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1st year - Nutrition I - post midterm > Calcium > Flashcards

Calcium Flashcards

1
Q

What is the most abundant mineral in the body?

A

calcium

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2
Q

Calcium distribution

A
  • 99% - bones and teeth

* 1% - intra/extra-cellular fluids

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3
Q

Calcium sources

A
  • Dairy products: milk (300 mg/250 ml); yogurt (450 mg/250 ml); cheeses (50-300 mg/28.5 g)
  • Some seafood: salmon & sardines, canned with bones (200-325 mg/85 g); clams, oysters
  • Some vegetables: turnip, spinach, broccoli, cauliflower, okra, kale (30-90 mg/125 ml cooked)
  • Legumes: especially soy beans & tofu (especially if calcium was added during processing )
  • Nuts & seeds: especially sesame seeds
  • Dried fruits: especially figs
  • Black strap molasses (135 mg/15 ml)
  • Fortified foods: vegetarian milks, fruit juices
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4
Q

Calcium bioavailability

A

• Vegetables like spinach, Swiss chard and rhubarb, have high calcium contents but it is poorly absorbed as it is mostly bound to oxalic acid which is has poor solubility

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5
Q

Calcium digestion

A
  • Calcium is present in foods (and supplements) as relatively insoluble salts
  • Calcium can be solubilized from most calcium salts in 1 hour at an acidic pH
  • However, solubilization does not necessarily ensure absorption because free calcium can bind to other dietary constituents and become unavailable for absorption
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6
Q

Calcium absoption Duodenum & proximal jejunum

A

Cellular
Active transport - requires ATP
Saturable
Involves calcium-binding transport protein (CBP)
• aka calbindin D9k
• Stimulated by calcitriol
• Stimulated by low-calcium diets (<400 mg/d)

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7
Q

Calcium absorption Jejunum and ileum

A 
Paracellular 
Passive diffusion - requires no energy
Unstaurable
Requires no carrier
•	Stimulated when high concentrations of Ca in the lumen and intracellularly 
•	Stimulated by FOS & inulin
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8
Q

Calcium absorption large intestine

A

o Bacteria in the colon can release Ca that has bound to some fermentable fibers
o 4-10% (~8 mg/d) of dietary calcium is absorbed by the colon

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9
Q

Enhance calcium absorption

A 
Growth, pregnancy & lactation
Vitamin D  
Simple sugars 
Protein
Food in general
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10
Q

inhibit calcium absorption

A 
Phytate (phytic acid)
Oxalate (oxalic acid)
Fiber
Other divalent cations & other minerals
Fat maldigestion
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11
Q

Calcium transport

A
  • Ca is transported across the cytoplasm of the enterocyte bound to CBP
  • Ca is transported from the enterocyte into the extracellular fluid by Ca/Mg-ATPase

In the blood
• Ca is transported in the blood in 3 forms
o ~50% is found free (ionized) in the blood
o ~40% is bound to proteins, primarily albumin
o ~10% complexed with sulfate, phosphate, or citrate

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12
Q

Calcium homeostasis regulation - Extracellular calcium

A

• Concentrations are regulated by: parathyroid hormone (PTH), calcitriol, and calcitonin
o Low plasma Ca levels stimulates PTH secretion and calcitonin secretion is diminished
• PTH and calcitriol increase plasma Ca concentrations through interactions with the kidney, intestines, and bone
• PTH increases renal synthesis of calcitriol from 25(OH)VitD
• PTH and calcitriol increases renal tubular reabsorption of calcium
• Calcitriol enhances intestinal Ca absorption
• PTH and calcitriol stimulate osteoclasts which demineralize bone releasing Ca into the blood
o High plasma Ca levels stimulate calcitonin secretion
• Calcitonin lowers serum Ca by:
• Inhibiting osteclast activity which stimulates osteoblasts
• Inhibits calcitriol production which decreases Ca absorption and increases excretion

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13
Q

Calcium homeostasis regulation - Intracellular calcium

A

o Low free Ca concentrations are maintained within the cytoplasm of cells
o Ca is needed in higher concentrations at times to carry out certain cellular functions
o Cell activation by depolarization, neurotransmitters, or hormones results in increased calcium entering the cell by diffusion or by channels
o Concentrations are returned to low levels within a short time as Ca is exported from the cells by ATP-ase dependent Ca pumps which exchange magnesium and sodium for calcium.

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14
Q

Calcium functions

A

• Bone mineralization
o 99% of calcium is found in bones and teeth
o Calcium, phosphorus, magnesium and other minerals enter bone fluid from the blood and then attach to bone matrix and bone proteins
o Free calcium and calcium salts are converted into crystalline compounds such as hydroxyapatite
• Other roles
o Blood clotting
• Calcium is essential for the formation of fibrin and participates in nearly every step of the coagulation cascade
o Nerve conduction
• When a nerve impulse is transmitted to the end of a motor neuron it increases its permeability to calcium and calcium entering the neuron triggers the release of acetyl choline
o Muscle contraction
• When a muscle fiber receives a nerve impulse that stimulates it to contract, calcium channels in the cell membrane open to allow a small number of calcium ions into the muscle cell. These calcium ions bind to activator proteins within the cell, which release a flood of calcium ions from storage vesicles inside the cell. Calcium facilitates the interaction between myosin and actin causing muscle contraction.

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15
Q

Calcium excretions

A
  • Primarily lost in the urine and feces. Most of the Ca in the blood is filtered and reabsorbed by the kidney
  • Perspiration can account for significant Ca loss in active individuals
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16
Q

Calcium deficiency conditions

A

o Hypocalcemia:
• Tetany, muscle spasms
• Muscle pain
• Paresthesias
o Osteoporosis – increased bone fragility and fracture risk
o Rickets/osteomalacia (see vitamin D lecture notes)

17
Q

Calcium tests for deficiency

A

o Chvostek’s sign
• An abnormal spasm of the facial muscles elicited by light taps on the cheek to stimulate the facial nerve in patients who are hypocalcemic.
o Trousseau’s sign
• The wrist and metacarpophalangeal joints flex, the DIP and PIP joints extend, and the fingers adduct.
• To elicit the sign, a blood pressure cuff is placed around the arm and inflated to a pressure greater than the systolic blood pressure and held in place for 3 minutes. This will occlude the brachial artery. In the absence of blood flow, the patient’s hypocalcemia and subsequent neuromuscular irritability will induce spasm of the muscles of the hand and forearm.

18
Q

Calcium deficiency most common in

A

• Deficiency is most common in any woman >12 years of age and the elderly

19
Q

Calcium clinical indications

A
  • Hypocalcemia
  • Osteoporosis
  • Periodontal disease
20
Q

Calcium preparations

A

• Carbonate
o Inexpensive
o High proportion of elemental Ca (40%)
o Requires adequate gastric acid for absorption on an empty stomach but not with food
o Some studies show decreased absorption compared to Ca citrate or Ca citrate/malate but other studies show equal absorption
o Avoid products derived from oyster shell, dolomite, or bone meal may be contaminated with aluminum or lead
• Hydroxyapatite
o Derived from refined bone powder
o A study showed this form was more effective in improving bone mineral density than Ca gluconate in patients with cirrhosis

•	The following provide 500 mg of elemental calcium:
o	5.49 g calcium gluconate 
o	3.53 g calcium lactate
o	2.37 g calcium citrate
o	2.16 g calcium acetate
o	1.26 g calcium carbonate

• Forms
o Tablets – most common and convenient but need to breakdown in the stomach to be absorbed
o Capsules, powders, liquids, and chewables may be better absorbed
o Combined with magnesium and other minerals
• Common calcium:magnesium ratios: 2:1, 1:1, 1:2

21
Q

Calcium toxicity

A 
•	Tolerable Upper Intake Level
o	19-51 years:  2,500 mg
o	>51 years: 2,000 mg 
•	Adverse effects:
o	Kidney stones
o	Urinary tract infections
o	Cardiovascular disease
o	Constipation
o	Milk alkali syndrome
22
Q

Calcium nutrient interactions

A
  • Magnesium – Ca may decrease tissue levels of Mg and therefore may accentuate signs of a Mg deficiency
  • Sodium – high sodium intake can increase Ca excretion
  • High Ca intake may also decrease the absorption of phosphorus, non-heme iron, zinc, iodine, manganese, riboflavin, and fatty acids
23
Q

Calcium assessment of status

A

• Dietary history
• Serum calcium – total Ca (includes protein-bound) and ionized (free)
o Calcium correction for hypoalbuminemia
• Corrected Ca (mmol/L) = total Ca (mmol/L) + 0.02 (40 - serum albumin [g/L])
• Where 40 represents the average albumin level
• In other words each 1 g/L decrease of albumin, will decrease 0.02 mmol/L in measured serum Ca and thus 0.02 must be added to the measured value to take this into account and get an accurate representation of the free calcium
• Dual-energy X-ray absorptiometry (DEXA)

1st year - Nutrition I - post midterm (10 decks)

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