Respiratory System Flashcards
(21 cards)
Describe the physical law that governs the movement of air into and out of the lungs.
- Boyle’s Law defines the relationship between gas pressure, and volume - pressure is inversely proportional to volume.
- During inspiration, the diaphragm and external intercostal muscles contract, increasing the volume of the thoracic cavity.
- Due to Boyle’s law, pressure decreases below atmospheric levels and therefore air will move down the pressure gradient and into the lungs.
Describe the three pressures involved in pulmonary ventilation.
- Atmospheric pressure: 760mm/Hg, is the basis for pulmonary ventilation.
- Intrapulmonary pressure: 760mmHg therefore no difference in atmospheric pressure.
- Intrapleural pressure: 756mmHg, therefore is slightly lower than atmospheric pressure. This is due to the elasticity of the lung. When the lung tries to recoil, it pulls the membrane so the visceral pleura is being pulled away from the parietal pleura, increasing the volume and decreasing the pressure.
Describe the process of inhalation and exhalation.
At rest:
Inhalation:
- diaphragm and external intercostals contact to increase the volume of thoracic cavity.
- Pressures drops to be sub atmospheric and therefore air moves into the lungs, filling the lungs with the maximum amount of oxygen. This means exchange can occur so oxygen comes in and carbon dioxide comes out.
Exhalation:
- The elastic tissue of the lungs recoil the lungs back to atmospheric pressure and due to the inward pull of surface tension of alveolar fluid.
- As the volume decreases, the intrapulmonary pressure increases and the air flows out.
Forceful breathing:
Inspiration:
- sternocleidomastoid muscle and scalene muscles pull the ribcage upward to increase the thoracic cavity volume.
Expiration:
- Internal intercostal muscles and abdominals contract to flex the trunk and compress the abdomen, decreasing the volume of the thoracic cavity and therefore increasing the intrapulmonary pressure.
Describe the factors that affect pulmonary ventilation.
- Lung compliance: The ease at which the lungs can stretch and expand. Most of the work is due to overcoming resistance of elastic lungs and thoracic cage to stretching. Lungs that are less compliant mean more work is required (increasing pressure) to produce inflation.
- Elasticity: The inverse of compliance which is readily the lungs rebound after being stretched, because they have a natural tendency to collapse. But due to elastic fibres and surface tension the lungs do rebound.
- Surface tension of alveolar fluid: Surfactant reduces the surface tension of water. Low surface tension increases compliance but decreases elasticity because water molecules try to move close together (like absorbs like) so if you have a greater surface tension, you will get more rebound.
- Airways resistance: Airflow is inversely proportional to airway resistance. It is the friction air encounters moving through a passage way. The primary determinant of resistance is the radius of conducting airways were F=change in pressure/ radius.
What are the different lung volumes and capacities?
Lung volumes:
Tidal volume: breathing at rest
inspiratory reserve: The volume of air you inspire on top of normal breathing
Expiratory reserve: The air you expire when breathing out forcefully.
Residual volume: The constant amount of air volume you have in your lungs - can’t remove it.
Lung Capacities:
Inspiratory: Total amount of air during inspiration - tidal volume + inspiratory reserve.
Functional residual: Total amount of expired air + residual volume
Vital: total amount of air which can be exchanged = inspiratory capacity + functional residual
Total lung: Everything - form highest point (inspiratory reserve) to minimal volume, = inspiratory capacity + functional residual capacity.
What is respiratory minute volume, alveolar ventilation, and anatomic dead space?
Respiratory minute volume: the amount of air moved in and out of our lungs in one minute = respiratory rate x tidal volume.
Anatomic dead space: Fresh air in our conducting pathways which does not part take in gas exchange, ie., in the trachea, bronchi, and bronchioles.
Alveolar ventilation: how much air is reaching our alveoli to undergo gas exchange = respiratory rate x (tidal volume - anatomical dead space)
What factors govern the exchange of gases among the air, blood, and tissues?
Fick’s law: Relates to the rate of diffusion. States that diffusion is proportional to surface area, partial pressure gradient and permeability. Diffusion is inversely proportional to distance.
Dalton’s Law: States that each gas in a mixture exerts its own pressure known as partial pressure. The partial pressure is proportional to its concentration in the mixture. Partial pressure = total pressure x fictional constant (fractional composition of the gas in the mixture).
Henry’s Law: States that the quantity of gas that dissolves in a mixture is proportional o the partial pressure and solubility coefficient.
What are the normal partial pressures of O2 and CO2 in the air, blood, and tissue?
Air:
PO2 = 160
PCO2 = 0
Blood and Lungs: Arterial blood
PO2 = 100mmHg
PCO2 = 40 mmHg
Tissue:
PO2 = 40
PCO2 = 45
What is the function of haemoglobin?
Transports a maximum of four oxygen molecules per haemoglobin molecule. This is because oxygen cannot travel through the blood on red blood cells since it is not dissolvable in blood.
Therefore it requires a transport protein.
Haemoglobin establishes an equilibrium with O2 to form oxyhemoglobin. O2 is unloaded at the lungs and tissues.
Describe the physiological significance of the oxygen-haemoglobin curve and why it is advantageous during exercise.
- The oxyheamoglobin curve shows the % of haemoglobin saturation vs PO2.
- Higher PO2 leads to greater Hb saturation because when one oxygen binds, it becomes more favourable to another, therefore causing a cascade.
- Even if you lose a lot of O2 because the PO2 drops, your Hb molecules will still have a lot of available oxygen attached (100% saturation) until the partial drops to roughly 40mm/hg from 100. This is called the plateau region on the graph.
- Therefore, we still have a good oxygen reserve, and unless PO2 drops to below 60mmHg, normal amounts of O2 can still be carried to cells to perform vital functions, such as during exercise.
- The curve can shift to the right, under exercise conditions such as increased body temperature, and therefore more oxygen can be released to our tissues even when at lower PO2 of oxygen.
What is the Bohr effect?
- The Bohr effect is the effect of pH from CO2.
- When Co2 is in solution in plasma, it binds with H20 to form carbonic acid (H2CO3) using carbonic anhydrase as an enzyme. H2Co3 can disassociate to release H+ and form hydrogen carbonate. This release of hydrogen ions decreases the pH of the interstitual fluid, causing the oxyheamoglobin curve to shift to the right. This offloads more oxygen to nearby cells as a result.
What are the three effects of Haemoglobin’s Affinity for oxygen and what happens when you shift the curve either way in response to this?
- pH: Increasing pH shifts the curve to the left, increasing the binding of of oxygen to Hb. Shifting to the right decreases unloading of O2 from Hb as pH decreases.
- Temperature: Decreasing temperature shifts curve to the left, increasing temp shifts curve to the right.
- Effect of PCO2: Decreased partial pressure shifts curve to the left whilst increasing PCO2 shifts curve to the right.
How does neural control of respiration work?
Neural:
- involuntary control of breathing, controlled by neurons in the pons and receptor feedback from lungs and airways.
- The phrenic nerve innervates the diaphragm whilst the lower intercostal nerves innervate the intercostal muscles involved in inspiration. They stimulate a contraction and hence cause inhalation. When the impulse ceases, these muscles relax and the passive process of expiration occurs.
- There are two neuronal groups in the medullary centre which also play a role in breathing.
- The dorsal respiratory group (DRG) is an inspiratory centre involved in both quiet and forced breathing.
The ventral respiratory group (VRG) is the inspiratory and expiratory centre, and functions in forced breathing only. - The neurons of the pons adjust the breathing rate and depth to match metabolic demands, therefore people who damage the pons don’t have a smooth pattern in between breaths.
How does the chemical control of respiration work?
- there are two types of chemoreceptors which detect PO2, PCO2, and H+ levels.
1) peripheral chemoreceptors:
- located in the aorta and carotid arteries.
- Strongly detect changes in pH
- Weak resonse to PCo2 directly
- Weak response to PO2 - only when very low levels.
2) central chemoreceptors:
- located in the medulla
- detect pH in cerebrospinal fluid caused by changes in arterial PCO2.
- If a low pH is detected, this means that there is a high amount of CO2 in the CSF because CO2 can easily move across the blood-brain barrier but H+ are not easily diffsuable. Therefore, we know that there are high CO2 concentrations which are undergoing the equilibrium reaction. Therefore we need to exert more CO2, and will breathe out more readily and forcefully.
How do the neuronal and chemical control of respiration interact?
- Neural response is the primary tool we use, however the chemical control is a secondary thing put in place.
Describe the negative feedback loop of increased arterial PCO2 levels (hypercapnia).
1) Chemoreceptors in the medulla detect a decrease in pH at the CSF.
2) information is sent by afferent neurons to the medulla control centre via nerve impulses.
3) The medulla oblongata processes this information and adjusts breathing rate accordingly, through stimulation of respiratory muscles.
4) Abdominals and external intercostals are innervated by motor nerves (nerves T7-T12, and T8-12, and intercostal nerves) to expire forcefully.
5) These effectors (muscle cells) trigger a response to expire forcefully and remove CO2.
6) CO2 levels decrease, shifting equilibrium to the left and increasing the pH.
How does ventilation affect the blood gasses? Talk about hyperventilation in response.
- As areolar ventilation increases, PO2 increases and PCO2 decreases.
- As CO2 is mores soluble than O2, changes in alveolar respiration affect the number of dissolved CO2 more than O2.
- Hyperventilation blows off CO2, removing the stimulus to breathe.
- Therefore, you can hold your breath for a longer period of time because it takes longer to build up those levels of carbon dioxide.
How do the inspiration and expiration times compare to to what is expected for normal breathing based on the rhythm set by our medullary respiratory centre
Inspiration takes a shorter mount of time because this is an active process and expiration is a passive process.
- During inspiration, the volume of the thoracic cavity is increasing, therefore the resistance to airflow decreases, hence why it is easier for air to flow in.
- During expiration however, the lungs are collapsing through the passive recoiling of elastic tissue and therefore, as volume is decreasing, resistance to airflow is increasing, making it harder to air to escape and hence why it takes longer to complete.
During which phase of respiration can the breath be held longer? Why is this?
- After inspiration because the lungs have a full volume of gas. This means that it takes longer for CO2 to build up because more gas exchange can occur in the lungs.
- After expiration you have little gas in the lungs, therefore there is a more rapid build of CO2 during gas exchange into the blood, and therefore the stimulus to breath occurs faster.
Explain the effect of holding the breath on the recovery breathing pattern (rate and depth) post breath hold.
- Breathing rate and depth will increase after holding your breath.
- Depth will increase because more O2 is required to by filling the lungs with gas, this allows for more gas exchange.
- Rate increases because the partial pressure of CO2 has increased, therefore we require more frequent exhalation to remove it.
What happens to the partial pressure of gases after rebreathing (breathing in air that had previously been expired)?
- No changes to breathing rate but breathing depth increases.
- Breathing in expired air increases the PCO2 level further and is not breathing in an oxygen rich air.
- This means, after this process breathing will become deeper to increase the the amount of O2 entering the body.
