Skeletal System

Skeletal SystemOur support system

Two Types of BoneThere are two

types of boneCompact bone

The outer more dense portion of bone

Composed of cylinder of dense white osseous tissue

Sponge BoneDespite its name

it is relatively hard and strong

Name given because of the appearance of its cross section.

It provides support for bone marrow and reduces the density of bone

All bone is covered in periosteum which is a tough membrane that contains a network of blood vessels to supply nutrients, and nerves which signal pain.

Periosteum also works with tendons and ligament to attach bone together.

Histology and Bone Growth

Osteoprogenitor cellsnon-specialized cells found in periosteum, endosteum, and central canal of compact bones; can turn into other types of cells as needed

Osteoblastscells that actually

form bones; arise from non-specialized osteoprogenitor cells and are cells that secrete a matrix of calcium with other minerals that give bone its typical characteristics

Osteocytesconsidered mature bone cells that started as

osteoblasts; osteoblasts surround themselves with matrix to then become mature osteocytes

Osteoclastsbelieved to originate from a type of white

blood cell called monocyte found in red bone marrow; job is to tear down bone material and help move calcium and phosphate into blood; and aids in remodeling

Osteon: consisting of concentric bone layers called lamellae and the central canal

Lamellae: A thin layer of calcified matrix around a central canal

Central Canal: hollow tube with central to an osteon and provides an opening for blood vessels and nerves into the bone.

Osteocytes live in little “caves” called lacuna. From their lacuna osteocytes reaches through

canaliculi or little tunnels to connect with one another or a blood supply.

Anatomy of a long Bone

Long bones are made up of a diaphysis and two epiphysis. Proximal

Closer to the trunkDistal

Further from the trunk

Long bones contain both yellow and red bone marrow.Yellow marrow is located in the shafts of

the long bones.Yellow bone marrow contains mostly fat

cells and works as an energy reserveRed Marrow is found in spongy bone, the

ends of long bones, Ribs, vertebrae, the sternum and the pelvis.From specialized stem cells it produces

red blood cells, platelets, and white blood cells.

Bone Growth Most bones develop from cartilage

In the second month of fetal development, much of the skeleton is made of cartilage during, and in the third month, osteocytes begin to develop and release minerals that lodge in the spaces between the cartilage cells, turning the cartilage to bone.

Ossification: the process by which cartilage is slowly replaced by bone as a result of the deposition of minerals

Many area remain cartilage to lend flexibility and support to the body.

Bone Growth There are two forms of bone growth intramembranous ossification and endochondral ossification.Intramembranous ossification is

how flat bones formEndochondral is how long /short

bones form

Endochondral Ossification First there is a cartilage model that forms Next osteoblasts are produced by the

perichondrium and they form what is known as a bone collar around the middle of the cartilageEncircling it like a napkin ring; providing

physical reinforcementWhat was perichondrium is now periosteumPrimary ossification center arises

Blood vessels penetrate the bony collar and will the primary ossification center into the primary marrow cavity. And the secondary ossification cent shows up.

Endochondral Ossification The secondary ossification cent becomes hollowed

out by the same process as the primary one creating a secondary marrow cavity in the epiphysis. At the time of birth infant bones primarily look like step

four. During infancy and childhood, the epiphyses fill with

spongy bone. Cartilage is then limited to the articular cartilage

covering each joint and the epiphyseal.

Bone Elongation and Appositional Growth Bones continue to develop after a person’s

birth During early childhood and late adolescence

bone cells gradually replace the cartilage of the epiphyseal plate in long bones Such as the one on the arms and legs

Epiphyseal plate is composed of cartilage cells that divide and form columns, pushing older cells toward the middle of the bone As older cells die the are replaced by new bone

cells.

After a late adolescents the epiphyseal plate ossifies.

Appositional Growth (or widening of the bone)is where new bone is layed on the outside of the bone by osteoblasts and old bone is being broken down by osteoclast in the middle.

Joints Joint: the place where two bones meet Three major types of joints:

Fixed Semimovable Movable

Joints Joint: the place where two bones meet Three major types of joints:

Fixed Semimovable Movable

Fixed Joint Fixed joints prevent movement Found in the skull where they permit no

movement of those bones Small amount of connective tissue in a

fixed joint also helps absorb impact to prevent the bones from breaking

Semimovable Joints Semimovable joints permit limited

movement Found in the vertebral column; allow the

body to bend and twist Also found in the rib cage; connect the

upper ten pairs of ribs to the sternum

Movable joints Movable joints enable the body to

perform a wide range of movements and activities Include:

Hinge Ball-and-socket Pivot Saddle Gliding

Movable Joints Hinge joint: found in the elbow Ball-and-socket: shoulder joint Pivot joint: formed between the top two

vertebrae in the neck Saddle: found at the base of each

thumb Gliding: fount between the small bones

of your foot

Joint Structure Joints are subjected to a great deal of

pressure and stress, but their structure is well suited to meet these demands Bones that come into contact are covered

with cartilage Protects against friction

Joint Structure Ligaments: tough bands of connective

tissue Hold the bones of the joint in place

Synovial fluid: lubricating substance that helps protect the ends of bones from damage by friction

Joint Structure Knee joint is the most susceptible

because it carries the body’s weight

Joint Structure Arthritis: used to describe disorders that

cause painful, swollen joints Two forms of arthritis:

Rheumatoid arthritis: develops when the immune system begins to attack body tissues

Osteoarthritis: degenerative joint disease in which cartilage becomes thinner and rougher, so bones rub against each other