Calcium Homeostasis Flashcards
What are some intracellular roles of calcium?
- muscle contraction
- secondary messenger
- release of neurotransmitters
What are some extracellular roles of calcium?
- electrical excitability of cell is reduced
- important in bone structure
- involved in clotting
What is the proportion of serum calcium that is bound to unbound?
Bound to plasma protein - 40% - albumin (90%) - globulin (10%) Bound to anions - 10% - phosphate - citrate Free calcium - 50% - physiologically active
It is important to keep calcium within a tight normal range of
2.15-2.55mmol/L
If calcium levels are deranged, you will start to see
neurological signs
In hypoalbuminemia, there are low levels of ______, and thus ____ protein bound Ca++ is present, causing _____
albumin
less
hypocalcaemia.
For every 4g/L that albumin falls below 40g/L, add ____ to calcium concentration
0.1mmol/L
What are some signs + symptoms of HYPOcalcaemia?
- carpopedal spasm
- chvostek’s sign (facial spasms)
- epileptic fits
What are some consequences of acute hypercalcaemia?
- abdominal pain
- thirst and polyuria
What are some consequences of chronic hypercalcaemia?
- musculoskeletal aches
- osteoporosis
- constipation
How is calcium maintained within a tight narrow range? (2.15-2.55mmol/L)
There are systems to decrease Ca++ and systems to increase Ca++. They ‘fight’ each other and maintain Ca++ within the tight narrow range.
What happens when calcium is too high?
When there is an increase in Ca++, the thyroid gland detects this and releases calcitonin. Calcitonin causes Ca++ to be deposited in the bones and reduces the calcium uptake in kidneys. Blood Ca++ levels then decline to set point.
What happens when calcium levels are too low?
When there is a decrease in Ca++, the parathyroid gland detects this and releases PTH. PTH stimulates the release of Ca++ from bones into the blood and stimulates Ca++ uptake in the kidneys. The kidneys release active Vit D and this increases Ca++ uptake in the intestines. Blood Ca++ levels rises to set point.
Which cells in the parathyroid gland make PTH?
Chief cells
How is low calcium level detected?
- Less Ca++ molecules in blood
- Calcium sensing receptor detects this
- Modified chief cell processes
- PTH secretion
PTH (Type 1 receptor), NH3 is present ________, whilst COOH is present ______
extracellularly
intracellularly
PTH activates the ____ receptor by…
The activated receptor then initiates
PTH/PTHrP receptor
changing its shape
a cascade of intracellular events, leading to Ca++ uptake and cAMP synthesis.
Where are the PTH receptors?
Bone
Kidneys
In the kidney, PTH blocks
the reabsorption of PHOSPHATE into the proximal tubule.
In the kidney PTH promotes
calcium reabsorption into:
- ascending LoH
- distal tubule
- collecting tubule
As well as PTH, Calcium may also exert a direct affect on
renal reabsorption
PTH promotes absorption of calcium from bone in 2 ways.
- Rapid phase - rise in ca++ in minutes. occurs at level of osteoblasts and osteoclasts. When PTH binds to receptors on these cells, osteocytic membrane pumps ca++ from bone fluid into extracellular fluid
- Slow phase of bone reabsorption occurs over several days and has two components. (a) osteoclasts are activated to digest formed bone (b) proliferation of osteoclasts
Calcitonin stimulates _____ to lay down bone and therefore _____ serum calcium
osteoblasts
decrease
PTH stimulates _______ to destroy bones and therefore ______ serum calcium
osteoclasts
increase
