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Physiology 215 Week 12 Notes

by: Maddie Butkus

Physiology 215 Week 12 Notes phys 215

Marketplace > Ball State University > phys 215 > Physiology 215 Week 12 Notes
Maddie Butkus
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These notes cover week 12 of pH.
Human Physiology
Dr. Kelly-Worden
Class Notes
PHYS 215, Week 12, Worden, notes
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This 4 page Class Notes was uploaded by Maddie Butkus on Friday April 1, 2016. The Class Notes belongs to phys 215 at Ball State University taught by Dr. Kelly-Worden in Summer 2015. Since its upload, it has received 9 views.

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Date Created: 04/01/16
• pH and Acid/Base Balance • What is pH? – Can be thought of as the power of Hydrogen concentration in a solution – Mathematical definition- negative logarithmic value of the hydrogen ion (H+) concentration, or • pH = -log [H+] – Negative Logarithm- a negative scale based on ten • As the hydrogen ion concentration goes up, the scale goes down • Example: 1 is ten times more that 2 » 3 is a hundred time less than 1 (10 x 10 = 100) • What is the pH for an Acid? Neutral? A base? • pH of Common Products • Physiological pH • Normal body pH is between 7.35-7.45 or ~ 7.4 • So, normal body pH is slightly basic • What pH range is compatible with life? – pH 6.8 to pH 8 • Acid Disassociation Constant • Given a weak acid “HA”, its disassociation in water is subject to the following equilibrium : + – – HA + H+O ↔ H–O + A or HA ↔ H + A • Ka is the disassociation constant for acid – The stronger the acid, the higher the Ka • Ka=1, almost completely disassociated • Ka=0, almost completely associated pKa- the acidity constant is often represented by the inverse of its logarithm • Types of acids 1. Volatile - carbonic acid (can leave solution and enter the atmosphere) 2. Fixed acids - sulfuric and phosphoric (doesn't leave solution) 3. Organic acids - lactic acid and ketone bodies • Buffers and buffer systems a) Consist of a weak acid or base and a salt form of that acid or base b) Prevent changes in pH by converting strong acids to weak acids and strong bases to weak bases c) Neutralizes H+ as it moves from the point of origin to the lungs or to the kidneys for excretion • Important Buffers in the Body • a) Protein buffers – slow adjustment of ECF • b) Hemoglobin buffer – intracellular buffer; has an immediate effect on ECF • c) Carbonic acid - bicarbonate buffer system 1. Prevent pH changes caused by organic and fixed acids 2. Cannot protect from changes resulting from abnormal levels of CO2 3. Only functions when respiratory system and respiratory control centers are working correctly 4. Limited by the availability of HCO3- • d) Phosphate buffer system – plays a minor role in ECF major role in ICF • Controlling pH in the Body • There are two major processes; pH regulation and pH compensation • Regulation is a function of the buffer systems of the body in combination with respiratory and renal systems • Compensation requires further intervention of the respiratory and/or the renal system to restore normal body pH. • Regulation of the Lungs and Kidneys • The lungs remove carbon dioxide (the respiratory acid) and there is a large amount to be removed (at least 12,000 to 13,000 mmols/day). • The kidneys excrete acids. This is critical even though the amounts (70-100 mmols/day) are smaller because there is no other way to excrete these acids and the amounts involved are still very large when compared to the plasma [H+] of only 40 nmoles/liter. • The kidneys also reabsorb filtered bicarbonate. Bicarbonate is the predominant extracellular buffer against acids. • Respiration and Acid/Base Changes • changes in pH due to pCO2 changes from alterations in ventilation (changes in pCO2 result in rapid changes in [H+] in all body fluid compartments) • Changes in alveolar ventilation are inversely related to changes in arterial pCO2 and directly proportional to total body CO2 production • paCO2 is proportional to [VCO2 / VA] – paCO2 = 0.863 x [ VCO2 / VA ] • paCO2 = Arterial partial pressure of CO2 • VCO2 = Carbon dioxide production by the body • VA = Alveolar ventilation • Henderson-Hasselbalch Equation • changes in arterial pCO2 cause changes in pH • pH = pKa + log { [HCO3] / (0.03 x pCO2) } • [H+] = 24 x ( pCO2 / [HCO3] ) • Renal Regulation • Remember, H+ leaves the proximal tubule cell by 2 mechanisms: – Via Na+-H+ antiporter (major route) – Via H+-ATPase (proton pump) • Filtered HCO3- cannot cross the apical membrane PT. Instead, it combines with the secreted H+ and is converted to CO2 and H2O by carbonic anhydrase. • CO2 is lipid soluble and easily crosses into the cytoplasm of the PT cell. In the cell, the reverse reaction takes place and HCO3- crosses the basolateral membrane via a Na+-HCO3- symporter. • The sodium pump keeps intracellular Na+ low maintaining the gradient for the H+-Na+ antiport at the apical membrane. The H+-Na+ antiport (secondary active transport). • Net effect- reabsorption of one molecule of HCO3 and one molecule of Na+ from the tubular lumen into the blood stream for each molecule of H+ secreted. . • Physiological Conditions • Acidosis - an abnormal process or condition which would lower arterial pH if there were no secondary changes in response . • Alkalosis - an abnormal process or condition which would raise arterial pH if there were no secondary changes in response . • Simple (Acid-Base) Disorders are those in which there is a single primary acid-base disorder. • Mixed (acid-Base) Disorders are those in which two or more primary disorders are present simultaneously. • Acidaemia - Arterial pH < 7.36 (ie [H+] > 44 nM ) – Blood is below 7.4 • Alkalaemia - Arterial pH > 7.44 (ie [H+] < 36 nM ) – Blood is above 7.4 (basic) • Acid/Base Disorders • Respiratory acidosis- arterial pCO2 rises to a level higher than expected • Respiratory alkalosis- arterial pCO2 falls to a level lower than expected • Metabolic acidosis- a process or condition leading to an increase in acids in the blood • Metabolic alkalosis- a disorder which causes the plasma bicarbonate to rise to a level higher than expected • Respiratory Compensation • Compensation for metabolic acidosis is hyperventilation to decrease the arterial pCO2 – Maximum compensation can be calculated – Expected pCO2 = 1.5 [HCO3] + 8 mmHg – Compensation for metabolic alkalosis is hypoventilation to increase arterial pCO2 – Maximum compensation can be calculated – Expected pCO2 = 0.7 [HCO3] + 20 mmHg • Renal Compensation • Chronic Respiratory Acidosis- the kidneys respond by retaining bicarbonate – response occurs because increased arterial pCO2 increases intracellular pCO2 in proximal tubular cells (PTC) and this causes increased H+ secretion from the PTCs – Acute respiratory acidosis is buffered by proteins • Respiratory alkalosis is compensated by a decrease in bicarbonate reabsorption by the kidneys


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