Respiratory System 6.4 & D6

Partial Pressure Partial pressure: the pressure exerted by each component in a mixture. The pressure of a gas in a mixture is the same as the pressure it would exert in the same volume and temperature alone.

Oxygen Dissociation Curves Oxygen binds to hemoglobin of erythrocytes. (oxyhemoglobin HbO2) Each hemoglobin can bind a maximum of 4 molecules of oxygen (1 for each heme group) If the maximum number of oxygen molecules have attached, the hemoglobin is fully saturated.

When the pO2 is 100mmHg, the HbO2 is 100% (That means there are 4 O2 bonded to each hemoglobin molecule. See Fig 1, page 700

The amount of saturation of hemoglobin depends on the concentration of oxygen in the air pO2 depends on the concentration of oxygen in the air and the air pressure. If [O2] decreases, the pO2 decreases If air pressure decreases, pO2 decreases

Oxygen Dissociation Curve The pO2 in the lungs is high (~100mm Hg), which encourages hemoglobin to become saturated with pO2. The pO2 in the muscles is low (~20 mm Hg) which encourages pO2 to dissociate from hemoglobin and enter the cells where they are needed.

High Altitudes At higher altitudes, the air pressure decreases, and so does the pO2. The means that the saturation of hemoglobin is lower i.e.: less oxygen bonded to hemoglobin and therefore less oxygen transported by the rbcs

The reduced air pressure also reduces the rate of diffusion of gases across the respiratory membrane As a result, less oxygen is available for the body cells This can cause altitude sickness SYMPTOMS: shortness of breath, headaches, dizziness, tiredness, nausea, alkalemia (high blood pH)

Your body will adjust after a few days. Increase ventilation rate (shallower, more frequent breaths The kidneys will excrete akaline urine (blood remains acidic, continues increased ventilation rate) Over time, when O2 supply is reduced, the body will secrete the hormone erythropoietin (EPO) which will increases the number of red blood cells in the body.

An increase in rbc, means and increase in O2 absorption, which means more O2 for the body cells. People who permanently live at high altitues will also have a greater lung surface area and larger vital capacity than those living at sea level.

Altitude and Athletic Training Endurance athletes (long-distance runners and triathletes) often train at high altitudes for a few weeks to increase their rbc so they have more O2 and therefore more ATP energy for their event

Sea Level At sea level, air pressure is 760 mm Hg ~21% oxygen pO2 = 0.21 x 760 = 159 mm Hg pO2 of air in the alveoli is ~100 mm Hg Because… water vapour added, and pO2 in active muscles is ~20 mm Hg

Oxygen Dissociation Curve Sigmoid shaped curve (S-shape) Caused by cooperative binding When the first oxygen molecule binds, the hemoglobin changes slightly in shape This makes it easier for the next molecule to bind

Fetal Hemoglobin A pregnant mother and her unborn baby have separate circulatory systems The fetus’ hemoglobin must be capable of taking oxygen from the mother’s hemoglobin in the placenta.

Fetal hemoglobin Fetal hemoglobin (HbF) is structurally different from “normal” hemoglobin (HbA) This causes it to have a higher affinity for oxygen. So oxygen will dissociate from maternal hemoglobin and bind to fetal hemoglobin

Myoglobin When oxygen reaches the muscles, the oxygen is taken over and stored by myoglobin. Therefore, myoglobin must have a higher affinity for oxygen than hemoglobin

Myoglobin is made of 1 polypeptide chain (hemoglobin is made of 4) Therefore, only 1 heme group and therefore myoglobin can only bind one oxygen molecule. So no cooperative binding Curve is not sigmoidal

The Bohr Effect The pH of the blood is directly related to the CO2 concentration As CO2 in the blood increases, pH lowers (gets more acidic) Why?

WHY? Remember, 70% of CO2 is transported to the lungs as bicarbonate ions. The formation of bicarbonate produces H+ And an increase in H+ means a more acidic environment CO2 + H2O  H2CO3 (carbonic acid) H2CO3  H+ + HCO3- So more CO2 means more H+ which means more acidic environment (ie lower pH)!!!

The Bohr Effect Remember: A change in pH will change the ionization of a protein This will change the shape and functionality of the protein A lower pH will cause the oxygen dissociation curve of hemoglobin to shift to the right This is known as the BOHR SHIFT

Bohr Shift This means that the saturation of hemoglobin is reduced (does not hold on to O2 as well) Which means, that more O2 is released from the hemoglobin So increased CO2 concentration will reduce the saturation of hemoglobin and release more oxygen to the cells This is good because pH is lower when cells are respiring and need more O2 anyway!