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IMS: Nutrition > Calcium, Phosphate, and Iron > Flashcards

Calcium, Phosphate, and Iron Flashcards

1
Q

Physiological Calcium

A

Human body with 830g ♀ and 1100g ♂ of Ca2+

99% in teeth and bones as hydroxylapatite

1% circulating or within cells

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2
Q

Hydroxylapatite

Functions

A
  1. In slow, dynamic eq. with soluble Ca2+
  2. Structural role
  3. Reservoir for Ca2+​ and base
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3
Q

Circulating/Intracellular Calcium

Functions

A

Critical role in metabolism and cellular processes:

  1. Ca2+​/calmodulin signaling
  2. IP3 signal transduction cascade
  3. neurotransmitter secretion
  4. muscle contraction
  5. electrical signaling
  6. blood clotting, osteocalcin, and other 𝛾-carboxyl-containing proteins that depend on Vit K
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4
Q

Dietary Calcium

A
  1. Dairy products
    • milk, cheese
    • lactose aids in absorption for infants only
  2. Green vegetables
    • broccoli, kale, collard greens
    • spinach calcium poorly absorbed d/t oxalate salts
  3. Tortillas w/ lime
  4. Fish with soft bones
    • sardines, canned salmon
  5. Fortified fruit juices
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5
Q

Calcium

RDA & Toxicity

A

RDA Levels:

  • Low in early childhood
  • ↑ throughout teenage years: 1,300 mg/day during max bone mineralization
  • adults: 1,000 mg/day
  • elderly: 1,200 mg/day for ♂>70, ♀>50

Toxicity:

  • No effects up to 2,400 mg/day
    • maybe some constipation
  • Higher amounts → kidney stones
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6
Q

Calcium Supplementation

A
  • Insoluble calcium salts (CaCO3)
    • poorly absorbed with achlorhydria if taken w/o food
    • well-absorbed w/ food
  • Calcium citrate salts
    • do not have to be taken with food
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7
Q

Calcium

Absorption

A

Absorbed in duodenum and upper jejunum:

  1. Paracellular
    • driven by transepithelial potential & H2O bulk flow
  2. Transcellular
    • depends on transporters
    • major path
    • ⊕ by Vit D
      • ↑ TRPV5/6, NCX1, and calbindin
      • more important with Ca2+ poor diet
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8
Q

Phosphate Sources

A
  • Inorganic phosphate present as phosphate or related compounds (e.g. pyrophosphate)
    • Abundant in many foods
    • Easily absorbed
    • Overnutrition > undernutrition in Americans
    • Chronic acidosis or aluminum hydroxide in antacids can deplete body phosphorus stores
  • At physiological pH: mix of HPO42- and H2PO4-
  • Phosphorus content of foods/plasma expressed as amount of elemental phosphorus [P]
  • Found in:
    • most seafoods
    • nuts
    • grains
    • legumes
    • cheeses
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9
Q

Calcium/Phosphate Balance

A

Ca2+/P intake ratio of 1-1.4 to 1 recommended.

  • ↑ [phosphate]plasma → ↑PTH & ↓calcitriol
    ⟾ bone demineralization → Ca2+release → osteopenia/osteoporosis
    ⟾↑Ca2+reabsorption by kidneys → ↑ [Ca2+]plasma → metastatic calcification
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10
Q

Bone Matrix Formation

A

Calcium, phosphate, and protein required.

Bone remodeling:

  • Mineralization dominates early in life
    • Rises rapidly during adolescence
    • Bone density peaks ~ 20-30 y/o
  • Demineralization then dominates
    • Occurs slowly then rapidly
    • Ca2+ lost
    • Women with rapid ∆ after menopause
      • Vit D & calcium supplements may ↓ risk of osteoporosis
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11
Q

Bone Mass

A

Peaks ~ 20 to 30 y/o.

Women with rapid decline after menopause.

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12
Q

Factors Effecting

Calcium Levels

A

[Ca2+]plasma depends on:

  1. Intestinal Ca2+ absorption
    • relies on dietary Ca2+​ and active transport
      • determined by calcitriol levels
        • controlled by Vit D status
  2. Release from bone
  3. Ca2+​ excretion by kidneys
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13
Q

Calcium/Phosphorus

Hormonal Control

A

PTH released when [Ca2+]plasma low:

  1. ⊕ calcidiol → calcitriol ⟾ ⊕ Ca2+ absorption
  2. ⊕ Ca2+ reabsorption by kidneys
  3. ⊕ osteoclasts ⟾ Ca2+ release from bone

Cacitonin released when [Ca2+]plasma high:

  1. Opposes PTH action in animals
    • Blocks Ca2+ reabsorption
    • Promotes bone mineralization
  2. Minimal role in human Ca2+ and phosphate homeostasis
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14
Q

Calcium Homeostasis

Summary

A
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15
Q

Calcium Excretion

Regulation

A

Most renal Ca2+ reabsorption occurs in proximal tubule via paracellular route.

  • Junctional permeability partially due to claudin-2
    • High salt diets → ⊖ claudin-2 synthesis → ⊖ Ca2+ reabsorption → ⊕ Ca2+ loss
      • long term ⟾ risk of bone demineralization
  • Estrogen conserves Ca2+ by ⊕ renal reabsorption
    • post-menopausal women w/ ⊕ urinary Ca2+ loss ⟾ bone demineralization ⟾ osteoporosis
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16
Q

Calcium & Vit D

Summary

A
17
Q

Hypocalcemia

A

Low [Ca2+]plasma suggests malabsorption or hypoparathyroidism over dietary deficiency.

Low [albumin]plasma can show as low [Ca2+]plasma ​because it binds calcium.

Symptoms include:

  • paresthesias
  • muscle cramps
  • arrhythmias and cardiac arrest (rare)
  • bone fractures
  • loss of height d/t spine compression
18
Q

Hypercalcemia

A
  • Can result from hyperparathyroidism
    • parathyroid adenoma
    • cancer releasing parathyroid hormone-related peptide (PTHrP)
  • Can lead to heart block or cardiac arrest
19
Q

Osteoporosis

Risks & Tests

A

Results from uncoupling of bone formation from resorption.

  • Risk factors include:
    • family hx
    • menopause before 48 y/o
    • caucasian/asian race
    • inadequate exercise
    • inadequate intake calcium/vit D
    • small bone frame
    • smoking, alcohol abuse, excessive caffeine
    • prolonged use of some meds (methotrexate)
    • chronic diseases that cause bone loss
      • renal failure, chronic malabsorption, diabetes
  • DEXA scan used to assess bone density
  • High homocysteine levels weaken bone
    • prevents collagen cross-linking
20
Q

Osteoporosis

Treatments

A
  • Fosamax (bisphosphonate)
    • slows osteoclast activity & bone breakdown
      • prevents farnesylation of GTPases needed for attachment
  • Forteo (recombinant PTH fragment)
    • activates osteoblasts > osteoclasts
    • increases bone growth
21
Q

Bone Health

Suggestions

A
  • 1:1 dietary ratio of calcium to phosphorus
  • avoid excess NaCl
  • get adequate protein
    • excess protein + low calcium = bad for bones
  • weight-bearing exercises
    • promotes bone formation
22
Q

Iron

Absorption

A

2 forms of dietary iron:

  1. Heme iron
    • better absorbed (10-12%)
  2. Inorganic iron
    • < 10% absorbed
    • Fe2+ >> Fe3+
    • depends on particular salt
    • co-ingestion with Vit C enhances absorption
      • ascorbate reduces Fe3+ to Fe2+
    • lactoferrin in breast milk greatly improves rate of absorption
      • but [iron] in breast milk low
23
Q

Iron

Requirements

A

RDA

10 mg for ♂

10 mg for post-menopausal ♀

15 mg for ♀ age 11-50

Assumes 10% bioavailability.

Regular intense exercise up to 30% greater requirements.

24
Q

Sources of Iron

A
  • meats
  • eggs
  • oysters
  • dark green leafy vegetables
  • legumes
  • whole grains
25
Q

Iron

Transport

A

Transported in blood bound to transferrin.

[Transferrin]plasma determines total iron-binding capacity (TIBC).

Normally only ~35% saturated.

At low saturation levels, iron absorption can be up-regulated.

26
Q

Iron

Storage

A

Stored in liver, marrow, spleen, and muscles bound to ferritin.

Saturation of apoferritin ⟾ appearance of hemosiderin.

27
Q

Iron Deficiency Anemia

Causes and Characteristics

A

Iron deficiency most common nutritional deficiency worldwide.

Most common cause of anemia in the U.S.

  • Causes:
    • poor intake
    • excessive blood loss
    • dialysis
    • low Vit A
    • some inflammatory diseases
28
Q

Iron Deficiency Anemia

Symptoms

A
  • Early stage:
    • relatively asymptomatic
  • Middle stage:
    • fatigue
    • anorexia
    • reduced immunocompetence
    • difficulty maintaining body temp
    • abnormal cognitive development in children
    • premature delivery in pregnant women
  • Final stages
    • hypochromic, microcytic anemia
29
Q

Iron Deficiency Anemia

Assessment and Treatment

A
  • Test:
    • Transferrin content of blood
      • ↑ TIBC
      • ↓ %transferrin saturation
  • Treat:
    • Ferrous iron supplements recommended if dietary doesn’t work
30
Q

Iron Toxicity

A
  • Usually seen in children
  • Due to supplement over-ingestion
  • Can be fatal
31
Q

Hemochromatosis

A

Genetic condition with iron excess.

  • Causes:
    • Most commonly due to HLA-linked hemochromatosis gene (HFE)
      • HFE likely ↓ hepcidin
    • Less common due to transferrin receptor 2, ferroportin, hepcidin, or ferritin genes
  • Symptoms:
    • fatigue
    • weakness
    • chronic abdominal pain
    • aching joints
    • impotence
    • cirrhosis
    • heart failure
  • Lab tests:
    • TIBC
    • serum iron
    • serum ferritin
    • ratio of serum iron:TIBC > 60%
    • iron overload per se = %transferrin sat > 50%
  • Treat with phlebotomy and iron avoidance

IMS: Nutrition (15 decks)

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