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

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Chapter 6 & 7: The Skeletal System

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Chapter 6 7 the skeletal system

Chapter 6 & 7: The Skeletal System


Skeletal cartilages structures types locations

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

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

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

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

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

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

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 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

Bone Textures

  • External layer = compact bone

  • Internal layer = spongy bone

    • Made of trabeculae


Long bones cont

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 cont1

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

  • 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

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

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

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

Compact Bone


Gross anat cont1

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

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

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

Intramembranous Ossification


Endochondral ossification

Endochondral Ossification


Postnatal bone growth

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

Growth in Length of Long Bones


Postnatal bone growth1

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 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

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

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 repair1

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

Spiral fractures


Comminuted

Comminuted


Compression

Compression


Dislocations open fractures

Dislocations & open fractures


Bone repair cont

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

Steps of Bone Repair


Homeostatic imbalances

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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