bone structure and development Flashcards
skeletal system consists of
bones, cartilage, ligaments, and other connective tissue that stabilize or interconnect bones
functions of the skeletal system
- support and framework
- structural support for body
- attachment for soft tissues and organs - protection
- bone is hard; protects organ it surrounds - leverage, movement
- forces generated by muscle, move bones
- * tendons (CT) attach muscles to bone (contract –> shorten –> tension –> enough tension pulls on tendon then bone to create movement
- joints form where bones come together - hemopoiesis - process by which you make blood cells
- occurs in RBW in bone cavaities - storage of minerals and lipids
- lipids (E reserves) found in yellow bone marrow
- minerals (Ca and phosphate ions) stored in bone matrix
axial skeleton
midline
- skull - cranium and face
- thoracic cage - sternum and ribs (12 pairs)
- vertebral column - cervical (7), thoracic (12), lumbar (5) ; sacral bone (1); coccygeal bone (1)
appendicular skeleton
bones of upper and lower limbs; limbs + girdles that attach limbs to axial
- pectoral girdle (2 scapulae and 2 clavicles)
- pelvic girdle (right and left coxae join each other anteriorly and sacrum posteriorly
connective tissue
bone, cartilage, tendons, and ligaments
- matrix contains: collagen, proteoglycan (ground substance), and other organic molecules plus water and minerals
collagen
tough, ropelike fiber
proteoglycans
large molecules consisting of polysaccharides attached to core proteins
- good shock absorber (cartilage)
- attract and retain large amounts of water between polysaccharide (ions= hard –> bone)
long bones
- long and slender
- arms, forearm, thigh, leg, palms, soles, fingers, toes
- femur is largest and heaviest
flat bones
- thin roughly parallel surfaces
- form. roof of skull, sternum, ribs, scapulae
- provide protection and large surface area for muscle attachment
sutural bones
- wormian bones
- small, flat, irregularly shaped bones,
- bones of the skull
- range in size: grain of sand - quarter
- like pieces of a jigsaw puzzle
irregular bones
-complex shapes with short, flat, notched, or surfaces
- spinal vertebrae, bones of pelvis, several skull bones (ethmoid and sphenoid)
short bones
- small and boxy
- carpal and tarsal
sesamoid bones
- generally small, flat, shaped like sesame seed
- develop inside tendons
- near joints at knee, hands and feet
- all have patellae, others vary from individual to individual
bone markings
help to determine size, age, sex, and general appearance of an individual
- elevations or projections (form where tendons and ligaments attach and at articulations - at a joint)
- depressions, grooves, and tunnels (foramen - where BVs or nerves lie or penetrate bone)
general features of a long bone
- diaphysis - general shaft
- epiphysis - at ends of diaphysis
- epiphyseal plate = growth plate (cartilage)
- in growing bones; growing in length
- * composed of cartilage between each epiphysis and diaphysis
- when growth stops, replaced by bone = epiphyseal line (bones cannot grow anymore when this forms, no more cartilage) - medullary cavity - cavities in bone filled with marrow
marrow
soft tissue
- yellow marrow: mostly of fat
- red marrow: consists of blood-forming cells; only site of blood formation in adults
children have more marrow because as you age red is replaced with yellow
diaphysis
- consists of compact bone: dense
- solid
- forms sturdy protective layer that surround a central space (medullary cavity = marrow cavity)
epiphysis
- consists of spongy bone = cancellous bone = trabecular bone
- open network/latticework with thin covering (cortex = compact bone = cortical one)
compact bone
- dense, composes diaphysis, outer surfaces
- lamellae: organized into sets of concentric rings surrounding a central canal - ring of bone matrix
- central canal - site of BVs which interact w vessels of peri- and endosteum
- blood vessels located inside
- osteon
osteons
- smallest functional unit of a compact bone
- contains central canal, surround lamellae, and osteocytes which are house in lacunae
- osteocytes in lacunae connected to each other via cell processes in canaliculi
cancellous bone
- spongy bone due to appearance
- located mainly in epiphysis of long bones and forms interior of all other
- blood vessels located on outside
- lighter than compact bone
- framework of trabeculae supports and protects cells of bone marrow
trabeculae
delicate interconnecting rods or plate of bone: resemble scaffolding
- spaces between filled with marrow (red & yellow)
- each consist of several lamellae with ostecytes between lamellae
- no BV penetrate; no central canal!
- nutrients exit vessels in marrow and pass by diffusion through canaliculi to osteocytes of trabeculae
periosteum
- dense CT covering outer bone except at articulations
- provide route for blood vessels and nerves
- actively participates in bone growth and repair
- never cover articular cartilage
endosteum
- lines surface of medullary cavity [in bone]
- surround trabecular bone
- thinner CT
- actively participates in bone growth, repair, and remodeling
cells in bone
osteoprogenitor, osteoblasts, osteocytes, osteoclasts
osteoprogenitor
bone stems cells (stage 1); divide and differentiate into osteoblasts
located in periosteum, endosteum, and lining of passageways containing BVs which penetrate compact bone
osteoblasts
bone forming cells (stage 2); make and release protein and other organics of matrix; trigger deposition of calcium salts to matrix (Ca + phosphate)
once surrounded by matrix they help to create and mature into osteocytes
osteocytes
mature bone cells (stage 3); maintain protein and mineral content of matrix
can not divide: can regress to earlier form
osteoclasts
stage 4; break down bone matrix with acids and proteolytic enzymes (break down proteins - collagen); release Ca and P back into circulation (out of bone matrix)
when no longer surrounded by matrix they regress back to osteoblast
you need osteoblast activity to = osteoclast activity in order to have healthy bones
lamellae
- thin sheets of extracellular matrix
- forms bone
- osteocytes located between lamellae
lacunae
spaces that house osteocytes
canaliculi
- tiny canals
- house cell precesses that extend from osteocytes across extracellular matrix of lamellae
- run through bone matrix and allow for diffusion of gasses and nutrients
ossification
formation of bone by osteoblasts; osteoblast surrounded by matrix becomes osteocytes
intramembranous ossification and endochondral ossification
intramembranous ossification
occurs within CT membranes; start with generalized CT membrane and results in formation of skull cap bones
- fake existing CT and replace w bone
- uses osteoblasts
- occurs in utero
endochondral ossification
occurs on cartilage model; starts with cartilage model (hyaline; shape of bone model) and results in formation of all other bones (not skull)
- fake existing CT and replace w bone
- uses osteoblasts
- occurs in utero
bone growth in length
- increases height in individuals
- occurs in epiphyseal plate
- chondrocytes increase in number on epiphyseal side of epiphyseal plate
- line columns parallel in long axis of bone, causes elongation
- cartilage removed by osteoclasts and replaced by osteoblasts
- osteoblasts form lamellae on surface of calcified cartilage
- produces bone on diaphyseal side of EP
- diaphyseal side of GP - osteoblasts sit on existing cartilage… replace bone matrix at cancellous 1st… can get remodeled to compact bone
- epiphyseal side of GP - chondrocytes (cartilage cells) are going to grow and divide
bone growth through mid twenties
@ GP from puberty to age 25 osteoblast activity > osteocyte activity to allow GP to eventually close/convert to epiphyseal line
prior to puberty @ GP see osteoblast activity = osteocyte activity to allow bone to grow in length while maintains growth plate
bone growth in diameter
- primarily see osteoblasts within periosteum forming bone matrix radiating outward –> overall diameter grows
- osteoclasts within endosteum “eating” away at inner, existing bone –> to increase diameter of medullary cavity
- diameter of entire bone relatively constant with medullary cavity
bone remodeling
- occurs in all bone
- depends on balance between bone formation and resorption (between osteoblasts and osteoclasts)
- newly formed cancellous bone in epiphyseal plate remodeled to form compact bone
- responsible for changes in bone shape, adjustment to stress, bone repair and calcium ion regulation in body fluids
bone remodeling… if to much bone is deposited
- bones become thick
- have abnormal spurs or lumps; can interfere with normal function
bone remodeling…if too little bone formation or to much bone removed
- weakens bone
- susceptible to fracture
- loss of mass can occur quickly, within 3 wks of inactivity, can loos 1/3 of mass
bones and calcium homeostasis
- bone is major storage site for Ca
- movement of Ca into and out of bone helps determine blood calcium levels (regulated by hormones)
- Ca moves into bone as osteoblasts build new bone
- Ca moves out of bone as osteoclasts break down bone
when blood calcium level are too low
- osteoclast activity increases
- calcium released by osteoclast from bone into blood
- blood calcium levels are restored
when blood calcium levels are too high
- osteoclast activity decreases
- osteoblast activity increases
- calcium taken from blood by osteoblasts to produce new bone
- blood calcium level decrease
calcium homeostasis: PTH
parathyroid hormone - increases blood Ca levels
- stimulates increased bone breakdown; increases blood Ca levels
- stimulates osteoclast activity
- increases Ca reabsorption from urine to kidneys
- stimulates kidneys to form vitamine D
- decreasing blood Ca levels stimulates PTH secretion
calcium homeostasis: calcitonin
secreted from thyroid - decreases blood Ca levels
- inhibits osteoclast activity
- increases rate of excretion of Ca ions at kidneys
- decreases blood Ca level
- increasing blood Ca levels stimulates calcitonin secretion
osteopenia
- inadequate ossification
- part of natural aging process
- reduction in bone mass occurs between ages 30-40
- osteoblast activity begins to decline while osteoclast activity remains normal
- women lose it faster than men
- epiphyses, vertebrae and jaws loose more mass than other
- results in fragile limbs, reduction in height and loss of teeth
osteoporosis
- condition when reduction in bone mass leads to compromise normal functioning
ie hip fracture due to standing - in women, condition accelerates after menopause due to decline in circulating estrogens; estrogens stimulates osteoblasts
- develops in secondary effect with many cancers which release many chemicals: osteoclast-activating factor
this is not apart of the normal aging process it is a matter of severity
