part 1 electrolytes. electrolytes electrolytes are ions capable of carrying an electricl charge...
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ElectrolytesElectrolytes
Electrolytes are ions capable of carrying an electricl charge Anions: (-) → Anode Cations: (+) → Cathode
Major cations of the body Na+, K+, Ca+2 & Mg+2
Major anions of the body Cl-, HCO3
-, HPO4-2 & SO4
-2
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Essential Component in Numerous Essential Component in Numerous processesprocesses
1. Volume and osmotic pressure (Na+, K+, Cl-)2. Myocardial rhythm and contraction (K+, Mg2+,
Ca2+)3. Cofactors in enzyme activation (Mg2+, Ca2+,
Zn2+).4. Regulation of ATPase ion pump (Mg2+)5. Acid/Base balance (pH) (HCO3
-, K+, Cl-)
6. Coagulation (Mg2+, Ca2+)7. Neuromuscular (K+, Mg2+, Ca2+)
The body has complex systems for monitoring and maintaining electrolyte concentrations
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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
-)
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WaterWater
Average water content of human body is 40-75% of total body weight.Solvent for all body processesTransport nutrients to cellsRegulates cell volumeRemoves waste products → urineBody Coolant → sweating
Water is located in intracellular and extracellular compartments
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WaterWaterNormal plasma ~ 93 % H2O, the rest is
mixture of Lipids and proteins.Concentration of ions within the cells and
plasma is maintained by:1.Energy consumption: Active transport 2.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
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OsmolalityOsmolality
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 osmolalityThirst → more water intakeAVP → increase water absorption in kidney
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Clinical SignificanceClinical Significance
Osmolality is the parameter to which hypothalmus responds to maintain fluid intake.
The regulation of osmolality also affects the Na+ concentration in plasma90% of osmotic activity in plasma
Another process affects Na+ concentration is regulation of blood volume.
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Clinical significanceClinical 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.
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Water LoadWater Load
Excess intake of water lower plasma osmolality
Kidney is important in controlling water excess
AVP and thirst are suppressedWater 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
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Water deficitWater 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
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Regulation of blood Regulation of blood volumevolume
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.
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Regulation of blood Regulation of blood volumevolume
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.
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Regulation of blood Regulation of blood volumevolume
Other Factors effecting blood volume:
1. Atrial natriuretic Peptide (ANP) → sodium excretion → ↓ blood volume
2. Volume receptors → release of AVP → conserve water → ↑ blood volume
3. Glomerular filtration rate (GFR) ↑ in volume expansion and ↓ in volume depletion
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Determination of Determination of OsmolalityOsmolality
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 pointVapor pressure
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Determination of Determination of OsmolalityOsmolality
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.
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Osmolal GapOsmolal GapOsmolal 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 β-hydroxybutyrate)
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SodiumSodiumMost 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/LATPase 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.
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Regulation of Sodium Regulation of Sodium BalanceBalance
Plasma Na+ concentration depends: on the intake and excretion of water and, on the renal regulation of Na+
Three processes are of primary importance: 1.intake of water in response to thirst (p. osmolality)
2.the excretion of water (AVP release)3.the blood volume status, which affects Na+ excretion through aldosterone, angiotensin II, and ANP (atrial natriuretic peptide).
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Regulation of Sodium Regulation of Sodium BalanceBalance
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 systemAtrial natriuretic Peptide (ANP) → sodium excretion
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HyponatremiaHyponatremia
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.
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HypernatremiaHypernatremia
Hypernatremia: increased sodium concentration > 145 mmol/l
Result of excess water loss in the presence of sodium excess, or from sodium gain
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Sodium determinationSodium determination
Methods:1. Flame emission
spectrophotometry2. Atomic absorption
spectrophotometry3. Ion Selective electrode
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Atomic absorption Atomic absorption spectrophotometryspectrophotometry
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PotassiumPotassiumMajor intracellular cation20 X greater concentration in the cell vs. outside.
2% of the bodies potassium circulates within the plasma.
Function:Regulates neuromuscular excitabilityHydrogen ion concentrationIntracellular fluid volume
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Effects on Cardiac Effects on Cardiac musclemuscle
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
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Potassium Role in Hydrogen Potassium Role in Hydrogen ConcentrationConcentration
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.
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Regulation of Regulation of potassiumpotassium
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.
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HyperkalemiaHyperkalemia Increase potassium serum levels > 5 mmol/l Associated with diseases such as renal and
metabolic acidosis
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Potassium Potassium determinationdetermination
Assay method: Ion selective Electrode a valinomycin membrane is
used to selectively bind K+
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ChlorideChloride
Major extracellular anionCl– 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
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ChlorideChlorideCl– 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–.
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Electric NeutralityElectric Neutrality
Sodium/chloride shift maintains equilibrium within the body.
1. Na reabsorbed with Cl in proximal tubules.2. 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
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