lecture 17 - respiratory system 4 Flashcards
transport of gases in blood
oxygen diffusion
enters blood from the alveoli moving from high to low concentration
in arterial blood it travels to the tissues where it diffuses into the cells
carbon dioxide diffusion
made in the tissues
much lower gradient - sufficient to drive the transfer
dropped off at the lungs
what does oxygen do after moving out of the alveoli?
moves into the plasma - some remains dissolved but most moves into RBCs where its bound to haemoglobin
RBCs move around the body until it reaches an area where its needed
what happens when haemoglobin reaches an area where oxygen is needed?
haemoglobin and oxygen dissociate
O2 is released and dissolves back into plasma and moves into the cells where its required
O2 carrying capacity of haemoglobin can be modified to match O2 delivery to demand
what is the maximum saturation we find in the lungs?
100 mmHg of PO2
doesn’t ever quite reach 100% saturation
what does a oxygen dissociation curve tell us?
at high PO2 there is very little change in the saturation for a big change in O2
• lung concentrations of O2
at low PO2 there is a steep relationship
• small changes have a big effect on saturation
• tissue concentrations of O2
what does the steepness of an O2 dissociation curve tell you?
speed - has to be a quick reaction to unload O2 quick enough
haemoglobin in the lungs and arterial blood
fully saturated
haemoglobin at rest
PO2 arterial blood: 100mmHg
PO2 tissue level: 40mmHg
25-30% of O2 dissociates from HbO4 - rest of it stays bound and goes back to the lungs
large carrying capacity
haemoglobin during exercise
PO2 arterial blood: 100mmHg
PO2 tissue level: 15-40mmHg
85% O2 dissociated from HbO4
exercise increases cellular respiration which increases CO2 and H+ production - pH decreases
effect of PCO2 on O2 saturation curves
increased PCO2 moves curve to the right
decreases moves it to the left
effect of pH on O2 saturation curves
if you increase pH curve moves to the left
• decrease H+
if you decrease pH curve moves to the right
• increase H+
what does a shift to the left on an O2 dissociation curve show?
shows a higher binding affinity
O2 is bound more tightly so stays associated longer
what does a shift to the right on an O2 dissociation curve show?
shows a lower oxygen binding affinity
haemoglobin is more likely to drop O2 off
process of CO2 diffusion into RBCs
1) CO2 in plasma diffuses into RBC where it reacts with H2O to make carbonic acid by carbonic anhydrase
2) carbonic acid dislocates into H+ and HCO3-
3) HCO3- diffuse out into plasma
4) negative moves out so Cl- moves in to keep charge balance
5) H+ displaces oxygen from haemoglobin to release O2
what is Cl- moving in called?
chloride shift
what is the Bohr effect?
Hb•4O2 + H+ –> HHb+ + 4O2
describes the reduction in oxygen affinity of haemoglobin when pH is low and the increase in affinity when the pH is high
what forms does haemoglobin exist in?
tense
relaxed
binding of H+ to the global chains of haemoglobin favours the tense formation
tensed haemoglobin
deoxygenated
global chains are tightly packed and pockets are narrowed necked so oxygen can’t get in
once 1 oxygen binds, it causes a conformational change and opens up the spaces slightly
pockets open and allow oxygen in
cooperative binding of oxygen
relaxed haemoglobin
oxygenated
effect of temperature on O2 dissociation curves
increase in temperature • increased O2 release at any one PO2 • curve moves to right • decreased affinity • decreased O2 binding
decrease in temperature • decreased O2 release at any one PO2 • curve moves to left • increased affinity • increased O2 binding
exercise increases core temperature - increase oxygen delivery to the muscles
effect of 2,3-DPG on O2 saturation curve
LONG TERM ADAPTATION
important adaptive mechanism to match O2 demand to delivery
2,3-DPG produced by RBCs interacts with beta chains of haemoglobin causing a conformational change which promotes dissociation of oxygen
at any PO2 more O2 is released from Hb in the presence of 2,3-DPG
improves O2 delivery to tissues which might otherwise become hypotonic
how do RBCs produce 2,3-DPG?
don’t have mitochondria so no oxidative mechanism or ATP production
produce energy by glycolysis - 2,3-DPG is a side product of glycolysis
anaemia and O2 saturation curve
total oxygen content of blood is reduced - less Hb
O2 curve shifts to the right
• O2 easily dissociates from Hb - reduced saturation point
• occurs at high PO2 than normal
• due to increased 2,3-DPG concentration
factors that affect O2 dissociation curve
C - CO2 A - acid or anaemia D - diphosphoglycerate E - exercise T - temperature
increase in any of them causes a shift to the right
foetal haemoglobin
curve shifts left
made of 2 alpha and 2 gamma globins
has a higher affinity for O2 than maternal Hb
not affected by 2,3-DPG as has no beta chains
what 3 ways are CO2 transported by in the blood?
dissolved in plasma
bound to Hb
as HCO3 in plasma
CO2 dissolved in plasma
7%
CO2 has a high solubility in plasma
CO2 bound to Hb
23%
CO2 + Hb = carbaminohaemoglobin
CO2 as HCO3 in plasma
70%
CO2 + H2O –> H2CO3 –> HCO3 + H+
HCO3 exits RBC in exchange for Cl- anion (chloride shift)
what happens if tissue [CO2] is higher than [CO2] in blood?
CO2 + H2O –> H2CO3 –> HCO3 + H+
results in bicarbonate and hydrogen ion formation
what happens if blood [CO2] is higher than [CO2] in alveoli?
CO2 + H2O
carbon monoxide and Hb
CO binds tightly but reversibly to the iron in Hb forming carboxyhemoglobin
affinity of Hb for CO is 200x than of O2
2 effects of CO on O2 dissociation curves
limits the amount of oxygen than haemoglobin can carry
• competes for Hb molecule
• plateau of curve moves down
binds and shifts haemoglobin to the relaxed conformation
• O2 is more tightly bound and not dissipated at low PO2 in tissues
• curve changes to hyperbola and shifts left
CO poisoning treatment
hyperbaric oxygen therapy
facilitates dissociation of CO from Hb
