Quiz 18
Hemoglobins' affinity for oxygen is directly related to how much oxygen is actually currently held by the hemoglobin. So, if hemoglobin has high oxygen saturation, hemoglobin's affininty for oxygen is high. What do you think happens to hemoglobin's affinity for oxygen after it moves through the systemic capillaries?
As the RBC moves through the systemic capillary, hemoglobin's affinity for oxygen decreases. - Hemoglobin is a protein molecule that behaves differently in different situations. When oxygen level changes, hemoglobin's affinity for oxygen changes. When oxygen is very abundant in the environment (high pO2), hemoglobin binds oxygen very tightly due to the way the molecule is shaped. When environmental oxygen is very low (low pO2), hemoglobin is shaped differently and does not bind oxygen as readily. In the case of the body, when hemoglobin travels through the pulmonary capillary it moves into a very high oxygen environment, causing it to have a high oxygen affinity. When the hemoglobin moves through the systemic capillary, it becomes exposed to a lower oxygen environment and then decreases its affinity for oxygen. This loss of affinity from a high state (bound with lots of oxygen) to a low state (less oxygen bound) causes oxygen to be released to the tissues.
What happens to hemoglobin's affinity for oxygen when blood becomes more acidic?
Hemoglobin's affinity for oxygen decreases - When the level of CO2 increases (or conditions become acidic or temperature increases), hemoglobin's affinity for oxygen decreases. This means that hemoglobin holds on to oxygen less tightly, thus releasing it more readily to a hungry tissue. This is also a right shift in the oxygen-hemoglobin dissociation curse and is beneficial because it allows more oxygen delivery for the same level of PO2. It would seem that this lower affinity of hemoglobin for oxygen would be bad because it would limit how much O2 could bind in the lung. But remember that hemoglobin is fully saturated at low levels of PO2 naturally (as low at 70 mmHg) and the high level of CO2 or H+ is erased at the pulmonary capillary when CO2 diffuses into the alveoli and is removed from the blood. So, while the hemoglobin curve shifts right when the hemoglobin is in the systemic capillaries, it shifts to the left again when the hemoglobin is in the pulmonary capillaries.
What happens to hemoglobin's affinity for oxygen when levels of CO2 increase?
Hemoglobin's affinity for oxygen decreases. - When the level of CO2 increases (or conditions become acidic or temperature increases), hemoglobin's affinity for oxygen decreases. This means that hemoglobin holds on to oxygen less tightly, thus releasing it more readily to a hungry tissue. This is also a right shift in the oxygen-hemoglobin dissociation curse and is beneficial because it allows more oxygen delivery for the same level of PO2. It would seem that this lower affinity of hemoglobin for oxygen would be bad because it would limit how much O2 could bind in the lung. But remember that hemoglobin is fully saturated at low levels of PO2 naturally (as low at 70 mmHg) and the high level of CO2 is erased at the pulmonary capillary when CO2 diffuses into the alveoli and is removed from the blood. So, while the hemoglobin curve shifts right when the hemoglobin is in the systemic capillaries, it shifts to the left again when the hemoglobin is in the pulmonary capillaries.
Which of the following occur when ATP production increases at the tissues?
More CO2 is produced in the RBCs at the pulmonary capillary - When the tissues begin making more ATP they also make more CO2 (by aerobic metabolism). That CO2 diffuses into the blood and causes more O2 to be offloaded because high CO2 decreases hemoglobin's affinity for O2 and thus more O2 is released to the tissues. More H+ ions are made and the hemoglobin can buffer them because they have given up more O2 and now can bind more H+ to form HHb. At the tissues, more HCO3- is made when CO2 production increases. The confusing part is that the HCO3- and HHb travel in the blood up to the lungs and in the pulmonary capillary, the H+ comes off of the HHb (as oxygen binds to Hb) and binds to the HCO3-. When this happens, CO2 and H2O are formed. SO, CO2 is made in RBC in pulmonary capillaries because that CO2 can then diffuse into the alveoli and be removed from the body. Albumin does not transport CO2.
What is the correct path of a red blood cell as it moves through the healthy kidney?
Renal artery - afferent arteriole - glomerulus - efferent arteriole - peritubular capillary - renal vein - inferior vena cava - Blood cells are not filtered into the Bowman's capsule. They remain within the walls of the blood vessels and so this question really just asks about the flow of blood through the kidney. This answer would be the same if the question asked What is the correct order for a sodium ion that is not filtered at the glomerulus or secreted into the tubule? Please review blood flow through the kidney using your lecture notes so that you know what vessels you are expected to know.
Where would you find hemoglobin that is 75% saturated with O2 in a healthy resting person?
Systemic veins & pulmonary arteries - During rest, tissue PO2 is 40 mmHg. Blood that loads oxygen in the pulmonary capillaries becomes fully saturated with O2 (hemoglobin saturated to maximum, effectively 100%). When blood arrives at the resting tissues and equilibrates, the blood achieves a PO2 of 40 mmHg. At 40 mmHg, hemoglobin is only 75% saturated (as determined by the oxygen-hemoglobin dissociation curve). Therefore, systemic venous blood is 75% saturated with oxygen. O2 does not leave the blood except at capillaries and so as blood flows through the heart from the systemic veins to the pulmonary arteries, no further oxygen is lost. Acordingly, pulmonary arterial blood has a PO2 =40 mmHg and also contains hemoglobin that is 75% saturated with oxygen.
Where does most reabsorption of the filtrate occur (most by total volume of the filtrate)?
The proximal convoluted tubule - Most of the filtrate is reabsorbed immediately in the proximal convoluted tubule. The remaining filtrate is reabsorbed along the Loop of Henle, DCT & collecting duct. The hormones ADH & aldosterone affect the amount of water and salt reabsorbed in the DCT & collecting duct. Even though most of the filtrate is reabsorbed by the time it reaches the DCT & collecting duct, the affect of ADH is significant enough to allow more water to be reclaimed and a very low volume, concentrated urine can be produced.
Think about the equation: HHb + O2 --> HbO2 + H+ when answering: The lower hemoglobin's affinity for oxygen, the more hemoglobin can prevent blood acidosis.
True - Affinity here refers to hemoglobin's greediness for oxygen. When affinity is high, hemoglobin binds oxygen tightly and does not release it. When affinity is low, hemoglobin releases oxygen readily. High levels of CO2, H+ ions (low pH) and high temperature cause shape changes in hemoglobin molecules that decrease hemoglobin's affinity for oxygen. When hemoglobin releases an oxygen molecule, it provides a binding site on the hemoglobin for an H+. Free H+ cause pH to decline - creating acidosis - but H+ bound to a protein cannot affect pH (the binding protein buffers against pH changes). Hemoglobin does just this - it binds a H+ when oxygen affinity is low and acts to prevent acidosis of the body.
In the pulmonary capillaries:
hydrogen ions combine with bicarbonate ions to form carbon dioxide and water - In the pulmonary capillaries oxygen loads into the blood and CO2 moves into the alveoli. CO2 is made in the systemic tissue mitochondria (there are no mitochondria in the RBCs) and transported away from tissue cells using the blood. Some CO2 dissolves in the plasma, some attaches to hemoglobin (NOT at the same binding site for oxygen) and the rest is converted to bicarbonate ions. The most conversion occurs inside RBCs where the enzyme carbonic anhydrase combines CO2 & water to create a hydrogen ion (H+) and bicarbonate ion (HCO3-). [Even though all the components of CO2 are found in bicarbonate ion, they are in the form of bicarbonate ion and not CO2.] The RBC then pushes bicarbonate out to the blood plasma and hemoglobin binds the H+. Some dissolved CO2 spontaneously combines with water to also make bicarbonate and H+ - acidifying the venous blood. The RBC then moves through the vascular tree up to the pulmonary capillaries. Once in the pulmonary capillaries, CO2 must move out of the blood into the alveoli for removal from the body. Bicarbonate ion cannot diffuse out of the blood into the alveolus, instead we need to "remake" CO2. To recreate CO2, bicarbonate ions combine with H+ and form CO2 and water in the RBC (also due to carbonic anhydrase). The CO2 then diffuses into the alveoli. The blood leaving the pulmonary capillary has less CO2 dissolved (because dissolved CO2 also moved into the alveoli) and therefore also has less free H+, making the pulmonary venous blood less acidic than the pulmonary arterial blood. O2 does not combine with water to make bicarbonate.
