Bone Flashcards
What are the functions of calcium and the normal level of ionised calcium?
Function of Calcium
1.Muscle contraction
2.Blood clotting
3.Nerve conduction
4.Bone mineralization
5.Hormonal communication
Normal level ofionizedin adults=4.64 to 5.28 milligrams per deciliter (mg/dL)
What is calcium homeostasis regulated by?
●Hormones
1.Parathyroid (PTH) hormone
2.Calcitriol or vitamin D3
3.Calcitonin
●Principal organ
4.Intestines
5.kidneys
6.the bone
What are the hormones responsible for maintaining bone health?
- Testosterone/Oestrogen
oMaintain Bone Density by inhibiting activity of osteoclast
oStimulation of Osteoblasts
oCalcium Absorption
oInhibit bone resorption
- Growth hormone/insulin-like growth factor
oStimulates bone formation
oStimulates longitudinal growth
- Thyroid hormone
oToo much stimulates bone resorption
oActivates osteoclastic activity
- Cortisol
oInhibits bone formation
oDecreases calcium absorption from the intestines
What is recommended to maintain bone health?
●Calcium intake- Particularly important during childhood, adolescence, pregnancy, and lactation
●Vitamin D- Get some sunshine
●Regular Exercise- Muscle-strengthening exercises, Weight bearing exercise
●Avoid smoking and drinking to excess
●Maintain a Healthy Body Weight
●Hormonal health
What cells secrete PTH?
- There are four parathyroid glands in humans
- Thechief cellsof the parathyroid glands synthesize and secrete PTH
- Chief cells would secrete PTH in response to adecreasein Ca2+
- PTH is the most important regulator of ECF Ca2+
How does PTH raise blood calcium levels?
- Resorptionof calcium frombone
- Increasingrenal reabsorptionofcalcium
- Absorptionof calcium fromGIT (indirect)
PTH leads todecrease phosphate reabsorption
What is the process of bone resorption?
- PTH binds to osteoblasts
- RANKL and M-CSF are proteins on osteoblasts that preosteoclasts bind to
- this activates bone resorption by the osteoclasts
- phosphate and calcium are excreted into the blood
How is vitamin D synthesised?
Vitamins D2(plant) and D3(animal) are both inactive until they undergo twohydroxylations
- The first hydroxylation occurs in the liver, creatingcalcidiol (25alpha hydroxylase)
- The second hydroxylation occurs in the kidneys and formscalcitriol,the biologically active form of vitamin D (1alpha hydroxylase stimulated by PTH, inhibited by fibroblast growth factor 23)
Active vitamin Dincreases the absorption of both calcium andphosphorusin the intestine, as well as working with PTH to reduce calcium loss in the urine and stimulaterelease of calcium and phosphorus from the bone. Check liver for vitamin D status
What is the source and action of calcitonin?
Source of calcitonin
- Is secreted by C cells of the thyroid gland in response to hypercalcemia
- PTH antagonist
Action of Calcitonin
- OnBones: Inhibit activity of osteoclast
- Onkidney: increase urinary excretion of phosphate and calcium
Primary vs secondary hyperparathyroidism
stones (renal stones), bones (bone pain), moans (abdominal pain and constipation) and groans (psychiatric - lethargy, depression)
What bone diseases are associated with vitamin D deficiency?
Rickets- In children
- Demineralisation of bone – soft pliable bones
- Characteristic bow-leg deformity
- Overgrowth at costochondral junction – rachitic rosary
- Pigeon chest deformity
- Frontal bossing
Osteomalacia- In adults
- Softening of bones – frequent fractures
Diagnosis
- Hypocalcemia
- Hypophosphatemia
- Increased alkaline phosphatase
What is renal osteodystrophy/CKD mineral bone disorder?
- Renal osteodystrophy is a broad term that incorporates all the biochemical abnormalitiesandskeletal manifestations**in patients suffering from chronic kidney disease or end-stage renal disease.
- Reports suggest these abnormalities are most likely to be seen at a GFR below 60 mL/min
- Symptoms- Bone pain and fractures, Joint pain, Bone deformation, Slow bone growth, Low bone mineral content But Some people with early forms of the disease may not have any symptoms
What is FGF23 produced by and what is its action in CKD?
FGF23 is mainly produced in bone by osteoblasts and osteocytes under physiological conditions
- Increase urinary phosphate excretion
- Involvedin vit D metabolism and regulation
In chronic kidney disease, as a compensatory mechanism, FGF23 levels rise 1000-fold to maintain a neutral phosphate distribution. This compensatory increase in FGF23 promotes thesuppression of 1-25-dihydroxyvitamin D production**leads toreduction of intestinal calcium absorption increase of PTH level and ultimatelydevelopsecondary hyperparathyroidism.
What are the causes and symptoms of osteoporosis?
What is Dual energy x-ray absorptiometry (DXA Scanning) and what do the T scores indicate?
- Also known as bone mineral density scan (BMD scan)
- It measure bone density and bone loss
- Bone densities are often given to patients as aT score.
- A T score tells the patient what their bone mineral density is in comparison to a young adult of the same gender with peak bone mineral density.
- Anormal T score is -1.0and above,low bone density is between -1.0 and -2.5 and is osteopenia, andosteoporosis is -2.5 and lower
Indication
- For those with significant risk factors
- When it is uncertain if bones are fragile
- To decide whether drug treatment is necessary
- Not used as Screening tool
