The Skeletal System

SupportProtectionMovement

Topics covered

Structure and development Remodel and repair How bones fit together to make

the skeleton How joints enable bones and

muscles to work together Problems with the skeletal system

Skeletal system consists of 3 types of connective tissue

1. Bones – the hard elements2. Ligaments – dense, fibrous

connective tissue that binds bone to bone

3. Cartilage – special connective tissue of fibrous & elastic collagen in a gel-like fluid called “ground substance”

Long bone

ligaments

Cartilage

Bones: The hard elements

Most bone mass consists of nonliving extra cellular crystals of calcium minerals

Also consists of: Living bone cells, nerves and blood

vessels (bones bleed when they are cut or broken!)

5 Bone Functions

1. Support2. Movement3. Protection4. Formation of blood cells5. Mineral storage

1. Support

Bones form the structure (skeleton) to which the skeletal muscles are attached

http://kidshealth.org/misc/movie/bodybasics/bodybasics_knee.html

2. Movement

Bones support and interact with muscles making movement possible

3. Protection As hard elements

bones surround and protect many delicate internal organs

4. Blood cell formation Certain bones

contain cells that are responsible for making different types of blood cells

5. Mineral Storage

Calcium, phosphates which are important to metabolic function

http://www.octc.kctcs.edu/GCaplan/anat/Notes/API%20Notes%20H%20Skeletal%20System.htm

Long bones Longer than wide Cylindrical shaft called diaphysis Enlarged knobs at each end called

epiphysis Compact bone forms the shaft and

covers each end Central cavity of the shaft is filled with

yellow bone marrow (primarily fat for energy)

Epiphysis

Inside each epihysis is spongy bone that is less dense than compact bone making it light, but strong

Spongy bone is a lattice work of hard relatively strong trabeculae (L. little beams) made of calcium, minerals and living cells

Long bone special function

Upper arms and legs (humerous and femur) contain spaces between the trabeculae that are filled with red bone marrow.

Stem cells in the red marrow are responsible for the production of red and white blood cells and platelets

Outer surface - periosteum

Bones are covered by tissue called periosteum that contains specialized bone forming cells: osteocytes (Gk. Bone & cells)

Osteocytes are arranged in rings in cylindrical structures called osteons (sometimes called Haversian systems)

Periosteum cont’d

As bone develops and hardens osteocytes become trapped in chambers called lacunae – but stay in touch with each other via canals called canaliculi.

Canaliculi are used to pass nutrients between adjacent osteocytes to nurture bone cells when far from blood vessels

Osteocytes in lacunae Waste products

diffuse in the opposite direction and are removed by the blood vessels for transport to urinary system

Osteocytes in trabeculae

In spongy bone osteocytes don’t need canals for nutrients and waste transportation – the trabeculae structure gives the osteocytes access to nearby blood vessels in the red marrow

http://cellbio.utmb.edu/microanatomy/bone/compact_bone_histology.htm

Ligaments hold bones together

Attach bone to bone Packed collagen fibers all oriented

in the same direction Confer strength to certain joints

while permitting movement of bones in relation to each other

Cartilage lends support

Fibers of collagen and elastin in a ground substance of mostly water

Smoother and more flexible than bone

Found where support under pressure is needed and where some movement is necessary

3 types of cartilage Fibrocartilage – found in areas

requiring ability to withstand high pressure & tension (intervertebral discs, menisci of knees)

Hyaline cartilage – forms the embryonic structures that become bones; covers the end of mature bones in joints

Elastic cartilage – highly flexible (ears, epiglottis

Development of bone

Chondroblasts – cartilage forming cells of earliest stages of fetal development

At 2-3 months in utero the cartilage models begin to dissolve and are replaced by bone = ossification

When chondroblasts die the matrix they produced breaks down making room for blood vessels

Development continued The blood vessels carry osteoblasts (Gk

bone + to form) into the area where the matrix was from the periosteum.

Osteoblasts secrete osteoid (a mixture of proteins and collagen) that becomes the strong internal structure of the bone

Osteoblasts also secrete enzymes that help form hydroxyapatite (crystals of hard mineral salts around the osteoid matrix)

Eventually mature osteocytes become embedded in hardened lacunae where they maintain the bone matrix

Bones continue to lengthen throughout childhood and adolescence because of the growth plate (epiphyseal plate) in each epiphysis

As bone lengthens the plates at each end grow farther apart

Bones also grow in width as osteoblasts lay down bone just below periosteum

Bone development controlled by hormones Growth hormone during preadolesence Sex hormones during puberty stimulate

growth plates at first By 18 in women and 21 in men the

same sex hormones signal the growth plates to stop growing

Growth plates close but bones can still grow wider

Remodeling and repair

Bone is either forming or disintegrating as long as you live

Osteoclast (Gk: bone + to break) is another type of bone cell that cuts through mature bone tissue and dissolves the hydroxyapatite and digests the osteoid matrix

Released calcium and phosphate ions enter the blood

Bone remodel & repair

Where bone has been removed osteoblasts are attracted to lay down new osteoid matrixes and stimulate new deposits of hydroxyapatite crystals

Bones change size, shape & strength

Compression causes tiny electrical currents (jogging) within the bone that stimulate bone-forming activity of the osteoblasts

So new bone is laid down in areas under high compressive stress and bone is reabsorbed in areas of low stress

Weight-bearing exercise increases bone mass!

Jogging, weight lifting causes your bones to become stronger & more dense

Homeostasis of bone structure depends on a balance of the activities of the osteoblasts and osteoclasts

Osteoporosis – great loss of bone mass due to imbalance of the activities of the 2 types of bone cells

Your body will take minerals from your bones if blood levels are low

PTH will stimulate osteoclasts to dissolve bone

About 10% of bone is remodeled or replaced each year in young adults

Repair - fractures First a blood clot or hematoma forms at

the break site as the bone bleeds Inflammation, swelling and pain

immobilize the area Repair begins within days as fibroblasts

migrate to the area Some become chondroblasts and

together with fibroblasts make a callus

Repair

The callus appears between the broken ends of the bone

Osteoclasts arrive and clear fragments of original bone as well as the blood cells of the hematoma

Finally osteoblasts arrive to lay down new matrix and start hydroxyapatite formation & callus becomes bone

Repair

Bones rarely break in the same place twice because the repaired area is thicker than the original bone

The repair process slows with age and applications of weak electrical current can increase the rate of healing – perhaps by attracting osteoblasts

The skeleton protects, supports and permits movement

Classification of 206 bones: Long bones – limbs, finger Short bones - wrists Flat bones – cranium, sternum, ribs Irregular bones – coxal (hip),

vertebrae

3 functions of skeleton

Support of soft organs Protection from injury (skull) Permits flexible movement (joints0

Skeletal organization

Axial skeleton – skull, vertebral column, ribs, sternum

Appendicular skeleton – pectoral girdle, pelvic girdle, limbs

Axial – Skull bones

Cranial – flat bones enclose and protect brain

Frontal bone: forehead and upper ridges of eye sockets

Parietal bones: upper left and right sides of skull

Temporal bones: lower left and right (ears)

Skull bones cont’d Sphenoid bone: back of the eye sockets Ethmoid bone: contributes to eye

sockets and helps to support the nose Occipital bone: curves underneath to

form the back & base of the skull Foramen magnum (L. great opening):

where vertebrae connects to skull

But wait, there’s moreSkull bones!

Facial bones - front Maxilla – forms part of eye sockets

and sockets to anchor upper row of teeth

Palatine bones – hard palate (roof of mouth)

Vomer bone – behind palatine & part of nasal septum

But wait, there’s moreSkull bones!

Zygomatic bones: cheek bones & outer portion of eye socket

Nasal bones: underlie the upper bridge of nose (space between maxilla & nasal bones is the nasal cavity)

Lacrimal bones: inner eye sockets with tear duct (drains to nasal cavity)

All skull bones joined tightly except for mandible (speak & chew)

Mandible: lower jaw w/ sockets for teeth

Sinuses are air spaces which make the skull lighter and give the human voice its tone and resonance

Each sinus is lined with tissue that secretes mucus & connects to nasal cavity by small passageways

Blocked sinuses = pain

Respiratory infections cause sinus tissue to become inflamed and block the passages to the nasal cavity

Sinusitis = sinus inflammation Fluid gets trapped causing sinus

pressure headache