D6 Transport of Respiratory Gases Flashcards
Transport this fart bitch
Partial Pressure
The individual pressure exerted by a particular gas within a mixture of gases
At sea level the total atmospheric pressure is 760 mmHg
Partial pressure = total pressure times fractional composition of the gas in mixture
E.g Total pressure = 760 mmHg, 21% of that is O2 so,
pO2 = 760 x 0.21 = 159.6, around 160 mmHg
Gases diffuse from areas of higher partial pressure to areas of lower partial pressure
Partial pressure during ventilation & respiration
1) Inspiration
160mmHg of pO2 in air. During inspiration the O2 moves into the alveoli.
In the alveoli, the pO2 is 108mmHg
2) Exhalation
40mmHg of pO2 in deoxy blood arriving at alveoli.
Since in the alveoli 108mmHg > 40mmHg, the oxygen diffuses directly into the blood from the alveoli
3) Departing Blood
Oxygen enters the blood and by the time it leaves the alveoli the mmHg = 100.
The blood returns back to the heart
4) In Arteries and Arterioles
No gas exchange occurs, this is because the pO2 is still at 100mmHg as it is entering the systemic capillaries
5) Diffusion
The resting body cells have a partial pressure of 40mmHg
40 < 100 so the O2 diffuses within the cells.
The O2 diffuses out of the capillary so that when the blood is leaving through the veins its partial pressure is 40mmHg
The deoxygenated blood goes to the vena cava and gets pumped by the right side of the heart.
When exercising
The pO2 in body tissue, in the blood leaving tissue capillaries and in the blood arriving at the alveoli decreases
Oxygen dissociation curves
Demonstrates the affinity of haemoglobin for oxygen
O2 is transported in the body within erythrocytes
Erythrocytes have an oxygen binding molecule known as a haemoglobin
Haemoglobin
Composed of four polypeptide chains
Each chain has an iron-containing heme group that reversibly binds to O2
4 oxygen molecules can bind to haemoglobin at a time, one per polypeptide chain.
As each oxygen binds, it slightly alters the conformation of haemoglobin, which makes subsequent binding easier this is known as cooperative binding
Haemoglobin also has a higher affinity for O2 in oxygen rich areas (such as the lungs) which promotes oxygen loading.
In oxygen starved areas (such as the muscle) oxygen affinity is decreased, so it promotes oxygen deloading.
Structure and Function of Haemoglobin
Oxygen-binding protein
Heme group (iron-containing pigment) that reversibly binds to oxygen
When binding oxyhemoglobin, when non binded, deoxyhemoglobin
Two different colours, blue & red.
Red Blood Cells
Contain this haemoglobin
O2 binds to the iron within the haemoglobin
It grabs oxygen when the partial pressure of oxygen is high
It lets go of oxygen when the partial pressure of oxygen is low
Haemoglobin Saturation
The percentage of haemoglobin binding sites in the bloodstream occupied by oxygen.
Haemoglobin Affinity
A measure of how tightly haemoglobin attaches to oxygen
High affinity = tight hold.
Myoglobin
Myoglobin is an oxygen binding molecule that is found in skeletal muscle tissue
Myoglobin consists of a single polypeptide with only one heme group and hence it cannot do cooperative binding
Myoglobin’s oxygen dissociation curve is hence logarithmic and not sigmoidal like the adult haemoglobin one.
It has a higher affinity for oxygen than haemoglobin
It is saturated at lower oxygen levels
It holds onto its oxygen supply until levels in the muscle cells are extremely low.
This delayed release of oxygen slows the onset of anaerobic respiration which decreases lactic acid formation during exercise.
Fetal haemoglobin
Fetal haemoglobin is structurally different than adult haemoglobin
It has a higher oxygen affinity than adult
This allows it to load oxygen from the placenta and inclines the adult ones to do unloading.
6 months after birth the cells are replaced with adult cells
They can be pharmacologically induced to treat diseases such as sickle cell anemia
It allows the transfer of oxygen in the placenta on to the fetal haemoglobin
At any given partial pressure of oxygen the fetus will take up oxygen from the mother
Carbon Dioxide Transport
Some carbon dioxide is bound to the haemoglobin to form HbCO2
It binds to the globin, not the heme group meaning that there is no competition for oxygen
Only a very small fraction gets dissolved in the water and is carried in the blood solution
5%
75% (majority) of the CO2 diffuses in the erythrocytes and gets converted into carbonic acid
Transport of CO2 in erythrocytes as carbonic acid
CO2 + H2O → H2CO3 (catalysed by carbonic anhydride)
H2CO2 → H+ + HCO3- (dissociation reaction)
HCO3- is pumped out of the cell in exchange for Cl- ions (ensures that the erythrocyte remains unchanged)
HCO3- is now in the blood plasma and it mixes with Na+ ions to form NaHCO3 (sodium bicarbonate) which travels to the lungs
H+ makes the environment less alkaline, which causes haemoglobin to release its oxygen
Haemoglobin absorbs the H+ and acts as a bugger to maintain the intracellular pH
When red blood cells reach the lungs, HCO3- is pumped back into the cells and the process is reversed
Blood pH
Aqueous carbon dioxide can mix with water in the blood plasma to form carbonic acid.
The carbonic acid can then dissociate
H2CO2 → H+ + HCO3-
H2CO2 → 2H+ + CO3-
The hydrogen ions lower the pH of the blood plasma, making it less alkaline.
Chemoreceptors are sensitive to the pH changes in the blood and can trigger body responses in order to maintain a balance.
They can tell the lungs to monitor the rate of respiration
They can tell the kidneys to control the reabsorption of bicarbonate ions and clear any excess in urine.
The pH of blood has to be maintained around 7.35-7.45 to avoid the onset of disease
This is partially maintained by plasma proteins which act as buffers
The buffering solutions resists changes to pH by removing any XS hydrogen ions (acidic) or hydroxide ions (alkaline)
Amino Acids are zwitterions (they have a positive and a negative charge)
The amine group takes up H+ ions
The carboxyl group releases H+ ions to form H2O
Respiratory Control
Chemoreceptors stimulates the medulla oblongata to control ventilation
Central chemoreceptors detect changes in CO2 levels
Peripheral chemoreceptors also detect changes in CO2, O2 and pH.
During exercise metabolism is increased, which results in a buildup of carbon dioxide and a reduction in the supply of oxygen
These changes are detected by chemoreceptors and impulses are sent to the respiratory control centre in the brainstem
Signals are sent to the diaphragm and intercostal muscles to increase the rate of ventilation (this process is involuntary)
As the ventilation rate increases, CO2 levels in the blood will drop, restoring blood pH (also O2 levels will rise)
Long term effects of continual exercise may include an improved vital capacity
Bohr Shift
Explains the increased release of O2 by respiring tissues
pH changes alter the affinity of haemoglobin for oxygen
When CO2 levels are up, the pH decreases due to the carbonic acid dissociation so it causes the haemoglobin to decrease its affinity and release its oxygen.
This is known as the bohr effect and when pH is low the curve on oxygen dissociation curves shift towards the right.
Effect of Altitude
As altitude increases, the pO2 decreases and O2 saturation also decreases
Effects of less O2 due to altitude depends on how fast you ascend and let your body acclimate (get used to) the altitude.
