D6 Transport of respiratory gases Flashcards
What does the oxygen dissociation curve show?
The affinity of hemoglobin for oxygen
Describes the saturation of hemoglobin by oxygen at different partial pressures of oxygen
What determines the degree to which oxygen binds to hemoglobin?
by the partial pressure of oxygen (pO₂) in the blood
What does the significant change in saturatin over a narrow range of oygen partial pressure represent?
represents oxygen pressures surround cells are under normal metabolism
Where would low pO₂ occur?
in muscles
O₂ will dissociate from hemoglobin
Where would high pO₂ occur?
in the lungs
hemoglobin will become saturated
How is carbon dioxide transported in the blood?
carried in solution and bound to hemoglobin in the blood
In what 3 forms is carbon dioxide carried in in the blood plasma?
- Dissolved as carbon dioxide
- reversibly converted to bicarbonate (hydrogencarbonate) ions (HCO₃-) that are dissolved in the plasma
- bound to plasma proteins
What is the majority of CO2 produced by the body during cellular respiration converted to?
Bicarbonate (hydrogencarbonate) ion
* more soluble
* less toxic
What is the conversion reaction from CO2 to hydrogencarbonate ions catalysed by?
the enzyme carbonic anhydrase
What is the reaction from CO2 to hydrogencarbonate?
is reversible
How is the conversion from carbon dioxide to hydrogencarbonate ions reversible?
In the tissues
* CO2 is generated
* rection proceeds to the right
* more bicarbonate ions is generated as are H+ ions
* =Lowers pH of blood
In the lungs
* CO2 leaves the blood
* reaction proceeds to the left
* bicarbonae ion is converted to carbon dioxide
What does the Bohr shift explain?
explains the increased release of oxygen by hemoglobin in respiring tissues
What release does increased metabolism result in?
greater release of CO2 in the blood
What is the consequence of more CO2 in the blood?
lower pH of the blood
How does acidity from more CO2 in the bood from metabolism do to the Bohr Shift?
- Shifts the oxygen dissociation curve to the right
What does a shift to the right of the oxygen dissociation curve mean?
Shift to the right = increase in acidity
which results in a decreased affinity of the hemoglobin for oxygen
= greater release of oxygen from hemoglobin at the partial pressure of oxygen
How does an increase in CO2 in blood affect the release of oxygen? (i.e. when excerising)
- metabolism increase
- more CO2 released into the blood
- lower the pH
- increased accidity shifts the oxygen dissociation curve to the right
- results in a decreased affinity of the hemoglobin for oxygen
- = greater release of oxygen from hemoglobin at the same partial pressure of oxygen
- ensures that respiring tissues have enough oxygen when their need for ocygen is greatest
How is saturation of hemoglobin able to occur at lower partial pressures of oxygen in the lungs?
Because the pCO2 is lower in the lungs
How does exercise increase the rate of ventilation?
- Exercise increases metabolisms
- leads to an increase in the produciton of CO₂ (waste product of cellular respiration)
- Blood pH decrease because CO₂ dissolves in water to form carbonic acid (H₂CO₃)
- H₂CO₃ dissociated into H+ and HCO₃- (more H+ more acidic)
- Chemoreceptors in the medulla, the aorta and the carotid artery detects a change in blood carbon dioxide
- High levels of carbon diocide in the blood triggers an increase in the ventilation rate in order to rid the body of CO₂ buildup
- CO₂ diffuses into alveoli and ventilation expels it
- explains the hyperventilation in response to exercise
How are changes in the blood carbon dioxude detected in the body?
chemoreceptors in the medulla, the aorta and the arotid artery
What does high levels of carbon dioxide in the blood trigger?
increase in the ventilation rate
What does the increase in ventilation rate do?
get rids of th CO₂ buildup in the body
Ventilation expels the carbon dioxide that diffused into the alveoli
Where is the rate of ventilation regulated by?
by the respiratory centre in the medulla oblongata of the brain stem
Where is the rate of ventilation regulated by?
by the respiratory centre in the medulla oblongata of the brain stem
What are the two sets of nerves that travel to the lungs from the respiratory centre in the medulla oblongata of the brainstem?
- the intercostal nerves
- the phrenic nerves
What do the intercostal and phrenic nerve stimulate?
- intercostal nerves - stimualte the intercostal muscles of the thorax
- phrenic nerves - stimulate the diaphram
What stimulates the lungs to expand?
the intercostal nerves and phrenic nerves from the respiratory centre in the medulla oblongata of the brainstem
What causes the cessation of the signals that stimulate the lungs to expand?
stretch receptors in the walls of the chest and lungs send signals to the respiratory centre which triggers a cessation of the signals leading to inspiration until the animal exhales
What happens after the stretch receptors send signals to trigger the cessation of the signals leading to inspiration?
the animal exhales
then a new signal is sent
What happens when an increase in blood carbon dioxide or a drop in blood pH is detected?
- chemoreceptors in the carotid artery and the aorta sends a message to the breathing centre in the medulla oblongata
- nerve impulses are then sent fro the medulla to the diaphragm and intercostal muscles
- causes them to increase the ventilation rate = increased rate of gas exchange
Where are chemoreceptors present that can detect an increase in blood carbon dioxide?
- carotid artery
- aorta
- medulla oblongata
What range of pH of blood does the body regulate to stay within?
7.35 - 7.45
What does hyperventilation do to carbon dioxide?
withdraws carbon dioxide from the blood driving the carbonic acid reaction to the left
* withdraws hydrogen ions from the blood raising the pH
How can pH be raised in the kidney?
H+ ions can be secreted into the urine bound to buffers to raise the pH
Greater amounts of bicarbonate will be reabsorbed from the tubules to neutralize the acid
How does the kidney respond when the blood becomes to basic?
bicarbonate ions can be secreted into the distal convoluted tubule of the kidney
What can cehmical buffers within the extracellular fluid do and cant do?
- cant remove the acids or bases
- can minimize their effects
What is myoglobin?
a specialized oxygen transport protein in mucles
What does myoglobin have compared to hemoglobin?
- it has a much higher affinity for oxygen
- will only release its oxygen when the PO₂ is quite low (in muscles during heavy exercise)
- Has 1 chain and 1 heme group whereas hemoglobin has 4 chains with 4 heme groups
How is the release of O₂ from hemoglobin more rapid than myoglobin?
- the release of each O₂ from hemoglobin triggers a conformational change, which causes the hemoglobin to more rapidly release subsequent O₂ molecules
How does the O₂ dissociation curves of hemoglobin and myoglobin differ?
What does this graph tell you about the affinity for O₂ in fetal and adults?
fetal hemoglobin has a higher affinity for O₂ at all partial pressures
Why is fetal hemoglobin different from adults?
To ensure that O₂ is transferred to the fetus from the maternal blood across the placenta
How is the pO₂ at high altitude?
low pO₂ in the air
What is the consequence of having a low pO₂ in the air?
- hemoglobin may not become fully saturated
- = tissues may not be adequately supplied with oxygen
How can human physiology to some degree adapt to high altitude?
- increase red blood cell production = increase the toal amount of circulating hemoglobin
- ventilation rate increases to increase gas exchange
- muscles produce more myoglobin to ensure delivery of oxygen to the tissues
What do populations living permanently at high altitude have compared to people living at sea level?
- geater mean lung surface area
- larger vital capacities
- their oxygen dissociation curve shifts to the right , encouraging release of oxygen into the tissue
Describe the entire process of oxygen diffusing out of the cell into respiring tissues starting from CO2 leaving respiring cells
- CO2 leaves respiring cells
- A small concentration dissolves in the plasma
- The majority enters the red blood cells
- Here CO2 combines with water to form carbonic acid
- This reaction is catalysed by the enzyme carbonic anhydrase
- Carbonic acid accumulates in red blood cells and becomes unstable
- H+ ions are relseased
- Hydrogen carbonate ions are released
- These diffuse out of the cell into the plasma
- In order to re-establish the electrical neutrality of the cell chloride ions enter the cell
- Oxyhaemoglobin is reduced to Haemoglobinic acid (HHb) and Oxygen (4O2)
- These diffuses out of the cell into respiring tissues
How does carbon monoxide poisoning affect Hb?
Hb does not get re-saturated
What was the belief in the early part of the 20th century about tabacco smoking?
it could improve ventilation
* even doctos prescribed smoking of medicine for such conditions as asthma
What is emphysema?
A lung condition in which the walls between individual alveoli break down leading to an increase in their size and therefore a reduction in the surface area for gas exchange, which restricts oxygen uptake into the blood
What does this computer tomography scan of the lung show?
One of the characteristic indications of emphysema
* large areas of trapped air (transparent areas in image)
* Lungs trapped in “inspiration” position in the ventilation cycle
* known informally as “barrel chest”
What is the main cause of emphysema?
long term exposure to airborne irritants, most commonly tobacco smoke, but possibly also air pollution, coal and silica dust
What 3 factors that cause damage to lung tissue by smoke?
- oxidation reactions produced by high concentrations of chemicals known as free radicals in tobacco smoke
- Inflammation due to the body responding to the irritating particulates within smoke
- Free radicals and other components of tobacco smoke impair the activity of enzyme alpha-1-antitrypsin which would normally block the activity of proteases that degrade the proteins that maintain the elasticity of the lung
What is a rare genetic cause of emphysema?
a deficiency in the enzyme alpha-1-antitrypsin
Can emphysema be cured?
no
but symptoms can be alleviated and the spread of the disease can be checked by treatment
What is oxygen therapy?
supplies oxygen-enriched air to emphysema patients
How can symptoms of emphysema be alleviated in patients?
- trained in breathing techniques - reduce breathlessness and improve the ability of the patient to exercise
- quitting smoking (prescription medications can faciliate this process)
- sugery - to reduce the volume of lungs by removing damaged lung tissue
- lung transplant
What is the wall of the alveolus composed of?
2 types of cells
* 90% type I
* and type II pneumocytes
What is the difference between type I and type II pneumocytes?
Type I
* 90% of the surface of the alveolus
* extreemly thin
* primary purpose is gas exchange
Type II
* covered in microvilli
* thicker
* function to secrcete surfactant
What is surfactant released by type II pneumocytes?
a substance that reduces surface tension, preventing the alveolus from collapsing
