Bone health Flashcards
(35 cards)
What are the functions of calcium in the body?
Muscle contraction
Blood clotting
Nerve conduction
Bone mineralisation
Hormonal communication
Where does the total body calcium lie?
Bone - 99%
Body fluids - 1%
-> Ionised/free - 50%
-> Bound to anions - 10%
-> Protein bound - 40%
Which calcium store can be measured, and what is the normal level?
Ionised/free calcium in body fluids
4.64 - 5.28 mg/dL
What hormones and organs regulate calcium ion levels?
Hormones:
- Parathyroid hormone
- Calcitrol or vit D3
- Calcitonin
Organs:
- Intestines
- Kidneys
- Bone
What releases parathyroid hormone (PTH), and what stimulates its release?
From chief cells in the four parathyroid glands
Released in response to a decrease in Ca2+
Most important regulator ECF Ca2+
By which mechanisms does PTH raise calcium levels by?
- Resorption of calcium from bone
- Increasing renal reabsorption of calcium
- Absorption of calcium from GIT (indirect)
What is the bone reabsorption mechanism?
- PTH upregulates RANKL on osteoblasts on surface of bone
- Osteoclasts adhere to bone like a suction cup under influence of RANKL and integrins and forms sealing zone with a ruffled border
- OC secrete protons to decrease pH idssolving minerals
- Release of proteolytic enzymes and non-proteolytic enzymes degrade the bone matrix - make pits
How does vitamin D become active?
Vitamins D2 and D3 are both inactive until undergoing two hydroxylations
- First occurs in liver to form calcidol
- Second occurs in kidneys to form calcitriol - active form of vit D
What is the role of vitamin D?
Active vit D:
increases absorption of both calcium and phosphate in the intestine
works with PTH to reduce Ca2+ loss in urine and stimulate the release of calcium and phosphorus from the bone
Where is calcitonin released from?
Secreted by C cells in the thyroid gland in response to hypercalcemia
What is the action of calcitonin?
PTH antagonist
On bones: inhibits activity of osteoclast (responsible for bone formation)
On kidney: increase urinary excretion of phosphate and calcium
Summarise the hormonal regulation of high blood calcium levels
High blood calcium level > activates thyroid gland > calcitonin released > stimulates calcium deposition in bones, reduces calcium uptake in kidneys, reduces calcium uptake in intestines > normal calcium in blood
Summarise the hormonal regulation of low blood calcium levels
Calcium levels too low > parathyroid gland stimulated > releases parathyroid hormone > stimulates calcium release from bones, increases calcium uptake in kidneys > increased Ca2+ and increases calcium uptake in intestines > increased calcium
What hormones are involved in regulation of bone health? (by class)
Calcium regulating hormones:
- PTH
- Calcitonin
- Active vit D (Calcitriol)
Sex hormones:
- Testosterone
- Oestrogen
Other hormones:
- Growth hormone
- Thyroid hormone
- Cortisol
What function does growth hormone have on bone regulation?
Stimulates bone formation
Stimulates longitudinal growth
What function does thyroid hormone have on bone regulation?
Too much stimulates bone resorption
Activates osteoclastic activity
What function does glucocorticoid have on bone regulation?
Inhibits bone formation
Decreases calcium absorption form the intestines
What function does oestrogen/testosterone have on bone regulation?
Maintain bone density by inhibiting activity of osteoclasts
Stimulation of osteoblasts
Calcium absorption
Inhibit bone resorption
How can bone health maintained?
Calcium intake: particularly important during childhood, adolescence, pregnancy, and lactation
Vitamin D
Regular excercise: muscle strengthening, weight bearing
Avoid smoking and drinking to excess
Maintain a healthy body weight
Hormonal health
Primary hyperparathyroidism
- Level of parathyroid hormone
- Level of serum calcium
- Level of phoshate
- Causes
PTH= high
Serum calcium= increased
Phosphate= decreased
Causes: parathyroid tumour, ectopic parathyroid tissueP
Primary hyperparathyroidism symptoms and treatments
Symptoms:
- renal stones
- bone pain
- abdominal pain
- constipation
- Depression
Treatments:
parathyroidectomy
Secondary hyperparathyroidism
- Levels of parathyroid hormone
- Level of serum calcium
- Level of phosphate
- Causes
PTH: High
Ca2+: decreased/normal
Phosphate: Increased/normal
Causes:
- Vit D deficiency
- End stage kidney disease
Secondary hyperparathyroidism symptoms and treatments
Symptoms:
- Osteoporosis
- Renal stone
- Bone and joint pain
Treatments:
- Vit D supplement
- Treat underlying cause
What is the presentation of Vitamin D deficiency in children?
- Demineralisation of bone - soft pliable bones
- Characteristic bow-leg deformity
- Overgrowth at costochondral junction - rachitic rosary
- Pigeon chest deformity
- Frontal bossing
- Osteomalacia
