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The Bone and Acid Base Balance

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Title: The Bone and Acid Base Balance


1
The Bone and Acid Base Balance
  • By Helen Yang Liu, Justin Lin, Sara Zhang, Joyce
    Chenzi Zhang

2
Topics
  • Overview of the bone
  • Acute metabolic acidosis
  • Chronic metabolic acidosis
  • Osteoporosis

3
The importance of acid-base homeostasis
  • The body requires a pH between 7.35 and 7.45 in
    order to maintain its proper functioning
  • The body has many mechanisms to maintain an
    acid-base balance
  • Kidney
  • Lungs
  • Bone

4
The bone
  • Bones
  • a combination of mineral (bicarbonate,
    electrolytes, phosphate) and collagen forms the
    mineralized connective tissue of the bone giving
    it rigidity
  • A dynamic tissue reshaped by bone cells

5
Bone cells
  • Osteoblasts
  • building up bone tissue in a process called
    deposition.
  • Secrete collagen that forms the matrix of bone
    which then calcifies
  • Osteoclasts
  • breaking down bone tissue by removing its
    mineralized matrix, a process called resorption.
  • An equilibrium between osteoblasts and
    osteoclasts maintains bone tissue.

6
Bicarbonate buffer system
  • pH of blood is dependent on the ratio of the
    amount of CO2 to HCO3- present in the blood.
  • Decreases in blood pH buffered by reacting H
    with bicarbonate to form carbonic acid, which is
    then converted to CO2. Removal of CO2 from the
    blood helps increase the pH. (Even though the
    amount of HCO3- decreases, the amount of the
    change is small compared to the amount of HCO3-
    present in the blood.)

7
Acute Metabolic Acidosis
  • physicochemical processes
  • not cell-mediated
  • take place immediately (under 3 hours)

8
Release of Calcium
  • CaCO3 present in bone is more soluble in acidic
    environment
  • more dissolution of Ca from bone during acidosis
    (pH below 7.35)
  • when pH increases, CaCO3 becomes less soluble
  • more deposition of Ca into the bone during
    alkalosis (pH greater than 7.45)

9
Release of Sodium and Potassium Ions
  • there are negatively charged sites on the surface
    of the bone that allow binding of Na, K, and H
  • bound ions can exchange freely with the
    surrounding fluid
  • more H bind and displace Na and K in acidosis
  • more Na and K bind and displace H in alkalosis

10
Chronic Metabolic Acidosis
  • Possible Causes
  • Impaired renal function
  • Long term high protein/fat diet
  • Has features of acute acidosis
  • Additional feature Cell Mediated/Physiological
    Response

11
Osteoblast Acitivity- inhibited
  • Inhibition of collagen synthesis via genes
    codings for collagen-1
  • Inhibition of alkaline phosphatase activity
  • High concentration in osteoblasts
  • Indicative of osteoblast activity

12
Osteoclast Activity- enhanced
  • Stimulation of beta-gluronidase
  • Enzyme stored in lysozyme
  • Catalyze hydrolysis of complex carbohydrates and
    proteoglycans

13
Metabolic vs. Respiratory Acidosis vs. Alkalosis
14
Osteoporosis The Clinical Relevance
15
What is Osteoporosis
  • Definition by the National Osteoporosis
    Foundation (NOF)
  • Osteoporosis is a disease in which bones become
    fragile and more likely to break.
  • This is the leading cause of fractures in the
    elderly.

16
Whats the Pathology?
  • Osteoblasts are building bone while Osteoclasts
    are absorbing bone.
  • During adulthood, these processes occur in
    balance with each other
  • Aging, in addition to other medical conditions
    can upset this balance. E.g. estrogen deficiency
    leads to excess bone reabsorption and inadequate
    formation.

17
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18
How is this Related?
  • What do we know?
  • Chronic acidosis stimulates activity of
    osteoclasts
  • Chronic acidosis also inhibits the activity of
    osteoblasts.

19
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20
What else do we know?
  • There is slight metabolic acidosis with advancing
    age.
  • Probably due to
  • Reduced renal, respiratory and vascular function
    with advancing age.
  • Respiratory and Renal systems are unable to
    fulfill the role of maintaining acid/base
    balance.
  • Vascular impairment leads to local ischemia of
    bone and acidosis due to build up of metabolic
    wastes.

21
The Contribution of Acidosis to Osteoporosis
  • Advancing age leads to Mild Chronic Acidosis
  • This leads to increased Osteoclast Activity and
    inhibition of Osteoblast Activity.
  • Loss of bone mass, weakening of bone.
  • Therefore, raise the pH, have beneficial effect
    on bone and osteoporosis

22
Show me the Evidence!
  • Hormone Replacement Therapy, causes respiratory
    alkalosis, which may be part of its beneficial
    effect.
  • Dietary supplementation of Alkaline Calcium Salts
    have a bone sparing effect. This is most
    effective in acidotic individuals.

23
Pictures Courtesy of
  • Cartoon Cartoon Stock. http//www.cartoonstock.
    com/lowres/dro1023l.jpg
  • Woman with Osteoporosis. Medline Plus.
    http//www.nlm.nih.gov/medlineplus/ency/imagepages
    /17287.htm
  • Microscopy of Osteoporotic Bone. International
    Osteoporosis foundation.
  • http//www.iofbonehealth.org/download/osteofound/
    filemanager/publications/images/visuals_bone_xl.jp
    g
  • Osteoclast. Bone Research Society.
    http//www.brsoc.org.uk/gallery/arnett_osteoclast.
    jpg

24
References
  • Arnett, T. (2003). Regulation of bone cell
    function by acid-base balance. Proceedings of
    the Nutrition Society. 62, 511-520.
  • Bushinsky, D. (2001). Acid-base imbalance and
    the skeleton. European Journal of Nutrition.
    40(5), 238-242.
  • Krieger et al. (2004). Mechanism of acid-induced
    bone resorption. Current Opinion in Nephrology
    and Hypertension. 13, 423-436.
  • University of Oulu. (2008). Acid-base balance,
    dentinogenesis and dental caries Experimental
    studies in rats. Retrived January 16, 2009, from
    Univeristy of Oulu. http//herkules.oulu.fi/isbn95
    14253620/html/x274.html
  • National Osteoporosis Foundation. (2008). What
    is Osteoporosis? Retrieved January 16, 2009,
    from National Osteoporosis Foundation.
  • http//www.nof.org/osteoporosis/index.htm
  • Kosman, DJ et al. (2008). Osteoporosis.
    Retrieved January 16, 2009, from eMedicine.
    http//emedicine.medscape.com/article/330598-overv
    iew

25
Summary Slide
  • There is slight metabolic acidosis with advancing
    age. Probably due to
  • Reduced renal, respiratory and vascular function
    with advancing age.
  • Respiratory and Renal systems are unable to
    fulfill the role of maintaining acid/base
    balance.
  • Vascular impairment leads to local ischemia of
    bone and acidosis due to build up of metabolic
    wastes.
  • Hormone Replacement Therapy, causes respiratory
    alkalosis, which may be part of its beneficial
    effect.
  • Dietary supplementation of Alkaline Calcium Salts
    have a bone sparing effect. This is most
    effective in acidotic individuals.
  • 1) Bone is affected by the pH of its
    environment 
  • 2) Bone plays a role in maintaining the acid/base
    balance in the body (physiochemical and cell
    mediated) 
  • 3) The effects of acidosis on Bone can contribute
    to Osteoporosis, and it can be improved by
    raising the pH.
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