L4: Chapter 6- skeletal system

what is the skeletal system comprised of

skeletal bones, cartilage, ligaments, and connective tissue to stabilize the skeleton

what ratio should osteoblasts and osteoclasts be in

they should be in a one to one ratio for balance, if too much of osteoclasts then osteoporosis can occur

how does exercise help bone density

with more muscle, it creates more tension on the bones so therefore the osteoblasts will come in and reinforce the bone structure to support the muscle on the skeleton

osteolysis

the process of breaking down bone

what two divisions are within the skeletal system

the axial skeleton and the appendicular skeleton

what are the functions of the skeletal system

• support

• storage of minerals- 98 percent of the bodies calcium ions are found in the bones and phosphate ions are found in bones as well

• blood cell production- bone marrow produces the blood cells

• leverage- muscles pull on bones to produce movement

• protection

osseous tissue

supporting connective tissue that is a matrix of bone; consists of calcium phosphate that converts into hydroxyapatite crystals and resists compression

how much calcium phosphate is in bone mass

2/3

collagen fibers

makes up 1/3 of bone matrix and provides tensile strength. alongside hydroxyapatite it makes bone tissue strong

bone cells composition in bone?

contribute only 2 percent of the bone mass

osteocytes

mature bone cells, they maintain protein and mineral content of the matrix. they cause the calcium release from bone to blood

where are osteocytes found

they sit in depressions called lacunae

layer of osteocytes

the matrix layer is called the lamella

canaliculi

small channels extending from the osteocytes to the bone capillaries

osteoblasts

immature bone cells, found in inner and outer surfaces of bone

osteogenesis

process of making new bone and is performed by osteoblasts

osteoblast product

osteoid is produce by these cells and is involved in making the matrix

osteoprogenitor cells

bone stem cells, found on the innermost layer of the periosteum and inner lining of endosteum

differentiate to form new osteoblasts

what cells are involved in repair of bones

osteoblasts are heavily involved and is followed by osteoclasts

osteoclasts

multinucleated cells that secrete lots of acids and enzymes to dissolve bones by causing release of stored calcium ion and phosphate ions into the blood

compact bone (dense bone)

these form the walls of the bone

spongy bone

trabecular or cancellous bone

open network of plates, surrounds the medullary cavity

medullary cavity

holds bone marrow

what is basic compact bone comprised of

central canal, canaliculi, osteocytes, lacunae, lamellae and perforating canals

what is concentric lamellae

this is normal lamellae that is found around central canals

interstitial lamellae

found in between concentric lamellae and fill in the triangular space

circumferential lamellae

found around all of the bone between the other two lamellae layers and the periosteum

perforating canals

aka volkmanns canal and is found perpendicular to central canals

spongy bone structure

is arranged in branching plates called trabeculae —> forms an open network

where is spongy bone found mostly

at ends of bones

compact bone function

generates lots of strength from one end to another. weak strength is from the side of a long bone

how is osteon arranged in compact bone

found parallel to bone axis

spongy bone function

trabeculae creates strength to deal with stress from the side

contains lots of cross bracing and supports yellow marrow in shaft of the bone and red marrow in the epiphysis of bone

epiphysis

ends of long bones and contains red marrow

diaphysis

shaft of long bones and the medullary cavity contains yellow marrow. if the shaft breaks a fracture will occur

metaphysis

narrow growth zone between the epiphysis and the diaphysis

periosteum location

outer surface of the bone that consists of fibrous layer and an osteogenic layer

attaches the bone to the connective tissue network of the deep fascia via perforating fibers

periosteum function

it isolates and protects the bone from surrounding tissue

provides route and place for attachment for circulatory and nervous supply

actively participates in bone growth and repair

endosteum

inner surface of the bone, lines medullary cavity, consists of osteoprogenitor cells and actively involved in repair and growth

what happens with bone in the first eight weeks of development

it starts as hyaline cartilage and the fibrous tissue and cartilage cells are replaced by bone cells (ossification)

intramembranous ossification

bone formed from fibrous tissue

involved in development of clavicle, mandible, skull and face

mesenchymal cells differentiate to form osteoblasts, they secrete a matrix, become trapped in matrix and differentiate into osteocytes. more osteoblasts are produce n builds outward

blood vessels are trapped by formation of spicules

endochondral ossification

bone formed from cartilage tissue

involved in development of limbs, vertebrae and hips

chondrocytes near the center of the diaphysis increase in size and blood vessels grow around the cartilage

perichondrial cells begin to form the periosteum; thin layer of compact bone forms

osteogenesis

the process of bone formation

calcification

the deposition of calcium ions into the bone tissue

what is the primary ossification center

in endochondral ossification, cartilage cells die and are replaced by osteoblasts

osteoblasts begin to form spongy bone, cartilage in metaphysis region is invaded by osteoblasts

increase in bone length and diameter begins

secondary ossification center

in endochondral ossification osteoblasts begin to migrate to epiphysis region (secondary OC)

osteoblasts replace cartilage with bone and results in pushing the epiphysis away from the diaphysis therefore longer bones

epiphyseal closure

area of cartilage in the metaphysis that forms the epiphyseal line/plate

this is cartilage near the diaphysis and is converted to bone

articular cartilage

found at the ends of bone

appositional growth

inner layer of periosteum differentiates to form osteoblasts and adds bone matrix to the surface

this forms circumferential lamellae to the outer surface, osteons form and bone continues to enlarge in diameter

what are the four major blood vessels in long bones

nutrient vessels(arteries and veins)

metaphyseal vessels

epiphyseal vessels

periosteal vessels

nutrient vessels structure

they enter the diaphysis and branch toward the epiphysis, they enter through the nutrient foramen of the bone (in middle of shaft)

penetrates the shaft and enter the medullary cavity, divides into ascending and descending branches to go toward the epiphysis regions

what enters the nutrient foramen

sensory nerves and nutrient artery

what forms perforating vessels

nutrient vessels divide into ascending and descending branches and branch for another time forming these

what provides nerve and blood supply to bones

metaphyseal vessels-nutrient to diaphyseal edge of epiphysis

epiphyseal vessels- nutrients to cavities of epiphysis

periosteal vessels- nutrients to superficial osteons

what factors regulate bone growth

minerals, vitamins, calcitriol, hormones, and sex hormones

how do minerals affect bone growth

calcium ions, phosphate ions, magnesium ions, citrate/carbonate ions and sodium ions

bones need constant supply from the diet

how do vitamins affect bone growth

vitamin A stimulates osteoblasts

vitamin C is necessary for collagen formation and osteoblast differentiation

how is calcitriol important in bone growth

made in the kidneys from cholecalciferol (D3)

vitamin D3 is made in the skin by UV radiation and diet

it is necessary for absorption of calcium ions and phosphate ions

how do hormones affect bone growth

parathyroid gland releases parathyroid hormone

the thyroid gland releases calcitonin

thyroid gland releases thyroxine

pituitary gland releases growth hormone

parathyroid hormone

stimulates osteoclasts, stimulates osteoblasts, increases circulating calcium levels by aiding calcium ion absorption from small intestine and reducing calcium ion loss from kidneys

calcitonin

released by thyroid gland

inhibits osteoclasts and decreases circulating levels of calcium by increasing rate of calcium ion loss in urine and removing calcium ions from blood and adding it to bone (opposite of PTH)

thyroxine

released by thyroid gland and maintains normal activity in the epiphyseal region for growth

growth hormone

released by pituitary gland and maintains normal activity in the epiphyseal region for growth

sex hormones in growth

estrogen and testosterone stimulate osteoblast activity- produces bone faster than epiphyseal cartilage expansion

ultimately the epiphyseal region narrows and bone growth ceases

what is the definition of remodeling of bone

bone changes shape in response to external (to the bone) conditions

what are examples of remodelings of bone

realignment of teeth can change shape of teeth sockets

increased muscular development increases bone strength due to higher stress

different features develop on the bone, ligaments and tendons

what happens when bones become stressed and then less stressed

stressed bones become thicker and stronger

inactivity can cause degeneration and after a few weeks unstressed bones can lose about a third of their mass

what kind of fractures are there

transverse, displaced, non-displaced, compression, spiral, epiphyseal, comminuted, greenstick, colles, and pott fracture

what happens when a bone is broken

lots of bleeding occurs and a network of spongy bone forms

osteoblasts are overly activated then resulting in an enlarged callused area

this area is stronger now and thicker than normal, osteoclasts will remove callus over time

what happens to bone cell activity when young

osteoblast activity balances with osteoclast activity

how does bone cell ratios change as we age

osteoblast activity declines and osteoclast maintains level

ossification decreases (formation of bone) resulting in osteopenia

if osteoclast activity is faster than osteoblast activity bones become porous

what happens when estrogen levels drop in older women

osteoclast control is lost and are overactive, bones become porous causing osteoporosis

what are the classifications of bones

sutural, irregular, short, pneumatized, flat, long, and sesamoid

what kinds of bone marking are present

projections, depressions (fossa), openings (sinuses, canals, fissues, foramina), and processes

transverse fracture

break horizontally (transverse) to the long axis

displaced fractures

produce new and abnormal bone arrangements, breaks both bones in a dual bone limb (example, radius and ulna)

nondisplaced fractures

retain the normal alignment of the bone

compression fractures

when the bones jam together

spiral fractures

bones twist along the length of the bone, signal child abuse

epiphyseal fractures

fractures within the epiphyseal region

comminuted fractures

fractured area shatters into many bony fragments

greenstick fractures

only on edge of the bone breaks while the other ends bends, forms a sort of sliver of bone on one side of long bone

colles fracture

a break at the distal portion of the radius

pott fracture

occurs at the ankles and affects both the tibia and fibula

how are bones integrated with other systems

bones are not inert and are dynamic structures

they are attached to muscles, under physiological control via endocrine system

digestive and excretory system provides calcium and phosphate needed for growth

bone serves as storage of calcium, phosphate and other minerals