Skeletal System

Support (function of the skeletal system)

provides attachment of tissues and cradles organs; provides framework for organs and tissue to attach.

Storage (function of the skeletal system)

Minerals (calcium, potassium) and lipids (yellow bone marrow)

Blood (function of the skeletal system)

Cell production (RBC,WBC, platelets)

Protection (function of the skeletal system)

organs (ribs, protect the heart)

Leverage (function of the skeletal system)

used as a leverage system for muscle to move or lift

Axial Skeleton

80 bones of the head and trunk region

Appendicular Skeleton

126 bones of the arms and legs and supporting girdle (attachment points to the trunk)

Bone classification

shape and formation

Long bone

has a shaft plus two ends; humorous, femur, fingers and toes

Short bone

cube shaped bones; carpal bones (wrists) tarsal bones (ankles); as tall as they are wide

Flat bones

parietal bone, sternum, ribs and scapula

Irregular

vertebrae, pelvis

Sutures

Also called wormian bones, sutural bones or Sutures

Sesamoid bone

patella; “sesame seed” develop inside tendon; found at knees, hands, feet

Canal (meatus)

large passageway through a bone

Foramen

a small rounded hole which blood vessels and nerves pass

Process

any bump or projection

Tubercle

small rounded projection

Trochanter

a large rough projection

Sinus

A chamber within a bone normally filled with air

Fissure

Elongated cleft or gap

Facet

a small flat smooth area

Fossa

shallow depression or recess

Sulcus

A deep, narrow groove

Tuberosity

Small rough projection where tendons/ligaments attach

Ramus

Extension of a bone that makes an angle

Condyle

A smooth rounded articular process

Intramembranous (membranes or dermal)

bones-bones which are formed inside of a collagen membrane; (frontal and parietal bones)

Endochondral Bone

Tissue is initially formed in hyaline cartilage then becomes bones; (vertebrae, long bones)

Compact or dense bone

Forms a protective outer layer; always located on surface of bone. Made up of haversian canal system; thickest at areas where stresses are coming from (top and bottom)

Spongy bone (“cancellous bone”)

solf, forms open networks; makes up the interior part of bone contains trabeculae which support the epiphysis of bone and create open networks which acts as a cross brace.

Central Canal (haversian canal)

provides passageway for blood vessels and nerves

Osteocytes

bones cells which are bound in the matrix and cannot move; arranged around the central Canal

laucnae

cavity/depression in bone matrix in which osteocytes reside

Lamellae

“concentric circles” which are circles of osteocytes form around the central canal

Canaliculi

“little canals” which radiate out from the central canal like
spokes on a wheel, which provide for nutrient and waste exchange.

Osteon

several “concentric circles” or lamellae; this structure
provides strength. This is the entire structural unit of a mature compact bone.

Diaphysis (long bone structures)

Extended tubular shaft with three layers periosteum, compact bone, and marrow cavity.

periosteum (Diaphysis)

outer wrapping of bone made up of collagen fibers; has nerve and blood vessels; during bone growth will contain osteoblasts and osteoclasts.

compact bone (diaphysis)

middle layer; dense layer which provides strength against stress from sides or top/bottom.

marrow cavity (diaphysis)

(also called medullary cavity) inner layer that contains blood cell forming tissue (red marrow) or lipid/fat storing marrow (yellow marrow).

Metaphysis (long bone structure)

where diaphysis connects to epiphysis.

Epiphysis (long bone structures)

expanded area at each end of long bone; consists primarily of “spongy bone” with a covering of compact bone called “cortex”.

Function of Periosteum

isolates bone from surrounding tissue, provides route for vessels and nerves to grow/attach, and assists in bone repair.

Endosteum

incomplete cellular layer that lines the “marrow cavity” in “spongy bone”; consists of a layer of osteoprogenitor cells that covers the bone matrix. If this cellular layer is not complete and matrix is exposed, osteoblasts and osteoclasts can remodel at those exposed points.

Yellow bone marrow

dominated by fat cells; great energy reserve (lipids)

Red bone marrow

mixture of mature and immature RBCs, WBCs and stem cells that produce them; make blood cells

Bone matrix

is dense and is composed of deposits of collagen fibers and calcium salts. Contains osteocytes within pockets called lacunae

collagen fibers (proteins)

are very strong but also flexible to allow some flexing and twisting; the organic without the calcium salts is called “osteoid”

calcium salts

Are comprised of calcium phosphate (2/3) and calcium hydroxide (1/3) which form crystals called hydroxyapatite on the collagen fibers

Hydroxyapatite and collagen fibers

are the major components of bones with cells only 2%.

canaliculi

Narrow passageways located in the matrix is called… form a network of exchange of nutrients and waste for the osteocytes.

Osteoprogentitor cells (mesenchymal cells/osteogenic cell)

These are “stem cells” that produce daughter cells that become osteoblasts. These cells can also differentiate into other cells such as adipose, fibroblasts

Osteoblasts

Produce new bone matrix in a process called “osteogenesis”. are considered to be a specialized form of fibroblasts. can differentiate into osteocytes during “dermal ossification”

Osteogenesis (ossification)

is the process of converting osteoid to bone

Osteocytes

most common type of bone cell. Mature cells occupy a “lacuna” “pocket” between layers (lamellae/concentric circles). Cannot dividee if occupying a lacunae; however on rare accasions can develop back into osteoblasts if no lacunae is present. Receive nutrients via Canaliculi. Repair damaged bone and maintain proper protein and mineral content in matrix

Osteoclast

remove bone matrix, large cells with 50 nuclei, erode bone by process called osteolysis, this regulates amount of calcium in blood stream, uses acids to destroy/breakdown minerals in bone, and can phagocytize dead osteocytes in bone.

Ossification

bone formation

Calcification

depositing calcium salts; this takes place during ossification

Intramembranous/Dermal ossification

Bone develops from fibrous connective tissue (mesenchymal cells) within the periosteum, normally occurs about 8th week, this occurs in deepest layer of dermis, and bone that are made are called “dermal bones” ex. clacicles, mandible, patella, frontal and parietal bones.

Step one (intramembranous ossification)

mesenchymal cells cluster together and differentiate into osteoblasts; they secrete organic molecules upon which the calcium salts crystalize.

Step two (intramembranous ossification)

as the matrix is being created, some osteoblasts are trapped in small depressions called lacuna, and differentiate into osteocytes.The bone grows outward creating extensions called spicules.

Step three (intramembranous ossification)

Blood vessels grow among the spicules; as the spicules connect they trap the blood vessels inside.

Step four (intramembranous ossification)

Osteoblasts continue to lay down the matrix around the blood vessels and fill in voids.

Step five (intramembranous ossification)

The spongy bone can be remodeled and be converted into compact bone with a central canal and lamellae.

Endochondral ossification

bone replaces existing hyaline cartilage. Examples are all bones below the skull except clavicle and patella. Embryo is six weeks old humerus (arm) and femur (thigh) is present but is made up of Hyaline cartilage

Subtypes of Endochondral ossification

Growth in lenght- interstitial growth and growth in width- Appositional growth

Step one (Endochondral ossification)

Chondrocytes at center of hyaline cartilage expand in size then die which leaves holes/cavities in cartilage. This area is known as the primary ossification center.

Step two (Endochondral ossification)

Blood vessels grow beside cartilage; a superficial layer of bone is laid down.

step three (Endochondral ossification)

Capillaries grow into holes/cavities in cartilage; Osteoblasts start to lay down the matrix at Primary ossification center and extending towards each end of bone.

Step four (Endochondral ossification)

Remodeling occurs, growth occurs creating a medullary cavity

Step five (Endochondral ossification)

Osteoblasts and capillaries migrate to epiphysis, which is primarily cartilage, creating secondary ossification centers. Interstitial Growth takes places in the secondary ossification centers.

Step six (Endochondral ossification)

On the epiphysis side (ends) of the epiphyseal plate, the chondrocytes continue to divide and increase the cartilage thickness. On the diaphysis side, (shaft), osteoblasts convert the cartilage into the bone matrix. Both of these work at approximately the same rate

Step seven (Endochondral ossification)

At puberty, the osteoblast activity speed up, while the chondrocytes slow down. This causes closure of the epiphyseal plate, the location that this growth took place is now called the epiphyseal line.

Appositional Growth

bone increases in diameter, by growing in outer surface as each new layer is added to the outer section of bone, the interlayer is removed by osteoclasts.

Steps in Appositional growth

1). New bone forms at surface of old bone producing ridges which run parallel to blood vessels. 2). The ridge enlarges creating a pocket containing the blood vessels. 3). The two ridges meet and grow together creating a small void and trapping blood vessel inside. 4). Bone matrix and osteocytes are next deposited into the void close to the capillary creating an osteon.

Nutrient artery and vein

most bones only have one of each, (femur has two of each)

-enters through “nutrient foramina” in diaphysis

Metaphyseal vessels

supplies blood to deeper inner surface where cartilage is being replaced by bone. These vessels will also provide blood to the epiphysis.

Periosteal vessels

provide blood to superficial “osteons” of the shaft and periosteum.

Remodeling of the Bone

The organic and mineral components are constantly being recycled and renewed- this is called “remodeling”

Calcium levels in the blood stream ( remodeling of the bone)

if Calcium blood levels become too low, parathyroid hormone (PTH) is released, and If calcium blood levels become too high; calcium turns off PTH and stimulates the release of calcitonin (CT).

Stress on bones from muscles and gravity. (remodeling of the bone)

Activity or stress upon bones cause them to be remodeled; therefore exercise is good for the bones.

Nutrients needed for bone growth

Calcium and phosphate, calcitriol and D3 essential for calcium and phosphate digestion of SI, vitamin C causes osteoblasts to differentiate AND production of collagen; lack of Vitamin C causes scurvy, and vitamin A,K,B12

Hormones needed for bone growth

Growth hormones (GH) and thyroxine (T4) increases bone mass which stimulate bone growth. Sex hormones (estrogen and testosterone), and Calcitonin (CT) and parathyroid hormone (PTH) control blood calcium levels.

Calcium

most abundant mineral in human body and it is used in places other than bone. Neurons and muscles also use calcium. When other systems need calcium, the body gets it from the skeleton.

Factors that Alter the Concentration of Calcium in the Body (decrease)

When calcium concentration decreases in blood stream, or other system of body runs low on calcium, PTH is released. Parathyroid hormone (PTH) is releases when Ca+2 drops in blood stream. This causes:

1. stimulates osteoclasts to work faster and breakdown bone.

2. intestines to absorb more Ca+2 from food.

3. decreases rate of Ca+2 urinated out from kidneys.

Factors that Alter the Concentration of Calcium in the Body (increase)

When calcium concentration increases in blood stream then calcitonin (CT) is released which:

1. Inhibits osteoclasts.

2. Increases excretion of calcium at kidneys.

3. Decreases absorption of Calcium by intestines.

Homeostatic range of Clacium in bloodstream

Homeostatic Calcium blood levels are 8.5 – 11 mg / dL

Nondisplaced (classified by position of end of bone after fracture)

bones are in natural position.

Displaced (classified by position of end of bone after fracture)

bone end(s) are out of alignment.

Complete ( by completeness of fracture)

bone is broken completely through

Incomplete ( by completeness of fracture)

bone is only partial fractured

Compound (if bone break the skin)

bone penetrates skin

Simple (if bone break the skin)

bone did not penetrate skin