Anatomy of Bones: Structure, Classification, Functions, and Histology - Prof. Jeffrey Geor, Study notes of Physiology

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CHAPTER 6

1. Skeletal Cartilage a. Structure i. Hyaline 1. Most abundant 2. Found: a. Articular cartilage b. Costal cartilage c. Respiratory cartilage d. Nasal cartilage ii. Elastic
2. More elastic fibers
3. Found: a. External ear b. Epiglottis iii. Fibrocartilage
4. Highly compressible with great strength
5. Found: a. Menscii b. Vertabral disks b. Growth i. Appositional growth- external ii. Interstitial growth- internal
6. Classification of Bones a. Long bones i. Longer then they are wide, includes shaft and two ends ii. Ex: limbs b. Short bones i. Roughly cube shaped ii. Sesamoid bones- formed in cartilage iii. Ex: wrists and ankles c. Flat bones i. Thin, flattened ii. Ex: sternum, scapulae, ribs, most skull bones d. Irregular bones i. Complicated shapes ii. Ex: vertebrae and hip bones
7. Functions of Bones a. Support b. Protection c. Movement d. Mineral and growth factor storage e. Blood cell formation f. Triglyceride storage
8. Bone Structure a. Long bones i. Diaphysis- shaft 1. Has compact bone that surround medullary cavity a. Adults- fat/ kids- red bone marrow ii. Ephyses- bone ends

1. Compact exterior, spongy interior
2. Surface covered in hyaline cartilage
3. Ephyseal line- remnants of a epiphyseal plate (disc of cartilage) iii. Membranes
4. Entire external bone covered in periosteum a. outer fibrous layer i. consists of blood vessels and nerves b. inner osteogenic layer i. consists of osteoblasts and osteoclasts
5. Internal bone covered in endosteum a. Covers trabeculae of spongy bone, lines canals that pass though compact bone b. Consists of osteoblasts and osteoclasts b. Short, Flat, Irregular bones i. All contain periosteum covered compact bone, and endosteum covers spongy bone ii. Contains bone marrow iii. Spongy bone in flats bones is called diploë
6. Bone Histology i. Osteoclasts- break down bone ii. Osteoblasts- bone forming cells iii. Osteocytes- located in lacunae and connected through canaliculi a. Cancellous bone (Spongy) i. Lamellae combine to form trabeculae
7. Beams of bone that interconnect to form lattice like structure
8. Oriented along lines of stress to provide structural strength b. Compact bone (Cortical) i. Dense, solid bone ii. Osteons serve as weight bearing pillars
9. Individual groupings of hollow tubes made of bone matrix
10. Each ring of osteons makes up a lamella a. Circumferential lamellae- cover outer surface of compact bones b. Concentric lamellae- surrounding Haversian canals form osteons c. Interstitial lamellae- remnants of other lamellae left after bone remodeling iii. Haversian canals
11. Parallel with long axis
12. Contain blood vessels and nerves iv. Volkmann’s canals
13. Perpendicular to long axis
14. Contain blood vessels and nerves VI. Bone Formation a. Intramembranous Ossification i. Formation of bone directly from fibrous membrane b. Endochonrdal Ossification i. Formation of bone within hyaline cartilage VII. Bone Growth a. Length i. Epiphyseal plate (cartilage growth plate)
15. Cartilage cells are produced on epiphyseal side of plate, then destroyed and replaced by bone on diaphyseal side of plate
16. Between 18-25, epiphyseal plate closes, cartilage cells stop dividing and bone replaces cartilage b. Width

i. Osteoclasts resorb bone on endosteal surface of diaphysis ii. Osteoblasts secrete bone matrix on external surface (beneath periosteum) iii. Greater deposition then resorption c. Short, flat, irregular bones mostly increase in size by appositional growth d. Hormonal regulation i. Need hGH(growth), thyroid (T3 &T4), and insulin e. Hormonal Abnormalities i. Over-secretion of hGH during childhood produces gigantism ii. Under-secretion of hGH or thyroid hormone during childhood produces dwarfism iii. Both men or women that lack estrogen receptors on cells grow taller than normal

1. Estrogen is responsible for closure of growth plate f. Bone remodeling and repair i. Mechanical stress- pull on bone by skeletal muscle and gravity
2. Stress increases deposition of mineral salts and production of collagen a. Weight bearing exercises build bone mass
3. Lack of mechanical stress results in bone loss a. Reduced activity while in cast, astronauts in weightlessness, bedridden ii. Bone repair
4. Hematoma formation a. Damaged blood vessels produce clot in 6-8 hours, bone cells die
5. Callus formation a. Fibroblasts invade the callus and lay down collagen fibers b. Chondroblasts produce fibrocartilage to cover broken ends of bone
6. Ossification of the soft callus a. Osteoblasts secrete spongy bone that joins 2 broken ends of bone b. Lasts 3-4 months
7. Bone remodeling a. compact bone replaces the spongy in the bony callus b. surface is remodeled back to normal shape g. Bone Disorders i. Osteoporosis
8. Bone resorption surpasses bone deposition
9. Bone mass becomes reduced because of increase in pores
10. Demographic: female, Caucasian, postmenopausal, smoking, sedentary lifestyle, poor nutrition
11. Prevention/management: increase and support bone deposition a. Calcium and vitamin D suppliments, weight bearing exercises, hormonal therapy ii. Rickets
12. Calcium salts are not deposited properly
13. Bones of growing children are soft
14. Bowed legs, skull, rib cage, and pelvic deformities iii. Osteomalacia
15. New adult bone produced during remodeling doesn’t ossify
16. Hip fractures are common