Functions of the Skeletal System. Chapter 6: Osseous Tissue and Bone Structure. Classification of Bones. Bone Shapes

Transcription

1 Chapter 6: Osseous Tissue and Bone Structure Functions of the Skeletal System 1. Support 2. Storage of minerals (calcium) 3. Storage of lipids (yellow marrow) 4. Blood cell production (red marrow) 5. Protection 6. Leverage (force of motion) Classification of Bones Bone are identified by: shape internal tissues bone markings 1. Long bones 2. Flat bones 3. Sutural bones 4. Irregular bones 5. Short bones 6. Sesamoid bones Bone Shapes 1

2 Long Bones Long Bones Are long and thin Are found in arms, legs, hands, feet, fingers, and toes Figure 6 1a Flat Bones Flat Bones Are thin with parallel surfaces Are found in the skull, sternum, ribs, and scapula Figure 6 1b 2

3 Sutural Bones Sutural Bones Are small, irregular bones Are found between the flat bones of the skull Figure 6 1c Irregular Bones Irregular Bones Have complex shapes Examples: spinal vertebrae pelvic bones Figure 6 1d 3

4 Short Bones Short Bones Are small and thick Examples: ankle wrist bones Figure 6 1e Sesamoid Bones Sesamoid Bones Are small and flat Develop inside tendons near joints of knees, hands, and feet Figure 6 1f 4

5 Bone Markings Long Bones The femur Table 6 1 (1 of 2) Figure 6 2a Long Bones Diaphysis: the shaft Epiphysis: wide part at each end articulation with other bones Metaphysis: where diaphysis and epiphysis meet The Diaphysis A heavy wall of compact bone, or dense bone A central space called marrow cavity 5

6 The Epiphysis Mostly spongy (cancellous) bone Covered with compact bone (cortex) Flat Bones The parietal bone of the skull Figure 6 2b Flat Bones Resembles a sandwich of spongy bone Between 2 layers of compact bone What are the types and functions of bone cells? 6

7 Bone (Osseous) Tissue Dense, supportive connective tissue Contains specialized cells Produces solid matrix of calcium salt deposits Around collagen fibers Characteristics of Bone Tissue Dense matrix, containing: deposits of calcium salts bone cells within lacunae organized around blood vessels Characteristics of Bone Tissue Canaliculi: form pathways for blood vessels exchange nutrients and wastes Characteristics of Bone Tissue Periosteum: covers outer surfaces of bones consist of outer fibrous and inner cellular layers 7

8 Matrix Minerals 2/3 of bone matrix is calcium phosphate, Ca 3 (PO 4 ) 2 : reacts with calcium hydroxide, Ca(OH) 2 to form crystals of hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 which incorporates other calcium salts and ions 1/3 of bone matrix is protein fibers (collagen) Bone Cells Make up only 2% of bone mass: osteocytes osteoblasts osteoprogenitor cells osteoclasts Osteocytes Mature bone cells that maintain the bone matrix Osteocytes Live in lacunae Are between layers (lamellae) of matrix Connect by cytoplasmic extensions through canaliculi in lamellae Do not divide Figure 6 3 (1 of 4) 8

9 Osteoblasts Immature bone cells that secrete matrix compounds (osteogenesis) Osteoprogenitor Cells Mesenchymal stem cells that divide to produce osteoblasts Figure 6 3 (2 of 4) Figure 6 3 (3 of 4) Osteoprogenitor Cells Are located in inner, cellular layer of periosteum (endosteum) Assist in fracture repair Osteoclasts Secrete acids and protein-digesting enzymes Figure 6 3 (4 of 4) 9

10 Homeostasis Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance: more breakdown than building, bones become weak exercise causes osteocytes to build bone What is the difference between compact bone and spongy bone? Compact Bone Osteon The basic unit of mature compact bone Osteocytes are arranged in concentric lamellae Around a central canal containing blood vessels Figure

11 Perforating Canals Perpendicular to the central canal Carry blood vessels into bone and marrow Circumferential Lamellae Lamellae wrapped around the long bone Binds osteons together Spongy Bone Spongy Bone Does not have osteons The matrix forms an open network of trabeculae Trabeculae have no blood vessels Figure

12 Red Marrow The space between trabeculae is filled with red bone marrow: which has blood vessels forms red blood cells and supplies nutrients to osteocytes Periosteum and Endosteum Compact bone is covered with membrane: periosteum on the outside endosteum on the inside Periosteum Periosteum Covers all bones: except parts enclosed in joint capsules It is made up of: an outer, fibrous layer and an inner, cellular layer Figure 6 8a 12

13 Perforating Fibers Collagen fibers of the periosteum: connect with collagen fibers in bone and with fibers of joint capsules, attached tendons, and ligaments Functions of Periosteum 1. Isolate bone from surrounding tissues 2. Provide a route for circulatory and nervous supply 3. Participate in bone growth and repair Endosteum Endosteum An incomplete cellular layer: lines the marrow cavity covers trabeculae of spongy bone lines central canals Figure 6 8b 13

14 Ossification What is the difference between intramembranous ossification and endochondral ossification? The 2 main forms of ossification are: intramembranous ossification endochondral ossification Intramembranous Ossification: Step 1 Intramembranous Ossification: Step 1 Mesenchymal cells aggregate: differentiate into osteoblasts begin ossification at the ossification center develop projections called spicules Figure 6 11 (Step 1) 14

15 Intramembranous Ossification: Step 2 Intramembranous Ossification: Step 2 Blood vessels grow into the area: to supply the osteoblasts Spicules connect: trapping blood vessels inside bone Figure 6 11 (Step 2) Intramembranous Ossification: Step 3 Intramembranous Ossification: Step 3 Spongy bone develops and is remodeled into: osteons of compact bone periosteum or marrow cavities Figure 6 11 (Step 3) 15

16 Endochondral Ossification Ossifies bones that originate as hyaline cartilage Most bones originate as hyaline cartilage Growth and ossification of long bones occurs in 6 steps Endochondral Ossification: Step 1 Chondrocytes in the center of hyaline cartilage: enlarge form struts and calcify die, leaving cavities in cartilage Figure 6 9 (Step 1) Endochondral Ossification: Step 2 Endochondral Ossification: Step 2 Blood vessels grow around the edges of the cartilage Cells in the perichondrium change to osteoblasts: producing a layer of superficial bone around the shaft which will continue to grow and become compact bone (appositional growth) Figure 6 9 (Step 2) 16

17 Endochondral Ossification: Step 3 Blood vessels enter the cartilage: bringing fibroblasts that become osteoblasts spongy bone develops at the primary ossification center Endochondral Ossification: Step 4 Remodeling creates a marrow cavity: bone replaces cartilage at the metaphyses Figure 6 9 (Step 3) Figure 6 9 (Step 4) Endochondral Ossification: Step 5 Capillaries and osteoblasts enter the epiphyses: creating secondary ossification centers Endochondral Ossification: Step 6 Figure 6 9 (Step 5) Figure 6 9 (Step 6) 17

18 Endochondral Ossification: Step 6 Epiphyses fill with spongy bone: cartilage within the joint cavity is articulation cartilage cartilage at the metaphysis is epiphyseal cartilage Endochondral Ossification Appositional growth: compact bone thickens and strengthens long bone with layers of circumferential lamellae Figure 6 9 (Step 2) Epiphyseal Lines Epiphyseal Lines When long bone stops growing, after puberty: epiphyseal cartilage disappears is visible on X-rays as an epiphyseal line Figure

19 Mature Bones As long bone matures: osteoclasts enlarge marrow cavity osteons form around blood vessels in compact bone Blood Supply of Mature Bones 3 major sets of blood vessels develop Figure 6 12 Blood Vessels of Mature Bones Nutrient artery and vein: a single pair of large blood vessels enter the diaphysis through the nutrient foramen Metaphyseal vessels: supply the epiphyseal cartilage where bone growth occurs Periosteal vessels provide: blood to superficial osteons secondary ossification centers How does the skeletal system remodel and maintain homeostasis, and what are the effects of nutrition, hormones, exercise, and aging on bone? 19

20 Remodeling The adult skeleton: maintains itself replaces mineral reserves Remodeling: recycles and renews bone matrix involves osteocytes, osteoblasts, and osteoclasts KEY CONCEPTS Bone continually remodels, recycles, and replaces Turnover rate varies If deposition is greater than removal, bones get stronger If removal is faster than replacement, bones get weaker KEY CONCEPTS What you don t use, you lose Stresses applied to bones during physical activity are essential to maintain bone strength and mass Calcitriol The hormone calcitriol: is made in the kidneys helps absorb calcium and phosphorus from digestive tract synthesis requires vitamin D 3 (cholecalciferol) 20

21 Vitamins Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation Vitamin A stimulates osteoblast activity Vitamins K and B 12 help synthesize bone proteins Other Hormones Growth hormone and thyroxine stimulate bone growth Estrogens and androgens stimulate osteoblasts Calcitonin and parathyroid hormone regulate calcium and phosphate levels Hormones for Bone Growth and Maintenance Calcium Regulation Calcium ions in body fluids: must be closely regulated Homeostasis is maintained: by calcitonin and parathyroid hormone which control storage, absorption, and excretion Table

22 Calcitonin and Parathyroid Hormone Control Bones: where calcium is stored Digestive tract: where calcium is absorbed Kidneys: where calcium is excreted Parathyroid Hormone (PTH) Figure 6 14a Parathyroid Hormone (PTH) Calcitonin Produced by parathyroid glands in neck Increases calcium ion levels by: stimulating osteoclasts increasing intestinal absorption of calcium decreases calcium excretion at kidneys Figure 6 14b 22

23 Calcitonin Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by: inhibiting osteoclast activity increasing calcium excretion at kidneys KEY CONCEPTS Calcium and phosphate ions in blood are lost in urine Ions must be replaced to maintain homeostasis If not obtained from diet, ions are removed from the skeleton, weakening bones Exercise and nutrition keep bones strong Fractures Fracture Repair: Step 1 Fractures: cracks or breaks in bones caused by physical stress Fractures are repaired in 4 steps Figure 6 15 (Step 1) 23

24 Fracture Repair: Step 1 Fracture Repair: Step 2 Bleeding: produces a clot (fracture hematoma) establishes a fibrous network Bone cells in the area die Figure 6 15 (Step 2) Fracture Repair: Step 2 Fracture Repair: Step 3 Cells of the endosteum and periosteum: Divide and migrate into fracture zone Calluses stabilize the break: external callus of cartilage and bone surrounds break internal callus develops in marrow cavity Figure 6 15 (Step 3) 24

25 Fracture Repair: Step 3 Fracture Repair: Step 4 Osteoblasts: replace central cartilage of external callus with spongy bone Figure 6 15 (Step 4) Fracture Repair: Step 4 Osteoblasts and osteocytes remodel the fracture for up to a year: reducing bone calluses The Major Types of Fractures Epiphyseal fractures Figure

26 Age and Bones Bones become thinner and weaker with age Osteopenia begins between ages 30 and 40 Women lose 8% of bone mass per decade, men 3% Effects of Bone Loss The epiphyses, vertebrae, and jaws are most affected: resulting in fragile limbs reduction in height tooth loss Osteoporosis Severe bone loss Affects normal function Over age 45, occurs in: 29% of women 18% of men Hormones and Bone Loss Estrogens and androgens help maintain bone mass Bone loss in women accelerates after menopause 26