respiration 2, transport and exchange for gases

what are the two stages of gas exchange

 - the exchange of gases between compartments, which requires diffusion across cell membranes e.g from capillaries to alveolar
- the transport of gases in the blood

explain how differnt partial pressures of O2 and CO2 lead to gas diffusion

Oxygen (O₂)

• Cells use O₂ → intracellular PO₂ ≈ 40 mmHg

• Arterial blood has PO₂ ≈ 100 mmHg

• O₂ moves from blood → cells down its gradient

• Venous blood leaving cells has PO₂ ≈ 40 mmHg

Carbon dioxide (CO₂)

• Cells produce CO₂ → PCO₂ ≈ 46 mmHg

• Arterial blood has PCO₂ ≈ 40 mmHg

• CO₂ moves from cells → blood down its gradient

• Venous blood leaving cells has PCO₂ ≈ 46 mmHg

In the lungs

• Venous blood arrives: PCO₂ = 46 mmHg

• Alveolar air: PCO₂ = 40 mmHg

• CO₂ moves from blood → alveoli until equilibrium (PCO₂ = 40 mmHg)

what 3 variables affecting efficiency of alveolar gas exchange

1. o2 reaching the alveoli 

2. gas diffusion between alveoli and blood 

3. good perfusion of alveoli (blood flow through capilaries around alveoli)

  

what is perfusion

movement of blood through the circulatory system to a tissue or organ o that it gets oxygen and nutrients  

when are lung capilaries open and when are they closed for both apex and base of lung

• lung capilaries are collapsible 

• at the base due to gravity presssure is high so capillary stays open 

• at the apex the pressure is low  so some of the capilaries are closed at rest 

• when you excersize the blood pressure increases so the capillaries that are closed at the apex open so more blood gets oxygen 

what is reserve capcity in the lungs

when the capilarries open so more oxygen can get to the blood and so tissues

how does the body match air flow and blood flow in the lungs ( ventular-perfusion matching)

by regulating the diameters of the; 
arterioles  ( blood flow)
bronchioles ( air flow ) 

what is a healthy persons V/Q ratio

0.8

what does it mean if your VQ ratio is above 1

ventilation exceed perfusion so there is more oxygen in the alevoli that bloof can absorb. 

this leads to wasted ventilation/ pathalogical dead space

what happens if someones V/Q ratio is below 1

perfusion is higher than ventilation so there is good bloodlfow but not enough oxygen for exchange 

this leads to hypoemia 

how is the diameter of bronchioles controlled

• partial pressure of CO2

• PCO2 increase, bronchioles dialate so more air comes in and removes CO2 faster 

• PCO2 decrease bronchioles constrict so less air comes in and stop CO2 from dropping too low 

when do pulmonary arteries constrict and dialate

carry deoxygenated blood from right ventricle to lungs
PCO2 increase: constrict - alot of CO2 in the alveoli 
PCO2 decrease: dialates - blood flow increases to remove CO2
PO2 increase: dialates -  alveolus have alot of O2 so send more blood to pick it up 
PCO2 decrease: constricts -alveolus dont have ocygen divert blood to another aleoli that has more O2

when do systemic arteries ( arteries carrying O2 from heart to tissues) dialate and constrict

PCO2 increase: dialtes - ↑ blood flow to remove CO₂ and supply O₂
PCO2 decrease: constricts -  less need for increased blood flow
PO2 increase: constrict - less blood flow needed
PO2 decrease: dialates - Tissue needs more O₂ → ↑ blood flow

Tissue needs more O₂ → ↑ blood flow

Tissue needs less CO₂ → ↑ blood flow

what are 2 causes of low alveolar pO2

1.  inspired air has low O2 content ( depending on the atmospheric concentration of oxygen) 

2. alveolar ventilation is inadequate ( hypoventilation)

what is hypoventilation and its causes

 low alveolar ventilation

can be caused by:
- decreased lung compliance ( less strecthign and recoiling) 
- increased airway resistance ( e.g somthing blocking, or asthma) 
- CNS depression that slows ventilation and decreased depth

what is hypoxia and how does hypoxia occur

• low levels of O2

• if theres a porblem with gas exchange between blood and alveoli  

• id theres a problem in the transport of blood to the tissues 

whast the link between hypoxia and hypercapnia

• hypOxia is when you have low levels of O2

• hyperCapnia is when you have high Co2 

• these usually occur together as if gas exchage is ipared both uptake of O2 and removal of CO2 decreases

effect of hypercapnia

high co2 conc slwos down the activty of the  nervous system acting as a depressant leading to respiratory acidosis  (when blood becomes to acdidic)

what does the body do to avoid getting hypoxia and hypercapnia

body uses sensors that monitor the aterial blood composition of O2 CO2 and PH  high level of CO2 leads to incease of PH 

how do diffusion problems cause hypoxia

• usully gas exchange is fast as the blood moves slowly through capilaries so theres alot of time for the o2 to difuse 

• but if something blocks or slows down diffusion ( thickness of membrane) even if the blood is moving slowly O2 wont reach equilibrium 

what physics factors affect gas exchange

• surface area

• barrier thickness 

• duffision distance

what is emphysema

• effect on gas exchange

• how its caused

• decrease surface area so slower diffusion

• the alveoli elastic breakdown 

• this makes the alevoli get bigger but there is fewer alveoli in total so surface area decreases 

• caused by tar in smoke that leads the the release of enzyems that destroy the elastic fibres

what is fibrotic lung disease

• effect on gas exchange

• how its caused

• scar tissue causes thickens the alveolar wall 

• diffusion is slower

what is pulmonary odema

• how does it affect gas exchnage

• how is it caused

• increase in diffusion distance so slower diffuision 

• build up of fluid in the lungs and alveoli due to the hydrostatic pressure increases because the heart cant pumpblood effectivly so pressure builds up pushing fluid from blood vessels into air sacs 

• common in heart faliure 

what is the effect of gas solubility on gas exchange of O2 and Co2, including in diseases

• low solubility of oxygen means it neds a carrying molecule to transport molecule ( haemogloblin) 

• CO2 has high solubility so can exchange well in all thickness

• in pulmonary oedema when the diffusion distance is thickened the O2 wont be able to reach the blood but CO2 can 

what are the two ways oxygen is transported in the blood

• boud to haemoglobin ( 98% of oxygen)

• dissolved in plasma ( 2% of oxygen ) 

how does haemogloblin carry oxygen around the body

• 4 haem groups

• iron and O2 interaction whic are weak 

• when O2 dissolves into pasma it binds with haemogloblin making oxyhaemalobin 

• once transported to the end place the o2 unbinds and dissolves into the plasma 

what 2 factors affect the amount of O2 bond to Hb

- pO2 in the plasma surrounding RBCs 

- amount of Hb

what does an oxyhaemoglobin saturation curve look like

• x axis: Po2

• y axis: haemogloblin saturation 

• in a resting cell the pO2 is 40mHg and saturation is 75%

• before this the curv is more steep so small changes in pO2 make big efects on saturation 

• after this the cuve levels off and slowly increases to around 100%^ saturation

how is haemogloblin saturation an example of built in resevoir

• at rest only 25% of the bound 02 is released into tissue and 75% is still bound to haemogloblin so this can be used when needed

effect of pH on affinity of Hb for o2

- as pH decreases, curve shifts right so affinity for o2 decreases

- this is known as the Bohr effect

effect of temperature on affinity of Hb for o2

- as temp. increases, curve shifts right so affinity for o2 decreases, as more demand for oxygen 

effect of pCO2 on affinity of Hb for o2

as pCO2 increases, curve shifts right so affinity for o2 decreases as more o2 is needed

effect of 2,3-BPG on affinity of Hb for o2

- increased 2,3-BPG shifts curve to the right which decreases affinity for o2

- as there is a higher demand for O2 fro cellular respiration 

- chronic hypoxia triggers an increase in 2,3-BPG production in RBCs

why does foetal Hb have a higher affinity for o2

• foetal haemogloblin has a change in structure it has  2 gamma proteins instead of 2 beta chains in adult Hb

• this increases foetal Hb affinity for o2 so it can bind to o2 in the low o2 environment of the placenta
  

how is co2 transported in the blood

•  5-7% of co2 is dissolved in plasma

• 20-23% binds to Hb to form HbCO2

•  70-75% is converted into bicarbonate

why is conversion of co2 to bicarbonate useful

• additional way to transport co2 to the lungs

• acts as a buffer to stabilise body pH

how is co2 converted to carbonate

• co2 diffuses into RBCs where it reacts with water in presence of carbonic anhydrase (CA) to form bicarbonate

• this is a reversiblereaction

• HCO3- diffuses out into plasma on an antiport protein and Cl- enters plasma (chloride shift)

what is the Bohr effect

- anaerobic metabolism releases H+ into cytoplasm which decreases pH

- Hb affinity for o2 decreases so more o2 is released in tissues as blood becomes more acidic