Respiratory 4.1 Flashcards
1) What is the Fick Principle?
2) What are key factors of Fick Principle?
“The volume of gas which diffuses per unit time
across a tissue sheet is
1.proportional to the area of the sheet,
2.inversely proportional to the thickness of the sheet
3.Proportional to the difference in partial pressure of the gas
on the two sides
4.Dependant upon the permeability for that gas in the tissue
We maximise gas transport in the lungs by having a large
exchange area, a thin diffusion membrane, and a high
partial pressure difference.
Why do we need a chemical reaction to transport more O2 per litre of blood?
Why is there more CO2 than O2 present in plasma at equal partial pressures?
MORE SOLUBLE BECAUSE
- reacts chemically with water
More CO2 in plasma than oxygen
What is the equation for partial pressure of respiratory gases?
What is the role of the CV system?
Why is the carriage of oxygen a problem?
1) to supply oxygen and metabolic fuel (eg glucose) to tissues and
to take away the waste products of metabolism (eg CO2)
2) to maintain defenses against invading micro-organisms
2) oxygen is a
powerful oxidising agent; Most organic molecules are
damaged by too high a concentration of O2. Red cells
(erythrocytes) are specially designed to carry this dangerous
cargo!
Describe the structure of heamoglobin
What is the importance of “steric hinderance” ?
4 subunits
Each with haem posthetic grop attached
Four polypeptide chains bound to each other by salt bridges
Hydrogen bonds
Hydropbic interactions
3 dimensional folding of subunits. Oxygen molecule cannot get physically close to iron to remove the electron. Oxygen attached to iron but not get close to oxidis it.
Parial pressure high (lungs), oxygen binds to form oxyhaemoglobin. In tissues dissociates to form deoxyhaemoglobin. This is transported back to lungs for reoxygenation
What happens if steric hinderence is not right?
Oxygen too close to iron therefore, oxidises it (removes electron).
Iron now in ferric state
Haemoglobin with ferric iorn called methaemoglobin + cannot carry oxygen the ferric iron in
methaemoglobin no longer has the 6th
electron to attract the oxygen molecule
1) How can methaemoglobin be formed without an issue with steric hinderance?
2) How is methaemoglobin converted back to fucntional haemoglobin?
3) As RBCs age, why do levels of methaemoglobin increase?
4) State a signal that RBCs should be removed from circulation
1) Gradual formation of methaemoglbin (a form of haemoglobin where iron is oxidized from Fe²⁺ to Fe³⁺) is UNAVOIDABLE over time
2) In newly formed RBCs, it is done by methaemoglobin reductase. NADH-dependent enzyme.
3) Efficiency of methaemoglobin reductase dcreases
4) Increased methaemoglin lecels rise. Leads to surface markers on RBCs changing. Detected by liver, spleen, which remove aged RBCs from circulation
1) What is 2,3 - DPG?
2) Mechanism of action of 2,3 - DPG
1) 2,3 - Diphosphoglycerate: small molecule, binds loosely to haemoglobin. Regulates haemoglbin’s ability to release oxygen to tissues.
2) De-oxygenation of beta-subunits: Beta-subunits of haemoglobin start to release oxygen, 2-3 DPG binds more tightly to haemoglobin
2,3- DPG moves into centre of haemoglobin molecule, increasing affinity for deoxygenated state, promoting release of oxygen
Thus it
enhances the ability of RBCs to release oxygen in hypoxic tissues
1) How does acidosis influence 2,3 DPG concentration?
2) Which hormones increase conc of 2,3 DPG?
1) Acidosis (low blood pH) inhibts red cell glycolysis
2-3 DPG cocn decrreases
Reduces RBC ability to releasse oxygen efficiently
2) Thyroid, Growth, Androgens (TAG)
1) What is percent satutration / Hb saturation %?
2) What do we use to measure Hb saturation?
3) Level for healthy indivudals
1) Percent saturation = Hb saturation %. arterial blood as
SaO2
2) Pulse oximeter
1) Hb saturation level for healthy individuals?
2) What happens when it is below 90%?
3) Oxygen Saturation vs. Tissue Oxygenation:
1) 96% and 99%, and should be above 94%
2) Hypoxaemia which indicates insufficient oxygen levels in the arterial blood.
SaO2 represents the percentage of haemoglobin in the blood that is bound to oxygen.
3) Oxygen saturation - how much oxygen bound to Hb. Does not indicate how well oxygen is being deliverted to and used by tissues.
Tissue oxygenration depends on ability of haemoglobin to unload oxygen in tissues where needed
1) What is the name of the curve that describes oxygen unloading?
Oxygen-
haemoglobin dissociation curve
Curve
- S shaped
- Flat at high PO2
- Steep at medioum + low PO2
Oxygen-
haemoglobin dissociation curve
The upper portion of the curve is relatively flat.
In this range, haemoglobin is more than 90% saturated with oxygen over a wide range of pO2 (from 70 mmHg to >100 mmHg).
This flat portion means that even with a significant drop in the oxygen levels in the lungs (pO2), haemoglobin remains almost fully saturated, ensuring that oxygen is efficiently loaded onto haemoglobin in the lungs.
Steep Middle Part of the Curve:
The middle portion of the curve is steep. In this range (pO2 between 20-40 mmHg), a small decrease in pO2 results in a large amount of oxygen being released from haemoglobin. This steep part of the curve is critical for oxygen delivery in the tissues because it allows haemoglobin to rapidly unload oxygen where it is needed
How does temperature effect Oxygen-Haemoglobin Dissociation Curve ?
Why can a patient experience feelings of fatigue + reduced function in a cold limb?
Effect on Heat
- Heavily metabolising tissue (muscles during exercise) generate heat
- Increase temp, shifts curve to right
-Rightward shift, decreases haemoglobin affinity for O2 = more oxygen is unloaded at any given partial pressure of oxygen (pO2).
- allows metabolically active tissues to receive more oxygen as their demands increase.
Effect on cold
- Cold tissues are metabolising more slowly
- Decreased temperature shifts the dissociation curve to the left.
- A leftward shift increases haemoglobin’s affinity for oxygen, making it harder for oxygen to unload from haemoglobin.
- oxygen delivery to the cold tissue decreases
- This can cause hypoxia (lack of oxygen) in cold tissues
- atigue and reduced function, such as in a cold limb.
Describe Bohr Shift
What key factors contribute towards it?
rightward shift of the oxygen-haemoglobin dissociation curve in response to increased CO₂ production and lower pH (acidity) in the blood.
- Increased CO2 production. Heavily metabolising tissues produce more carbon dioxide (CO₂) as a byproduct of metabolism.
- CO₂ combines with water to form carbonic acid, which dissociates into hydrogen ions (H⁺), lowering the pH and making the environment more acidic
- A lower pH (more acidic) decreases haemoglobin’s affinity for oxygen.
This causes the oxygen-haemoglobin dissociation curve to shift to the right, which facilitates greater oxygen unloading in tissues that need it most (e.g., active muscles).
What is myoglobin? Where is it found?
How does Mb form a buffer store of oxygen in muscle?
What is the main factor affecting amount of oxygen carried in blood?
How is CO2 transported back to the lungs?
- RBCs carry CO2 back to lungs
- Although CO2 soluble inw ater, solubility not enough to carry all CO2 bakc to lungs
- So, red cells conveRT co2 TO BICARBONATE via cabronic anhydrase
- Bicarbonate formed expelled into plasma, carried in venous blood back to lungs. As this happens, Cl- diffuses into red cell to mainain electrical neutrality
- In lungs, bicarbonate re-enters red cells, converted back to CO2, to be released by alveoli.
- Chloride leaves the red
cell to balance the electrical charge of the bicarbonate entering the cell - CO2 is also carried to the lungs in the
form of carbaminohaemoglobin. CO2
can bind to the oxyhaemoglobin and
displace oxygen in acid conditions. - In the lungs the high partial
pressure of oxygen and high pH
displaces the CO2 from the
haemoglobin and
oxyhaemoglobin is reformed.
What is the affect of CO binding to Hb?
Carbon monoxide (CO) gas binds to haemoglobin with an affinity 210
times that of oxygen to form carboxyhemoglobin. Once CO binds to one of
the haem groups on a haemoglobin molecule it is very difficult to detach
because of its high affinity.
The binding of one CO molecule
to Hb increases the affinity of
the other binding spots to
oxygen, leading to a left shift in
the oxygen dissociation curve.
This prevents oxygen unloading
in the peripheral tissues and
therefore the oxygen
concentration of the tissue is
much lower than normal.
