Bone Tissue Chapter 6

Bone Classifications Skeleton-divisions A. Axial- skull, thorax, vertebral column B. Appendicular- shoulder girdle and arm; pelvic (hip) girdle and leg

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Bone Types Long bones-length bigger than width Long bones-length bigger than width Short bones-roughly cube shaped Short bones-roughly cube shaped Flat bones-thin, flat, usually curved Flat bones-thin, flat, usually curved Irregular bones-bones whose shape doesn’t fit the 3 previous categories eg. Hip bones, vertebrae Irregular bones-bones whose shape doesn’t fit the 3 previous categories eg. Hip bones, vertebrae

Function of bone Support-framework for body Support-framework for body Protection Protection Movement-helped by skeletal muscle via attachment with tendons Movement-helped by skeletal muscle via attachment with tendons Mineral storage-calcium, phosphate Mineral storage-calcium, phosphate Blood Cell formation-completed in marrow Blood Cell formation-completed in marrow

Bone Markings p. 179 Table 6.1 Fossa  depression Foramen  hole Tuberosity  Larger round projection, rough (muscle) Condyle  rounded projection (joint) Spine  slender

Long Bone Structure Diaphysis-shaft or long axis of bone Diaphysis-shaft or long axis of bone Medullary cavity-hollow space inside; contains fat; also called marrow Medullary cavity-hollow space inside; contains fat; also called marrow Epiphysis-rounded ends of bone; covered in hyaline cartilage Epiphysis-rounded ends of bone; covered in hyaline cartilage Epiphyseal plate-disc of hyaline cartilage; growth plate in children Epiphyseal plate-disc of hyaline cartilage; growth plate in children

Quiz Picture p. 180 Fig. 6.3 a, c

Short, Irregular, Flat bone structure Thin external covering of compact bone Thin external covering of compact bone Internally contain spongy bone (called diploe in these bones) Internally contain spongy bone (called diploe in these bones)

Bone Coverings External Coverings Periosteum-double layer membrane Outer = dense irregular CT Outer = dense irregular CT Inner = thin ET  Inner = thin ET  osteoblast cells (forming) osteoclasts cells (destroying) Internal Coverings Endosteum-thin, CT membrane, both cells

Microscopic Anatomy of Bone Compact bone (Lamellar bone) Haversian System- structural unit of compact bone; also called osteon Haversian System- structural unit of compact bone; also called osteon Cylinders of concentric lamellae  collagen fibers run opposite each other Cylinders of concentric lamellae  collagen fibers run opposite each other Center of Osteon - Haversian canal- Center of Osteon - Haversian canal- contains blood vessels, nerve fibers contains blood vessels, nerve fibers Osteocytes- bone cells that live in lacunae surrounding the lamellae Osteocytes- bone cells that live in lacunae surrounding the lamellae

Lamella(e) Growth circles, like a tree Growth circles, like a tree Opposite twisting collagen fibers Opposite twisting collagen fibers Resist torque forces Resist torque forces Two special ones Interstitial  fill in spaces between osteons Interstitial  fill in spaces between osteons Circumferential  around all the osteons Circumferential  around all the osteons

Quiz Picture p. 183 Fig 6.6a

Quiz Picture p. 183 Fig 6.6 b

Microscopic Anatomy of Bone Spongy Bone- no osteons present; lamellae are irregularly arranged Two types Trabeculae  middle of long bones Trabeculae  middle of long bones Dipolë  middle of short/irregular bones Dipolë  middle of short/irregular bones *same thing in different spots*

Chemical Composition of Bone Organic portion (1/3)- cells  osteoblasts, osteoclasts, osteocytes & osteoid  ground substance proteoglycans & glycoproteins, collagen fibers Inorganic portion- 2/3 hydroxyapatite (mineral salts); calcium phosphate packed tightly around collagen fibers

67% 33%

Bone Formation Intramembranous Bone Formation- results in formation of cranial bones of skull and clavicles (Flat and Irregular Bones) Intramembranous Bone Formation- results in formation of cranial bones of skull and clavicles (Flat and Irregular Bones) 1. Mesenchyme cells invade membrane; become osteoblasts 2. Osteoblasts secrete matrix; calcifies 3. Spongy bone forms; develops periosteum 4. Grows outward to develop external compact bone; internal bone becomes mature diploe; develops red marrow

Bone Formation Endochondral Ossification (Long bones) Endochondral Ossification (Long bones)

Growth of Long Bones Growth Zone- epiphyseal plate cartilage cells reproduce and grow away from the diaphysis Growth Zone- epiphyseal plate cartilage cells reproduce and grow away from the diaphysis Transformation Zone- chondrocytes die as the cartilage matrix calcifies Transformation Zone- chondrocytes die as the cartilage matrix calcifies Osteogenic Zone- osteoblasts invade the area and form spongy bone Osteogenic Zone- osteoblasts invade the area and form spongy bone

Transformation

Wolff’s Law Bone resists mechanical stress Trabeculae form scaffolding along stress lines Thicker compact bone (markings) where tendons and ligaments attach

Bone Remodeling Bone deposit- addition of bone; occurs with injury or need for added strength; deposit osteoid which calcifies; alkaline phosphatase necessary; osteoblasts Bone deposit- addition of bone; occurs with injury or need for added strength; deposit osteoid which calcifies; alkaline phosphatase necessary; osteoblasts Bone resorption- removal of bone; osteoclasts; about the bone and release enzymes from lysosomes and HCl Bone resorption- removal of bone; osteoclasts; about the bone and release enzymes from lysosomes and HCl Occurs at periosteal and endosteal surfaces Occurs at periosteal and endosteal surfaces

Hormonal Control of Bone Growth Growth Hormone- especially important in childhood Growth Hormone- especially important in childhood Thyroid Hormone- helps to modulate the effects of GH Thyroid Hormone- helps to modulate the effects of GH Estrogen, Testosterone- early in puberty their release causes growth spurts; by 18 in females and 21 in males it closes the epiphyseal plates Estrogen, Testosterone- early in puberty their release causes growth spurts; by 18 in females and 21 in males it closes the epiphyseal plates

Hormonal Control Of Bone Formation

Osteoporosis Bone resorption out paces bone deposit, bone is porous and light Bone resorption out paces bone deposit, bone is porous and light Many causes: Many causes: Lack of exercise, poor diet Post menopausal women  lack of estrogen Post menopausal women  lack of estrogen leaves osteoclasts unchecked leaves osteoclasts unchecked Exercise, vitamins and hormone therapy are most common treatments Exercise, vitamins and hormone therapy are most common treatments Main key is calcium during childhood (Prevention) Main key is calcium during childhood (Prevention)

Normal Bone Osteoporosis

Homeostatic Imbalances Paget Disease Improper bone formation To much spongy bone Osteomalacia/Rickets Osteoid improperly calcified Growth plates in children Extra long and wide bones No calcium or sunlight

Bone Repair