6.4 & h6 gas exchange
DESCRIPTION
ib notes on gas exchangeTRANSCRIPT
Gas Exchange 1/4/15 9:59 AM
O2 in
CO2 out
Adaptation of the alveolus ( singular form of alveoli)
-Need a large surface area
-Has to be moist, because materials can only diffuse in the same state
( liquid into liquid) the gas first dissolves into the outer liquid then diffuses in.
therefore it secrets fluid which also acts a detergents, preventing the sticking
together of the alveoli
-Needs to have a good transport system has to have a rich blood supply
( rich capillary network)
- small spaces for diffusion therefore thin walls.
All of the gas exchange happens with diffusion, so therefor there has to be a
concentration gradient, therefore a good transport system
3 mechanisims
ventilation breathing- moving air in and out using muscles
Gas exchange - O2 in CO2 out
Cell Respiration – releasing energy to form ATP with the use of oxygen which
produces CO2
Internal Intercostal muscles and external intercostal muscles on the ribs
Diaphragm is the muscle that separates the abdomen ( intestine) and
thoracic cavity
So when the diaphragm contracts it lowers the arch
When you inhale the
External intercostal muscle contracts moving the ribs up and out
The diaphragm contracts becoming flatter
The volume increase in the thoracic cavity
The pressure then decreases below atmospheric pressure
So the air want to come in because of pressure gradient
Therefore the lungs inflate
Air goes from high pressure in the chest cavity to less pressure to the lungs
which is now expands because of the contracts of muscles, so it comes via
the trachea into the lungs
When you exhale the
External intercostal muscle relaxes moving the ribs up and in
Abdominal muscle contract moving diaphragm into a dome shape
Volume decrease of the thorax
Pressure increases rises above atmospheric pressure
Air moves out to equalize till the lungs are back to atmospheric pressure
Diagram relaxes and the eicm relaxes too
No muscles in the lungs, it all has to with pressure
Because gas exchange is a passive process, a ventilation system is needed
to maintain a concentration gradient within the alveoli
This requires a high concentration of oxygen - and a low concentration of
carbon dioxide - in the lungs
A ventilation system maintains this concentration gradient by continually
cycling the air in the lungs with the atmosphere
concentration gradients,
20% oxygen in 16% oxygen out
Adaptation of the alveolus ( singular form of alveoli)
Gas Exchange 1/4/15 9:59 AM1/4/15 9:59 AM
Hemoglobin is a protein which carries oxygen in the blood
The cell in which it is found are called erythrocytes
This cell has a
-plasma membrane
-inside is cytoplasm
- no nucleus
- few organelles
- has lots and lots of hemoglobin
Hemoglobin can bing to 4 oxygen molecules at one time and one carbon
dioxide molecule
Hemoglobin has
4 polypeptides
each have a haem group near the center
and each haem has a iron near it
and can transport 4 O2 molecules
each oxygen molecule adds to hemoglobin’s affinity to bond with another
oxygen until full
partial pressure is the pressure exerted by one gas in a mixture of gases
Myoglobin is similar but found in the muscles
Only has one haem group
Faster saturation as only needs one oxygen to be saturated
Stores oxygen in muscles to delay anaerobic respiration
Fetus hemoglobin has a higher affinity for oxygen
Therefore the oxygen will move from adult hemoglobin to fetal hemoglobin
in the capillaries of the uterus
Bohr Shift- Cells with increased metabolism (e.g. hypoxic tissue) release
greater amounts of carbon dioxide into the blood
Carbon dioxide lowers the pH of the blood (via its conversion into carbonic
acid) which causes hemoglobin to release its oxygen
This is known as the Bohr effect – a decrease in pH shifts the oxygen
dissociation curve to the right in tissues
Hence more oxygen is released at the same partial pressure of oxygen,
ensuring respiring tissues have enough oxygen when their need is greatest
Carbon dioxide transport
1st – a small percent dissolves into your blood plasma
2nd – 15-20 % carbon dioxide bonds with hemoglobin ( but only one) this
therefore lowers the affinity for oxygen , causing the Bohr shift
3rd- around 70% of CO2 enters the erythrocytes and converts into hydrogen
carbonate, and then moves to the blood plasma to be transported and will
not affect the PH of your blood
first t diffuses into the cell, then reacts with water ( sometimes catalysesd by
carbonic anhydrase) which produces carbonic acid, this quickly disassociates
to become hydrogen carbonate and hydrogen ions. The carbonate diffuses
out of the cell, while chlorine comes in to counterbalance the charge change,
this is the chloride shift, and then the h binds with the hemoglobin so it does
not change the PH of the blood. This is a buffering the ph.
Affect of exercise on ventilation
The use of muscles and ATP causes cell respiration to change drastically,
therefore consuming a lot more oxygen and making more CO2
Ventilation is controls by your medulla oblongata which is in your brainstem.
There are two mechanisms that determine when the rate needs to increase.
–Receptor cells ( chemoreceptors) located in you aorta ( Heart) and carotid
arteries detect a decrease in the CO2 levels because of the change in ph. So
when detected send an action potential message to the medulla.
- the medulla also has thee chemoreceptors, and when the blood passes
through the capillaries in the medulla, a decrease in PH is detected.
Blood is around 7.4 ( but when exercising heavily the buffering is not that
efficient and more CO2 builds up in the plasma and more H ions build up
increasing the concentration of H which decreases the PH. This changes to
around 7.0
To increase ventilation, the medulla sends action potential to the diaphragm,
intercostal muscles and abdomen telling it to fasten up, therofre changing
the frequency.
When physical exertion decrease the PH starts changing back which is then
detected by the same chemoreceptors, and action potential is sent again
decreasing the rate
Asthma
Asthma is a common, chronic inflammation of the airways to the lungs (i.e.
bronchi / bronchioles)
Inflammation leads to swelling and mucus production, resulting in reduced
airflow and bronchospasms
During an acute asthma attack, constriction of the bronchi smooth muscle
may cause significant airflow obstruction, which may be life threatening
Common asthma symptoms include shortness of breath, chest tightness,
wheezing and coughing
Asthma may be caused by a number of variable and recurring environmental
triggers, including:
Allergens (e.g. pollen, moulds)
Smoke and scented products (e.g. cigarettes, perfumes)
Stress and anxiety
Food preservatives and certain medications
Arthropods (e.g. dust mites)
Cold air
Exercise (increased respiratory rate)
High Altitudes
There is not less oxygen at higher altitudes
There is just less pressure , so the molecules are more spread out. This
therefore is less dense air, making oxygen diffusion less efficient.
At high altitude physical activity can cause fatigue, vision problems, nausea,
and high pulse. This is called mountain sickness
Our bodies compensate with faster ventilation.
Is however is not a long term solution, so acclimatization occurs.
-increase in erythrocytes
- increase in hemoglobin
- increase in amount and size of hemoglobin
- increase surface area, and size of lungs
- increase of myoglobin in muscle tissues
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