skeletal system

Skeletal System

Functions• Support• Protection• Movement• Storage of minerals• Production of blood• Storage of Yellow Bone Marrow

Divisions of the Skeleton• There are 206 named

bones in the human body.

• Each bone belongs to 1 of 2 large groups:– Appendicular

• 126 bones– Axial

• 80 bones

Tortora & Grabowski 9/e 2000 JWS 7-4

Types of Bones• 5 basic types of bones:

– long = compact bone– short = spongy bone

except surface– flat = plates of compact

enclosing spongy– irregular = variable– sesamoid = develop in

tendons or ligaments (patella)

• Sutural bones = in joint between skull bones

Types of Bones – classified by shape

Parts of a Long Bone

• Diaphysis = main part of bone• Epiphysis = one end of a long

bone• Metaphysis = growth plate

region, mature bone• Articular Cartilage = over joint

surfaces, acts as friction & shock absorber

• Medullary cavity = marrow cavity

• Endosteum = lining of marrow cavity

• Periosteum = tough membrane covering the bone but not the cartilage

Axial Skeleton

• skull, hyoid, vertebrae, ribs, sternum, ear ossicles

• 80 bones

Vertebral Column• Backbone or spine built

of 26 vertebrae• Five vertebral regions

– cervical vertebrae (7) in the neck

– thoracic vertebrae ( 12 ) in the thorax

– lumbar vertebrae ( 5 ) in the low back region

– sacrum (5, fused)– coccyx (4, fused)

Atlas & Axis (C1-C2)

• Atlas - nodding movement that signifies “yes”, supports the skull

• Axis - pivotal movement that signifies “no”

Typical Cervical Vertebrae (C3-C7)

• Smaller bodies• Neck region• Larger spinal canal• 1st and 2nd

cervical vertebrae are unique– atlas & axis

Thoracic Vertebrae(T1-T12)

• Larger and stronger bodies

• Longer• Facets or demifacets on

body for head of rib

Lumbar Vertebrae (L1-L5)

• Strongest & largest• Short thick spinous

& transverse processes– back musculature

Sacrum

• Union of 5 vertebrae (S1 - S5) by age 30

Coccyx

• Union of 4 vertebrae (Co1 - Co4) by age 30

Intervertebral Discs

• Cushion like pad b/w vertebrae that absorbs shock• Permit various movements and support of the

vertebral column• Fibrocartilagenous ring with a pulpy center

Herniated (Slipped) Disc

• Protrusion of the nucleus pulposus

• Most common in lumbar region

• Pressure on spinal nerves causes pain

• Surgery

Normal Curves of the Vertebral Column

• Primary curves– thoracic and sacral are formed during fetal development

• Secondary curves– cervical formed when infant raises head at 4 months– lumbar forms when infant sits up & begins to walk at 1 year

Abnormal CurvatureScoliosis - abnormal curvature

Kyphosis - hunch back assoc. with old age

Lardosis - sway back, pregnant walk

Spina Bifida – congenital defect – failure of the vertebral laminae to unite, leaves nerve tissue unprotected, often leads to paralysis

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Thorax– Protects vital organs

(heart, lungs, blood vessels)

– Sternum (breastbone)

– Ribs• 1-7 are true ribs

(attached to sternum)• 8-12 are false ribs

(vertebrochondral)• 11-12 are floating

– Costal cartilages– Bodies of the

thoracic vertebrae.

Sternum• Manubrium-

– 1st & 2nd ribs• Body

– Midportion of ribs, bulk of sternum

• Xiphoid– Cartilages in youth– ossifies by 40– CPR position


Ribs

• Increase in length from ribs 1-7, thereafter decreasing• Head and tubercle articulate with facets• Body with costal groove containing nerve & blood vessels• Intercostal spaces contain intercostal muscles

Fracture at site of greatest curvature.

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The Skull

• 8 Cranial bones– protect brain & house ear ossicles– muscle attachment for jaw, neck & facial muscles

• 14 Facial bones– protect delicate sense organs -- smell, taste, vision– support entrances to digestive and respiratory systems


The 8 Cranial Bones

FrontalParietal (2)Temporal (2)Occipital

SphenoidEthmoid


14 Facial Bones

Nasal (2) Maxillae (2) Zygomatic (2)Mandible (1) Lacrimal (2) Palatine (2)

Inferior nasal conchae (2) Vomer (1)


Maxillary bones

• Floor of orbit, floor of nasal cavity or hard palate• Alveolar processes hold upper teeth• Cleft palate is lack of union of maxillary bones


Zygomatic Bones

• Cheek bones


Mandible


Sutures

• Lambdoid suture unites parietal and occipital• Sagittal suture unites 2 parietal bones

Tortora & Grabowski 9/e 2000 JWS

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Fontanels of the Skull at Birth• Dense connective tissue membrane-filled spaces

(soft spots)• Unossified at birth but close early in a child's life.• Fetal skull passes

through the birth canal.

• Rapid growth of thebrain during infancy

• Eventually turn into sutures

Tortora & Grabowski 9/e 2000 JWS

7-30

Hyoid Bone– U-shaped single bone– Articulates with no other bone of the body– Suspended by ligament and muscle from skull– Supports the tongue & provides attachment for

tongue, neck and pharyngeal muscles

Appendicular Skeleton

• Pectoral girdle• Pelvic girdle • Upper limbs• Lower limbs

Pectoral (Shoulder) Girdle• Scapula and Clavicle • Clavicle articulates with sternum• Clavicle articulates with scapula• Scapula held in place by muscle only• Upper limb attached to pectoral girdle at shoulder

Clavicle (collarbone)

• S-shaped bone with two curves• Extends from sternum to scapula above 1st rib.

Posterior Scapula

• Triangular flat bone

Anterior Scapula

Upper Limbs• Each upper limb = 30 bones

– humerus within the arm– ulna & radius within the forearm– carpal bones within the wrist– metacarpal bones within the palm– phalanges in the fingers

Humerus—Proximal End• Part of shoulder

Humerus --- Distal End• Forms elbow joint with ulna

and radius

Ulna & Radius • Ulna (on little finger side)

• Radius (on thumb side)

8 Carpal Bones (wrist)• Proximal row - lat to med

– scaphoid - boat shaped– lunate - moon shaped– triquetrum - 3 corners– pisiform - pea shaped

• Distal row - lateral to medial– trapezium - four sided– trapezoid - four sided– capitate - large head– hamate - hooked process

Metacarpals and Phalanges• Metacarpals

– 5 total– knuckles

• Phalanges– 14 total– 3 on fingers except thumb

Pelvic Girdle and Hip Bones

• Pelvic girdle = two hipbones united at pubic symphysis

• Each hip bone = ilium, pubis, and ischium– fuse after birth

• Bony pelvis = 2 hip bones, sacrum and coccyx


Ischium and Pubis

• Ischium– ischial spine & tuberosity– lesser sciatic notch– ramus

• Pubis– body– superior & inferior ramus– pubic symphysis is pad of

fibrocartilage between 2 pubic bones


Ilium

• Iliac crest and iliac spines for muscle attachment• Iliac fossa for muscle attachment• Gluteal lines indicating muscle attachment• Sacroiliac joint at auricular surface & iliac

tuberosity• Greater sciatic notch for sciatic nerve


Pelvis

• Pelvis = sacrum, coccyx & 2 hip bones

• Pelvic axis = path of babies head

Female and Male Skeletons• Male skeleton

– larger and heavier– larger articular surfaces– larger muscle

attachments

• Female pelvis– wider & shallower– larger pelvic inlet & outlet– more space in true pelvis– pubic arch >90 degrees

Female Male

Lower Extremity

• Each lower limb = 30 bones– femur and patella within the

thigh– tibia & fibula within the leg– tarsal bones in the foot– metatarsals within the

forefoot– phalanges in the toes

Femur and Patella• Femur (thighbone)

– longest & strongest bone in body• Patella (knee cap)

– triangular sesamoid

Tibia and Fibula• Tibia

– medial & larger bone of leg– Weight bearing

• Fibula– not part of knee

Tarsus

• Region of foot (contains 7 tarsal bones)• Talus = ankle bone (articulates with tibia &

fibula)• Calcaneus - heel bone• Cuboid, navicular & cuneiforms

Metatarsus and Phalanges

• Metatarsus = 5 metarsals– midregion of the foot

• Phalanges– distal portion of the foot– similar in number and

arrangement to the hand– big toe is hallux


Arches of the Foot• Function

– distribute body weight over foot– yield & spring back when weight is lifted

• Longitudinal arches along each side of foot• Transverse arch across midfoot region

– navicular, cuneiforms & bases of metatarsals

Clinical Problems• Flatfoot

– weakened ligaments allow bones of medial arch to drop• Clawfoot

– medial arch is too elevated• Hip Fracture

– ½ million/yr in US– Arthroplasty to fix

Bone Formation or Ossification• Intramembranous bone formation = formation of

bone directly from mesenchymal cells– Forms most flat bones, bones in skull– Growth of short bones and the thickening of long bones– Closes the fontanels

• Endochondral ossification = formation of bone within hyaline cartilage– Forms most bones within the body

Endochondral Bone Formation • Development of Cartilage

model– Mesenchymal cells form a

cartilage model of the bone during development

• Growth of Cartilage model– in length by cell division and

matrix formation ( interstitial growth)

– in width by formation of new matrix (appositional growth)

– cells in midregion burst and change pH triggering calcification

Developmental Anatomy5th Week =limb bud

appears6th Week = constriction

produces hand or foot plate and skeleton now totally cartilaginous

7th Week = endochondral ossification begins

8th Week = upper & lower limbs appropriately named

Osteogenesis - 10 week fetus

Osteogenesis - 16 week fetus

Bone Growth in Length• Epiphyseal plate or cartilage growth

plate– cartilage cells are produced by

mitosis– cartilage cells are destroyed and

replaced by bone• Between ages 18 to 25, epiphyseal

plates close– cartilage cells stop dividing and bone

replaces the cartilage (epiphyseal line)

• Growth in length stops at age 25

Aging & Bone Tissue• Bone is being built through adolescence,

holds its own in young adults, but is gradually lost in aged.

• Demineralization = loss of minerals – very rapid in women 40-45 as estrogens levels

decrease – in males, begins after age 60

• Decrease in protein synthesis– decrease in growth hormone– decrease in collagen production which gives

bone its tensile strength– bone becomes brittle & susceptible to fracture

Factors Affecting Bone Growth• Nutrition

– adequate levels of minerals and vitamins• calcium and phosphorus for bone growth• vitamin C for collagen formation• vitamins K and B12 for protein synthesis

• Sufficient levels of specific hormones• promotes cell division at epiphyseal plate• need hGH (growth), thyroid (T3 &T4) and insulin

– at puberty• growth spurt and closure of the epiphyseal growth

plate• estrogens promote female changes -- wider pelvis

Bone Remodeling• Ongoing since osteoclasts carve out small

tunnels and osteoblasts rebuild osteons.– osteoclasts form leak-proof seal around cell

edges– release calcium and phosphorus into interstitial

fluid– osteoblasts take over bone rebuilding– distal femur is fully remodeled every 4 months

Bone Remodeling

Calcium Homeostasis & Bone Tissue• Skeleton is reservoir of Calcium & Phosphate• Calcium ions involved with many body

systems– nerve & muscle cell function– blood clotting– enzyme function in many biochemical reactions

• Small changes in blood levels of Ca+2 can be deadly– cardiac arrest if too high– respiratory arrest if too low

• Parathyroid hormone (PTH) is secreted if Ca+2 levels fall– PTH triggers Osteoclasts (bone

cells) to break down the bone and put calcium back into the blood stream

• Calcitonin hormone is secreted from cells in thyroid if Ca+2 blood levels get too high– inhibits osteoclast activity– increases bone formation by

osteoblasts

Hormonal Influences

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Exercise & Bone Tissue• Pull on bone by skeletal muscle and gravity is

mechanical stress .• Stress increases deposition of mineral salts &

production of collagen (calcitonin prevents bone loss)

• Lack of mechanical stress results in bone loss – reduced activity while in a cast– astronauts in weightlessness– bedridden person

• Weight-bearing exercises build bone mass

Fracture & Repair of Bone• Fracture is break in a bone• Healing is faster in bone than in

cartilage due to lack of blood vessels in cartilage

• Healing of bone is still slow process due to vessel damage

• Clinical treatment– closed reduction = restore pieces to

normal position by manipulation - cast

– open reduction = surgery

Disorders of Bone Ossification

• Rickets• calcium salts are not deposited properly• bones of growing children are soft• bowed legs, skull, rib cage, and pelvic deformities

result• Osteomalacia

• new adult bone produced during remodeling fails to ossify

• hip fractures are common

Osteoporosis• Decreased bone mass resulting in porous bones • Those at risk

– thin menopausal, smoking, drinking female with family history

– athletes who are not menstruating due to decreased body fat & decreased estrogen levels

– people allergic to milk or with eating disorders whose intake of calcium is too low

• Prevention or decrease in severity -- adequate diet, weight-bearing exercise, & estrogen replacement therapy (for menopausal women)

Osteoporosis

Clinical Conditions• Osteomyelitis

– Osteo=bone + myelo=marrow + itis=inflammation.

– Inflammation of bone and bone marrow caused by pus-forming bacteria that enter the body via a wound (e.g., compound fracture) or migrate from a nearby infection.

– Fatal before the advent of antibiotics.

Clinical Conditions• Gigantism

– Childhood hypersecretion of growth hormone by the pituitary gland causes excessive growth.

• Acromegaly – Adulthood hypersecretion of

GH causes overgrowth of bony areas still responsive to GH such as the bones of the face, feet, and hands.

• Pituitary dwarfism– GH deficiency in children

resulting in extremely short long bones and maximum stature of 4 feet.

skeletal system

Documents

neckthoracic vertebrae

thoraxlumbar vertebrae

skull bones types of

pad bw vertebrae

vertebrae s1 s5

vertebrae co1 co4

named bones

ear ossicles80 bones