The Skeletal System

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Forms and Function

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Diseases + Disorders

Arthritis

cartilage covering the ends of bones wear out, results in increased friction b/w bones

inflammation of joints

Bursitis + Tendinitis

do not heal quickly due to low blood supply

caused by injuries, blows to the joints or bacterial infections

inflammation

response to injury characterized by redness, warmth, swelling + pain

Sprains

take long time to heal because the ligaments have few cells + poor blood supply

accompanies by internal bleeding, bruising, swelling + pain

damage to ligaments

Osteoporosis

decline in estrogen after menopause can cause it

slight imbalance b/w rates of osteoclasts (breaking down bone) + osteoblasts (making new bone)

caused by excessive bone loss

Appendicular Skeleton

Pelvic Girdle

broader in women

14 bones that form the toes

Metatarsal Bones

5 long bones that form the foot

Tarsal Bones

7 ankle + heel bones

Patella

triangular bone that protects + stabilizes knee joint

kneecap

Fibula

smaller lower bone

Tibia

larger lower bone that is in contact w/ femur

Femur

rounded upper end of each fits into socket in coxal bone

longest + strongest bone in body

Coxal Bones

attach to sacral region of vertebral column + then curve forward to meet in front at the pubic symphysis where they are joined by cartilage

protects organs inside pelvic cavity + is attachment site for legs

primary function is to support weight of upper body against force of gravity

Pectoral Girdle

Phalanges

14 bones that form the fingers + thumb

Metacarpal Bones

5 bones that form the palm of the hand

Carpal Bones

Carpal Tunnel Syndrome

often due to repetitive typing on a computer keyboard

repetitive stress syndrome

held together by sheath of connective tissue

8 small bones that make up the wrist

Ulna + Radius

forearm bones

Humerus

long bone

upper arm

fits into a socket in the scapula

Right + Left Scapulas

triangular bones in upper back

Right + Left Clavicles

extend across top of our chest

supportive frame for upper limbs

The Human Skeleton

flat + irregular bones (sternum + hips) contain red bone marrow

irregular bones

don't fit into the other categories

coxal bones + vertebrae

flat bones

thin, flattened bones with small amount of spongy bone b/w compact bone

cranial bones + sternum

short bones

wrist bones

wide as they are long

long bones

bones of limbs + fingers

Functions of the Skeleton

permits flexible movement of most parts of the body

protects certain organs from physical injury

serves as structural framework for support of soft organs

Bone Cell Regulation

when Ca levels RISE

calcitonin stimulates osteoblast activity which causes Ca + P to be removed from blood + deposited into bone

when Ca levels FALL

PTH stimulates osteoclasts to secrete bone-dissolving enzymes to release Ca + P into bloodstream

regulated by hormones

Joints

Synovial Joints

held tightly together by ligaments + stabilized by tendons

can withstand tremendous use

Ball + Socket Joint

wide range of movement

Hinge Joint

allows movement in one plane

knee + elbow

knee also includes 13 bursae sacs

to reduce friction, there are small disks on either side of knee joint called menisci

two bones are fastened together + stabilized by ligaments

bones are separated by thin fluid filled cavity

synovial membrane + surrounding hyaline cartilage create a joint capsule

articulating surfaces of two bones covered with tough smooth layer of hyaline cartilage

interior is lined with synovial membrane secretes synovial fluid to lubricate + cushion joint

Cartilaginous Joints

vertebrae + ribs

slightly moveable + allow some flexibility

bones are connected to hyaline cartilage

Fibrous Joints

fontanels

soft spots on baby's heads that change shape

immovable

Axial Skeleton

The Ribs + Sternum

shields heart, lungs + other thoracic region organs

helps us breathe by expanding + contracting

have 12 ribs

11-12 are floating ribs

have no attachment

8-10 are false ribs

attach via cartilage

1-7 are true ribs

attach directly to sternum

The Vertebral Column

Intervertebral Disks

strong impacts can cause herniated disks

permit limited degree of movement

shock absorbers

composed of fibrocartilage

separate vertebrae

contains 33 vertebrae

4 fused coccygeal

vestigial structure

5 fused sacral

5 lumbar

12 thoracic

7 cervical

supports head, protects spinal cord + serves as site of attachment for limbs + muscles

main axis of body

The Hyoid Bone

serves as point of attachment for muscles of tongue, larynx + pharynx

attached to temporal bone by ligaments

does not make direct contact with other bones

The Skull

foramen magnum

where vertebral column connects to the skull + spinal cord enters skull to communicate w/ brain

large opening at base of skull

occipital bone

back + base of skull

facial bones

mandible

attached to the temporal bone only

lower jaw + teeth

lacrimal bones

tiny opening where the tear ducts drain tears from the eye sockets into the nasal cavity

nasal bones

upper bridge of nose

zygomatic bones

cheekbones + outer portion of eye sockets

vomer bone

divides nose into left + right

part of the nasal septum

palatine bones

roof of the mouth

also formed by maxilla bones

maxilla

part of the eye sockets + anchor upper teeth

front of the skull

ethmoid bone

eye sockets + supports the nose

sphenoid bones

forms back of both eye sockets

b/w frontal + temporal bones

temporal bones

lower left + right sides of the skull

parietal bones

upper left + right sides of the skull

frontal bone

forehead + upper eye sockets

cranial bones

flat bones that enclose + protect the brain

Bone Repair

4. osteoblasts arrive + deposit osteoid matrix + encourage crystallization of CaP minerals + convert the callus into bone

3. osteoclasts arrive + remove dead fragments of bone + hematoma

2. fibroblasts migrate to area + some become chondroblasts that produce a callus b/w the broken ends of the bone

1. blood vessels create a hematoma at site of fracture, inflammation, swelling + pain happen

Bone Remodeling

Cells Involved In Bone Development

Osteoclasts

bone dissolving cells

Osteocytes

mature bone cells that maintain the structure of a bone

Osteoblasts

young bone forming cells that cause hard extracellular matrix of bone to develop

Chondroblasts

cartilage-forming cells that build a model of future bone

bone is a dynamic tissue that undergoes constant replacement, remodeling + repair

homeostasis of bone structure depends on the balance of osteoclast + osteoblast activity

OSTEOPOROSIS

condition in which bones lose great deal of mass because of an imbalance over many years in the rates of osteoclasts + osteoblasts

weight bearing exercise increases overall bone mass + strength

compression stress on a bone causes electrical currents within the bone that stimulate the bone forming activity of osteoblasts

consists of bones, ligaments + cartilage

CARTILAGE

ELASTIC CARTILAGE

lends structure to outer ear + epiglottis

highly flexible

mostly elastin

HYALINE CARTILAGE

covers ends of mature bones in joints creating smooth low friction surface

forms embryonic structures that then become bone

controlled by hormones (growth hormone)

4. growth plates in long bones move farther apart + the bone lengthens + widens

3. osteoblasts secrete osteoid + enzymes, facilitating the deposition of hydroxyapatite crystals

conversion of cartilage to bone is concentrated INSIDE growth plate

2. cartilage starts to dissolve + periosteum begins to develop, new blood vessels transport osteoblasts into area to form periosteum

1. chondroblasts form hyaline cartilage, creating a rudimentary model of future bone

chondroblast activity is concentrated OUTSIDE growth plate

smooth glossy cartilage of thin collagen

FIBROCARTILAGE

intervertebral disks + menisci

withstands pressure + tension

collagen arranged in thick bundles

found where support under pressure is needed + movement is necessary

smoother + more flexible than bone

specialized connective tissue made of collagen + elastin in a ground substance + reduces friction in joints

LIGAMENTS

confer strength to certain joints while still permitting movement in relation to each other

attach bone to bone

consist of dense fibrous connective tissue + bind bones to each other

BONES

outer surface is called the periosteum

tough layer of connective tissue that contains specialized bone forming cells

long bones like the arms and legs contain red bone marrow

stem cells in red bone marrow produce red + white blood cells + platelets

central cavity in diaphysis is filled with yellow bone marrow

primarily fat that can be used for energy

less dense spongy bone fills inner region of epiphysis

osteocytes do not need to rely on central canals for nutrients + waste removal

slender trabecular structure of spongy bone gives each osteocyte access to nearby blood vessels in red bone marrow

as hard as compact bone, but is less dense + allows for bone to be light + strong

latticework of hard + strong trabeculae

dense compact bone forms the shaft + covers each end

made up of extracellular deposits of calcium phosphate surrounding + enclosing cells called osteocytes

as bone develops + becomes hard, osteocytes become trapped in lacunae

waste products are exchanged in in opposite direction + removed by blood vessels

remain in contact with each other via canaliculi

within it are extensions of the cell cytoplasm in adjacent osteocytes joined together by gap junctions

by exchanging nutrients across gap junctions, osteocytes can be supplied with nutrients even though most osteocytes are not located near a blood vessel

channels that permit movement of ions, water + other molecules b/w adjacent cells

ones near the center of an osteon receive nutrients by diffusion from blood vessels that pass through a central canal

arranged in rings in osteons

also called Haversian Systems

nearly a solid structure w/ central canals containing nerves + blood vessels

Contains 5 Functions

Mineral storage

Blood cell formation

Movement

Protection

Support

actually a living tissue containing several cells, nerves + blood vessels

consist of nonliving extracellular calcium minerals

gives bones hard + rigid appearance