pH

Question 1

Why is maintaining pH in body fluids crucial for animals?

Answer 1

Abnormal H+ concentrations can influence protein function, change molecular conformation, and have serious functional consequences.

Question 2

How does pH vary with temperature in animals?

Answer 2

Neutral pH is higher at low temperatures and lower at high temperatures.

Question 3

What is the alphastat hypothesis?

Answer 3

It suggests that changes in pH with temperature help maintain a constant state of electrical charge on protein molecules.

Question 4

What are the main consequences of fluctuations in H+ concentration?

Answer 4

They include altered enzyme activity, disturbed K+ levels, and changes in excitability of nerve and muscle cells

Question 5

How do respiratory disturbances affect pH balance in animals?

Answer 5

High CO2 levels lead to respiratory acidosis, lowering pH due to increased H2CO3 in body fluids.

Question 6

What is environmental acidosis, and how does it affect marine life?

Answer 6

Environmental acidosis is the increase in H+ concentration in oceans, weakening shells and coral skeletons and affecting growth and survival.

Question 7

How do marine animals like corals respond to increased acidity?

Answer 7

Coral growth declines, and diversity drops in areas with increased acidity, as seen near volcanic CO2 seeps.

Question 8

What is the effect of ocean acidification on bivalve molluscs?

Answer 8

Acidic conditions slow larval growth and shell development, negatively impacting populations.

Question 9

How do echinoderms like sea urchins respond to pH changes?

Answer 9

Slight pH decreases can block their egg metabolism, affecting development and fitness.

Question 10

What is the effect of pH changes on fish like walleye pollock?

Answer 10

Increased acidity causes them to use more energy for bicarbonate buffering, potentially harming growth.

Question 11

What are the three lines of defense against changes in H+ concentration?

Answer 11

Chemical buffer systems, respiratory mechanisms, and excretory mechanisms.

Question 12

What are the four buffer systems in vertebrates?

Answer 12

The four buffer systems are CO2-HCO3− buffer system, peptide and protein buffer system, hemoglobin buffer system, and phosphate buffer system.

Question 13

Why is the CO2-HCO3− buffer system effective in the extracellular fluid (ECF)?

Answer 13

It is effective because HCO3− is abundant in the ECF, and both HCO3− and CO2 are closely regulated by the kidneys and respiratory system.

Question 14

What is the role of hemoglobin (Hb) as a buffer?

Answer 14

Hemoglobin buffers H+ generated from CO2 in transit between tissues and the lungs or gills, binding H+ at systemic capillaries and releasing it at respiratory organs to form CO2.

Question 15

How does the phosphate buffer system function in the intracellular fluid (ICF)?

Answer 15

It consists of Na2HPO4 and NaH2PO4, which donate or accept H+ to buffer pH changes, primarily in the ICF and urine.

Question 16

How do respiratory mechanisms regulate pH?

Answer 16

By altering ventilation to control CO2 exchange in the lungs or gills, which in turn affects H2CO3 levels in body fluids.

• increase of ventilation typically results in an increase of pH
• why?
• it Leads to decrease of CO2 level

Question 17

What happens when arterial pH decreases in air-breathing vertebrates?

Answer 17

The respiratory center in the brain stem is stimulated to increase ventilation, reducing CO2 and H2CO3 in the body fluids.

Question 18

How do fish primarily handle acid loads?

Answer 18

Fish primarily handle acid loads through membrane transporters rather than changes in ventilation.

Question 19

What is the role of excretory organs in pH regulation?

Answer 19

Excretory organs remove H+ from the body and reabsorb HCO3−, contributing to long-term pH balance.

Question 20

What mechanisms do fish gills use for H+ excretion?

Answer 20

Fish gills use H+-ATPase, V-ATPase, and Na+/H+ antiport for H+ excretion.

Question 21

How do mammalian kidneys regulate pH?

Answer 21

Mammalian kidneys regulate pH by adjusting H+ excretion, HCO3− reabsorption, and ammonia (NH3) secretion.

Question 22

What is the function of Type A intercalated cells in the kidneys?

Answer 22

They secrete H+ into the tubular lumen via H+/K+-ATPase and H+-ATPase pumps, contributing to acid-base balance.

Question 23

How is renal HCO3− reabsorption linked to H+ secretion?

Answer 23

Secreted H+ combines with filtered HCO3− to form H2CO3, which breaks down into CO2 and H2O, allowing CO2 to be reabsorbed and form new HCO3−.

Question 24

What are the primary transport mechanisms in the proximal tubule?

Answer 24

The primary transport mechanisms include primary active transport via H+-ATPase pumps and secondary active transport via Na+/H+ antiporters.

Question 25

How does the Na+/H+ antiporter function in the proximal tubule?

Answer 25

The Na+/H+ antiporter exchanges Na+ ions from the filtrate with H+ ions from the tubule cells, contributing to H+ secretion and Na+ reabsorption.

Question 26

What role does H+-ATPase play in the proximal tubule?

Answer 26

H+-ATPase actively transports H+ ions into the tubular lumen, aiding in acid-base balance by secreting H+.

Question 27

How is bicarbonate (HCO3−) reabsorbed in the proximal tubule?

Answer 27

H+ ions secreted into the lumen combine with filtered HCO3− to form H2CO3, which then breaks down into CO2 and H2O. CO2 diffuses back into the tubule cells, where it is converted back to HCO3− and reabsorbed.

Question 28

What enzyme is involved in the reabsorption of bicarbonate in the proximal tubule?

Answer 28

Carbonic anhydrase, specifically isoform IV in the lumen and isoform II inside the tubule cells, catalyzes the conversion of H2CO3 to CO2 and H2O.

Question 29

What types of transporters are found in the distal tubule?

Answer 29

The distal tubule contains transporters such as H+/K+-ATPase and H+-ATPase pumps in Type A intercalated cells.

Question 30

What is the function of Type A intercalated cells in the distal tubule?

Answer 30

Type A intercalated cells actively secrete H+ into the tubular lumen via H+/K+-ATPase and H+-ATPase pumps, helping to regulate acid-base balance.

Question 31

How does H+/K+-ATPase function in the distal tubule?

Answer 31

H+/K+-ATPase exchanges H+ ions from the tubule cells with K+ ions from the tubular lumen, facilitating H+ secretion and K+ reabsorption.

Question 32

How does the H+-ATPase pump work in the distal tubule?

Answer 32

The H+-ATPase pump actively transports H+ ions into the tubular lumen, contributing to the acidification of urine and maintaining systemic pH balance.

Question 33

How is bicarbonate reabsorbed in the distal tubule?

Answer 33

In the distal tubule, secreted H+ combines with filtered HCO3− to form H2CO3, which is then converted to CO2 and H2O. CO2 diffuses into the tubule cells, where it is converted back to HCO3− and reabsorbed.

Question 34

What role does carbonic anhydrase play in the distal tubule?

Answer 34

Carbonic anhydrase facilitates the conversion of H2CO3 to CO2 and H2O in the tubular lumen and the conversion of CO2 back to HCO3− in the tubule cells.

Question 35

What are the main differences in transport mechanisms between the proximal and distal tubules?

Answer 35

The proximal tubule primarily uses Na+/H+ antiporters and H+-ATPase for H+ secretion and HCO3− reabsorption, while the distal tubule relies on H+/K+-ATPase and H+-ATPase pumps in Type A intercalated cells for these processes.

Question 36

Why is the regulation of H+ secretion important in both the proximal and distal tubules?

Answer 36

Regulation of H+ secretion is crucial for maintaining acid-base balance, preventing acidosis or alkalosis, and ensuring proper reabsorption of bicarbonate.

Question 37

How do transporters in the proximal and distal tubules contribute to overall kidney function?

Answer 37

These transporters play key roles in acid-base homeostasis, electrolyte balance, and the excretion of metabolic waste products, supporting the kidney's role in maintaining systemic homeostasis.