Gas Exchange and Respiratory Control

Describe the mechanisms for gas transport and exchange (both CO2 and O2).

CO2: Chloride Shift which is an antiport which exchanges bicarbonate which pumps most of the HCO2 out of the RBC in exchange for a Cl from the blood plasma. This bufferes the intracellular pH Aerobic respiration produces a molecule of CO2 for every molecule of O2 that it consumes. The tissue fluid is therefore contains a relatively high PCO2. The change in partial pressure from the alveoli (high concentration) to the capillaries (low concentration) drives the oxygen into the tissue and the carbon dioxide into the blood (high concentration) from the tissues (low concentration), which is then returned to the lungs and exhaled. CO2 + H2O <-Carbonic Acid-> H2CO3 <-> H+ + HCO3 Which is catalyzed by carbonic anhydrase O2 is transported by partial pressure gradients

Describe what happens to O2 and CO2 in the alveoli and tissues.

O2: Hemoglobin binds to O2 in the alveoli and releases it into the tissues and binds to the CO2 in the tissues to then bring into the lungs.

Describe the function of hemoglobin.

Oxyhemoglobin when bound to Oxygen CO2 + Hb = Hb CO2 easily reversed Carbanimohemoglobin- attractionf of CO2 to hemoglobin

Identify the conditions that cause changes in hemoglobin affinity for oxygen.

Right Shift: less affinity of O2. Which means greater release. You'd want this in the tissues. Increase in pH and an increase of temperature Left shift: more affinity you'd want this in the lungs. O2 magnet. lesser release. Also caused by in an increase in pH and an increase in temperature.

Explain the significance of Dalton's and Henry's laws to gas exchange.

Dalton's Law: THe total atmospheric pressure is a sum of the contributions of indiviual gases (&8.6% nitrogen, 20.9% oxygen, 0.04% CO2. The seperate contribution of each gas in a mixture is called its partial pressure and is symbolized with a P. the atomspher is about 760 mm Hg. Air in the alveolus is in contact with the film of water covering the alveolar epithelium. for O2 to get to the blood it must dissolve in this water and pass through the respiratory membrane separating the air from the blood stresam. For CO2 to leave the blood it must pass the other way and diffuse the water film into the alveolar air. This back and forth traffic of O2 and CO@ across the respiratory membrane is called the alveolar gas exchange. The reason the O2 can dffuse in one direction and CO2 in the other is that each gas diffuses down its own partial pressure gradient. Henry's Law: That at air-water interface for a given temperature the amount of gas that dissolves in the water is determined by its solubility in water and partial pressure in the air. Thus the greater the PO2 in tthe alveolar air the more O2 the blood picks up. And since the blood arriving iat an alvelous has a higher PCO2 than air it release CO2 into the alveolar air. At the alvelous the blood is said to unload CO2 and load O2.

Explain the significance of the oxygen-hemoglobin saturation curve, and describe conditions that alter it.

Has an s-shape due to the increased hemoglobin affinty for oxygen with each moecule bound. Areas of the curve with a steep slope have large changes in Hb saturation with small changes in plasma PO2 Left shift: Decrease in temp. Decrease in DPG, INcrease pH ( decreased H+ ions) Decrease O2 offload to tissues Right Shift: Increase In Temp, Increase in DPG, Decrease pH (increase H+ ions) Hemoglobine Affinity for O2 decreases. Increase O2 offload in tissues. Fetal hemoglon also shifts the curve to the left.

Explain how respiration is regulated to meet changing demands.

Self regulating system: As blood PO2 falls more O2 is released. Say to due increased metabolism. Oxygen store even in venous blood. Exercise: Increased Breathing. When the brain sends motor commands to the muscles (via the lower motor neuron of the spinal cord) it also sends this information to the respiratory centers, so the increase pulmonary ventilation in anticipation of the needs of the exercising muscle. 2. Excericise stimulates proprioceptors of the muscles and joings and they transmet excitatory signals to the brainstem respiratory centers. Thus the respiratory centersincrease breathing because they aer informed that the muscles have been told to move or are acually moving. The increase in pulmonary ventilation keeps blood gas value at their normal levels inspite of the elevated O2 consumption and CO2 generation by the muscles. THe main chemical stimulus to pulmonary ventilation is the H+ in the CSF and the tissue fluid of the brain these hydrogen ions arise mainly from CO2 diffusing into the CSf and the brain and generating H+ through the carbonic aci reaction. Therefore the PCO2 of the arterial blood is an important driving force in respiration even though its action on the chemorecptors is indirect. Vetilation is adjusted to maitain arterial pH at about 7.4 and arterial PCO2 at about 40 mm Hg. This autu ensures that the blood is at least 97% saturated with O2 as well

Explain the significance of the shape of the oxygen-hemoglobin saturation curve.

The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second, third and fourth, this is due to the induced conformational change in the structure of the haemoglobin molecule induced by the binding of an oxygen molecule. In its most simple form, the oxyhemoglobin dissociation curve describes the relation between the partial pressure of oxygen (x axis) and the oxygen saturation (y axis). Hemoglobin's affinity for oxygen increases as successive molecules of oxygen bind. More molecules bind as the oxygen partial pressure increases until the maximum amount that can be bound is reached. As this limit is approached, very little additional binding occurs and the curve levels out as the hemoglobin becomes saturated with oxygen. Hence the curve has a sigmoidal or S-shape. At pressures above about 60 mmHg, the standard dissociation curve is relatively flat, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure. To get more oxygen to the tissue would require blood transfusions to increase the hemoglobin count (and hence the oxygen-carrying capacity), or supplemental oxygen that would increase the oxygen dissolved in plasma. Although binding of oxygen to hemoglobin continues to some extent for pressures about 50 mmHg, as oxygen partial pressures decrease in this steep area of the curve, the oxygen is unloaded to peripheral tissue readily as the hemoglobin's affinity diminishes. The partial pressure of oxygen in the blood at which the hemoglobin is 50% saturated, typically about 26.6 mmHg (3.5 kPa) for a healthy person, is known as the P50. The P50 is a conventional measure of hemoglobin affinity for oxygen. In the presence of disease or other conditions that change the hemoglobin's oxygen affinity and, consequently, shift the curve to the right or left, the P50 changes accordingly. An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity. The 'plateau' portion of the oxyhemoglobin dissociation curve is the range that exists at the pulmonary capillaries (minimal reduction of oxygen transported until the p(O2) falls 50 mmHg). The 'steep' portion of the oxyhemoglobin dissociation curve is the range that exists at the systemic capillaries (a small drop in systemic capillary p(O2) can result in the release of large amounts of oxygen for the metabolically active cells). To see the relative affinities of each successive oxygen as you remove/add oxygen from/to the hemoglobin from the curve compare the relative increase/decrease in p(O2) needed for the corresponding increase/decrease in s(O2).

Describe the ways that respiratory gases are carried in the circulatory system.

Two subunits of hemoglobin 2 alpha and 2 beta. Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule allowing each hemoglobin molecule to bind 4 oxygens. As a result oxygenated arterial blood where the Hb is carrying four oxygen molecules bright red, while venous blood is deoxygenated is darker. O2 is uploaded in the lungs and CO2 is uploaded in the tissues.

Identify the expected values of PCO2 and PO2 at various locations of the circulatory system under normal conditions.

Venous blood in exercise: 18 PO2 Normal Venous Blood PO2: 40 Normal Arteriole Blood PO2: 98 Alveolar Air PCO2: 40mmhg Deoxygenated blood systemic PCO2: 46mm hg Oxygenated Blood Systemic: 40mm Hg