BIOL10002 Lecture Notes - Lecture 17: Sickle-Cell Disease, Carbonic Anhydrase, Respiratory Pigment
Lecture 17
Respiration, part 1
Respiration
Respiration oxidation of the end-products of glycolysis, breathing or cellular respiration
Ventilation movement of the medium (air, water) over a gas exchange surface.
Respiratory mediums
O2 doesn’t dissolve as easily in water as CO2 So air is a better respiratory medium than water.
More energy is required to move O2 through water than over a gas exchange site.
Hypoxia = low O2 (in blood or environment), Anoxia = complete absence of O2 in environment, Hypercapnia = excessively high
CO2 levels in blood (low O2)
Rate of diffusion of O2 between air and body fluids depends on the difference between partial pressures
Small animals can take up oxygen directly from environment through body surface (simple diffusion)
Note: diffusion is the only way to get oxygen into tissues.
In larger animals, there is a greater demand for oxygen; 1. Higher cellular metabolic rate, 2. Reduction in surface area available
for gas exchange, 3. They are too large for diffusion
Oxygen must be soluble, so it can dissolve into liquid around the alveoli. Otherwise the cells would die.
Gas exchange is maximised by Fick’s Law. 1. surface area, 2. pressure/concentration difference, 3. Distance (thickness), 4.
Diffusion coefficient
Oxygen cascade: ever-decreasing pp of O2 as you go through the system, but starting with enough so there are still 2
milometers of oxygen left in the mitochondria
An exchange site has; 1. high surface area, 2. high pressure difference, 3. Many blood vessels on surface
Ventilation systems maintain constant supply of medium across the respiratory exchange site improves rate of gase
exchange fresh supplies of O2-rich medium are supplied to the exchange surface
Transport of oxygen
Without body fluids only 0.3% of dissolved oxygen would be held.
Oxygen-carrying capacity of blood is increased by respiratory pigments:
- complexes of proteins and metal ions, have a characteristic colour that changes when it binds O2
- Haemoglobin (Hb): dark→ bright red when oxygenated
- Haemocyanin: colourless → blue when oxygenated (has copper instead of iron hence difference in colour)
Respiratory pigments Haemoglobin (Hb)
- each heme group can bond with one O2 molecule 4 heme units per Hb = 4 × O2 molecules
- CO = stronger heme group binding affinity than O2 => carbon monoxide poisoning
Different environments can change how easily oxygen is bound to haemoglobin: binding affinity
Type of respiratory pigment e.g. muscles – bind oxygen more strongly than Hb *Llama haemoglobin
pH – blood in active tissues has a lower pH and H+ ions bind to the haemoglobin molecule in place of O2 lots of CO2 = decrease
in PH = decrease in O2 binding affinity
2,3-bisphosphoglyceric acid (BPG) – lowers the affinity of hb for O2 - delivers more O2 where it’s needed
Transport of carbon dioxide
- Converting CO2 to H2CO3 decreases the PCO2 in the blood, causing more CO2 to diffuse out of tissues
- If [carbonic acid] increases, reaction will reverse (as reverse reaction is also catalysed by carbonic anhydrase) so this is
prevented by removing the bicarbonate ions from red blood cells.
1. Tissues produce CO2, which diffuses out into capillary then into blood cells
2. 10% of CO2 is held in blood plasma (compared to 0.3% O2), 30% reversibly bound to Hb (carbaminohaemoglobin), remainder
(60%) catalysed into bicarbonate
3. Carbonic acid naturally disassociates into bicarbonate ions and protons
4. Bicarbonate ions swapped for chlorine ions to maintain appropriate change across membrane:
Chloride shift – bicarbonate ions get taken back into RBC and chloride ions are pumped out, so increase of bicarb within blood
cell creates carbonic acid, which then is converted back into CO2 and H2O by carbonic anhydrase
Stuff that shouldn’t happen
Sickle cell anaemia
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Respiration oxidation of the end-products of glycolysis, breathing or cellular respiration. Ventilation movement of the medium (air, water) over a gas exchange surface. O2 doesn"t dissolve as easily in water as co2 so air is a better respiratory medium than water. More energy is required to move o2 through water than over a gas exchange site. Hypoxia = low o2 (in blood or environment), anoxia = complete absence of o2 in environment, hypercapnia = excessively high. Rate of diffusion of o2 between air and body fluids depends on the difference between partial pressures. Small animals can take up oxygen directly from environment through body surface (simple diffusion) Note: diffusion is the only way to get oxygen into tissues. In larger animals, there is a greater demand for oxygen; 1. Reduction in surface area available for gas exchange, 3. Oxygen must be soluble, so it can dissolve into liquid around the alveoli. Gas exchange is maximised by fick"s law.
