Lesson 9 Flashcards
the formation of bone is called (2)
ossification or osteogenesis
calcification
process of depositing calcium salts during bone ossification and in other tissues
bone develops by two methods:
- intramembranous ossification
- endochondral ossification
intramembranous ossification
also called dermal ossification
- occurs in the dermis
- produces flat bones of the skull, most of the clavicle, and part of the mandible
summary of stages of intramembranous ossification (4)
- deposition of osteoid tissue into embryonic mesenchyme
- calcification of osteoid tissue and entrapment of osteoblasts, causing them to become osteocytes
- honeycomb of spongy bone with developing periosteum
- filling of space to form compact bone at the surfaces, leaving spongy bone in the middle
endochondral ossification
bone develops from hyaline cartilage model
- produces most bones in the body
- limbs, vertebrae, ribs, sternum, scapula
summary of stages of endochondral ossification (6)
- mesenchyme forms early hyaline cartilage model
- formation of primary ossification center (center of the long bone), bone collar, and periosteum
- vascular invasion, formation of primary marrow cavity, and appearance of secondary ossification center (at an epiphysis)
- bone at birth contains enlarged marrow cavity and secondary marrow cavity in one epiphysis
- bone of a child contain an epiphyseal plate
- adult bone contains a single marrow cavity and the epiphyseal plate
metaphysis: zone of reserve cartilage
typical histology of resting hyaline cartilage
metaphysis: zone of cell proliferation
chondrocytes multiplying and lining up in rows of small, flattened lacunae
metaphysis: zone of cell hypertrophy
cessation of mitosis; enlargement of chondrocytes and thinning of lacuna walls
metaphysis: zone of calcification
temporary calcification of cartilage matrix between columns of lacunae
metaphysis: zone of bone deposition
breakdown of lacuna walls, leaving open channels; death of chondrocytes; bone deposition by osteoblasts forming trabeculae of spongy bone
interstitial growth
cartilage growth from within
achondroplastic dwarfism
long bones stop growing in childhood, results in normal torso and short limbs
what causes achondroplastic dwarfism?
genetic mutation in the FGFR3 gene which is important in bone development and maintenance
pituitary dwarfism
caused by lack of growth hormone; normal proportions but short stature
appositional growth
deposition of new tissue at the bone surface, growth in diameter and thickness
- intramembranous ossification at bone surface
Wolff’s law of bone
architecture of bone determined by mechanical stresses placed on it
mineralization
crystallization process in which calcium, phosphate, and other ions are taken from blood and deposited in bone
osteoblasts produce _____ _____ that spiral the length of the osteon
collagen fibers
ectopic ossification
abnormal calcification of tissues, such as a lung, brain, eye, muscle, tendon, or artery
calculus
a calcified mass in an otherwise soft organ
heterotopic bones
bones formed in non-skeletal tissue
heterotopic bones: myositis ossification
rare genetic form, causes muscles to ossify
heterotopic bones: traumatic myositis
repeated trauma or single hard hit to soft tissue triggers ossification of tissue there
heterotopic bones: neurogenic heterotopic ossification
frequent complication to spinal cord injury
fibrodysplasia ossificans progressiva (FOP)
rare genetic heterotopic ossification disorder causes progressive muscle and connective tissue conversion to bone
mineral resorption
process of dissolving bone; releases minerals into blood
how does mineral resorption work? (4)
- hydrogen pumps on the plasma membrane secrete hydrogen into the space between osteoclast and bone surface
- chloride ions follow by electrical attraction
- hydrochloric acid (pH4) dissolves bone minerals
- acid-tolerant protease enzyme digests collagen
hypocalcemia
calcium deficiency; causes excessive excitability of nervous system and muscles
- caused by low vitamin D, diarrhea, thyroid tumors, etc.
hypercalcemia
calcium excess; causes nerve and muscle cells to be less excitable than normal
calcium homeostasis is regulated by three hormones
calcitriol, calcitonin, and parathyroid hormone
calcitriol
form of vitamin D produced by sequential actions of the skin, liver, and kidneys
how is calcitriol formed in the body? (3)
- epidermal keratinocytes use UV radiation to convert 7-dehydrocholesterol to previtamin D; warm sun converts this to vitamin D3
- liver adds hydroxyl group converting it to calcidiol
- kidney ads a hydroxyl group converting that to calcitriol
calcitriol acts to raise blood calcium in three ways
- increase calcium absorption by small intestine
- increase calcium resorption from skeleton
- weakly promotes reabsorption of calcium from the kidneys
calcitonin
produced by parafollicular cells of the thyroid gland (C cells); secreted when blood calcium levels are too high
how does calcitonin lower blood concentration? (2)
osteoclast inhibition, osteoblast stimulation
parathyroid hormone (PTH)
secreted by the parathyroid glands on posterior surface of the thyroid in response to low calcium in the blood
PTH raises blood calcium levels by four mechanisms:
- binds to receptors on osteoblasts, which then stimulate osteoclasts to resorb bone
- promotes calcium reabsorption by the kidneys, so less is lost in urine
- promoties the final step of calcitriol synthesis in kidneys, enhancing calcium-raising effects
- inhibits collagen synthesis by osteoblasts, inhibiting bone deposition
how does calcitriol raise phosphate levels?
promotes its absorption by the small intestine
how does PTH lower blood phosphate levels?
promoting its urinary excretion
_____ is required for collagen synthesis and stimulation of osteoblast differentiation
vitamin C
_____ stimulates osteoblast activity (important for normal bone growth in children
vitamin A
______ and _____ help synthesize bone proteins
vitamin K and vitamins B12
_____ _____ and _____ stimulate bone growth
growth hormone, thyroxine
_____ and _____ stimulate osteoblasts
estrogens and androgens
growth hormone (GH)
released by the pituitary gland that affects all cells in the body
orthopedics
branch of medicine dealing with prevention and correction of injuries disorders of bones, joints, and muscles
what are bone fractures classified as? (2)
stress fractures of pathological fractures
stress fracture
berak caused by abnormal trauma to a bone (ex. a fall)
pathological fracture
breaks in bone weakened by disease, usually caused by a stress that would not break healthy bone
major types of fractures: transverse
across the long axis
major types of fractures: displaced
produced new/abnormal bone arrangements
major types of fractures: nondisplaced
bone fragments are in normal alignment
major types of fractures: compression
produced on vertebrae on hard falls to seat
major types of fractures: spiral
twisting stress on length of bone
major types of fractures: compound
bone fractures that breaks through skin
major types of fractures: epiphyseal
usually occurs where bone matrix is undergoing calcification, can permanently stop growth of that bone
major types of fractures: comminuted
shatters bone into multiple fragments
major types of fractures: greenstick
only one side of the bone is broken, other side is bent (generally occurs in children)
major types of fractures: colles
break in distal portion of the radius (usually caused by reaching out to cushion a fall)
major types of fractures: pott’s
occurs at ankle affecting tibia and fibula
stages of healing fractures: hematoma formation
first step: blood clots converted to granulation tissue
stages of healing fractures: soft callus formation
deposition of collagen and fibrocartilage converts granulation tissue to a soft callus
stages of healing fractures: hard callus formation
osteoblasts deposit temporary bony collar to unite broken pieces while ossification occcurs
stages of healing fractures: bone remodeling
small bone fragments are removed by osteoclasts while osteoblasts deposit spongy bone and convert it to compact bone
closed reduction
procedure in which bone fragments are manipulated into their normal positions without surgery
open reduction and internal fixation
involves surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments
osteopenia
measurable decline in bone density; may advance to osteoporosis
osteroperosis
severe loss of bone density; bones fracture easily
who is at more risk for bone disorders? (4)
women, smaller people, white women of asian/european origin, older people
what two hormones help maintain bone tissue?
estrogens and androgens
what can cancerous bone tissue secrete to break down bone?
osteoclast-activiating factor
