Chapter 5 : skeletal system

the skeletal system is made of

• skeletal bones

• cartilage

• ligaments

• connective tissue to stabilize the skeleton

Osseous tissues are a major component

functions of the skeletal system

• support - provides the framework for the attachment of other organs (muscles)

• storage of minerals - calcium and phosphate ( 98% of the calcium in the body is stored in bones)

• Blood cell production - major site of production

  • Red marrow

  • Yellow marrow - adipose cells

• leverage - gives muscles a platform to exert force on to cause movement

• Protection - every important organ is protected ( ribs protect the heart and lungs, skull protects the brain, ect)

Red marrow -

all the formed elements of blood are produced

Yellow marrow

• - adipose cells

histological organization of mature bone

• Osseous tissue is a type of connective tissue

• Specialized cells called osteocytes make up 2 % of the mass of this tissue

• has a solid matrix

  • made of collagen fibers surrounded by calcium salts (which gives strength to the bones)

Periosteum

outlining continues with the deep fascia

Endosteum

inner lining

Osteocytes

• similar to fibrocytes, maintain the protein and mineral content of the matrix

• Mature bone cells

• Mature = maintain

they oversee everything !!!

Osteoblast

• responsible for building bone

• immature bone cells

• found in the periosteum and endosteum

• Produced osteoid, which is involved in making the matrix

• make new bone, but the process is called osteogenesis

Osteoprogenitor cells

• Produced osteoblasts

• differentiate to form new osteoblasts

• found in the periosteum and endosteum

• Really important for repairing bones after they break

Osteoclast

• found in the periosteum and endosteum

• performs osteolysis

  • The dissolving of bone tissue, thereby causing the release of stored calcium ions and phosphate ions into the blood

• It makes bones weak, but you’re supposed to replenish them through your diet

• Used in muscles, movement

• really important in muscle movement

Ground bone slide

What is this slide ?

osteon

What is this whole structure called ?

Canaliculi

What is number 3 ?

( strings that connect osteocytes)

Central canal

What is 1 ?

( blood vessels run through )

Lamella

What is 4?

( similar to rings of a tree)

Osteocytes in lacunae

volkmann’s canals

• perpendicular to the surface of the blood vessels

• designed to give blood to deeper osteons

Epiphysis

ends

Diaphysis

Shaft

Metaphysis

• at the neck of the bone, it’s a narrow growth zone between the epiphysis and diaphysis

• found on the distal and proximal portions of the bone ( so not just the neck )

Medullary cavity

where the bone marrow is held

Articular cartilage

• usually found on the epiphysis

• thin layer of hyaline cartilage over the epiphysis

• reduces friction and absorbs shock

Compact bone

• aka dense bone

• More compact, thicker compact bone in the diaphysis bc its where you find the medullary cavity

• Compact bone outlines the medullary cavity

• Also covers spongy bone

Function:

• gerentes tremendous strength from end to end, so when force is applied, the compactness is what prevents it from breaking.

• conducts stress from one area of the body to another area of the body

Spongy bone

• trabecular bone

• no true osteon

• Made of an open network of plates (called trabeculae or spicules)

  • irregular latticework

  • makes the lightweight nature of bones

  • larger spaces filled with red marrow - especially within epiphyses and irregularly shaped bone

• Osteocytes and lacunae are found in trabeculae

  • Not in true osteons, in structures that look like osteons bc they don’t have a central canal

  • In this type of bone, they get their nutrients from blood

  • don’t need central or perforating canal bc they are really close to red bone marrow, making them bathed in blood

function:

to deal with stress from the side

Periosteum

• outer surface of the bone

• covering over bone not covered by articular cartilage, or where tendons and ligaments

Structure :

fibrous layer - outer

• connective tissue with blood vessels, lymphatic vessels, and nerves that pass into the bone

Osteogenic Layer - inner

• elastic fibers, blood vessels, osteoprogenitor cells, osteoclasts, and osteoblasts

• The main job is cell growth, making new bone

Endosteum

• inner surface of bone

• lines the medullary cavity

• consists of osteoprogenitor cells

  • actively involved in repair & growth

Osteogenesis

• the process of bone formation

included

• ossification

• calcification

Ossification

takes place during calcification, cartilage is replaced by bone cells

Calacififcation

• Taking the cartilages jelly like matrix and turning it solid

• The deposit of calcium ion salts into the bone tissue makes it solid

Intramembranous ossification

• formation of bone directly on or within the fibrous connective tissue membranes

• Cells of compact connective tissues undergo differentiation to form osteoblasts, which divide to form bone

• involved in the development of the clavicle, mandible, skull, and facial bones

  • have softer connective tissue within them, which is why they are formed in these membranes

Endochondral ossification

• How most of the bones in the body are actually formed

• formation of bone from hyaline cartilage

  • Hyaline cartilage makes a template for the bone

• Cartilage is eroded away and eventually replaced with bone

Epiphyseal plate

• where endochondral ossification occurs

• cartilage in the metaphysis, converted to bone, increasing bone length

  • A layer of cartilage that slowly turns to bone

• As we age, the width of this zone narrows. until at a point it just becomes a line called the epiphyseal line - which is a bony remnant of the epiphyseal plate

Appositional growth

• increasing the diameter of the bone

• Blood vessels that run parallel to the bone become surrounded by bone cells

  • which creates “ tunnels.”

  • Each “tunnel” has a blood vessel in it, technically making it an osteon

• Osteoblasts surrounding the bone begin to produce a matrix, thus creating concentric rings, making it larger

• Osteoclasts are dissolving the inner bone, thus creating the marrow cavity

Major blood vessels associated with the long bone

• nutrient vessels

• metaphyseal vessels

• epiphyseal vessels

• periosteal vessels

nutrient vessels

• enter the diaphysis and branch towards the epiphysis ( both ends, splits )

• Re-enter the compound bone leading to the central canal of the osteons

Metaphyseal vessels

• supply nutrients to the diaphyseal edge of the epiphysis

• region of the metaphysis

Epiphyseal vessels

supply nutrients to the medullary cavities of the epiphysis

Periosteal vessels

• supply nutrients to the superficial osteons - outer part of compact bone

• found in the periosteum

• nutrient muscles are named after where they go, they enter the bone and split

Nutrition

• A factor regulating bone growth

• mineral: calcium, phosphate, magnesium, citrate, carbonate, and sodium

• Vitamins: A, C, and D

  • calcitriol : vitamin D3 - helps in Ca absorption

• If taking vitamins, take calcium citrate instead of calcium carbonate, as it absorbs better; also why milks are fortified

Hormones

• A factor regulating bone growth

• thyroxine - growth hormone

  • maintain normal activity in the epiphyseal region

• sex hormones - stimulate osteoblast activity

  • You get a higher influx of sex hormones during adolescence, which is where puberty happens, which is why growth and puberty happen during this time

  • development of secondary sexual characteristics

  • growing pains, mostly at night, because growing pains happen at night

Fracture

• injury and repair

• When a bone is broken or cracked

• The healed area is stronger and thicker than normal bone

• sometimes susceptible to atmospheric pressure, aches

Aging in the skeletal system

• When osteoclast activity is faster than osteoblast activity, bones become more porous - osteoporosis

• You dissolve bone faster than you make it

• easy to break as you get older

Start bulking up on calcium before you get older bone density exams, as you get older

classification of bone shapes

• sutural bones

• irregular bone

• short bone

• pneumatize bones

• flat bone

• long bone

• sesamoid bones

sutural bones

small bones between the joints of certain cranial bones

Irregular bone

• Irregular amount of spongy vs compact bone

• vertebral column, certain facial bones

Short bones

• cube shaped

• spongy with a thin layer of compact bone

• wrist and ankle

Pneumatized bones

Hollow or contains numerous air pockets

Flat bones

• thin; composed of 2 more or less parallel plates of compact bones over spongy bone

• protection for soft tissue

• extensive areas for muscle attachment

• cranial bone, sternum, ribs, scapula

• spongy bone sandwich

  • compact bone, spongy bone, compact bone

• really big area important for muscles attachments

• important for the protection of soft tissue ( like the brain )

long bones

• greater length than width

• diaphysis, metaphyses, epiphyses, and medullary cavity

• slightly curved for strength- body stress

• thighs, legs, toes, arms, forearms. fingers

Processes

any projections or bump

Ramus

an extension of a bone that forms an angle that forms an angle with the rest of the structure

Sinus

a chamber within a bone, normally filled with air

canal

a passageway for blood vessels and or nerves

Fissure

a deep furrow, cleft, or slit

Foramen

a rounded passage way ( hole ) for blood vessels and or nerves

Trochanter

a large, rough projection. A runner that rotates

crest

a prominent ridge

Spine

a pointed process

Line

a low ridge

Tubercle

a small, rounded projection

Tuberosity

a large rough projection

Sulcus

a narrow groove

fossa

a shallow depression

Head

the expanded articular end of an epiphysis, often separated from the shaft by a narrower neck

Neck

a narrower connection between the epiphysis and diaphysis

Facet

a small, flat articular surface

Condyle

a smooth, rounded articular process

• a knuckle

Trochlea

a smooth, grooved articular process shaped like a pulley