Calcium Homeostasis Flashcards
We take in calcium through our diet, but which of the following can influence the absorption of calcium from our GI system?
A. Eating a lamb kebab B. Visiting Cornwall in the Summer D. Eating Lemons E. Watching TV F. All of the above
E. All of the above
- Dietary fat can stimulate or inhibit intestinal Ca absorption depending upon the type and amount of fat intake. High fat diets (HFD) may reduce Ca absorption by forming insoluble Ca soaps.
- Vitamin D is the sunshine vitamin that has been produced on this earth for more than 500 million years. During exposure to sunlight 7-dehydrocholesterol in the skin absorbs UV B radiation and is converted to previtamin D3 which in turn isomerizes into vitamin D3 or calcitriol. Calcitriol as we will find out is important for the absorption of calcium from the stomach
- Vitamin C or ascorbic acid in orange and pepper juices enhances intestinalcalcium absorption
- Moderate enduranceexerciseandphysical activityhave a positiveeffectoncalciummetabolism and bone by increasing bone mineral density and reducing urinarycalciumloss, whereas immobilization has the oppositeeffects
What is the normal range of total calcium in our plasma?
A. 0.2-0.6 mmol/L
B. 1.2-1.6 mmol/L
C. 2.2-2.6 mmol/L
D. 3.2-3.6 mmol/L
C. 2.2-2.6 mmol/L
But of this only half is in the free ionized form that is physiologically active
We all know that vitamin D is good for our bones. What is the active form of this hormone also known as?
A. Calcitonin
B. Calcidiol
C. Calcitriol
D. Solar Ray Juice
A. Another hormone that regulates ECF Ca2+ levels
B. Not quite vitamin D! A pre-form metabolised within the liver
C. Yes! Calcidiol is hydoxylated (+OH) within the kidneys to form its active form, calcitriol
D. Hmmm…don’t think so, but solar rays are involved in the synthesis of vitamin D!
Spot the thyroid gland A. A B. B C. C D. D
D. D
Where is calcium found in the body?
- 98.9% in the skeleton and teeth (in the form of hydroxyapatite crystals comprising calcium and phosphate)
- 0.9% intracellular
- 0.1% found within the extracellular fluid (ECF) (but only about half is in a free form that is biologically active)
What is hydroxyapatite also known as?
The crystallised calcium phosphate salt is also known as ‘bone mineral’
How moles or grams of calcium is in hydroxyapatite in the human body?
31 mol or 1250 grams
How many moles of ionised calcium is there in the cells and extracellular fluid combined?
1.2 mmol/L
How many moles of protein bound calcium is there in the cells and extracellular fluid combined?
1.2mmol/L
How many moles of anion-bound calcium is there in the cells and extracellular fluid combined?
0.2mmol/L
What is the function of ionised free calcium in the body?
- Maintenance of cell tight junctions
- Muscle contration
- Neurotransmitter release
- Wound Healing
- Bones
- Intracellular signalling and enzyme activation
- Blood clotting
- Hormone Release
Why is calcium important in the maintenance of cell tight junctions?
Calcium contributes to the intra-cellular ‘cement’ of tight junctions between certain cells e.g. blood-brain-barrier
Why is calcium important in muscle contraction?
Entry of extracellular fluid calcium into cardiac and smooth muscle cells is a key stop in excitation-contraction coupling (release of intracellular calcium stores triggers the contractile machinery in skeletal muscle)
Why is calcium important in neurotransmitter release?
Release of neurotransmitters from pre-synaptic neurons and at neuro-muscular junctions (NMJs) is triggered by the entry of extracellular fluid calcium (stimulus-secretion coupling)
Why is calcium important in bones?
It is needed to form hydroxyapatite crystals, which provides structural strength to bones - making them hard.
Why is calcium important in intracellular signalling and enzyme activation?
Calcium functions as a second messenger in cell signalling pathways and as a co-factor for enzyme function in chemical reactions.
Why is calcium important in blood clotting?
Calcium is a co-factor in several steps within the clotting cascade.
Why is calcium important in hormone release?
The movement of extracellular fluid calcium into endocrine cells triggers the release of hydrophilic hormones, such as adrenaline. This is another example of stimulus-secretion coupling.
What are the main proteins is bound to calcium in the cells and extracellular fluid?
Albumin
What can ionised calcium and anion-bound calcium do easily that protein bound calcium from the cells and extracellular fluid not do at all?
Diffuse across capillary membranes
What is the average daily calcium intake?
1000mg/day
How much calcium is mossed through faces per day?
900 mg
Define absorption
The act of taking up or in by specific chemical or molecular action; especially the passage of liquids or other substances through a surface of the body into body fluids and tissues
How much calcium is absorbed from the GI tract into the extracellular fluid per day?
350 mg/day
