Respiratory Physiology II

• how is co2 removed from cells to diffuse into lungs?


  1) Cl- ions in plasma are transported out of RBC

  
  

  2) HCO3- ions are transported into of RBCs via transport proteins.

  
  

  3) HHb ⇌ Hb + H+

  
  

  4) HCO3- + H+ ⇌ H2CO3 ⇌ Co2 + water

  
  

  5) CO2 will diffuse into plasma, tissue fluid, then cells in alveoli
• how does buffering in the blood occur (from cells to blood)?

  1) Co2 diffuses out of the cell into tissue fluid, into plasma, and into RBC cytoplasm.

  
  

  2) Co2 + water ⇌ H2CO3 ⇌ H+ + HCO3-

  -> Bicarbonate buffer

  (reversible reaction to form H2CO3 is catalysed by carbonic anhydrase)

  
  

  3) the increase in H+, decreases PH and so Hb also acts as a buffer:

  H+ + Hb ⇌ HHb (haemoglobinic acid)

  -> this changes the structure of Hb encouraging it to dissociate from O2.

  
  

  4) HCO3- ions are transported out of RBCs via trabnsport proteins to maintain high concentration gradient for Co2.

  (this causes charge imbalance)

  
  

  5)Cl- ions in plasma are transported into RBC to maintain electrical imbalance (chloride shift)

  
• how is CO2 transported around the body?

  - 5-7% of the CO2 carried by venous blood is dissolved in the plasma.

  
  

  - (95-93% diffuses into RBCs):

  20-23% binds to Hb (HbCO2- carbamiohaemoglobin)

  70-75% is converted to bicarbonate ion (HCO3-).
• Most of the CO2 that enters the blood binds to Hb (HbCO2)

  
  

  TRUE/FALSE

  FALSE

  
  

  Most of the CO2 that enters the blood is transported to the lungs as HCO3- dissolved in the plasma.
• what is acidosis?

  pH below 7.35

  
  

  If blood PCO2 is elevated, haemoglobin cannot soak up all the H+ and excess H+ accumulate in the plasma, causing the condition known as respiratory acidosis
• what does high levels of CO2 (hypercapnia) cause?

  The pH disturbance known as acidosis.

  
  

  Extremes of pH interfere with hydrogen bonding of molecules and can denature proteins. Abnormally high PCO2 levels also depress CNS function, causing confusion, coma, or even death.
• is CO2 toxic if not removed from the body?

  Carbon dioxide is a by-product of cellular respiration and is

  potentially toxic if not removed from the body
• show fetal Hb vs adult Hb on graph

  The altered binding affinity is reflected by the different shape of the foetal HbO2 saturation curve.

  
  

  At any given placental PO2, oxygen released by maternal Hb is picked up by the higher-affinity foetal Hb for delivery to the developing foetus.

  
  

  (Shortly after birth, foetal Hb replaced with the adult form as new RBCs are made)

  
• what does the presence of gamma chains do to fetal Hb?

  it enhances the ability of fetal Hb to bind oxygen in the low-oxygen environment of the placenta.
• what is the structure fetal haemoglobin?

  two gamma protein chains in place of the two beta chains found in adult Hb.
• Changes in haemoglobin's structure also change its oxygen binding affinity.

  TRUE/FALSE

  TRUE
• what triggers an increase in 2,3-BPG production in red blood cells?

  Chronic hypoxia (extended periods of low oxygen i.e. ascent to high altitude and anaemia)
• how does 2,3-BPG alter the oxygen binding affinity of Hb?

  Increased levels of 2,3-BPG decreases the affinity of Hb for O2

  
  

  decreased levels of 2,3-BPG increases the affinity of Hb for O2

  
• what is a shift in the Hb saturation curve that results from a change in pH called?

  the Bohr effect.

  
• how does PCO2 alter the oxygen binding affinity of Hb?

  - if PCO2 increases, PH decreases and so decrease the affinity of Hb for O2

  
  

  - if PCO2 decreases, PH increases and so increases the affinity of Hb for O2

  
• how does temperature alter the oxygen binding affinity of Hb?

  if temperature increases, decrease the affinity of Hb for O2

  if temperature decreases, increases the affinity of Hb for O2

  
• how does PH alter the oxygen binding affinity of Hb?

  if PH decreases, decrease the affinity of Hb for O2

  
  

  if PH increases, increases the affinity of Hb for O2

  
• what happens to the graph if the affinity of Hb for O2 is increased?

  the O2-Hb saturation curve is shifted to the left.

  
• what happens to the graph if the affinity of Hb for O2 is decreased?

  the O2-Hb saturation curve is shifted to the right.

  
• what factors can alter the oxygen binding affinity of Hb?

  - PH

  - tempertaure

  - PCO2

  - 2,3-bisphosphoglycerate (2,3-BPG)
• how does the body have a built-in reserve capacity with a PO2 of 40 mmHg (an average value for venous blood in a person at rest)?

  Hb is still 75% saturated.

  So, at the cells, blood releases only one-fourth of the O2 it can carry. The O2 that remains bound serves as a reservoir that cells can draw on if metabolism increases.

  
  

  -> When metabolically active tissues use additional O2, their cellular PO2 decreases, and Hb releases additional O2 at the cells.
• what happens to the % saturation if PO2 falls further, to 40 mmHg?

  the percent saturation goes to 75%.
• what happens to the % saturation if PO2 is in the 40-20 mmHg range?

  the curve is even steeper.

  Hb saturation declines from 75 to 35%.
• what is the % saturation at normal alveolar and arterial PO2 (100 mmHg)?

  98% of the Hb is bound to O2.
• what does it mean if half the available binding sites are carrying O2?

  the Hb is 50% saturated

  
• what does it mean if all binding sites on all Hb molecules are occupied by O2

  molecules?

  the blood is 100% oxygenated/saturated with O2.

  
• what would happen to O2 transport at normal PO2 in blood with Hb?

  The RBCs with Hb are carrying 98% of the total O2 carrying capacity.
• what would happen to O2 transport at reduced PO2 in blood with Hb?

  Reduced PO2 in plasma and bound to RBCs.
• what would happen to O2 transport in the blood without Hb?

  that alveolar PO2 = arterial PO2

  (relies solely on the solubility of O2 in plasma)
• what is % of Hb saturation dependent on?

  - pCO2

  - PH

  - Temperature

  - 2,3-BPG
• what two factors does the amount of oxygen that binds to haemoglobin

  depend on?

  1.The PO2 in the plasma surrounding the red blood cells.

  2.The amount of Hb therefore, the number of potential Hb-binding sites available in the red blood cells.

  
• what is haemoglobin called when bound to O2?


  Hb bound to oxygen is known as

  oxyhaemoglobin (HbO2)
• what makes haemoglobin an effective oxygen carrier?

  - a tetramer with four globular protein chains, each centred around an iron-containing haem group.

  
  

  - the central iron atom of each haem group can bind reversibly with one O2 molecule.

  
  

  The Hb acts like a sponge, soaking up O2 from the plasma until the reaction Hb + O2 ↔ HbO2 reaches equilibrium.
• Oxygen is mostly transported by being dissolved in the plasma.

  TRUE/FALSE

  FLASE

  
  

  Less than 2% of all oxygen in the blood is dissolved.

  -> haemoglobin transports more than 98% of our oxygen
• what are the two ways oxygen is transported in the blood?

  1. The oxygen is dissolved in the plasma.

  2. The oxygen is bound to haemoglobin.

  
  

  total blood oxygen content =

  dissolved oxygen + oxygen bound to haemoglobin.
• how many times is co2 more soluble than o2?

  20x
• what does low solubility of oxygen mean?

  - we need oxygen-carrying molecules to transport

  oxygen in the blood.

  - it is affected greatly by increased diffusion distance (diffusion will be slower)
• CO2 relatively soluble in body fluids, so increased diffusion distance may not significantly affect CO2 exchange. TRUE/FALSE

  TRUE

  
  

  In some cases of pulmonary oedema, arterial PO2 is low but arterial PCO2 is normal because of the different solubilities of the two gases.
• what factors affect the movement of gas molecules from air into a liquid?

  1.The pressure gradient of the gas.

  2.The solubility of the gas in the liquid

  3.Temperature.

  (Because temperature is relatively constant in mammals, we can ignore its contribution)
• other than pulmonary edema, what else can cause alveolar flooding?

  leakage when alveolar epithelium is damaged, such as from inflammation or inhaling toxic gases.