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PA10315 > Acid base balance > Flashcards

Acid base balance Flashcards

1
Q

Why must H+ concentrations be regulated in the human body?

A

Metabolic reactions are highly sensitive to changes in pH.

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2
Q

What is the range of blood pH?

A

7.35-7.45

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3
Q

What is it called when blood pH is below what it should be?

A

Acidosis.

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4
Q

What is it called when blood pH is above what it should be?

A

Alkalosis.

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5
Q

What substances are a H+ ion input?

A

Fatty acids, amino acids, CO2, lactic acid and ketoacids.

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6
Q

What are H+ buffers in the body?

A

HCO3- ions in the extracellular fluid, proteins, haemoglobin, phosphates in cells and phosphates and ammonia in the urine.

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7
Q

What are the two main ways to output H+? (fast and slow)

A

Ventilation (fast) and renal (slow).

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8
Q

What does carbonic anhydrase do?

A

It catalyses the combination of carbon dioxide and water to form carbonic acid.

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9
Q

What is the equilibrium equation for the interconversion between carbon dioxide, water, carbonic acid and bicarbonate ions?

A

CO2 + h20 -> H2CO3 -> Hco3- + H+.

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10
Q

How can hyperventilation or hypoventilation affect the blood pH?

A

It can cause an excess of CO2 to be lost or too much CO2 to remain.

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11
Q

What are some of the tissues that carbonic anhydrase is expressed in?

A

Lung, kidney, eyes, intestine and red blood cells.

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12
Q

What other organisms express carbonic anhydrase?

A

Plants and corals.

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13
Q

What are the ways in which CO2 can be carried around the body?

A

Dissolved CO2 in the tissues/red blood cells, carbonic acid in the red blood cells. combined with haemoglobin as haemoglobinic acid.

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14
Q

What is the chloride shift?

A

When the pH is balanced (due to HCO3- and H+ ions) by chloride ions diffusing into the red blood cells when HCO3- diffuses out.

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15
Q

Why can the CO2 in the blood diffuse into the alveoli?

A

The concentration of CO2 in the blood is greater than in the alveoli, so there is a concentration gradient.

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16
Q

What happens to the H+ in the red blood cell?

A

It combines with HBo2 to form HbH and oxygen.

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17
Q

What are the two ways in which ventilation can be controlled?

A

Peripheral chemoreceptors located in the bifurcation of the common carotid artery and arch of the aorta. There are also central chemoreceptors in the medulla.

18
Q

Can CO2 get through the blood-brain barrier?

A

Yes.

19
Q

What do peripheral chemoreceptors respond to?

A

An increase in arterial H+ concentration due an increase in CO2.

20
Q

What do both central and peripheral chemoreceptors stimulate?

A

Medullar inspiratory neurons to create ventilation.

21
Q

What are non-CO2 dependent changes that occur in pH?

A

Increase in lactic acid.

22
Q

Why does H+ only activate the peripheral chemoreceptors?

A

They cannot pass the blood brain barrier.

23
Q

What happens if there is a decrease in the H+ concentration?

A

There is depression of peripheral chemoreceptor firing.

24
Q

How can the kidneys regulate H+ concentration?

A

They can alter plasma HCO3- levels.

25
Q

What happens when bicarbonate ions enter the nephron?

A

It is completely filtered but most of it will get reabsorbed in the PCT, loop of henle and cortical collecting duct. The collecting duct can also secrete HCO3-.

26
Q

What is the bicarbonate ions in the filtrate exposed to when it enters the nephron?

A

Renal carbonic anhydrase .

27
Q

What are the two types of carbonic anhydrase found in the kidney?

A

Intracellular - in kidney epithelial cells lining tubules and extracellular such as in the brush border surface.

28
Q

Why do filtered bicarbonate ions want to be reabsorbed?

A

So they can continue to be used as a buffer.

29
Q

What happens with the carbonic acid in the tubular epithelial cells?

A

It dissociates into HCO3- and H+. The H+ diffuses into the tubular lumen and combines with HCO3- which is then broken down into H2O and CO2. This CO2 can pass the membrane and diffuse back into the cell.

30
Q

How does HCO3- get from the tubular epithelial cell to the interstitial fluid?

A

It is transported by facilitated diffusion.

31
Q

What are the two ways that hydrogen ions can be excreted into the lumen from a PCT cell?

A

From ATPase and sodium proton pump.

32
Q

What happens to excreted H+ ions from a PCT cell?

A

It combines with bicarbonate to form CO2 and H2O.

33
Q

What is the purpose of the intracellular carbonic anhydrase on the basal lateral side?

A

It forms new carbonate ions that are transported out of this side to enter the blood.

34
Q

What happens in the case of acidosis?

A

The kidney excretes H+ and reabsorbs HCO3-. to increase the pH.

35
Q

What happens in the case of alkalosis?

A

The kidney excretes K+ and HCO3- and reabsorbs H+ to lower the pH.

36
Q

What happens when all of the filtered bicarbonate has been reabsorbed?

A

Additional buffering can be gained with new bicarbonate ions that are synthesized in the tubule cells, as long as there is a sink for hydrogen ions. In this case it is HPO42-. There is a net gain in HCO3-.

37
Q

What is the process that occurs when all of the filtered bicarbonate has been reabsorbed?

A

H2O and CO2 combine (with the presence of carbonic anhydrase) to form carbonic acid, which dissociates into H+ and HCO3-. The HCO3- enters the interstitial fluid, and the H+ combines with HPO42- to form H2PO4- , which is excreted.

38
Q

What is the other method in which new bicarbonate ions can be synthesised?

A

Catalysis of the amino acid glutamine. This is a non-CO2 dependent pathway.

39
Q

What happens when glutamine is broken down?

A

It forms HCO3- ions and NH4+.

40
Q

What happens to the NH4+ produced from the breakdown of glutamine?

A

It is exchanged for sodium into the tubular lumen and then excreted.

41
Q

What is the net result of the renal response to acidosis?

A

More HCO3- is added to blood and plasma and the bicarbonate is increased. The urine will be acidic.

42
Q

What is the net result of the renal response to alkalosis?

A

Plasma bicarbonate is decreased which compensates for the alkalosis. The urine will be alkaline.

PA10315 (47 decks)

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