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29 Cards in this Set
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Osmolality
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Measures body electrolyte/water balance. It is proportional to the total concentration of all dissolved molecules. Sodium is the major influence of osmolality.
Normal Serum Osmolality: 280-300 mosmol/kg. Serum levels dependent on Na, glucose and urea. High osmolality - results in water moving out of the cell (ICF to ECF). Ex. High blood glucose (hyperglycemia) results in water shift from ICF(neurons) to ECF. Dehydration occurs, can manifest coma. |
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Osmotic Pressure
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Semipermeable membrane of cells allows water osmosis to occur between ECF and ICF. Plasma proteins do not cross the membrane and are responsible for osmotic pressure.
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Colloid Osmotic Pressure
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Role of albumin
Na+ is small and can exit from ICF to interstitial space, and carries with it water. To prevent loss of water, albumin binds to water. This results in colloid osmotic pressure. |
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Edema
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Low albumin results in increased water in in interstitial space (between cells). Commonly seen when osmotic pressure of blood is low.
Burns - damage to capillaries (loss of albumin) Low protein diet - protein responsible for osmotic pressure Renal/Liver diseas |
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Acids
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Are compounds that donate a H+ (hydrogen ion) to a solution/ accept electrons.
Strong acids tend to dissociate completely in solution, whereas weak acids dissociation is limited |
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Bases
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Are compounds that accept a H+ ion/donate electrons.
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pH
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Plasma pH = 7.4
[H+] = 35-45 nmol/L |
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Ka
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Dissociate constant of acid
Ka = [H+] [A-]/ [HA] The larger the Ka, the stronger the acid, because most of the HA has dissociated. Smaller the Ka, weaker the acid. |
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pKa
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= -logKa
Ka = acid dissociation constant, which is the measure of the strength of an acid in solution. |
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Buffers
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Consist of a weak acid and its conjugate base.
They resist change in pH from addition of small quantities of acids (H+) or bases (OH-) |
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Buffering Capacity
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When pH=pKa [weak acid] = [conjugate base].
Buffers in body fluids require pKa around 7.4 (arterial pH). The higher the buffer concentration, the higher its buffering capacity. |
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Henderson-Hasselbalch Equation
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pH = pKa + log [A-]/[HA]
If the pKa of a weak base is known, the equation can be used to calculate the ratio of the weak acid to the conjugate base at any pH. |
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Henderson-Hasselbalch in Pharmacology
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Most drugs are either weak acids or weak bases and are absorbed in their uncharged forms. Thus, a weak acid such as aspirin, the uncharged HA can pass through membranes and A- cannot.
For weak base, such as morphine, the uncharged form B can pass through and BH+ does not. |
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Acid Drugs
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(pK<7) Are better absorbed in the stomach. They are often present in uncharged form and because the pH <pK, it will be better absorbed
Acidic drugs [HA] release a proton [H+], causing a charged anion to form [A-] (conjugate base) HA <---> H+ + A- Ex. Aspirin (pH<pK) uncharged form R-COOH (stomach) (pH>pK) charged (-) form R - COO - (intestine, will not absorb) |
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Basic Drugs
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(pK<7) are better absorbed in the intestine. Because of pH of stomach is low (pH 1-2). Basic drugs will be present in their charged (+) forms and wont be absorbed. In the stomach it is present in the uncharged form.
Weak bases [BH+] also release H+, however the protonated form of basic drugs is usually charged and loss of a proton produces an uncharged B: BH+ <--> B + H+ Ex. Morphine (pH<pK) charged form R-NH4+ (stomach) (pH >pK) uncharged form R-NH3- (intestine) |
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Metabolic Production of Acids
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-Metabolism produces 22,000 mmol/day of acid
Volatile - CO2 (major 22,000) Noncolatile - sulfurice, phosphoric and ketone bodies (40-80 mmil/day) Maintained by buffer, respiratory and kidney systems |
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Body buffers
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Plasma pH is maintained at 7.36 - 7.44 and intracellular at 7.1 (lower because of metabolic acids)
Major Buffer systems: Bicarbonate-carbonic acid - (ECF buffer) Hemoglobin (histidine) Phosphate (ICF) |
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Bicarbonate Buffer
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CO2 + H20 <---carbonic anhydrase--> H2CO3 (carbonic acid)
Carbonic Acid dissociates --> H+ + HCO3- (bicarbonate) pKA of bicarbonate buffer = 6.1 |
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Normal [HCO3-] and Arterial PCO2
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[HCO3] = 22-25 mEq/L (regulated by renal system)
Arterial PCO2 = 40 mmHG (regulated by respiratory) Because these two levels are regulated independently, the bugger system is the most important in eCF. |
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Transport of C02 (Tissues to lungs)
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1) O2 unloads from Hb because of low O2 in the cells, and readily passes across cells.
2) CO2 in cells is high, so diffuses out into RBC 3) With water (H20) and carbonic anhydrous --> becomes carbonic acid (H2CO3) 4) Carbonic acid dissociates to produce H+ ions and bicarbonate anion [HCO3-] 5) Hb acts as buffer and attaches to H+ ions |
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Transport of CO2 (at the lungs)
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1) O2 passes from alveoli to RBC
2) HHb dissociates to form H+ ions and Hb, which binds with O2 from lungs to for HbO2 3) HCO3- (bicarbonate anion) binds with H+ to from carbonic acid 4) Carbonic acid with help of carbonic anyhydrase dissociates into water and C02, 5) CO2 diffuses into alveoli of lungs and is expelled |
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Acidosis
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When the blood pH falls.
Respiratory center is stimulated resulting in increased respiration (hyperventilation). There is an increased washout of CO2, lowering PCO2 (arterial). |
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Alkalosis
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When the pH increases.
The respiratory system is inhibited, resulting hypoventilation. Increases retention of CO2, increasing PCO2. |
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Hyperventilation
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Increase respiration.
Decrease in CO2 and PCO2 |
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Hypoventilation
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Decrease in respiration
Increase in CO2 and PCO2 |
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Reabsorption of filtered bicarbonate
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1) CO2 + water and carbonic anhydrase convers into carbonic acid
2) Carbonic acid dissociates into bicarbonate and H+ ions. Bicarbonate enters the blood 3) H+ enters the tubular lumen and binds with filtered bicarbonate and converts to carbonic acid 4) Carbonic Acid dissociates into CO2 and enters back into long NO FILTERED BICARBONATE IS LOST |
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Acetazolamide
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Inhibits carbonic anhydrase.
Used to treat metabolic or respiratory alkalosis. Interferes with bicarbonate (HCO3) reabsorption, thereby reacidifying the blood. |
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Role of Phosphate buffer in formation of new bicarbonate
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For every H+ that is excreted into the tubular lumen, one bicarbonate is gained in the blood. You need new bicarbonate because you loose bicarbonate through buffering. Filtered phosphate HPO4 acts as buffer and binds with H+ and is converted to H2PO4 which is excreted in the Urine
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Role of Ammonia in Formation of new bicarbonate
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Glutamine is broken down into ammonia by glutaminase.
Ammonia is then filtered in the tubular lumen and binds with H+ ions for dissociation of carbonic acid. - Ammonium chloride is excreted in urine NH4Cl -Ammonia has MORE capacity than phosphate |