RESPIRATION Internal vs. external

External and internal respiration During external respiration in the lungs, CO2 leaves the blood and O2 enters the blood. During internal respiration in the tissues, O2 leaves the blood and CO2 enters the blood. External Respiration: At the pulmonary capillaries, O2 enters red blood cells where it combines with hemoglobin (Hb) to form oxyhemoglobin (HbO2). Also, bicarbonate (HCO3-) is converted inside red blood cells to H2O and CO2. CO2 leaves red blood cells and capillaries and diffuses into the lungs to be exhaled. Internal Respiration: At the systemic capillaries, oxyhemoglobin (HbO2) inside red blood cells gives up its oxygen and becomes Hb and O2. Hemoglobin (Hb) now combines with H+ to form reduced hemoglobin (HHb). O2 leaves red blood cells and capillaries and enters tissue cells. At the same time, CO2 enters red blood cells. Some combines with Hb to form carbaminohemoglobin (HbCO2). Most CO2 is converted to bicarbonate (HCO3-), which is carried in the plasma.

External Respiration = Lungs Pulmonary Capillaries

Internal Respiration = Systemic Capillaries Body Tissue

The Biochemistry of Internal Respiration Check It Out !

Internal Respiration Internal respiration is the diffusion of O2 from systemic capillaries into tissues and CO2 from tissue fluid into systemic capillaries. Oxyhemoglobin gives up O2, which diffuses out of the blood and into the tissues because the partial pressure of O2 of tissues fluid is lower than that of the blood.

Dealing With CO2 About 9% of CO2 molecules end up dissolving in blood plasma and hitch a ride in the plasma back up to the lungs. About 27% of CO2 molecules attach themselves onto Hemoglobin (Hb) to form a new combined form of Hemoglobin called CARBAMINOHEMOGLOBIN (HbCO2) The majority (64%) of CO2 given off by cells must undergo a chemical reaction. This chemical reaction occurs inside Red Blood Cells (erythrocytes). The end product is BICARBONATE IONS. CO2 + H2O  H2CO3  H+ + HCO3- Carbonic Acid Hydrogen Bicarbonate Ion Ion An enzyme called Carbonic Anhydrase found inside RBC’s, will run this reaction

THE REACTION ! Know It ! Live It ! BREATHE It ! - Become One with the REACTION ! Carbon Dioxide Water Carbonic Acid Hydrogen Ion Bicarbonate Ion

Hemoglobin (Hb) – “MASTER CARRIER” Hemoglobin can alter shape to pick up and transport three key molecules/ions: OXYGEN – Oxyhemoglobin (HbO2) CARBON DIOXIDE – Carbaminohemoglobin (HbCO2) HYDROGEN IONS – Reduced Hemoglobin (HHb)

How Does Hemoglobin Do This ? Hemoglobin is a protein. What happens to proteins when we change the pH they are in or change the temperature of their environment? Lungs TISSUES Temperature around bodily tissues is slightly warmer, and pH is slightly lower – 6.9 Temperature around lungs is cooler, pH is slightly higher – 7.4

Saturation of Hb relative to temperature The partial pressure of oxygen (PO2) in pulmonary capillaries is about 98-100 mm Hg, but in tissue capillaries is only about 40 mm Hg. Hemoglobin is about 98% saturated in the lungs because of PO2, and also because the temperature is cooler (and pH is higher in the lungs). On the other hand, hemoglobin is only about 60% saturated in the tissues because of PO2, and also because the temperature is warmer (and pH is lower) in the tissues.

Saturation of Hb relative to pH Hemoglobin is about 98% saturated in the lungs because of PO2, and also because pH is higher in the lungs (and temperature is cooler). On the other hand, hemoglobin is only about 60% saturated in the tissues because of PO2, and also because the pH is lower (and temperature is warmer) in the tissues.

Binding Capacity of Hemoglobin The partial pressure of gases, temperature, and pH affect binding capacity of hemoglobin. The high pressure of oxygen, the low temperature and low pH aid the binding of oxygen to hemoglobin in the lungs; the opposite is true in the tissues. In both cases, environmental conditions are favorable to the uptake of the appropriate gases. Hemoglobin is about 98-100% saturated in the capillaries of the lungs and about 60-70% saturated in the tissues. During exercise, muscle contraction raises temperature (up to 103oF) and lowers pH (due to accumulation of lactic acid), decreasing hemoglobin saturation further in the tissues.

After CO2 diffuses from tissue cells into the blood, it enters red blood cells where a small amount is taken up by hemoglobin, forming carbaminohemoglobin – approx 25%-30% of CO2 Most of the CO2 combines with water to form carbonic acid (H2CO3), which dissociates to release hydrogen ions (H+) and bicarbonate ions (HCO3-); the enzyme carbonic anhydrase speeds this reaction.

The globin portion of hemoglobin combines with excess hydrogen ions to become reduced hemoglobin or HHb; this helps maintain a normal blood pH. So Hemoglobin acts as a BUFFER to help buffer blood. Blood leaving capillaries is a dark maroon color because red blood cells contain reduced hemoglobin.

External Respiration Individual gases exert pressure proportional to their portion of the total in a mixture of gases; this is called “partial pressure”. External respiration is the diffusion of CO2 from pulmonary capillaries into alveolar sacs and O2 from alveolar sacs into pulmonary capillaries. The principles of diffusion alone govern whether O2 or CO2 enters or leaves the blood in the lungs and in the tissues.

In both cases, diffusion occurs because the partial pressures are higher causing diffusion (from higher to lower concentrations) across the capillary wall. Most CO2 is carried as bicarbonate ions. Approx 65%-70% The enzyme carbonic anhydrase, in red blood cells, speeds up the conversion of bicarbonate and H+ to H2O and CO2; CO2 enters alveoli and is exhaled. Hemoglobin (Hb) takes up oxygen from alveoli and becomes oxyhemoglobin (HbO2). Because the lungs are cooler and the pH is higher, the reaction below runs to the left. H2O + CO2 H2CO3   H+ + HCO3- The reaction takes place inside erythrocytes and performed by the same enzyme – CARBONIC ANHYDRASE