Chapter 6 7 the skeletal system
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Chapter 6 & 7: The Skeletal System PowerPoint PPT Presentation


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Chapter 6 & 7: The Skeletal System. Skeletal Cartilages: structures, types & locations. Skeletal cartilage – Made from cartilage Consists primarily of water Allows for resilience No nerves or blood vessels Surrounded by a layer of dense irregular connective tissue – perichondrium

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Chapter 6 & 7: The Skeletal System

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Chapter 6 & 7: The Skeletal System


Skeletal Cartilages: structures, types & locations

  • Skeletal cartilage –

    • Made from cartilage

      • Consists primarily of water

      • Allows for resilience

      • No nerves or blood vessels

    • Surrounded by a layer of dense irregular connective tissue – perichondrium

      • Resists outward expansion when compressed

      • Source of blood vessels – feeds the matrix & chondrocytes

  • Hyaline cartilage –

    • Hyaline cartilage is the most abundant skeletal cartilage, and includes the articular (cover bone ends @ movable joints), costal (connects ribs to sternum), respiratory (larynx & reinforce passageways), and nasal (external nose) cartilages.

    • Provide support & flexibility (due to collagen fibers)


Skeletal cartilages cont.

  • Elastic cartilage –

    • More flexible than hyaline

      • Contains more elastic fibers

    • Located in the external ear & epiglottis

  • Fibrocartilage –

    • Located in areas that need to withstand a great deal of pressure & stretch

      • Chondrocytes & collagen fibers

      • Knee & intervertebral discs


Growth of cartilage

  • Appositional –

    • “growth from the outside”

    • Outward expansion due to production of cartilage matrix on the outside of tissue

    • Secrete new matrix against the external surface of the existing cartilage

    • Occurs in the shafts of long bones

  • Interstitial –

    • “growth from the inside”

    • Expansion within the cartilage matrix due to divisions of lacunae-bound chondrocytes & secretions of the matrix

    • Occurs in the ends of bone


Classifications of bones

  • 206 bones in the body

  • 2 divisions –

    • Axial –

      • Consists of:

        • The skull, vertebral column, & rib cage

      • Involved in protection, support, or carrying other body parts

    • Appendicular –

      • Consists of:

        • The bones of the upper & lower limbs & the girdles (shoulder & hip bones) that attach them to the axial skeleton


Shape

  • Long bones –

    • Longer than they are wide

    • Have a definite shaft & two ends

    • Consist of all limb bones except:

      • Patellas, carpals, & tarsals

    • Named for their shape not size (fingers are long bones even though they are small)

  • Short bones –

    • Somewhat cube-shaped

    • Include –

      • the carpals & tarsals

      • Sesamoid – bones that form with in tendons (patella)


Shape cont.

  • Flat bones –

    • Thin, flattened, and often curved bones

    • Include –

      • Skull bones, sternum, scapulae, and ribs

  • Irregular bones –

    • Complicated shapes

    • Don’t fit into any other class

    • Include –

      • Vertebrae

      • Hip bones & coxae


Functions

  • 5 main functions –

    • Support –

      • Support body

      • Cradle soft organs

    • Protection –

      • Protect vital organs

    • Movement –

      • Allow movement

        • Muscles attach to bones acting as levers for movement

    • Mineral storage –

      • Store calcium & phosphate

      • Released into the blood stream as ions for distribution to the body

    • Blood cell formation –

      • House hematopoietic tissue


Bone structure: gross anatomy

  • Bone markings –

    • Projections;

      • Muscle attach to and pull

      • Modified for where bones meet (joints)

      • E.g. heads, trochanters, spines

    • Depressions and openings;

      • Allows passages of nerves and blood vessels

      • E.g. fossae, sinuses, foramina, grooves

    • Table 6.1 pg. 179


Bone Textures

  • External layer = compact bone

  • Internal layer = spongy bone

    • Made of trabeculae


Long bones cont.

  • Diaphysis –

    • The bone shaft

    • Contains cavity with yellow marrow

  • Epiphysis –

    • Ends of long bones

    • Typically wider than diaphysis (shaft)

    • Consist of internal spongy bone & outer layer of compact bone

    • Ends are covered with hyaline (protects bone ends where they meet at the joint)

  • Epiphyseal line/plate –

    • Between epiphysis & diaphysis

    • Line = remnant of plate (hyaline cartilage disc in young adults that lengthens bone)


Long bones cont.

  • The external surface of bone is covered by the periosteum

    • Double layered membrane

    • Covers all bones except joint surfaces

    • Contains osteoblasts & osteoclasts

    • Richly supplied w/ blood, nerve fibers, & lymphatic vessels – enter bone shaft via nutrient foramen

    • Secured to bone shaft by – Sharpey’s fibers – tufts of collagen fibers

    • Provides insertion points for tendons and ligaments

  • The internal surface of bone is lined by a connective tissue membrane called the endosteum

    • Covers trabeculae of spongy bone

    • Lines canals that run through compact bone

    • Also contains osteoblasts & osteoclasts


Short, flat, & irregular bones

  • Short, flat, & irregular bones consist of thin plates of periosteum-covering compact bone on the outside, and endosteum-covered spongy bone inside, which houses bone marrow between the trabeculae

  • No shaft or epiphyses

  • Flat bones – internal layer of spongy bone = diploë


Hematopoietic tissue

  • Hematopoietictissue = red bone marrow

  • Located within trabecular cavities of the spongy bone, in diploëof flat bones & epiphysis of long bones

  • Infants – all areas of spongy bone contain red marrow

  • Adults – epiphysis of long bones – diaphysis – yellow marrow


Gross anat. cont.

  • 2 types of bone texture –

    • Compact –

      • Appears dense, smooth & solid

      • Contains passageways for blood vessels & nerves

      • Osteon –

        • structural unit of bones

        • tiny weight bearing pillars

        • arranged like tree rings

        • Each matrix tube = lamella

          • Collagen fibers run in same direction – in opposing lamella they run in opposing directions – allow extra strength

      • Haversian canal –

        • Center of osteon

        • Contain blood vessels & nerves

      • Lacunae –

        • Contain osteocytes – mature bone cells

        • Canaliculi– connect lacunae to each other and the central canals

      • Interstitial lamellae –

        • Incomplete lamellae between osteons

      • Circumferential lamellae –

        • Deep to the periosteum

        • Superficial to endosteum

        • Resist twisting of long bones


Microscopic anatomy

  • Compact bone – dense and solid

    • Structural unit = osteon

    • Contains lamellae, Haversian canal, & blood vessels and nerves

    • Volkmann’s canals –

      • Lie at right angles to the long bone axis

      • Connect blood & nerve supplies of the periosteum to the central canals & medullary cavity

    • Osteocytes –

      • Occupy lacunae & lamella junctions

      • Connected by canaliculi

    • Lamellae –

      • Circumferential –

        • Beneath periosteum

      • Interstitial –

        • Between osteons


Compact Bone


Gross anat. cont.

  • Spongy –

    • Internal to compact bone

    • Honeycomb, needle-like, flat pieces = trabeculae

      • Align along the lines of stress

      • Help the bone to resist stress

      • Contain irregularly arranged lamellae & osteocytes connected by canaliculi

      • No osteons present

    • Nutrients – diffused from canaliculi from capillaries in the endosteum


Chemical Composition of Bone

  • Organic components

    • Cells (osteogenic cells, osteoblasts, osteocytes, and osteoclasts)

    • Osteoid – ground substance and collagen fibers

    • Contribute to bone’s structure and flexibility

  • Inorganic components

    • 65% mineral salts (calcium phosphates)

    • Tightly packed crystals around collagen fibers

    • Contribute to bone’s hardness – resists compression


Formation of the Bony Skeleton

  • Ossification or osteogenesis = process of bone formation

  • Before week 8, skeleton made up of fibrous membranes and hyaline cartilage

    • Flexible and resilient, can accommodate mitosis

  • Intramembranous ossification –

    • Formation of cranial bones of the skull and clavicles

  • Endochondral ossification –

    • All bones below base of the skull (except clavicles)

    • Hyaline cartilage broken down as ossification proceeds


Intramembranous Ossification


Endochondral Ossification


Postnatal bone growth

  • During youth bones lengthen entirely by interstitial growth from the epiphyseal plates

  • Growth in length –

    • The cartilage cells at the top of the epiphyseal plate (closest to the epiphysis) push the epiphysis away from the diaphysis causing the bone to grow

    • Old chondrocytes (closer to the diaphysis) calcify & replace the cartilage with bone tissue

  • Growth in width –

    • Occurs through appositional growth

      • Bone growth due to deposition of bone matrix by osteoblasts beneath the periosteum


Growth in Length of Long Bones


Postnatal Bone Growth

  • Hormonal regulation

    • Infancy and childhood – growth hormone stimulates epiphyseal plate activity

      • Released by anterior pituitary gland

    • Thyroid hormones regulate the activity of growth hormone ensuring proper bone proportions

    • Testosterone and estrogens are released in increasing amounts at puberty

      • Initially – growth spurt, later induce epiphyseal plate closure


Bone homeostasis

  • Bone remodeling –

    • Weekly recycle 5-7% of bone mass

    • Spongy bone replaced every 3-4 yrs

    • Compact bone replaced every 10 yrs

    • Adults –

      • Balanced due to deposit & removal

      • Bone deposit occurs at a greater rate when bone is injured

      • Bone resorption allows minerals to be absorbed into the blood

      • Vit C (collagen synthesis), Vit D (absorption of dietary calcium), Vit A (needed for balance between deposit & removal of bone)

      • Bone Modeling & Remodeling

    • Control of bone remodeling –

      • Hormones – maintain blood calcium homeostasis

      • Mechanical stress & gravity – affect bone growth & allow bone to withstand stresses


Bone Remodeling

  • Response to mechanical stress

    • Wolff’s Law: a bone grows or remodels in response to the demands placed on it

      • Long bones are thickest midway along the diaphysis (where bending stresses are greatest)

      • Curved bones are thickest where they are most likely to buckle

      • Trabeculae of spongy bone form trusses or struts along lines of compression

      • Large, bony projections occur where heavy, active muscles attach


Bone repair

  • Classification of fractures –

    • Position of bone ends after fracture

      • Nondisplaced fractures = bone ends retain normal position

      • Displaced fracture = bone ends out of normal alignment

    • Completeness of break

      • Complete fracture = bone broken through

      • Incomplete = not broken all the way through

    • Orientation of break relative to the long axis of bone

      • Linear = parallels the long axis

      • Transverse = perpendicular to the bones long axis

    • Whether the bone ends penetrate the skin

      • Open/compound = bone ends penetrate the skin

      • Closed/simple = bone ends don’t penetrate the skin


Bone repair

  • Fractures are treated by reduction –

    • Closed (external) reduction

      • Bone ends coaxed into position by physician’s hands

    • Open (internal) reduction

      • Bone ends secured together surgically with pins or wires

  • Check out Fig 6.2 on pg. 192 for other types

    • Comminuted – common in elderly (brittle bones)

    • Compression – common in porous bones

    • Spiral – common sports fracture

    • Epiphyseal

    • Depressed – typical skull fracture

    • Greenstick – common in children (more organic matter)


Spiral fractures


Comminuted


Compression


Dislocations & open fractures


Bone repair cont.

  • 4 stages of fracture repair –

    • 1. Hematoma formation –

      • Blood vessels are torn during the break, blood clot forms

      • Nearby bone cells deprived of nutrition and die

    • 2. Fibroncartilaginous callus formation –

      • Vessels begin to form

      • Phagocytic cells clean up debris

      • Fibroblasts (produce collagen fibers that reconnect the bone) & osteoblasts (begin forming spongy bone) begin to reform the bone

    • 3. Bony callus formation –

      • Bone trabeculae convert callus into bone

      • Begins 3-4 weeks after injury

      • Continues for about 2-3 months

    • 4. Remodeling of bony callus –

      • Excess material removed

      • Compact bone is laid down


Steps of Bone Repair


Homeostatic Imbalances

  • Osteomalacia & Rickets (in children)

    • Bones inadequately mineralized

    • Caused by insufficient calcium or vitamin D deficiency

  • Osteoporosis

    • Bone resorption outpaces bone deposit, bone mass reduced

      • Spongy bone of spine most vulnerable and neck of femur (“broken hip”)

    • Caucasian women most susceptible group

      • Estrogen helps restrain osteoclast activity

    • GET ENOUGH CALCIUM WHILE BONES STILL INCREASING IN DENSITY! (Also, drink fluoridated water)

  • Paget’s Disease

    • Excessive and haphazard bone deposit and resorption

    • High ratio of spongy to compact -> spotty weakening


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