D6 Gas Transport Flashcards
What is the inner surface of the alveolus lined by?
The inner surface of the alveolus is lined by a special type of alveolar cell called a pneumocyte
What is the structure of type 1 pneumocytes?
Type I pneumocytes are very thin in order to mediate gas exchange with the bloodstream (via diffusion)
WHat is the structure of type 2 pneumocytes?
Type II pneumocytes secrete a pulmonary surfactant in order to reduce the surface tension within the alveoli
What are alveolar air spaces surrounded by?
Alveolar air spaces are surrounded by a dense network of capillaries, which transport respiratory gases to and from the lungs
Where are capillaries in the lungs located and what is their structure?
The capillaries are located close to the pneumocytes and are composed of a very thin, single-layer endothelium
What do capillaries transport?
The capillaries transport oxygen within red blood cells
How may white blood cells travel into the lung tissue?
white blood cells may extravasate into the lung tissue
how is oxygen transported around the body?
Oxygen is transported throughout the body in red blood cells, which contain an oxygen-binding protein called haemoglobin
What is the structure of haemoglobin?
Haemoglobin is composed of four polypeptide chains, each with an iron-containing heme group that reversibly binds oxygen
How many oxygens can bind to Hb?
As such, each haemoglobin can reversibly bind up to four oxygen molecules (Hb + 4O2 = HbO8)
What happens after each oxygen molecule binds to Hb?
As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
Where will Hb have a higher affinity for oxygen?
This means haemoglobin will have a higher affinity for O2 in oxygen-rich areas (like the lung), promoting oxygen loading
Where will Hb have a lower affinity for oxygen?
Conversely, haemoglobin will have a lower affinity for O2 in oxygen-starved areas (like muscles), promoting oxygen unloading
What does an oxygen dissociation curve show?
Oxygen dissociation curves show the relationship between oxygen levels (as partial pressure) and haemoglobin saturation
Is the saturation of Hb linear? Why
Because binding potential changes with each additional O2 molecule, the saturation of haemoglobin is NOT linear
What is the shape of the oxygen dissociation curve for adult Hb?
The oxygen dissociation curve for adult haemoglobin is sigmoidal (i.e. S-shaped) due to cooperative binding
When is there a low saturation of Hb?
There is a low saturation of haemoglobin when oxygen levels are low (haemoglobin releases O2 in hypoxic tissues)
When is there a high saturation of Hb?
There is a high saturation of haemoglobin when oxygen levels are high (haemoglobin binds O2 in oxygen-rich tissues)
Does foetal haemoglobin have the same composition as adult haemoglobin?
The haemoglobin of the foetus has a slightly different molecular composition to adult haemoglobin
How does the affinity of foetal Hb compared to adult Hb?
Consequently, it has a higher affinity for oxygen (dissociation curve is shifted to the left)
Why is the different affinity in foetal Hb important?
This is important as it means fetal haemoglobin will load oxygen when adult haemoglobin is unloading it (i.e. in the placenta)
When is foetal Hb almost entirely replaced by adult Hb?
Following birth, fetal haemoglobin is almost completely replaced by adult haemoglobin (~ 6 months post-natally)
What are the applications of foetal Hb?
Fetal haemoglobin production can be pharmacologically induced in adults to treat diseases such as sickle cell anaemia
What is myoglobin?
Myoglobin is an oxygen-binding molecule that is found in skeletal muscle tissue
What is the structure of myoglobin and how does this make it differ from Hb?
It is made of a single polypeptide with only one heme group and hence is not capable of cooperative binding
What is the shape for the oxygen dissociation curve of myoglobin?
Consequently, the oxygen dissociation curve for myoglobin is not sigmoidal (it is logarithmic)
What is the shape for the oxygen dissociation curve of myoglobin?
Consequently, the oxygen dissociation curve for myoglobin is not sigmoidal (it is logarithmic)
How does the affinity of myoglobin Hb differ from adult Hb?
Myoglobin has a higher affinity for oxygen than adult haemoglobin and becomes saturated at lower oxygen levels
Why is myoglobins high affinity important?
Myoglobin will hold onto its oxygen supply until levels in the muscles are very low (e.g. during intense physical activity)
Why is the delayed release of oxygen by myoglobin important?
The delayed release of oxygen helps to slow the onset of anaerobic respiration and lactic acid formation during exercise
What are the 3 ways for CO2 to be transported?
Some is bound to haemoglobin to form HbCO2
A very small fraction gets dissolved in water and is carried in
solution (~5% – carbon dioxide dissolves poorly in water)
The majority (~75%) diffuses into the erythrocyte and gets converted into carbonic acid
How does CO2 combine with Hb but not compete with O2 binding?
carbon dioxide binds to the globin and so doesn’t compete with O2 binding
TRANSPORT AS CARBONIC ACID
1. What does CO2 combine with when it enters the erythrocyte? What catalyses the reaction?
When CO2 enters the erythrocyte, it combines with water to form carbonic acid (reaction catalysed by carbonic anhydrase)
TRANSPORT AS CARBONIC ACID
2. What happens to the carbonic acid?
The carbonic acid (H2CO3) then dissociates to form hydrogen ions (H+) and bicarbonate (HCO3–)
TRANSPORT AS CARBONIC ACID
3. What happens to the bicarbonate ions? What is the purpose?
Bicarbonate is pumped out of the cell in exchange with chloride ions (exchange ensures the erythrocyte remains uncharged)
TRANSPORT AS CARBONIC ACID
4. What does the bicarbonate in the blood plasma combine with?
The bicarbonate in the blood plasma combines with sodium to form sodium bicarbonate (NaHCO3), which travels to the lungs
TRANSPORT AS CARBONIC ACID
5. what is the role of the H+ ions in the erythrocyte?
The hydrogen ions within the erythrocyte make the environment less alkaline, causing haemoglobin to release its oxygen
TRANSPORT AS CARBONIC ACID
6. What acts as a buffer in the Hb?
The haemoglobin absorbs the H+ ions and acts as a buffer to maintain the intracellular pH
TRANSPORT AS CARBONIC ACID
7. What happens when the RBC reaches the lungs?
When the red blood cell reaches the lungs, bicarbonate is pumped back into the cell and the entire process is reversed
What can be formed (2) when carbonic acid loses protons?
Carbonic acid may then lose protons (H+) to form bicarbonate (HCO3–) or carbonate (CO32–)
What do the released H+ ions do to the blood?
The released hydrogen ions will function to lower the pH of the solution, making the blood plasma less alkaline
What is sensitive to changes in blood pH?
Chemoreceptors are sensitive to changes in blood pH and can trigger body responses in order to maintain a balance
How do the lungs regulate blood pH?
The lungs can regulate the amount of carbon dioxide in the bloodstream by changing the rate of ventilation
How do the kidneys control the blood pH?
The kidneys can control the reabsorption of bicarbonate ions from the filtrate and clear any excess in the urine
What is the range for blood pH?
The pH of blood is required to stay within a very narrow tolerance range (7.35 – 7.45) in order to avoid the onset of disease
What in the blood buffers the pH?
This pH range is, in part, maintained by plasma proteins which act as buffers
How does a buffering solution resist changes to pH?
A buffering solution resists changes to pH by removing excess H+ ions (↑ acidity) or OH– ions (↑ alkalinity)
What molecules can buffer pH?
Amino acids are zwitterions – they may have both a positive and negative charge and hence can buffer changes in pH
How do amino acids act as buffers?
The amine group may take on H+ ions while the carboxyl group may release H+ ions (which form water with OH– ions)
What does the oxyhaemoglobin dissociation curve demonstrate?
The oxyhaemoglobin dissociation curve demonstrates the saturation of haemoglobin by oxygen under normal conditions
Does pH affect the Hb curve?
pH changes alter the affinity of haemoglobin for oxygen and hence alters the uptake and release of O2 by haemoglobin
How does CO2 affect the pH of the blood? What does this trigger Hb to do?
Carbon dioxide lowers the pH of the blood (by forming carbonic acid), which causes haemoglobin to release its oxygen
What is the Bohr Effect?
This is known as the Bohr effect – a decrease in pH shifts the oxygen dissociation curve to the right
What do cells with increased metabolism release?
Cells with increased metabolism (i.e. respiring tissues) release greater amounts of carbon dioxide (product of cell respiration)
Why is a high CO2 conc. in respiring cells beneficial?
Hence haemoglobin is promoted to release its oxygen at the regions of greatest need (oxygen is an input of cell respiration)
What receives signals from chemoreceptors to control ventilation?
he respiratory control centre in the medulla oblongata responds to stimuli from chemoreceptors in order to control ventilation
What is the role of central chemoreceptors?
Central chemoreceptors in the medulla oblongata detect changes in CO2 levels (as changes in pH of cerebrospinal fluid)
What is the role of peripheral chemoreceptors?
Peripheral chemoreceptors in the carotid and aortic bodies also detect CO2 levels, as well as O2 levels and blood pH
What increases during exercise?
During exercise metabolism is increased, which results in a build up of carbon dioxide and a reduction in the supply of oxygen
- What does the build-up of CO2 during exercise trigger?2
These changes are detected by chemoreceptors and impulses are sent to the respiratory control centre in the brainstem
- exercise - where are singles from brainstem sent?
Signals are sent to the diaphragm and intercostal muscles to increase the rate of ventilation (this process is involuntary)
- what is the role of an increase in ventilation rate?
As the ventilation rate increases, CO2 levels in the blood will drop, restoring blood pH (also O2 levels will rise)
- what are long term effects of continual exercise?
Long term effects of continual exercise may include an improved vital capacity
what is partial pressure?
Partial pressure is the pressure exerted by a single type of gas when it is found within a mixture of gases
What two factors determine the partial pressure of a gas?
The partial pressure of a given gas will be determined by:
The concentration of the gas within the mixture (e.g. oxygen forms roughly 21% of the atmosphere)
The total pressure of the mixture (e.g. atmospheric pressure)
What is the partial pressure at high altitudes?
At high altitudes, air pressure is lower and hence there is a lower partial pressure of oxygen (less O2 because less air overall)
How is O2 uptake affected at low partial pressures?
This makes it more difficult for haemoglobin to take up and transport oxygen (lower Hb % saturation)
What does a lower O2 uptake lead to?
Consequently, respiring tissue will receive less oxygen – leading to symptoms such as fatigue, headaches and rapid pulse
In what two ways will red blood cells acclimatise to lower oxygen levels at high altitudes?
Red blood cell production will increase in order to maximise oxygen uptake and transport
Red blood cells will have a higher haemoglobin count with a higher affinity for oxygen
How will vital capacity acclimate to lower oxygen levels at high altitudes?
Vital capacity will increase to improve rate of gas exchange
How will muscles acclimate to lower oxygen levels at high altitudes?
Muscles will produce more myoglobin and have increased vascularisation to improve overall oxygen supply
How will kidneys acclimate to lower oxygen levels at high altitudes?
Kidneys will begin to secrete alkaline urine (removal of excess bicarbonates improves buffering of blood pH)
How will lungs acclimate to lower oxygen levels at high altitudes?
People living permanently at high altitudes will have a greater lung surface area and larger chest sizes
What are the benefits of high altitudes?
Professional athletes will often incorporate high altitude training in order to adopt these benefits prior to competition
In what two ways do athletes make use of high altitudes?
Athletes may commonly either train at high altitudes (live low – train high) or recover at high altitudes (live high – train low)
What is emphysema?
Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
What does the loss of elasticity lead to?
The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
What does the degradation of the alveolar walls lead to/
The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)
What is the major cause of emphesyma?
The major cause of emphysema is smoking, as the chemical irritants in cigarette smoke damage the alveolar walls
What does damage to lung tissue lead to?
The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
What does elastase lead to?
This elastase, released as part of an inflammatory response, breaks down the elastic fibres in the alveolar wall
What can be another cause of emphysema apart from smoking?
A small proportion of emphysema cases are due to a hereditary deficiency in this enzyme inhibitor due to a gene mutation
Is there a cure for emphysema?
There is no current cure for emphysema, but treatments are available to relieve symptoms and delay disease progression
How are bronchodilators used to treat emphysema?
Bronchodilators are commonly used to relax the bronchiolar muscles and improve airflow
How can corticosteroids be used to treat emphysema?
Corticosteroids can reduce the inflammatory response that breaks down the elastic fibres in the alveolar wall
How can enzyme inhibitors be used to treat emphysema?
Elastase activity can be blocked by an enzyme inhibitor (α-1-antitrypsin), provided elastase concentrations are not too high
How can oxygen supplementation be used to treat emphysema?
Oxygen supplementation will be required in the later stages of the disease to ensure adequate oxygen intake
How can surgery be used to treat emphysema?
In certain cases, surgery and alternative medicines have helped to decrease the severity of symptoms
