Topic 7 : Mass Transport Flashcards
mass transport
large multicellular organisms, mass transport systems needed to carry substances between exchange surfaces and rest of body
why is mass transport needed?
most cells far away from exchange substances/each other for diffusion to maintain composition of tissue fluid within suitable metabolic range
maintains final diffusion gradients to and fro cells
maintains relatively stable immediate environments of cells that is tissue fluid
haemoglobins
group of chemically similar molecules
protein molecules with 4th structure has evolved to make it efficient at loading o2 in one set of conditions but unloading it in another set
structure of haemoglobins
primary structure = sequence of amino acids in 4 polypeptide chains
2nd structure = each of these polypeptide chains coiled into helix
3rd structure = each polypeptide chain folded into precise shape ( affects ability to carry O2)
4th structure = all 4 polypeptide chains linked to form globular shape
- each chain associated with haem group - Fe++
- ferrous ion combine with single O2 molecule
- single haemoglobin can carry 4 molecules
role of haemoglobin
to transport oxygen
to be efficient:
- readily associate with O2 at surface where gas exchange occurs
- readily dissociate from O2 at tissues requiring it
affinity of O2 under conditions
gas exchange surface = high O2 conc = low CO2 conc= high affinity = O2 associated
respiring tissues = low O2 conc = high CO2 conc - low affinity = O2 dissociated
why are there different haemoglobins?
many organisms have haemoglobin
different organisms have different properties dependent on affinity for O2
why do different haemoglobins have different affinities?
each species - slight difference in sequence of amino acids - thus different tertiary and quaternary structures so diff oxygen binding properties so different affinities for O2
description of oxygen dissociation curves
haemoglobin exposed to different partial pressures of O2 , doesn’t bind to O2 evenly
graph of saturation of haem with O2 and pp of O2 = oxygen dissociation curve - usually S shape
explanation of O2 dissocation curve S shape - 1
shape of Hbr mol makes it diff for 1st O2 to bind to 1 of 4 sites b/c they’re closely united
low O2 conc = little O2 binds to Hbr
gradient initially shallow
explanation of O2 dissocation curve S shape - 2
h/w binding of 1st mol changes 4th structure of Hbr - changes shape
makes it easier for other ( induces others to bind)
explanation of O2 dissocation curve S shape - 3
so takes small increase in pO2 to bind to 2nd O2 molecule than needed for 1st
positive cooperativity: binding of 1st makes binding of 2nd easier and etc
gradient steepens
explanation of O2 dissocation curve S shape - 4
theory reverses : becomes harder for Hbr to bind to 4th O2 due to probabilty
with maj of binding sites occupied - less likely O2 mol finds empty site to bind
gradient reduces and graph flattens over
affinities and O2 curves
further to left the curve = greater affinity of Hbr to O2 - loads O2 readily but unloads it less easily)
further to right curve = lower affinity of Hbr to O2 - loads O2 less readily / unloads more easily
effects of CO2 conc – 1
Hbr low affinity for O2 in presence of CO2
greater conc of CO2 - Hbr more readily releases O2 ( Bohr effect)
effects of CO2 conc – 2 gas exchange surface:
gas exchange surface:
conc of CO2 is low b/c diffuses across surface & excreted from organism
affinity of O2 increased & high conc of O2 = O2 readily loaded by Hbr
reduced CO2 conc - shift curve to left
effects of CO2 conc – 3 respiring tissues:
respiring tissues:
conc of CO2 is high - affinity for O2 reduced & low conc of O2 = O2 readily unloaded form Hbr to muscle cells
increased CO2 conc - shifts curves to right
why does greater conc of CO2 cause Hbr to release O2
greater conc of Co2 - Hbr more readily dissociates from O2 :
-dissolved Co2 is acidic & low pH causes Hbr to change shape
loading, transporting & unloading of O2
gas exchange surface : CO2 constantly removed
pH slightly raised due to low conc of CO2
higher pH changes shape of Hbr so enables to load oxygen more readily
also increases affinity of Hbr to O2 so not released while being transported in blood to tissues
in tissues: Co2 is produced by respiring cells
Co2 = acidic in aq so pH of blood lowered
lower pH changes shape of Hbr into one with lower affinitiy got O2
Hbr releases O2 into respiring tissues
LTU of O2 - 2
more active tissue is = more O2 is unloaded
higher rate of respiration - more CO2 produced = lower pH - greater Hbr shape change - more readily O2 unloaded - more O2 for respiration
LTU of O2 - 2
Hbr normally saturated with O2 as it passes through lungs
not all filled with 4 mol
overall saturation at atmospheric pressure : 97%
Hbr reaches tissue with low respiratory rate - only one mol released
blood returned to lungs still 75% saturated
why large organisms have transport system?
with increasing size, SA:V ratio decreases to point where needs of organism cannot be met by body surface only
specialist surfaces required to absorb nutrients/respiratory gases and excrete products
located in specific regions of organism
transport system required to take materials to and fro cells / exchange systems
