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Electrolytes

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Electrolytes Part 1 Regulation of potassium The kidneys are important in the regulation of K+ balance. Initially, the proximal tubules reabsorb nearly all the K+. – PowerPoint PPT presentation

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Title: Electrolytes


1
Electrolytes
  • Part 1

2
Electrolytes
  • Electrolytes are ions capable of carrying an
    electricl charge
  • Anions (-) ? Anode
  • Cations () ? Cathode
  • Major cations of the body
  • Na, K, Ca2 Mg2
  • Major anions of the body
  • Cl-, HCO3-, HPO4-2 SO4-2

3
Essential Component in Numerous processes
  • Volume and osmotic pressure (Na, K, Cl-)
  • Myocardial rhythm and contraction (K, Mg2,
    Ca2)
  • Cofactors in enzyme activation (Mg2, Ca2,
    Zn2).
  • Regulation of ATPase ion pump (Mg2)
  • Acid/Base balance (pH) (HCO3-, K, Cl-)
  • Coagulation (Mg2, Ca2)
  • Neuromuscular (K, Mg2, Ca2)
  • The body has complex systems for monitoring and
    maintaining electrolyte concentrations

4
  • Maintenance of water homeostasis is vital to life
    for all organisms
  • Maintenance of water distribution in various body
    fluids is a function of electrolytes (Na, K,
    Cl- HCO3-)

5
Water
  • Average water content of human body is 40-75 of
    total body weight.
  • Solvent for all body processes
  • Transport nutrients to cells
  • Regulates cell volume
  • Removes waste products ? urine
  • Body Coolant ? sweating
  • Water is located in intracellular and
    extracellular compartments

6
Water
  • Normal plasma 93 H2O, the rest is mixture of
    Lipids and proteins.
  • Concentration of ions within the cells and plasma
    is maintained by
  • Energy consumption Active transport
  • Diffusion Passive transport
  • Maintaining conc. of electrolytes affect
    distribution of water in compartments
  • Most membranes freely permeable to water
  • Conc. of ions on one side affect flow of water
    across the membrane

7
Osmolality
  • Physical property of a solution based on the
    concentration of solutes per kilograms of
    solvent. (mOsm/Kg)
  • Sensation of thirst arginine vasopressin
    hormone (AVP) formerly, Antidiuretic hormone
    (ADH) are stimulated by hypothalamus in response
    to increased blood osmolality
  • Thirst ? more water intake
  • AVP ? increase water absorption in kidney

8
Clinical Significance
  • Osmolality is the parameter to which hypothalmus
    responds to maintain fluid intake.
  • The regulation of osmolality also affects the Na
    concentration in plasma
  • 90 of osmotic activity in plasma
  • Another process affects Na concentration is
    regulation of blood volume.

9
Clinical significance
  • To maintain normal plasma osmolality (275-295
    mOsm/Kg) hypothalamus must respond quickly to
    small changes
  • 1-2 increase in osmolality 4 fold increase in
    AVP secretion.
  • 1-2 decrease in osmolality shuts off AVP
    secretion.
  • Renal water regulation by AVP and thirst play
    important roles in regulating plasma osmolality.
  • Renal water excretion is more important in
    controlling water excess,
  • whereas thirst is more important in preventing
    water deficit or dehydration.
  • Consider what happens in several conditions.

10
Water Load
  • Excess intake of water lower plasma
    osmolality
  • Kidney is important in controlling water excess
  • AVP and thirst are suppressed
  • Water is not reabsorbed, causing a large volume
    of dilute urine to be excreted
  • Hypoosmolality and hyponatremia usually occur in
    patients with impaired renal excretion of water

11
Water deficit
  • As a deficit of water, plasma osmolality begins
    to increase
  • Both AVP secretion and thirst are activated.
  • Although AVP contributes by minimizing renal
    water loss, thirst is the major defense against
    hyperosmolality and hypernatremia.
  • A concern in infants, unconscious patients, or
    anyone who is unable to either drink or ask for
    water

12
Regulation of blood volume
  • Blood volume essential in maintaining blood
    pressure and ensure perfusion to all tissue and
    organs.
  • Regulation of both sodium water are
    interrelated in controlling blood volume
  • Renin-angiotensin-aldosterone system of hormones
    that respond to decrease in blood volume and help
    maintain the correct blood volume.

13
Regulation of blood volume
  • Changes in blood volume detected by receptors in
  • the cardiopulmonary circulation ,
  • carotid sinus,
  • aortic arch
  • and glomerular arterioles
  • They activate effectors that restore volume by
  • appropriately varying vascular resistance,
  • cardiac output,
  • and renal Na and H2O retention.

14
Angiotensin converting enzyme (ACE)
15
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16
Regulation of blood volume
  • Other Factors effecting blood volume
  • Atrial natriuretic Peptide (ANP) ? sodium
    excretion ? ? blood volume
  • Volume receptors ? release of AVP ? conserve
    water ? ? blood volume
  • Glomerular filtration rate (GFR) ? in volume
    expansion and ? in volume depletion

17
Determination of Osmolality
  • Serum or urine sample (plasma not recommended due
    to the use of anticoagulants)
  • Based on properties of a solution related to the
    number of molecules of solutes per kilogram of
    solvent such as
  • Freezing point
  • Vapor pressure

18
Determination of Osmolality
  • Freezing Point Osmometer
  • Standardized method using NaCl reference
    solution.
  • Specimen is supercooled to -7ºC, to determine
    freezing point.
  • ? osmolality causes depression in the freezing
    point temp.
  • More solutes present the longer the specimen will
    take to freeze.

19
Osmolal Gap
  • Osmolal gap is the difference between the
    measured osmolality and the calculated one.
  • Osmolal Gap measured osmolality - calculated
    osmolality
  • The osmolal gap indirectly indicates the presence
    of osmotically active substances other than
    sodium, urea or glucose. (ethanol, methanol or
    ß-hydroxybutyrate)

20
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21
Sodium
  • Most abundant extracellular cation- 90
  • Major function is maintaining the normal water
    distribution osmotic pressure of plasma
  • Role in maintaining acid-base balance (Na, H
    exchange mechanism)
  • Normal range Serum 136-145 mmol/L
  • ATPase ion pump the way the body moves sodium
    and potassium in and out of cells.
  • 3 Na out of the cell for every 2 K in and
    convert ATP to ADP.

22
Regulation of Sodium Balance
  • Plasma Na concentration depends
  • on the intake and excretion of water
  • and, on the renal regulation of Na
  • Three processes are of primary importance
  • intake of water in response to thirst (p.
    osmolality)
  • the excretion of water (AVP release)
  • the blood volume status, which affects Na
    excretion through aldosterone, angiotensin II,
    and ANP (atrial natriuretic peptide).

23
Nephron
24
Regulation of Sodium Balance
  • 70 of sodium that is filtered is reabsorbed in
    proximal tubules.
  • Remainder occurs in the ascending loop of Henle
    (without water absorption) DCT under regulation
    of Aldosterone
  • Renin-Angiotensin system
  • Atrial natriuretic Peptide (ANP) ? sodium
    excretion

25
Hyponatremia
  • Defined as a serum/plasma level less than 135
    mmol/L.
  • One of the most common electrolyte disorders in
    hospitalized and non-hospitalized patients
  • Levels below 130 mmol/L are clinically
    significant.

26
Hyponatremia
27
Hypernatremia
  • Hypernatremia increased sodium concentration gt
    145 mmol/l
  • Result of excess water loss in the presence of
    sodium excess, or from sodium gain

28
Sodium determination
  • Methods
  • Flame emission spectrophotometry
  • Atomic absorption spectrophotometry
  • Ion Selective electrode

29
Atomic absorption spectrophotometry
30
Ion Selective electrode
31
Potassium
  • Major intracellular cation
  • 20 X greater concentration in the cell vs.
    outside.
  • 2 of the bodies potassium circulates within the
    plasma.
  • Function
  • Regulates neuromuscular excitability
  • Hydrogen ion concentration
  • Intracellular fluid volume

32
Effects on Cardiac muscle
  • Ratio of K intracellular extracellular is
    important determinant of resting membrane
    potential across cell membrane
  • Increase plasma potassium decreasing the resting
    membrane potential, increase excitability, muscle
    weakness
  • Decrease extracellular potassium decrease
    excitability

33
Potassium Role in Hydrogen Concentration
  • In hypokalemia (low serum K),
  • As K is lost from the body, Na and H move into
    the cell.
  • The H concentration is, therefore, decreased in
    the ECF, resulting in alkalosis.

34
Regulation of potassium
  • The kidneys are important in the regulation of K
    balance.
  • Initially, the proximal tubules reabsorb nearly
    all the K.
  • Then, under the influence of aldosterone, K is
    secreted into the urine in exchange for Na in
    both the distal tubules and the collecting ducts.
  • Thus, the distal tubule is the principal
    determinant of urinary K excretion.
  • Most individuals consume far more K than needed
    the excess is excreted in the urine but may
    accumulate to toxic levels if renal failure
    occurs.

35
Hypokalemia
  • Decrease of serum potassium below 3.5 mmol/l

36
Hyperkalemia
  • Increase potassium serum levels gt 5 mmol/l
  • Associated with diseases such as renal and
    metabolic acidosis

37
Potassium determination
  • Assay method
  • Ion selective Electrode
  • a valinomycin membrane is used to selectively
    bind K

38
Chloride
  • Major extracellular anion
  • Cl is involved in maintaining
  • osmolality,
  • blood volume,
  • and electric neutrality.
  • In most processes, Cl ions shift secondarily to
    a movement of Na or HCO3.
  • Cl ingested in the diet is Completely absorbed
    by the intestinal tract.

39
Chloride
  • Cl ions are filtered out by the glomerulus and
    passively reabsorbed, in Conjuction with Na, by
    the proximal tubules.
  • Excess Cl is excreted in the urine and sweat.
  • Excessive sweating stimulates aldosterone
    secretion, which acts on the sweat glands to
    Conserve Na and Cl.

40
Electric Neutrality
  • Sodium/chloride shift maintains equilibrium
    within the body.
  • Na reabsorbed with Cl in proximal tubules.
  • Chloride shift
  • In this process, carbon dioxide (CO2) generated
    by cellular metabolism within the tissue diffuses
    out into both the plasma and the red cell.
  • In the red cell, CO2 forms carbonic acid (H2CO3),
    which splits into H and HCO3- (bicarbonate).
  • Deoxyhemoglobin buffers H, whereas the HCO3-
    diffuses out into the plasma and Cl- diffuses
    into the red cell to maintain the electric
    balance of the cell

41
Chloride shift
42
Hypochloremia
  • Hypochloremia lt 98 mmol/l

43
Hypercholremia
  • Hypercholremia gt 109 mmol/l

44
Assay
  1. Coulometric titration (ref. method)
  2. Ion selective electrode
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