Limbs and back week 1 Flashcards
Describe the blood supply to bone
vessels enter through epiphyses and periosteum
main supply from the nutrient artery somewhere in the middle of the shaft
Nutrient artery enters through the nutrient foramen
Describe Volkmann’s canals
carry arteries into the cortex from the inside of the bone
these branch into small vessels of the central canals of osteons
How are the collagen fibres arranged in osteons?
In different directions from layer to layer - this gives strength
How is calcium obtained in the body?
mainly from dairy products in the diet
it is absorbed by the duodenum of the small intestine
What are the two major hormones that regulate calcium absorption?
vitamin D and parathyroid hormone (PTH)
Describe PTH
parathyroid hormone
most important regulator of calcium metabolism
secreted by chief cells of the parathyroid gland
secretion of PTH is increased on response to hypocalaemia and hyperphoshphataemia
Describe the role of PTH
mainly acts on the bones and the kidneys
stimulates osteoclasts and increases bone resorption - increases serum concentrations of calcium and phosphorus
Stimulates the 1-alpha hydroxylase activity in the kidney, resulting in increased 1,25dihydroxyvitamin D production
Increases calcium reabsorption in the distal renal tubules
Increases phosphorus excretion by the kidney
What is the overall effect of PTH?
hypercalcaemia
hypophosphataemia
high urinary phosphorus
How is the secretion of PTH regulated?
calcium has a negative feedback effect in the parathyroid gland through calcium-detecting sensors
Describe vitamin D
essential in the homeostasis of calcium and phosphorus
mainly synthesised in the skin but also through diet
Active form is called 1,25dihydroxyvitamin or calcitriol
Describe the actions of vitamin D
a required factor for the bone resorption process
reabsorption of calcium and phosphorus from the renal tubules
Suppresses PTH secretion
Describe calcitonin
calcitonin lowers serum calcium but normally only when it is pathologically elevated
its exact physiological action is unknown but it has an inhibitory effect on osteoclasts
Where is calcitonin secreted from?
specialised parafollicular cells of the thyroid in response to high calcium levels
Describe fibroblast growth factor 23
mainly secreted by osteocytes in response to hyperphosphataemia
increases phosphorus clearance in the kidney
inhibits the 1 -alpha hydroxalase enzyme so prevents the production of calcitriol.
Describe bone healing
immediately after the fracture there will be a haemorrhage within the bone due to ruptured vessels in the marrow cavity, and also around the bone related to the periosteum
A haematoma at the fracture site facilitates repair by providing a foundation for the growth of cells
Deviated bone fragments and soft tissue damage is removed in the initial phase of repair, along with organisation of the haemoatoma
The capillaries will be accompanied by fibroblasts and osteoblasts - bone is deposited in an irregularly woven patten
the mass of new bone is called callus bone
within the medullary cavity - internal callus
at the periosteum - external callus
Woven bone is subsequently replaced by more orderly lamellar bone
lamellar bone is gradually remodelled according to the direction of mechanical stress
What slows fracture healing?
if bone ends are mobile
infection
badly misaligned
avascular
describe osteoporosis fractures
most likely to occur in the thoracic region of the spine
due to thinning of bone they can collapse
compression fracture - vertebral wedging
pain, increased kyphosis, immobility
What is the management of vertebral fractures?
conservative
analgesics for pain
physiotherapy - increase mobility, weight bearing exercise
What is osteoporosis?
a disease in which there is a reduction in bone mass in the presence of normal mineralisation
What causes the bone to thin in osteoporosis?
a loss of coupling where bone resorption is greater than bone reformation
How might osteoporosis present?
fragility fracture
loss of height
stooping deformity