Bone And Skeletal Homeostasis Flashcards
What are some functions of calcium
Maintenance of healthy bones and teeth
Nerve impulse transmission
Muscle contraction
Cell division and transport
Blood clotting
Hormone secretion
Cell signalling
What is the distribution of calcium in the body split into
99% in bone
1% in blood and body fluids
What is the blood calcium distribution
35% non diffusible - 80% albumin bound, 20% globulin bound
65% diffusible - 80% ionized, 20% complexed (bicarbonate, citrate, phosphate)
What is the concentration of calcium in the blood
9 - 11 mg/dL
What are the 3 forms of calcium in plasma or serum
Protein bound calcium
Ionized or free calcium
Complexed or chelated calcium
What is protein bound calcium
Cannot diffuse through membranes and thus is not usable by tissues
What is ionized or free calcium
The physiologically active form
What is complexed or chelated calcium
Bound to phosphate, bicarbonate, sulfate, citrate and lactate
What happens if calcium levels rise above set point
Thyroid gland releases calcitonin- blood calcium level falls
What happens if calcium levels fall below set point
Parathyroid glands release parathyroid hormone (PTH) - blood calcium rises
What is the gut function of vitamin D
Stimulates transepithelial transport of calcium and phosphate in the small intestine (principally duodenum)
What is the bone vitamin D function
Stimulates terminal differentiation of osteoclasts
Stimulates osteoblasts to stimulate osteoclasts to mobilise calcium
What is the parathyroid function of vitamin D
Inhibit transcription of the PTH gene (feedback regulation)
What does the parathyroid hormone do
Preserve normal blood calcium and phosphate
Stimulates bone resorption
Stimulates renal tubular reabsorption of calcium
Stimulates renal 1 alpha hydroxylation of 25(OH) vitamin D stimulating intestinal absorption of calcium
What is calcitonin
Levels increased when serum Ca > 2.25mmol/L
Counteracts PTH
Bone - suppresses resorption
Kidney - increases excretion
How does bone turnover affect calcium
Shift toward formation or resorption removes Ca from blood or puts Ca into blood and correspondingly affects bone mass
When does skeletal mass in humans reach a peak
About age 30
What happens as skeletal mass is increasing in humans
Bone formation exceeds bone resorption
What happens at peak bone mass
The two processes are evenly matched/balanced
After the age of peak bone mass skeletal mass is lost for the rest of life
What is bone formation mediated by
Osteoblasts
What is bone resorption mediated by
Osteoclasts
How do OPG and RANKL link to bone turnover
PTH stimulates the osteoblast to secrete RANKL, which then goes on to stimulate the osteoclast precursor to become active
OPG is a competitive inhibitor of RANKL and thus blocks it from activating the osteoclast
In bone turnover what does OPG stand for
Osteoprotegerin
What does RANKL stand for in bone turnover
Receptor activator of NF - kB (ligand)
What effects does PTH have on the kidney
Stimulate activation of vitamin D
Promotes phosphate excretion
Reduces calcium resorption
