Bones III Flashcards
1
Q
What is metabolic bone disease?
A
- generalized or systemic diseases of bone usually caused by nutritional deficiencies or imbalances; hormonal deficiencies or excesses; or toxicities
- a metabolic bone disease is often called an osteodystrophy, which is a general term used to imply defective bone formation (literally, bad bone growth)
- it’s not clear why there are different forms of metabolic bone disease when the various nutrients & hormones related to bone metabolism are so closely interconnected
2
Q
What are the 3 different types of metabolic bone diseases?
A
- osteoporosis
- osteomalacia & rickets
- fibrous osteodystrophy
3
Q
What is osteoporosis?
A
- most common metabolic bone disease
- disease involves a reduction in bone density or bone quality (porosis = porosity or rarefaction)
- use of the term osteoporosis implies that the remaining bone is normally mineralized (is of normal quality)
- lesions of osteoporosis include, 1st, a reduction in trabecular bone w/ a corresponding increase in the medullary cavity (due to the large surface area available for resorption) & then a reduced thickness & increased porosity of cortical bone
- result is bone of decreased density that is more brittle & easily fractured
4
Q
What are some causes of osteoporosis?
A
- calcium deficiency: which leads to an increased demand for circulating calcium (+/- hypocalcemia), increased secretion of parathyroid hormone (PTH), & increased bone resorption. seen in cattle & sheep.
- starvation: b/c of a lack of energy, protein, & minerals. seen in grazing animals.
- lactation: due to inadequate calcium supplementation during pregnancy & lactation. seen in gilts.
- other, less common causes of osteoporosis include primary or secondary copper deficiency; hyperadrenocorticism, including chronic glucocorticoid therapy; & physical inactivity or disuse
5
Q
What is parathyroid hormone?
A
- parathyroid hormone is secreted by the parathyroid glands in response to low levels of calcium in extracellular fluid
- parathyroid hormone produces the release of calcium from bone by activating osteoclasts & inhibiting osteoblasts; indirectly promotes increased intestinal absorption of calcium; & promotes renal tubular reabsorption of calcium & increased renal excretion of phosphates
6
Q
what is osteopenia?
A
a decrease in bone matter density w/o clinical disease
- word that has been used in human med for a long time
- eventually, this word found its way into vet me
- unfortunately, this has led to some confusion in vet med
- by strict definition, osteopenia means ‘bone deficiency’
- therefore, osteopenia is used by some to describe any situation where there is a reduced about of bone compared to normal, regardless of the quality of the remaining bone
- others, however, use osteopenia almost synonymously w/ osteoporosis (where the remaining bone is of normal quality)
- still others use osteopenia to indicate the presence of decreased bone mass or bone density WITHOUT clinical disease
- the most common clinical disease associated w/ osteopenia in people is postmenopausal osteoporosis
7
Q
What is the difference btwn osteomalacia & rickets?
A
- both have to do w/ vitamin D & phosphorus deficiency
- osteomalacia is in mature skeletons while rickets is in growing skeletons
8
Q
What are the lesions of osteomalacia?
A
- the inadequate mineralization of osteoid leading to abnormally SOFT BONE that, w/ time, leads to deformed bones & fractures
- in mature animals, the defective mineralization is limited to the osteoid formed during remodeling
9
Q
What are the lesions of rickets?
A
- similar to those of osteomalacia, but also include the defective mineralization of cartilage & osteoid at sites of endochondral ossification, which results in irregular thickening of physes that is most severe in the most rapidly growing physes, as well as enlarged costochondral junctions
10
Q
What is vitamin D?
A
- vitamin D is now considered a hormone & can be both synthesized in the body & absorbed following digestion
- precursors of vitamin D (prohormones) are present in the epidermis of the skin
- exposure of these precursors to ultraviolet irradiation (sun light) produces vitamin D2 & D3 (cholecalciferol)
- vitamin d3 from the skin & diet are transported to the liver & converted to 25-hydroxyvitamin D3 (25-hydroxy-cholecalciferol)
- 25-hydroxyvitamin D3 is further converted to 1,25-dihydroxyvitamin D3 (1,25-dihydroxy-cholecalciferol) in the kidneys under the influence of parathyroid hormone
- 1,25-dihydroxyvitamin D3 is one of the more biologically active forms of vitamin D & functions to increase calcium levels in extracellular fluid by promoting the absorption of calcium in the intestines &, together w/ PTH, the mobilization of calcium from bone & resorption of calcium by the kidneys
- vitamin D also promotes the absorption of phosphorus in the intestines
11
Q
What is another name for 1,25-dihydroxycholecalciferol?
A
calcitriol
12
Q
What is fibrous osteodystrophy?
A
- refers to the skeletal lesions resulting from prolonged bone resorption & its replacement by fibrous tissue
- this process produces swelling & weakening of affected bones - often most noticeable in the head - that may result in lameness, deformities, infractions, & pathologic fractures
- fibrous osteodystrophy is most commonly the result of primary or secondary
13
Q
What is an infraction?
A
- an incomplete fracture of bone w/o displacement (folding fractures)
14
Q
what is hyperparathyroidism?
A
any condition associated w/ the prolonged elevation of circulating parathyroid hormone
15
Q
What is primary hyperparathyroidism?
A
- uncontrolled & excessive release of parathyroid hormone from parathyroid tissue
- IT IS CHARACTERIZED BY HYPERCALCEMIA
- primary hyperparathyroidism is rare in domestic animals & is seen in cases of parathyroid gland neoplasia (parathyroid adenoma or carcinoma) or idiopathic parathyroid gland hyperplasia
16
Q
What does idiopathic mean?
A
of spontaneous origin or unknown cause
21
Q
- What is renal secondary hyperparathyroidism (renal osteodystrophy)?
A
- develops b/c of chronic, severe, renal disease
- it is seen most commonly in older Ca & Fe
- pathogenesis of renal secondary hyperparathyroidism is complex & likely, varies w/ the nature & extent of the renal disease & availability of dietary vitamin D
- initial lesion in the kidneys is the loss of glomerular function, an inability to excrete phosphate, & hyper-phosphatemia
- phosphate reacts w/ calcium & promotes hypocalcemia w/ the calcium-phosphate products precipitating in soft tissues (soft tissue mineralization aka metastatic calcification)
- hypocalcemia & hyper-phosphatemia stimulate parathyroid secretion & the resorption of bone
- reduced glomerular filtration may also be associated w/ the accumulation of parathyroid hormone & biologically active parathyroid hormone fragments
- at the same time, the loss of renal mass associated w/ chronic renal disease is associated w/ impaired vitamin D metabolism
- low levels of vitamin D accentuates the problems w/ calcium homeostasis
- further, the acidosis associated w/ uremia promotes bone resorption & poor mineralization
- result is fibrous osteodystrophy complicated w/ a variable degree of osteomalacia
26
Q
What is Legg-Calve-Perthe’s disease?
A
- disease of children & the name has been borrowed to refer to ischemic necrosis of the head of the femur of immature, small, & miniature dog breeds
- b/c the articular cartilage is spared, it may continue to proliferate & become thickened if endochondral ossification was not completed at the time of onset of the ischemia
- after 1 or more episodes of ischemia, the head of the femur may become revascularized, which allows for removal of dead bone, deposition of new, woven bone, or both
- in some cases, this turnover of bone will lead to collapse of the articular surface
- chronic Legg-Calve-Perthe’s disease often results in degenerative joint disease
- the underlying cause & pathogenesis of this disease is not fully understood
35
Q
What is hematogenous osteomyelitis?
A
- in young farm animals occurs commonly
- in theory, hematogenous osteomyelitis can develop in any capillary bed w/in bone
- in practice, it occurs most often in young piglets, calves, & foals & starts in the metaphyseal areas of long bones & vertebrae
36
Q
A
37
Q
What is lumpy jaw?
A
- osteomyelitis
- in cattle, is caused by Actinomyces bovis
- bacterium enters the mandible through breaks in the oral mucosa
38
Q
What is metaphyseal osteopathy?
A
- used to be called hypertrophic osteoDystrophy
- disease of young, large & giant breed DOGS of unknown cause
- affected dogs are lame, febrile, & have swollen, painful metaphyses of long bones
- gross or radiographic lesions include lines of both decreased & increased bone density adjacent & parallel to the physes, & periosteal new bone growth over the metaphyses
- histologically, there is suppurative inflammation & necrosis of metaphyseal bone cells & marrow
- most animals recover spontaneously
