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Acids and Bases
Biology 1203 - Week 04
Fluids & Electrolytes
Terms in this set (34)
Ions and Ionic Bonds
Ions= Atoms with a charge
Ionic bond= electrostatic attraction between oppositely charged ions. Atoms become charged as a result of losing or gaining electron (transfer of electrons)
Most covalent bonds cannot be broken, except through chemical reactions, or intense heat.
Include organic compounds
e.g. lipids, carbohydrates, proteins, nucleic acids.
What is an electrolyte?
Compound that, when in water, DISSOCIATES to form ions.
Generally ionic compounds:
- INORGANIC ACIDS (that release H+ when in water).
- INORGANIC BASES (that release OH- when in water).
- SALTS (dissociate into cations & anions, not H+ or OH-).
Organic acids and bases.
Such solutions CONDUCTS ELECTRICITY (hence the name).
Contain COVALENT bonds .
Do not dissociate in water to form ions.
~ the bond made by the shared electrons cannot be disrupted by water molecules.
eg. Urea, creatinine, glucose.
Fluid compartments of the body
> Total body water:
~ Male = 60%; Female = 55%; Infant = 75%.
> 2 major fluid compartments:
> INTERCELLULAR (2/3 of body fluids)
~ Cytosol within cells.
> EXTRACELLULAR (1/3 of body fluids; internal environment):
~ Plasma (20%): liquid portion of blood
~ Interstitial fluid (80%): between TISSUE CELLS; lymph, cerebrospinal fluid, synovial fluid, eye fluid, fluids between serous membranes, perilymph and endolymph (ear).
Extracellular electrolytes (red/blue)
> Na+ is the major cation.
> Cation concentrations similar in plasma & interstitial fluid.
> Cl- is the major anion, followed by bicarbonate (HCO3-).
> Protein anion concentration higher in plasma.
Why are there protein anions?
Negatively charged R groups
Intracellular electrolytes (yellow)
> K+ is the major cation, but Mg2+ is also important.
> Phosphate is the major anion.
> Much larger concentration of protein anions in intracellular fluid.
> Sodium and potassium concentrations in extra- and intracellular fluids are nearly opposites.
> This reflects the activity of cellular ATP-dependent sodium-potassium pumps.
Electrolyte composition of body compartments
Resting Membrane Potential
> inside of the plasma membrane is negative relative to the outside.
> 3 factors that maintain the membrane potential:
1). Action of Sodium-Potassium Pump: It pumps 3 sodium ions out and 2 potassium ions in.
2.) Intracellular protein anions (trapped).
3.) Selective permeability of the membrane to ions:
It is more permeable to potassium than to sodium.
Acid (a special type of electrolyte)
> A substance that dissociates in water and RELEASE HYDROGEN IONS (H+; also called PROTONS).
> STRONG ACID completely dissociates, releasing large numbers of H+.
E.g. HCl ---->H+ + Cl-.
> WEAK ACIDS only partially dissociate, releasing small numbers of H+ .
E.g. carbonic acid.
Strong Acids vs. Weak Acids
> Strong acids dissociate in solution COMPLETELY and release many H+.
> Weak acids do not dissociate in solution completely and do not release many H+.
Base (another type of electrolyte)
> A substance which can ACCEPT A HYDROGEN ION, thus removing H+ from solution.
> Note that there are also STRONG and WEAK BASES
OH- (KOH) is a strong base.
OH- + H+ H20
> Weak Bases:
NH3 + H+ → NH4 +
pH & pH scale
> pH is a measure of the CONCENTRATION of H+ PER LITRE of SOLUTION.
> INVERSE LOGARITHMIC scale, ranging from 0 to 14.
~ pH7 indicates a NEUTRAL solution.
~ pH above 7 = BASIC/alkaline solution.
~ pH below 7 = ACIDIC solution.
- H+ concentration is greater at lower numbers.
- Each change in 1 pH value represents a 10-FOLD CHANGE in H+.
The pH Scale
> As the H+ concentration increases, the OH- concentration decreases, and vice versa.
> At pH 7 concentration of H+ and OH- is equal.
If you had two solutions of equal concentration, but one is a strong acid, and the other is a weak acid, which one would have a lower pH?
> Strong acids completely dissociate in water, releasing large numbers of hydrogen ions.
> Weak acids only partially dissociate in water, releasing small numbers of hydrogen ions.
pH value of selective substances
Sources of acids and bases in the body
ACIDS and BASES react to form SALTS and WATER.
HCl + KOH → KCl + H2O.
This type of reaction is a NEUTRALIZATION REACTION and removes the effect of the acid and base; the pH is prevented from changing (not H+ donor or acceptor)
Why is pH homeostasis important?
Normal blood pH between 7.35 and 7.45.
Drastic pH changes are harmful to metabolic processes because they interfere with protein shape and protein functions.
Mechanisms of pH balance in the body
1.) Chemical Buffers.
> Immediate, short-term mechanism for maintaining pH.
2.) Respiratory system (lungs).
> Regulates how much CARBON DIOXIDE leaves or stays in the body.
> Works within 1-3 minutes.
3.) Renal system (kidneys).
> Controls acid-base balance by excreting or secreting various IONS into urine.
> Requires hours to days to affect pH changes.
Buffer Systems - definition
> Buffer: a solution which resists a change in pH despite addition of acids and bases.
> How does it achieve that?
Essentially a solution that contains a WEAK ACID and IT SATL (a WEAK BASE) that do not react with each other, but does react with an added acid or base.
E.g. Carbonic acid- bicarbonate buffer system.
H2CO3 <--> HCO3- + H+.
> Acid component of buffer reacts (releases H+ ions) when base added.
> Base component of buffer reacts (absorbs H+ ions) when an acid is added.
Mechanisms of pH regulation in the body : Chemical Buffers
a) Carbonic acid-bicarbonate buffer system:
Most abundant buffer in ECF; REGULATOR OF BLOOD pH.
b) Phosphate buffer system:
Most effective buffer in URINE and INTERCELLULAR FLUID.
What happens when you add an ACID to a buffer? E.g. Carbonic acid-bicarbonate system
Adding an acid (HCl):
HCl + NaHCO3 -----> H2CO3 + NaCl
Hydrogen ions released by the strong acid combine with the bicarbonate ions and form carbonic acid (a weak acid).
> The strong acid has been converted to a weak acid.
> The pH of the solution decreases only slightly.
Mechanisms of pH regulation in the body: Respiratory System
Increase of acidity in the blood
> If the level of acidity increase in the blood, then there is an increase of hydrogen ions.
> These hydrogen ions will combine with bicarbonate to form more carbonic acid.
> Carbonic acid can then form more CO2 and H2O.
> This excess carbon dioxide is removed from the system (increased ventilation rate).
> Another way to look at things: the removal of carbon dioxide from the system will decrease the levels of hydrogen ions from the system.
Decrease of acidity in the blood
> A decrease of acidity in the blood means that there is a decrease of hydrogen ions.
> Carbonic acid can break down to form more hydrogen ions and bicarbonate.
> To do this, the lungs need to retain carbon dioxide to form more carbonic acid (decreased ventilation rate).
> Another way to look at things: the retaining of carbon dioxide in the lungs will increase the level of hydrogen ions in the blood.
how the respiratory system can be used to deal with changes in hydrogen ion concentration?
Blood pH is regulated by a negative feedback loop
that affects VENTILATION RATE.
If the blood pH lowers, what change would you expect from the respiratory system?
The respiration rate would decrease.
Mechanisms of pH regulation in the body: Kidney System
Acidosis (low blood pH):
> H+ are secreted (from blood) into urine (PROTON PUMP). Urine pH ranges from 4.5-8.
> Kidneys generate bicarbonate ions and add them to the blood.
ALKALOSIS (high blood pH):
> The mechanism to deal with acidosis decreases.
> Kidneys can also secrete bicarbonate ions and reabsorb hydrogen ions (this occurs less often).
Disturbances of Acid-Base Balance: Acidosis
* Blood may be alkaline but still considered acidosis at pH<7.35.
Disturbances of Acid-Base Balance: Alkalosis
Is there anything wrong with this patient?
Blood test results:
pH: 7.48 (normal: pH 7.35-45)
PCO2: 46 mmHg (normal: 35 - 45 mmHg)
HCO3-: 33 mEq/L (normal: 22-26 mEq/L)
Blood test results:
pH: 7.48 (normal: pH 7.35-45).
> increased and is alkalosis.
PCO2: 46 mmHg (normal: 35 - 45 mmHg).
HCO3-: 33 mEq/L (normal: 22-26 mEq/L).
has metabolic alkalosis.
Acid-base balance -summary
> Important to maintain pH in body within a narrow range to prevent denaturation of proteins that carry out metabolic reactions.
> The body has 3 main regulatory mechanisms to maintain acid-base balance.
- BUFFER SYSTEM (immediate; composed of weak acid and conjugate base):
1) HCO3- 2) phosphate 3) protein
- RESPIRATORY REGULATION (mins): ventilation (exhalation of CO2).
- KIDNEY REGULATION (h-days): excretion of H+ and reabsorption of HCO3-.
> Failure of pH homeostatic mechanisms leads to acidosis (pH<7.35) or alkalosis (pH>7.45) which can have respiratory or metabolic causes (determined by changes in pCO2 or HCO3- concentrations).
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