lecture 17 - respiratory system 4

Question 1

oxygen diffusion

Answer 1

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

Question 2

carbon dioxide diffusion

Answer 2

made in the tissues

much lower gradient - sufficient to drive the transfer

dropped off at the lungs

Question 3

what does oxygen do after moving out of the alveoli?

Answer 3

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

Question 4

what happens when haemoglobin reaches an area where oxygen is needed?

Answer 4

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

Question 5

what is the maximum saturation we find in the lungs?

Answer 5

100 mmHg of PO2

doesn’t ever quite reach 100% saturation

Question 6

what does a oxygen dissociation curve tell us?

Answer 6

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

Question 7

what does the steepness of an O2 dissociation curve tell you?

Answer 7

speed - has to be a quick reaction to unload O2 quick enough

Question 8

haemoglobin in the lungs and arterial blood

Answer 8

fully saturated

Question 9

haemoglobin at rest

Answer 9

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

Question 10

haemoglobin during exercise

Answer 10

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

Question 11

effect of PCO2 on O2 saturation curves

Answer 11

increased PCO2 moves curve to the right

decreases moves it to the left

Question 12

effect of pH on O2 saturation curves

Answer 12

if you increase pH curve moves to the left
• decrease H+

if you decrease pH curve moves to the right
• increase H+

Question 13

what does a shift to the left on an O2 dissociation curve show?

Answer 13

shows a higher binding affinity

O2 is bound more tightly so stays associated longer

Question 14

what does a shift to the right on an O2 dissociation curve show?

Answer 14

shows a lower oxygen binding affinity

haemoglobin is more likely to drop O2 off

Question 15

process of CO2 diffusion into RBCs

Answer 15

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

Question 16

what is Cl- moving in called?

Answer 16

chloride shift

Question 17

what is the Bohr effect?

Answer 17

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

Question 18

what forms does haemoglobin exist in?

Answer 18

tense

relaxed

binding of H+ to the global chains of haemoglobin favours the tense formation

Question 19

tensed haemoglobin

Answer 19

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

Question 20

relaxed haemoglobin

Answer 20

oxygenated

Question 21

effect of temperature on O2 dissociation curves

Answer 21

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

Question 22

effect of 2,3-DPG on O2 saturation curve

Answer 22

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

Question 23

how do RBCs produce 2,3-DPG?

Answer 23

don’t have mitochondria so no oxidative mechanism or ATP production

produce energy by glycolysis - 2,3-DPG is a side product of glycolysis

Question 24

anaemia and O2 saturation curve

Answer 24

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

Question 25

factors that affect O2 dissociation curve

Answer 25

C - CO2 
A - acid or anaemia 
D - diphosphoglycerate 
E - exercise 
T - temperature 

increase in any of them causes a shift to the right

Question 26

foetal haemoglobin

Answer 26

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

Question 27

what 3 ways are CO2 transported by in the blood?

Answer 27

dissolved in plasma

bound to Hb

as HCO3 in plasma

Question 28

CO2 dissolved in plasma

Answer 28

7%

CO2 has a high solubility in plasma

Question 29

CO2 bound to Hb

Answer 29

23%

CO2 + Hb = carbaminohaemoglobin

Question 30

CO2 as HCO3 in plasma

Answer 30

70%

CO2 + H2O –> H2CO3 –> HCO3 + H+

HCO3 exits RBC in exchange for Cl- anion (chloride shift)

Question 31

what happens if tissue [CO2] is higher than [CO2] in blood?

Answer 31

CO2 + H2O –> H2CO3 –> HCO3 + H+

results in bicarbonate and hydrogen ion formation

Question 32

what happens if blood [CO2] is higher than [CO2] in alveoli?

Answer 32

CO2 + H2O

Question 33

carbon monoxide and Hb

Answer 33

CO binds tightly but reversibly to the iron in Hb forming carboxyhemoglobin

affinity of Hb for CO is 200x than of O2

Question 34

2 effects of CO on O2 dissociation curves

Answer 34

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

Question 35

CO poisoning treatment

Answer 35

hyperbaric oxygen therapy

facilitates dissociation of CO from Hb