mod 12

Question 1

Why important to regulate H conc

Answer 1

• H ions can alter shape of proteins that act as enzymes that speed up chemical reactions
  
  • Any change in conc of H will affect activity of almost every cell

Question 2

Hydrogen atom vs ion

Answer 2

• H atom - single proton, single electron = result is neutral element
  
  • H+ ion - is H atom that lost its electron, so only a single proton = positive charge
  • Sometimes H ion may be called a proton

Question 3

What are acids + bases

Answer 3

• Acid - molecule that will release H ions when put in a solution (e.g. HCL dissociates into free H ion and Cl ions)
  
  • Presence of free H ion makes solution more acidic
  • More free H = more acidic solution and vice versa
  • Strong acids disassociate v quickly and release lots of H ions
  • Base - any molecule that will accept a H ion (e.g. HCO3 aka bicarbonate, binds w H ion to make carbonic acid)
  • Bases lower the conc og free H by combining w it
    Less free H = acidity decreases & becomes more basic/ alkaline

Question 4

pH scale

Answer 4

• Low H conc - alkaline/ basic - high pH
  
  • High H conc - acidic - low pH
  • pH scale tells conc of H in solution
  • Is negative logarithm (to the base 10) of H ion conc
  • Since neg log, more free H = lower pH
  • pH = -log 10 [H+]
  • 7 is water/ neutral, scale is 0-14, below 7 is acidic, above 7 is basic

Question 5

pH in body

Answer 5

• pH body fluids is avg 7.4, so slightly alkaline
  
  • Arterial blood is 7.45
  • Venous blood is 7.35
  • Acidosis - when pH of body fluid is below 7.4
  • Alkalosis - pH body fluids above 7.4
  • If pH is below 6.8 or above 7.8 for long period = death

Question 6

Source of acid in body

Answer 6

• Cells make ATP, they have CO2 as byproduct
  
  • Respiratory system + enzyme carbonic anhydrase - combine CO2 and water in RBC to make carbonic acid (H2CO3)
  • This carbonic acid disassociates into free H and bicarbonate ions (HCO3-)
  • Then in lungs, reaction reverses, carbonic acid reforms and converts to CO2 and H2O, then CO2 is exhaled
  • So, no NET increase in free H in plasma
  • Volatile acid - carbonic acid (bc reforms into CO2)
  • Non-volatile acids - hydrochloric acid, lactic acid, sulphuric acid
    ○ Non-volatile bc cannot be removed by lungs

Question 7

Regulation of H ion conc

Answer 7

• Body regulates free H conc by buffers, respiratory system, kidneys
  
  • Buffers - bind free H; reacts almost immediately, body’s first line of defense - do not remove H from body nor do they alter pH, they just bind up free H, which stabalizes pH until balance can be reestablished by next 2 systems
  • Respiratory system - regulates H conc from volatile acids from seconds to minutes
  • Kidneys - respond more slowly (hours, days) - powerful control over H conc, particularly from nonvolatile acids

Question 8

Regulation of H conc - buffers

Answer 8

• Buffer any molecule that reversibly binds (or release) free H = reduces amount of free H and stabilizes pH
  
  • X + H+ = XH
  • Do not prevent pH from chaning, they just minimize pH change until free H can be removed from body by lungs/ kidneys
  • e.g. bicarbonate ions, hemoglobin
  • Intracellular buffers - phosphates, intracellular proteins (eg hemoglobin)
  • Extracellular buffers - bicarbonate ions (HCO3-)
  • Hemoglobin binds w free H to fix acidity in RBCs, also can bind w CO2 to reduce potential acidity if CO2 binds w H2O to make carbonic acid

Question 9

Regulation of H conc - respiratory system

Answer 9

• Regulates CO2 levels (and thus pH) by central and peripheral chemoreceptors
  
  • CO2 lvls inc = receptors detect change, cause increase in ventilation
  • Increased ventilation = more CO2 exhaled = returns blood CO2 lvls to normal

Question 10

Regulation of H conc - kidneys

Answer 10

• Nonvolatile acids always being produced + need to be excreted to keep pH at 7.4
  
  • They do this by:
    ○ Excreting H that come from nonvolatile acids
    ○ Attempt to reabsorb all bicarbonate ions that are filtered at glomerulus
    ○ Create new bicarbonate ions which then get reabsorbed into circulation
  • 90% of bicarbonate filtered at glomerulus is reabsorbed at proximal tubule
  • For every bicarbonate reabsorbed, one H secreted
  • Bicarbonate cannot be reabsorbed by tubule cells, need to turn into CO2, which is reabsorbed
  • H ions also secreted in late distal tubule and collecting duct by active transport using ATP powered hydrogen ion pump
  • ATP pump is on luminal side of tubule cells + secretes 1 H for every ATP consumed
  • Pump responsible for only 5% of total H in filtrate, but is extremely important for making acidic urine
  • The CO2 for this comes from cell itself or interstitial fluid

Question 11

Acidosis vs Alkalosis

Answer 11

• Acidosis - blood pH below 7.4 (is acidic); too much acid (H) or too little bicarbonate
  
  • Alkalosis - blood is alkaline/ basic, above 7.4; too little acid (H) or too much bicarbonate
  • 2 types of acidosis: respiratory acidosis, metabolic acidosis
  • 2 types of alkalosis - respiratory alkalosis, metabolic alkalosis

Question 12

Respiratory acidosis + alkalosis

Answer 12

• Resp acidosis - caused by decreased ventilation + increased PCO2, can happen if respiratory centers in brain stem are damaged, or from lung damage resulting in decreased ability to remove CO2 from blood; counteracted by buffers in blood + excretion of excess H by kidney
  
  • Resp alkalosis - caused by increase in ventilation and decreased PCO2, can be caused by stress or emotionally induced hyperventilation
  • Hyperventilation will result in more removal of CO2 from blood causing decrease in PCO2
  • High altitudes can cause resp alk bc low oxygen causes low PO2 in blood which stimulates hyperventilation
  • Is compensated for by excretion of bicarbonate from kidney

Question 13

Metabolic acidosis + alkalosis

Answer 13

• Meta acidosis - caused by lots of things that result in decrease in extracellular bicarbonate ions; does not involve increased CO2 lvls in blood
  
  • Causes are:
    ○ kidney failure resulting in inability to excrete acids in urine or reabsorb bicarbonate from filtrate
    ○ Formation of excess metabolic acids in body
    ○ Ingestion of acids (aspirin, methyl alcohol)
    ○ Loss of bicarbonate in diarrhea (most common cause)
  • Meta alkalosis - caused by buildup of bicarbonate or loss of H from body; most common cause is loss of HCl from stomach from vomiting; can also be caused by ingestion of alkaline drugs (e.g. sodium bicarbonate for fixing ulcers)