Bones reflect stresses they encounter – Long bones thickest midway along diaphysis where bending stresses greatest Bones stressed when weight bears on them or muscles pull on them – Usually off center so tends to bend bones – Bending compresses on one side; stretches on other

69 Wolff’s Law Bones grow or remodel in response to demands placed on it Explains – Handedness (right or left handed) results in thicker and stronger bone of that upper limb – Curved bones thickest where most likely to buckle – Trabeculae form trusses along lines of stress – Large, bony projections occur where heavy, active muscles attach

70 © 2013 Pearson Education, Inc. Figure 6.13 Bone anatomy and bending stress. Load here (body weight) Head of femur Compression here Point of no stress Tension here

71 © 2013 Pearson Education, Inc. Figure 6.14 Vigorous exercise can strengthen bone. Cross- sectional dimension of the humerus Added bone matrix counteracts added stress Serving armNonserving arm

72 End Result Hormonal controls determine whether and when remodeling occurs to changing blood calcium levels Mechanical stress determines where remodeling occurs

73 Lab Today Lab Exercise 9 You can start on exercise 10 – Labs 10 and 11 are long and detailed – Will take you a long time to memorize and understand these two labs – Having more than 1 lab period to cover them is adviced


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