Lecture 4: Acid-Base Balance

Question 1

why is the regulation of pH so important?

Answer 1

dentaturing of proteins eg. ATPases, enzymes, rna, dna

Question 2

what is the normal ph of blood

Answer 2

7.4

Question 3

define the terms acidocis and alkalosis

Answer 3

acidosis - excess addition of H+
alkalosis - excess removal of H+ ions from the body fluids

Question 4

What are the three mechanisms of pH control in the body?

Answer 4

1. chemical acid-base buffer systems of the body fluids
2. the respiratory center
3. the kidneys

Question 5

explain how the chemical buffers in the blood work

Answer 5

• seconds
• act like sponges
• immediately commbine with acid or base to prevent excessive changes in H+ concentration

Question 6

what are the three chemical buffer systems in the body?

Answer 6

1. phosphate buffer
2. bicarbonate buffer
3. proteins as intracellular buffers

Question 7

explain how the phosphate buffer works

Answer 7

• especially important in the tubular fluids of the kidneys becuase..
• phosphate usually becomes greatly concentrated in the tubules, thereby increasing the buffering power of the phosphate system
• the tubular fluid usually has a considerably lower pH than the extracellular fluid does, bringing the operating range of the buffer closer to the pK (6.8) of the system.
• main elements are H2PO4- and HPO4-
• very potent but restricted
  *** NaH2PO4 + NaOH–+ Na2HPO4 + H20.
• Na2HPO4 + HC1–+ NaH2PO4 + NaC1,**

Question 8

explain how the bicarbonate buffer works

look into the equations again - dont understand

Answer 8

• powerful
• the pH of the extracellular fluid is about 7.4, whereas the pK of the bicarbonate buffer system is 6.1. = 20 times as much of the bicarbonate buffer system in the form of HCO3– as in the form of dissolved CO2.
• For this reason, this system operates on the portion of the buffering curve where the slope is low and the buffering power is poor.
  * CO2 (g) + H2O (l) ↔ H2CO3 (aq) ↔ HCO3 –(aq) + H +(aq)
• NaHCO3 → HCO3- + Na+
  *
• 20NaHCO3 + H20 → 20Na + 20H2O + 20CO2

Question 9

explain how protein buffes work

Answer 9

• Approx 60 to 70 percent of total chemical buffering of body fluids is inside the cells by intracellular proteins.
• slowness with which H+ and HCO3– move through the cell membranes often delays for several hours the maximum ability of the intracellular proteins to buffer extracellular acid–base abnormalities.
• RBC exeptions, fast buffering

Question 10

what is the secondary line of attack in the buffering systems?

Answer 10

respiratory regulation of acid-base balance

Question 11

explain how respiration regulation alters the ph of the body

Answer 11

• increased H+ = increased alveolar ventilation = decreased PCO2 in extrracellular fluid and H+ conc back to normal

Question 12

Explain what happens when CO2 is retained in the body i.e holding your breath

Answer 12

carbon dioxide will react with water to form carbonic acid which can dissocate to form hydrogen ions and a hydrogen carbonate ion, results in lower ph

Question 13

explain the physiology of hyperventilating

Answer 13

Blowing off more Co2, less co2 in body, less co2 conversion to carbonic acid, less acid in body, body becoming more basic, ph is going up

Question 14

explain the three mechansims of kidney pH regulation

Answer 14

reabsorption of HCO3-
secretion of H+ ions
Producion of new HCO3-

Question 15

how does the kidney try to achieve in acid base regulation?

Answer 15

tries to absorb as much bicarbonate as possible because we are basic humans

note: bicarb that is secreted in the intestine is the excess bicarb in the body, maintains ph by absorbing bicarb, secrete h to maintain ph

Question 16

explain the process of secretion of H+

Answer 16

• apical: Na+ into cell, H+ to tubular lumen
• intracellular: h2co3 breaks down into co2, co2 diffuse passively into the cell
• intracellular: CO2 and water combine to formh2co3 via carbonic anhydrase, breaks down into HCO3- and H+
• basal: H+ to exchanger, bicarb to ECF retained via Na+ HCO3- cotransporter

Question 17

explain the active secretion of H+

Answer 17

• active removal of hydrogen using 1 ATP in intercalated cells specifically
• interstitial fluid/intracellular: CO2 diffuse into cell, process to HCO3- and H+
• H+ secreted into tuble by hydrogen ATPase, Cl- passively secreted alongside
• for each H+ secreted, an HCO3- is reabsorbed into blood

active secretion of H+ occurs when in an acidic environment too

Question 18

explain the addition of new HCO3- (1)

Answer 18

Sodium potassium ATPase - low sodium in cell

• Lumen: sodium phospahte buffer, na reabsorbed in exchange for hydrogen ion (secreted)
• H to phosphate buffer
• Product excreted out of body (naH2Po4)

CO2 diffuses into the cell, carbonic acid dissocates to HCO3- and H+
HCO3- then reabsorbed to the blood

Question 19

explain the addition of new HCO3- (2)

Answer 19

Glutamine enters the cell from the lumen or the blood and breaks down into two bicarbonates and two ammonia, ammonia is secreted and excreted out of the bodynas NH4Cl-. HCO3- is absorbed

Question 20

explain the role of aldosterone in acid base regulation

Answer 20

aldosterone increases sodium reabsorption, activates sodium hdyrogen exchanger secreting more H+ leads to reabsorption of HCO3- via CO2 reaction pathway

Question 21

what are the two ways of quantifying renal acid base excretion

Answer 21

1. Bicarbonate excretion is calculated as
   urine flow rate x urinary HCO3— concentration.
2. The amount of new HCO3— contributed to the blood at any given time is equal to the amount of H+ secreted that ends up in the tubular lumen with non— bicarbonate urinary buffers.

Question 22

explain what happens when you Increase H+ Secretion and HCO3- Reabsorption

Answer 22

↑ PCO2 ↑ H+
↓ Extracellular fluid volume
↑ Angiotensin II ↑Aldosterone
Hypokalemia

H+ secretion is coupled to Na+ reabsorption by the Na+-H+ exchanger in the proximal tubule and thick ascending loop of Henle. Therefore, factors that stimulate Na+ reabsorption, such as decreased extracellular fluid volume, may also secondarily increase H+ secretion.

Question 23

explain what happens when you Decrease H+ Secretion and HCO3-Reabsorption

Answer 23

↓ PCO2 ↓H+
↑ Extracellular fluid volume
↓ Angiotensin II ↓Aldosterone
Hyperkalemia