Hemoglobin and Respiration Flashcards

Hemoglobin

• Hemoglobin is essential for gas transportation in the body within red blood cells.
• Red blood cells:
  • Made in red bone marrow.
  • Live for about 120 days.
  • Removed by the liver and spleen.
  • Each red blood cell contains over 200,000,000 hemoglobin molecules (Hb).
• Hemoglobin is a quaternary protein due to its four heme groups.
  • Each heme group has a central iron atom that can carry oxygen.
  • Four globin areas can carry carbon dioxide and hydrogen ions.
• Red blood cells contain carbonic anhydrase, which catalyzes the reaction:
  • H2O + CO2 \rightleftharpoons H2CO3 \rightleftharpoons H^+ + HCO_3^-
  • The enzyme converts poisonous carbonic acid into safer hydrogen ions and bicarbonate.
• Hemoglobin is sensitive to pH and temperature changes, affecting its affinity for oxygen, carbon dioxide, and hydrogen ions.

pH and Hemoglobin

• The pH between the lungs and the body differs, influencing hemoglobin's activity.
• External Respiration:
  • Temperature: Approximately 37°C.
  • pH: 7.4 (slightly more basic).
  • Occurs in the lungs.
  • Exchange of oxygen and carbon dioxide between air and lungs (alveoli to blood and blood to alveoli).
  • Oxygen dissolves in the moist lining of the alveoli.
  • Carbon dioxide diffuses out.
  • Gases diffuse down the concentration gradient, from high to low.
  • Blood returns with low oxygen levels and high carbon dioxide levels.
• Internal Respiration:
  • Temperature: Around 37°C (possibly slightly higher, e.g., 37.1-37.2°C).
  • pH range: 7.35 to 7.38.
  • Occurs at the cellular level.
  • Exchange of oxygen and carbon dioxide in systemic capillaries and tissues.
  • Oxygen moves into tissue fluid and then into cells.
  • Carbon dioxide diffuses out of cells into tissue fluid and then into the blood.

Oxygen Transport

• About 98% of oxygen is carried by the iron in the heme group of hemoglobin.
  • Each hemoglobin molecule can carry four oxygen molecules.
  • At a pH of about 7.4, hemoglobin loosely binds to oxygen.
  • Hb + O2 \rightleftharpoons HbO2 (Oxyhemoglobin)
• The remaining 2% of oxygen is carried in solution as O_2 aqueous (dissolved in blood plasma).

Carbon Dioxide Transport

• 60% of carbon dioxide combines with water to form carbonic acid (H2CO3), which breaks into hydrogen ions (H^+) and bicarbonate ions (HCO_3^-) with carbonic anhydrase.
• 30% of carbon dioxide binds with hemoglobin to form carbaminohemoglobin (HbCO_2).
• 10% of carbon dioxide is dissolved in blood plasma.

Carbon Dioxide Release from Red Blood Cells

• In the lungs (pH 7.4), carbaminohemoglobin releases carbon dioxide, which diffuses into the lungs.
• Oxygen binds to hemoglobin due to the favorable pH, and it is brought in and added to the red blood cells.
• In tissue fluid:
  • Carbon dioxide leaves the cells and enters the tissue fluid.
  • 10% dissolves in plasma.
  • The rest turns to carbaminohemoglobin and bicarbonate ions (60-70%).

Functions of Hemoglobin

• Carry oxygen:
  • Hb + O2 \rightleftharpoons HbO2 (Oxyhemoglobin)
• Carry carbon dioxide:
  • 27% of carbon dioxide binds with hemoglobin to form carbaminohemoglobin (HbCO_2).
• Act as a buffer:
  • Hydrogen ions attach to globin to form reduced hemoglobin (HHb).
  • The presence of some free hydrogen ions in the plasma lowers the pH from 7.4 to between 7.35 and 7.38.

External Respiration Details

• Temperature: ~37°C.
• pH: ~7.4.
• Oxygen enters the blood:
  • Hb + O2 \rightarrow HbO2
  • Oxygen is also carried as aqueous oxygen (dissolved in plasma).
• Carbon dioxide at the lungs:
  • Carbaminohemoglobin (HbCO_2) is transported to the lungs in the blood.
  • HbCO2 \rightarrow Hb + CO2
  • Aqueous carbon dioxide is released into the alveoli as carbon dioxide gas.
  • Hydrogen ions join with bicarbonate ions, and carbonic anhydrase breaks down carbonic acid into carbon dioxide gas, releasing water (H_2O).

Internal Respiration Details

• Temperature: ~37°C (possibly slightly higher).
• pH: Between 7.35 and 7.38.