Topic 6.4 Gas Exchange Flashcards
Physiological respiration
Involves the transport of oxygen to cells within the tissues, where energy production occurs.
Three processes of physiological respiration
- Ventilation: the exchange of air between the atmosphere and the lungs
- Gas exchange: the exchange of oxygen and carbon dioxide between the alveoli and bloodstream
- Cell respiration: the release of energy (ATP) from organic molecules
Purpose of ventilation
Needed to maintain a concentration gradient in alveoli.
- Oxygen is constantly being removed from the alveoli into the bloodstream, and carbon dioxide is continually being released
- Lungs function to ensure that O2 levels sty high in alveoli (diffuses into blood) and CO2 levels stay low (diffuses out of blood)
Respiratory system structure
- Air enters through the nose or mouth and passes through to the trachea until it divides into two bronchi, which connect to the lungs
- The right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to the heart)
- Inside each lung, the bronchi divide into smaller airways called bronchioles, increasing surface area
- Each bronchiole terminates with a cluster alveoli, where gas exchange with the bloodstream occurs
Alveolus structure
- Single-cell epithelial layer to minimize diffusion distances for gases
- Surrounded by a rich capillary network to increase the capacity for gas exchange with bloodstream
- Roughly spherical in shape in order to maximize the available surface area for gas exchange
- Internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream
Pneumocytes (alveolar cells)
Cells that line the alveoli and comprise of the majority of the inner surface of the lungs.
- Two types: Type I and Type II
Type I pneumocytes
- Involved in the process of gas exchange between the alveoli and the capillaries
- Squamous (flattened) in shape and extremely thin, minimizing diffusion distance
- Connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
- Amitotic and unable to replicate, but can be differentiated from Type II pneumocytes
Type II pneumocytes
- Responsible for the secretion of pulmonary surfactant, which reduces surface tension in the alveoli caused by the layer of liquid in the alveoli
- Cuboidal in shape and possess granules for storing surfactant components
- Only comprise a fraction of the alveolar surface but are relatively numerous
Breathing
The active movement of respiratory muscles that enables the passage of air into and out of the lungs, whereby the contraction of respiratory muscles changes the volume of the thoracic cavity.
Boyle’s Law
Pressure is inversely proportional to volume.
- When the volume of the thoracic cavity increases, pressure in the thorax decreases
- When the volume of the thoracic cavity decreases, pressure in the thorax increases
Movement of gas as a mechanism of breathing
Gases will move from a region of high pressure to a region of lower pressure.
- Inspiration: when the pressure in the chest is less than the atmospheric pressure, air will move into the lungs
- Expiration: when the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs
Functions of respiratory muscles
Contract to change the volume of thoracic cavity, altering the pressure in the chest to cause inspiration or expiration.
- Antagonistic groups, meaning when inspiratory muscles contract, expiratory muscles relax (and vice versa)
Inspiratory muscles
The diaphragm and external intercostal muscles, in addition to accessory muscles.
- Diaphragm muscles contract, causing the diaphragm to flatten and increase the volume of the thoracic cavity
- External intercostals contract, pulling ribs upwards and outwards (expanding chest)
- Additional muscle groups may help pull the ribs up and out
Expiratory muscles
The abdominal muscles and internal intercostal muscles, in addition to accessory muscles.
- Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
- Abdominal muscles contract and push the diaphragm upwards during forced exhalation
- Additional muscle groups may help pull the ribs downwards
Lung cancer
Describes the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumor).
- Abnormal growth can impact on normal tissue function, leading to a variety of symptoms
- The tumors can remain in place (benign) or spread to other regions of the body (malignant)
- Lungs possess rich blood supply, increasing risks of cancer spreading (metastasis)
- Symptoms: wheezing, coughing blood, weight loss, etc.
- Causes: smoke (first- and second-hand), pollution, infections, genetic predispositions, radiation, etc.
Emphysema
A lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls.
- Results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
- Can cause holes to develop in alveolar walls and alveoli to merge into huge air spaces
- Symptoms: shortness of breath, phlegm, expansion of ribcage, susceptibility to chest infections, etc.
- Causes: smoking (direct damage to elastic fibers) or more rarely, a hereditary deficiency due to a gene mutation in enzyme preventing breakage of fiber
Influence of exercise over ventilation
- Body’s energy demands are increased, resulting in increased production of CO2 and higher demand for gas exchange
- Increased ventilation rate (greater frequency of breaths)
- Increased tidal volume (volume of air per breath)
Measuring ventilation
Monitored through observation (# of breaths/ minute), chest belt and pressure meter (recording rise and fall of chest), and spirometry (volume of gas/ breath).
- Spirometer: device detecting changes in ventilation
Total lung capacity
Volume of air in lungs after maximal inhalation (around 6 liters for a normal adult male).
Vital capacity
Volume of air that can be exchanged by the lungs via a maximal inhalation and exhalation.
Residual volume
Volume of air that is always present in the lungs (around 20% of total lung capacity).
Tidal volume
Volume of air that is exchanged via normal breathing (around 500ml/ breath).
Factors affecting total lung capacity and ventilation rate
- Height
- Location (altitude)
- Lifestyle (weight, smoking habits, etc.)
Asthma
A common, chronic inflammation of the airways to the lungs.
- Inflammation leads to swelling and mucus production, resulting in reduced airflow
- During an acute asthma attack, constriction of the bronchi smooth muscle may cause significant airflow obstruction
- Symptoms of an asthma attack: shortness of breath, chest tightness, wheezing, coughing, etc.
- Causes: allergens, smoke, cold air, certain medications, arthropods, etc.
- Severe cases may be life threatening if left untreated
