Gas Exchange Flashcards
What is the pressure of the thoracic cavity compared to atmospheric air?
-ve pressure
What is the elastic property of lung tissue?
Wants to collapse/deflate
What structures bound the thoracic cavity?
Ribs, sternum, diaphragm
What keeps the lungs semi-inflated even during exhalation?
-ve pressure
What does high lung compliance indicate?
A small change in pressure leads to a large change in volume
How is compliance defined mathematically?
Change in volume/change in pressure
What substance increases lung compliance?
Surfactant
What are the benefits of surfactant in the lungs?
- Reduced energy needed to inflate lungs
- Prevents transudate (fluid) coming out of capillaries
What type of cells produce surfactant?
Type II pneumocytes
What disease states can alter lung compliance?
- Lack of surfactant (e.g., respiratory distress syndrome)
- Increase in connective tissue (e.g., fibrosis)
- Reduced lung elastic tissue (e.g., emphysema)
What type of process is inspiration?
Active or passive?
Active process
What happens during inspiration to lower pressure?
Increases volume of the thorax
What are the steps involved in inspiration?
- Diaphragm contracts and flattens
- External intercostal muscles contract to aid ribs opening
- Increased thoracic volume lowers pressure
- Lungs expand, increasing lung volume
- Air is drawn into the alveoli
What type of process is expiration at rest?
Active or passive?
Passive process
What occurs during passive expiration?
- Diaphragm relaxes, reducing thorax volume
- Thoracic wall and ribs return to resting position
- Elastic lung recoils, expelling air
What muscles are involved in active expiration?
- Internal intercostal muscles
- Accessory muscles (e.g., abdominal muscles)
How does ventilation differ in the horse?
- Firm thoracic wall shows biphasic inspiration and expiration
- Active and passive phases
What does partial pressure Px refer to?
Pressure exerted by a single gas
What is the principle of gas movement related to partial pressure?
Gas moves from area of high Px to low Px
What is the ultimate goal of respiration?
To keep correct concentrations of certain molecules in the tissues for correct function: O2, CO2, H+
These molecules are essential for cellular metabolism and maintaining homeostasis.
How are gases exchanged during respiration?
Via simple diffusion from alveolus to blood (external respiration) and from blood to tissue (internal respiration)
This process relies on concentration gradients.
What does Fick’s Law describe?
Factors influencing the rate of diffusion of a gas across a membrane, including:
* SA of membrane
* Membrane thickness
* Partial pressure difference
* Diffusion coefficient
Fick’s Law is crucial for understanding gas exchange efficiency.
What can affect gas diffusion according to Fick’s Law?
Diseases affecting:
* Alveolar destruction (SA)
* Fibrosis or edema (thickness)
* Ventilation disturbances
* Perfusion disturbances
Diseases like emphysema or pulmonary fibrosis can significantly impair gas exchange.
Describe external respiration for O2.
Diffusion of O2 from alveolus into blood follows pressure gradient
Rapid equilibriation occurs between capillary and alveolar PO2.
How does the rate of O2 diffusion change during external respiration?
Slower rate as PO2 difference gets smaller
This is due to the decreasing gradient as O2 diffuses into the blood.
Describe external respiration for CO2.
Diffusion of CO2 from blood to alveolus
PCO2 in blood varies depending on metabolic activity in different body regions.
What is internal respiration?
Diffusion down the pressure gradient of O2 from blood to interstitial fluid, and vice versa for CO2
This process is crucial for cellular respiration.
How is O2 primarily transported in the blood?
Most is transported by hemoglobin within RBCs
O2 has low solubility in blood, making hemoglobin essential for transport.
What is the role of iron-based haem groups in hemoglobin?
Haem binds to molecular oxygen
Each hemoglobin molecule contains 4 haem groups.
What happens when the first O2 binds to hemoglobin?
Causes a conformational change in hemoglobin
This change increases the affinity for subsequent O2 binding.
What does the Oxygen Dissociation Curve represent?
The relationship between PO2 and hemoglobin saturation
It illustrates how hemoglobin’s affinity for O2 changes with different partial pressures.
When is hemoglobin’s affinity for O2 low?
When PO2 is low, such as in tissues
This encourages hemoglobin to release O2 where it is needed most.
How is CO2 transported in the blood?
As:
* dissolved in plasma
* bound to amine group of hemoglobin
* as bicarbonate ions (HCO3)
This transport is crucial for maintaining acid-base balance.
What is the significance of bicarbonate (HCO3) in the blood?
Contributes to the bicarbonate buffer system, helping to buffer dramatic changes to pH
This system is vital for maintaining acid-base homeostasis.
Why is carbon monoxide (CO) considered poisonous?
Binds to hemoglobin with 200-300x greater affinity than O2
This binding is ‘irreversible’ and displaces O2, leading to hypoxia.
