Bone tissues pt 2 Flashcards
chapter 7
Bone development + 4 stages
osteogenesis (ossification): bone tissue formation
1. Initial formation: in embryo + fetus
2. growth: from infancy through adolescence
3. remodeling: of bone throughout life
4. repair: of fractures
what are the 2 types of ossification?
- Intramembranous ossification
- membrane bone develops from fibrous membrane
- forms flat bones, clavicles + cranial bones - Endochondral ossification
- cartilage (endochondral): bone forms by replacing hyaline cartilage
- forms most of the rest of the skeleton
Intramembranous ossification
- Development of ossification center
- Bone matrix (osteoid) secreted + calcifies
- Trabeculae of woven bone + periosteum (widening bones) form
- Bone collar of compact bone forms + red marrow appears
Endochondral ossification
- uses hyaline cartilage models
- requires breakdown of hyaline cartilage prior to ossification
- forms all bones below skull except for clavicles
Postnatal bone growth (2)
- Interstitial growth: increase length of long bones
- Appositional growth: increase thickness + remodeling of all bones by osteoblasts and osteoclasts on bone surfaces, bone matrix secreted under periosteum
Hormonal regulation of bone growth
- growth hormone: stimulates epiphyseal plate activity (from pituitary gland)
- thyroid hormone: modulates activity of growth hormone
- testosterone + estrogens (at puberty): promote adolescent growth spurts, end growth by inducing epiphyseal plate closure (18 y/o females; 21 y/o males)
Hormonal control of blood calcium
- primarily controlled by parathyroid hormone (PTH)
- stimulus: falling blood calcium levels
- Parathyroid glands release PTH hormone
- increases PTH
- PTH stimulates osteoclasts to degrade bone matrix and release calcium into blood
- increased calcium levels to maintain homeostasis
What controls continual remodeling of bone?
- Hormonal mechanisms that maintain calcium homeostasis in blood
- Mechanical + gravitational forces (wolff’s law)
Wolff’s law
Response to mechanical stress
- Wolff’s law: bone grows/remodels in response to forces/demands placed upon it
observations supporting wolff’s law
- handedness (right/left handed) results in bone of upper limb being thicker + stronger
- curved bones are thickest where tehya re most likely to buckle
- trabeculae form along lines of stress
- large, bony projections occur where heavy, active muscles attach
- increased stress/decreased stress (astronauts - gravity)
Fracture classification
- displaced/nondisplaced: complete fracture across or bone separates
- open/closed: bone sticks out of skin/still in the skin
- comminuted: bone fragments (crushing)
- spiral: excessive twisting force
- compression: common in osteoporosis (collapse in on itself due to a lot of weight)
- depressed
- greenstick: slight fracture on side (splintering)
4 stages of bone healing from bone fracture
- Hematoma (mass of clotted blood) forms and site becomes swollen, painful, and inflamed
- fibrocartilaginous callus: fibroblasts secrete collagen to connect bone ends, osteoblasts begin forming spongy bone in a week
- bony callus formation: firm union in 8 weeks
- bone remodeling: in response to mechanical stresses
Homeostatic imbalances
osteoporosis (osteopenia)
- loss of bone mass –> bone resorption outpaces deposits
- spongy bone of spine + neck of femur become most susceptible to fracture
- risk factors: lack of estrogen, calcium/vit D, petite body, immobility, low levels of TSH, diabetes mellitus
- at risk: petite white post menopausal female who is a nonexcercising smoker
Osteoporosis treatment
- calcium, vit d, fluoride supplements
- increase weight bearing exercise throughout life
- hormone (estrogen) replacement therapy (HST) slows bone loss
- some drugs (fosamax, SERMs, statins) increase bone mineral density
