Gas exchange Flashcards
Gas exchange surfaces properties
permeable, large, thin (short diffusion distance) and moist (to dissolve the gases) ensure a rapid exchange – in larger organisms, a specialized gas exchange surface is required that is much larger than the outer SA (alveoli)
Cell respiration, gas exchange and ventilation definition and relationship
- controlled release of E from organic compounds in a cell, byproduct is CO2, it uses up O2 – it constantly creates a concentration gradient of gases between tissue cells and blood
- diffusion of O2 and CO2 down their concentration gradients across the alveoli and capillary wall (deoxygenated blood flows to the gill/alveolus and oxygenated blood leaves it)
- breathing (inhalation of fresh air and exhalation of stale air), it maintains the concentration gradient between lungs (alveoli) and blood
These three processes maintain each other (if an organism dies, first goes cell respiration, then gas exchange and then ventilation, because of accumulation of both gases in the body)
The human respiratory system anatomy:
1) nasal and oral cavity
2) palate
3) epiglottis
4) larynx (voicebox, with a vocal cord at the beginning)
5) trachea
6) bronchi (sg. bronchus)
7) bronchioles
8) lung
9) alveoli (sg. alveolus)
10) diaphragm and intercostal muscles
How does gas move (freely)
muscles that act during the ventilation process
always flows from regions of higher to regions of lower pressure
muscle contractions cause pressure changes inside the thorax:
diaphragm – a smooth muscle (autonomic nerve control) attached to the ribs that separates the thorax from the abdominal cavity
muscle in the front wall of the abdomen
intercostal muscle between ribs (in two layer, internal and external)
Antagonistic muscles, examples
pair of muscles that work together to accomplish opposite movements, they have the opposite effect (one has to contract and the other relax to produce movement) – relaxation of a muscle happens passively, as a result of contraction of the opposite (pair) muscle
diaphragm and abdominal muscles, internal intercoastal and external intercoastal muscles
Inhalation vs exhalation processes
Inspiration: external IM and diaphragm contract (diaphragm moves down), lung V increases, air pressure drops below atm so air passively flows into lungs (because lung V increases but air V stays the same)
Expiration: internal IM and abdominal muscles contract, lung V decreases, air pressure rises above atm so air passively flows out of lungs
Adaptations of lungs for efficient gas exchange:
- Airways for ventilation: bronchioles, ending in alveolar ducts, leading to a group of alveoli
- Large surface area – around 300 million, tiny alveoli (40 x greater than outer surface)
- Extensive capillary beds surrounding alveoli
- Short distance for diffusion – alveolus and adjacent capillary walls are both single layers of flattened cells (pneumocyte type I and endothelial cells) – distance is less than a micrometer
- Moist surface with surfactant
Two types of pneumocytes, premature babies case
Pneumocyte type I – flat cell, permeable to gases and responsible for gas exchange
Pneumocyte type II – rounded, bigger cell which secretes fluid (mucus) for gas dissolution and surfactants which reduce the surface tension inside the alveoli due to the secreted fluid. They prevent the collapse of alveoli (water sticking sides of alveolus together) and loss of the surface area for gas exchange
In premature babies, pneumocyte type II can’t produce a sufficient amount of surfactant so the lungs would collapse if they were not connected to a respirator
How can lung V be measures and why
ventilation rate, tidal volume, vital capacity, inspiratory reserve volume and expiratory reserve volume using spirometer
help diagnose asthma, COPS and cystic fibrosis
Partial pressure
how do gases flow in terms of their partial pressure
p of O2 in the air and p of O2 (air) in lungs
pressure exerted by each gas in a gas mixture
Moving down their partial pressure gradient in diffusion
21 kPa, less than 21 kPa because some of the O2 is used up by cells that line the airway
How is O2 carried in blood and why, Hb structure
by Hb because its hydrophobic
Each Hb has 4 haem groups (Fe prosthetic groups) to which one O2 can bind reversibly (Hb is 100% saturated with eight oxygen atoms)
Cooperative binding
binding of O2 to any haem group causes conformational changes that increase Hb’s affinity for O2, and the same applies to dissociation of O2 so the most stable forms of O2 are 0% and 100% saturated
What is the correlation between p(O2) and % saturation of Hb, why is this significant
positive, but not proportional due to cooperative binding
it ensures rapid dissociation in active tissues – when in contact with an area of high p(O2), Hb has high affinity for oxygen 8doesnt let it dissociate) and when in contact with tissue of lower p(O2) (deoxygenated blood) the Hb’s affinity for O2 decreases so O2 dissociates from it and enters the tissue
oxygen dissociation curve of Hb, when does Hb reach 100% saturation
shows the % saturation of Hb with O2 at each p(O2)
Hb is already completely saturated at 10 kPa (when blood flows through capillaries around the alveoli). This allows Hb to provide O2 even to extremely active respiring tissue. The normal range of pO2 in naturally respiring tissue is from 5 to 10 kPa and in active tissue from 3 to 5 kPa
Myoglobin (Mb)
pigment in muscles that stores one O2 molecule
it has lower O2 capacity but higher O2 affinity than Hb so it acts as a reserve because it doesn’t release O2 easily – only if it’s really needed to postpone the onset of anaerobic CR
Mb’s O2 affinity doesn’t change with pH (unlike Hb’s)
Fetal Hb, importance of adaptation
A fetus obtains oxygen via placenta; O2 dissociates from HbA in the maternal blood and binds to HbF in fetal blood. This can only happen because HbF has a higher O2 affinity than HbA (has a slightly different a-a sequence)
At any p(O2) HbF is more saturated with O2 than HbA
This is important because rapid cell respiration occurs in the intensely growing foetus so a lot of O2 is needed to support that fast metabolism which means that pO2 is constantly low
If HbF had the same affinity for O2 as HbA, it would not accept oxygens as readily as it does which would cause an insufficient amount of O2 provided to the respiring cells
Oxygen dissociation curve shifted to the left (between Mb and HbA)
What happens to HbF after birth and why? Possible consequences?
replaced by HbA in the replacement of foetal with adult RBC because HbF at 21 kPa would provide too much oxygen
Massive breakdown of foetal RBC in combination with immature liver can cause physiological jaundice of a newborn. It is caused by overproduction of bilirubin, an end product of Hb breakdown whose increased levels can damage the brain. Treated by UV light which speeds up its breakdown
How does affinity of Hb for O2 depend on the p(CO2)? Why is this important?
It decreases as p (CO2) increases due to two reasons:
Increased p(CO2) = decreased pH, and Hb’s affinity for O2 drops with a decrease in pH – so when respiring tissue has high p(CO2), O2 tend to dissociate
CO2 binds to Hb, creating carbaminohaemoglobin whose affinity for O2 is lower than that of Hb
Shift of the O2 dissociation curve to the right = Bohr shift
It promotes the release of O2 in actively respiring tissue where CO2 is mass produced and allows blood to be fully oxygenated in the lungs where p(CO2) is low so pH is high and carbaminoHb has been converted back to Hb
Draw and annotate a leaf diagram. Adaptations of leaves for gas exchange. Importance of this?
Exchange of CO2 and O2 without excessive H2O loss maintains photosynthesis
1. Upper and lower epidermis
2. Waxy cuticle – epidermis covered in a layer of waterproof wax (secreted by epidermal cells) which restricts transpiration but also limits movement of CO2 and O2
3. Stroma – pores in leaves through which transpiration happens, connect outside air to a network of air spaces in the leaf
4. Guard cells – in pairs, can change their shape either to open or close a stroma, they usually close it at night (no photosynthesis) and during water stress (when plants might die from dehydration)
5. Air spaces – saturated with water vapor
6. Spongy mesophyll – contains loosely packed, round cells – provides a very large SA of permanently moist cell walls for gas exchange (CO2 into cels, O2 from cells), photosynthesis maintains the concentration gradients
7. Palisade mesophyll – contains tightly packed cells with chloroplast that perform photosynthesis
8. Vascular bundles (veins) – two types: xylem (transports H2O and minerals, upper half) and phloem (transports sugar and a-a, that is nutrients and end products of photosynthesis, lower half of leaf), they run in parallel and transport things at the opposite direction- veins replace the water lost by evaporation
Transpiration, significance, factors that affect the transpiration rate
Loss of metabolic water vapor (produced in CR) as the inevitable consequence of gas exchange – water from air spaces goes down its partial pressure gradient through the stomatal opening
1. Temperature – at higher T more E is available to break H-bonds so higher evaporation rate – air can hold more water molecules before becoming saturated
2. Humidity – the higher the air humidity, the smaller the C gradient of water between the leaf and air outside so the lower the rate of diffusion (if air is saturated, no transpiration)
3. Wind – no wind = transpiration restricted by formation of air pockets of saturated air near the stomata – wind = air pockets are lost so rate increases – strong wind = stromata close and rate drops
4. Light intensity – positive correlation as the amount of water produced is related to the rate of photosynthesis, there is a saturation point
