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Acids
- pH 0-6
- Acids are AH- acids dissociate into A- and H+
- AH <-> A-+H+
- Strong Acids, like HCl in the stomach, completely dissociate
- Weak acids, like H2CO3 carbonic acid, partially dissociate
- H++HCO3- -> H2CO3
- Free H++Free anion
- H+ increases...more acidic
- H+ decreases...less acidic
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Bases
- pH 8-14
- Bases, B, can bind H+ to become BH+
- The only significant physiological base is ammonia, NH3 becomes NH4
- Ammonia, buffers renal filtrate, allowing more H+ excretion
- H2O-> OH-+H+
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pH
- Measure of H+ in a solution
- pH=-log[H+], increases in H+ cause decreases in pH
- The average blood pH is 7.40, average cell pH is about 7.0
- Blood pH below 7.35 is acidosis, blood pH about 7.45 is alkalosis
- Acidosis is far more common than alkalosis
- cells will have bigger pH shifts than blood
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Acidosis Effects
- Depresses the neurons, especially in the CNS
- Alkalosis makes neurons hyper-excitable
- In general decreases enzyme activity, but a few increase
- Causes increased H+ excretion, and therefore decreased K+ excretion: Increased K+ causes cardiac and neural problems
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Sources of H+
- Small amounts in food, such as citric acid
- Most generated in the body: carbonic acid from CO2, sulfur and phosphoric acids from proteins, metabolic acids such as lactic acids
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Control of H+
- H+ is controlled in 3 ways:
- Chemical Buffering
- Respiratory Control of CO2
- Renal Control of H+ Excretion
- Buffers----(addition of 3 HCl to unbuffered solution)---> 3 free H+ present
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Buffers
- Different buffers work in different places
- Buffers work by binding H+ from the solution and from pH
- First line of H+ defense
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Extracellular Buffering
- Bicarbonate is the most important ECF buffer
- HCO3- bind H+ to form H2CO3, which dissociates to CO2+H2O
- Hemoglobin in RBCs buffers H+ produced by CO2 increases in venous blood
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Intracellular Buffering
- Proteins in cells bind H+ in ICF
- In some cells, especially muscle cells, phosphate helps buffer ICF
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Urine buffering
- Phosphate and bicarbonate are dissociated acids that buffer renal filtrate
- Ammonia is a base that also buffers renal filtrate
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Respiratory Control of H+
- Second line of H+ defense. Works with non-respiratory sources of H+
- Increased H+ or increased CO2, increases depth and frequency of respiration- this reduces CO2 in blood, reducing H+ back toward normal
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Kidney Control of H+
- Third line of H+ defense
- Removes H+ from any non-renal sources in the body
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H+ Excretion
- H+ ion pumps in the renal tubules secrete H+ into the filtrate
- Urine pH is normally 6.0 but can also be lower
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Acid-Base Imbalances
- Pathological changes in the control of H+ results in pH changes
- These can be compensated by the respiratory and renal systems, if not of respiratory or renal origin
- A system cannot compensate for its own problems: renal problems require respiratory compensation; respiratory problems require renal compensation
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Respiratory Acidosis
Abnormal CO2 retention from hypoventilation
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Respiratory Alkalosis
- Decreased CO2 by hyperventilation
- Fear/ anxiety, aspirin poisoning, conscious breathing
- Decreased H+ secretion removal condition
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Metabolic Acidosis
- *cancer with tumors (more energy)
- Most common acid base disorder
- Severe diarrhea, loss of bicarbonate
- Excess H+ production during fat use in diabetics
- Exercise leading to lactate and H+ production (bad breath)
- Kidney failure, cannot excrete H+ or conserve HCO3-
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Metabolic Alkalosis
- Decrease in H+ for non-respiratory reasons
- Vomiting loses H+ in vomitus
- Excess bicarbonate ingestion
- Decrease respiratory rate and retain H+ in kidneys in compensate
- H+ retention increases K+ loss
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