Gas Exchange and Gas Transport Flashcards
where and in what way does gas exchange occur
at capillaries in lungs (capillary beds at avioli) and at tissue capillary level
by diffusion oxygen and carbon dioxide down their partial pressure gradients
what is partial pressure and what is it typically at sea level
pressure exerted by a single gas or liquid on their own
basically when we breathe in we create a lower partial pressure than sea level in our avioli (by creating space), so that higher pressured gases can travel to it
typically 760 mm Hg varies with temperature and humidity
what is henry’s law
at a given temperature, the amount of a particular gas in a solution is directly proportional to the partial pressure of that gas
PO2 and PCO2 of deoxy blood going to the lungs
P02 = 40 mm Hg PCO2 = 45 mm Hg
PO2 and PCO2 of oxygenated blood in alveoli vs atmospheric air
why the difference
atmospheric - 160 mm Hg of O2, 0.3 mm Hg of CO2
alveoli - 104 mm Hg O2 (more like 100), 40 mm Hg CO2
in alveoli there is the partial pressure of water vapour and CO2 which reduces the P of oxygen (as the volume is not fixed)
PO2 and PCO2 of blood leaving the lungs
100 mm Hg O2 (more like 96)
40 mm Hg CO2
(notice all figures have higher oxygen difference, however with oxygen and carbon di end up with the same concentration of about 80%, as co2 has a higher solubility coefficient due to its polarity)
PO2 and PCO2 in interstitial fluid (blood after tissues have used oxygen and given off CO2)
less than 40 mm Hg O2
greater than 45 mm Hg CO2
what accounts for the difference between alveolar blood PO2 and the PO2 of the blood leaving lungs about to enter tissue capillaries
(there is no gas diffusion during the travel of the blood)
so this is due to anatomical right to left shunts (also physiological shunting in asthmatic people) (heart and bronchial tree veins) drain straight into left ventricles diluting oxygenated blood and hence oxygen partial pressure
factors other than partial pressure of gases that affect their diffusion
SA
thickness of membrane / travel distance
diffusion coefficient
what can increase the thickness of membranes
fluid build up or PULMONARY OEDEMA - high altitude pulmonary oedema for eg when you’re high up in the mountain. pulmonary arteries constrict creating pressure build up and fluid leaking into membranes
PNEUMONIA eg. COVID, infection and fluid build up in alveoli increased thickness of epithelium of bronchioles, reducing air flow
scar tissue can cause Pulmonary fibrosis, thickening of membrane
what is the diffusion coefficient connected to
solubility of a gas and its molecular weight
CO2 heavier and more polar so diffusion coefficient is about 20 X that of O2
how much oxygen is purely dissolved in blood and how much is otherwise transported by …
by haemoglobin is 98.5%
1.5% is dissolved
how many global chains does Hb have and what’s inside each
4
inside each Heme molecule which has an Fe2+ that binds to one oxygen molecule
so overall a Hb molecules only carries four oxygen molecules
once it carries 4 its considered fully saturated
what determines the saturation of a haemoglobin molecule
the partial pressure of O2
PO2 in systemic vs pulmonary capillaries and the correlating Hb saturation
sys - 40 mm Hg correlates to 75% sat
! 25% of carried oxygen from pulmonary circuit will be offloaded into the tissue, remaining 75% bonded to Hb will stay bonded to it
pul - 100 mm Hg t 100% sat
explain Bohr’s effect in relation to the change in relationship between haemoglobin saturation and PO2
Bohr’s effect is the influence of Co2 and acid (H+) on the release of O2.
both Co2 and H+ combine with Hb reversibly at site other than the O2, changing its structure and reducing its affinity for O2.
AKA presence of CO2 and H+ increases the release of O2 molecules
this is important for working muscles which also produce heat
difference in fetus oxygen uptake in relation to haemoglobin
fetus gets oxygen from placenta which is tissue and has an PO2 of 40 mm Hg.
(less o2 released)
the foetus actually has a structurally different haemoglobin molecule
unloading of O2 occurs at placenta, offloading occurs at about 20 mm Hg
normal blood values for haemoglobin, oxygen carrying capacity, O2 content of arterial and venous blood
15 g Hb / 100 mL
20 mL O2 / 100 mL (15 X 1.34mL)
same as above at 100% Hb saturation at 100 mm Hg
15 mL o2 / 100 mL
75% at 40 mm Hg
anaemic blood values
7.5 g Hb / 100 mL
10 mL O2 / 100 mL (15 X 1.34mL)
same as above at 100% Hb saturation at 100 mm Hg
7.5 mL o2 / 100 mL
75% at 40 mm Hg
4 locations CO2 can travel to when being excreted from tissue cells into systemic circulation
- dissolved in plasma
- in intracellular fluid of red blood cells
- bound to the globin chains of haemoglobin molecules
- binds to water molecules and in the presence of carbonic anhydrase forms carbonic acid which dissolved into hydrogen ions and bicarbonate (HCO3)
the H+ binds to globin chain so it doesn’t change the pH of the intracellular fluid of red blood cells
bicarb molecules get transported out of cell, for each one out a chlorine ion goes in (majority of CO2 produced gets transformed and transported out as HCO3-)
locations CO2 can travel to when being excreted from tissue cells into pulmonary circulation
- in alveoli which have a lower pp of CO2, by first dissolving in plasma (some stays there)
- reverse reaction of it binding with water and globin chains
how much co2 is dissolved in plasma and what reaction occurs with some of it
5%
5% reacts with water to form H2Co3 then HCO3- and H+ THIS ACIDIFIED BLOOD, so if you don’t breathe out your blood becomes acidic - respiratory acidosis
conversely if you hyperventilate, result is respiratory alkalosis
what is a body response to combat respiratory acidosis/alkalosis
(assuming you’re in respiratory failure)
changing the amount of bicarb in the plasma, bicarb is produced by kidneys and excreted into urine for instance (renal compensation). increasing HCO3- concentration increases pH and vice versa
(davenport’s diagram)
what is Haldane’s effect
globin chains increase their affinity for co2 molecules and hydrogen ions if the haemoglobin molecules have just offloaded oxygen
works in synchrony with Bohr effect for efficient gas transport
